In doing research for my last post, I happened to come across an article written by Joanne Ikeda and her colleagues (1), critiquing the National Weight Control Registry program. Ikeda is a member of the board of directors of the Association for Size Diversity and Health, which promotes the Health at Every Size program. Their paper recycles the claim (twice) that 95% of persons who lose weight regain it (without providing any references), and basically makes the argument that since weight loss efforts are generally futile, HAES should be promoted instead of weight loss.
This is an argument that has been picked up by many in the Fat Acceptance movement, and I can understand their motivation. After all, if you say that significant permanent weight loss is impossible, then obese people are not "culpable" for their obesity, because it is utterly beyond their control. And if you say that it is possible, then you can rightfully accuse obese people of sloth and gluttony, right?
Obviously, I'm utilizing some hyperbole here, so you can probably tell that I personally don't agree with these viewpoints. I think the evidence strongly suggests that some people can lose weight permanently and others can't. It may even be the case that some people are able to lose weight at certain times in their lives and not at others. And it's impossible to make a judgement about any one individual's ability to lose weight.
So, I don't agree with the FA movement when they say that nobody should try to lose weight. And I don't agree with fat bashers who say that all obese people should try to lose weight. Having a "normal" BMI takes a different amount of effort for everyone, and people should be left to make their own decisions about how much energy to invest in regulating their body weight without being judged or criticized by others (except, obviously, in extreme cases involving eating disorders).
And I hope people will feel free to share their own views on the matter in the comments...
1. Ikeda J, Amy NK, Ernsberger P, Gaesser A, Berg FM, Clark CA, Parham ES, Peters P. The National Weight Control Registry: A Critique. Journal of nutrition education and behavior 37: 203-205, 2005.
Tuesday, April 22, 2008
Friday, April 18, 2008
Losing weight and keeping it off
As I mentioned in my last post, there is significant debate over the rate of success in losing weight and keeping it off without the use of surgery or drugs. However, it is definitely possible for some people, and there has been great interest in characterizing the behaviors of those people.
Many, but not all, of the studies I will mention in this post use subjects in the National Weight Control Registry (which I will refer to as the NWCR). They have a pretty detailed website, so if this subject is of interest, you might want to check it out. While this is a tremendously valuable resource in the study of successful weight loss maintenance, in general, I would say that the studies that come out of this cohort are slightly less reliable, because the analysis is retroactive in nature, meaning that the people's habits are being studied after they have lost weight and kept it off. Other studies, in contrast, have looked at people's habits immediately after losing weight and then looked to see what lifestyle factors ended up being associated with maintaining that loss. The former approach is more susceptible to something called recall bias, meaning that the fact that the people being studied have already successfully maintained their weight loss might affect their memories and perceptions of their own habits as compared to people who did not maintain weight loss. With that caveat (and you can tell which studies are NWCR-related by the authors...Rena Wing and James Hill are the founders of the registry), here is a summary of some of the major findings.
Diet--The following dietary habits have been found to be associated with successful maintenance of weight loss:
-Eating five or more servings of fruits and vegetables per day (1, 2)
-Not eating at fast food restaurants (as compared to those who eat fast food at least twice a week) (1)
-Using low-calorie pre-packaged meals (2-4)
-Practicing portion control (2, 11)
-Moderating intake of fat (2, 11)
-Eating breakfast (11)
Exercise: Multiple studies have found that exercise improves one's chances of maintaining weight loss (1,2, 5-8). There is some debate, however, over how much exercise is necessary. Several studies have suggested that an hour of exercise each day is needed to improve chances of weight loss maintenance (1, 2) but at least one other study found that any amount of exercise was beneficial (5)
Weight loss as a percentage of starting weight: Multiple studies (5, 9, 10) have shown that basically, the more weight you lose, the harder it is to maintain. For this reason, many public health officials are now recommending that obese people strive to lose 10-15% of body weight and keep it off rather than trying to achieve a "normal" BMI and then rebound.
"Screen time": Television and computer use (outside of work) has been shown to be positively correlated with weight regain (5)
Consistent Monitoring of Weight: One of the characteristics identified in subjects in the NWCR was frequent weighing (11). 44% of these people said they weighed themselves daily and 31% weighed themselves weekly (11). A more detailed study also showed that subjects in the NWCR who started weighing themselves less frequently gained more weight than those who maintained their strict weighing schedule (14). However, it's not clear whether weighing itself somehow affected these people's motivation to maintain their weight or whether people who knew they'd "slipped" a bit had more trepidation about stepping on the scale regularly.
Online Support: A recent study published in JAMA (12) looked at people who had lost weight through a 6-month program of monitored diet and exercise and then looked at the efficacy of three different types of counseling in helping them to maintain their weight loss over 30 months. Following the initial weight loss period, the "self directed" group were given some literature with recommendations for diet and exercise and met with a counselor after 12 months. An "interactive technology-based intervention" group was given unlimited access to a web site which assisted them in monitoring their weights, monitoring their caloric intake and physical activity and charting their progress, as well as giving them access to a message board where they could interact with other members of that group. The third group received monthly personal contact with a counselor either over the phone or in person. While all three groups regained some weight, they found that the technology-based intervention group regained less than the self-directed group, and the personal contact group regained the least.
While personal monitoring of weight maintenance may not be widely feasible, this does suggest that support provided through the internet may assist in weight loss maintenance. However, at least one other study (13) had different findings that a (different) website they set up to support maintenance of weight loss after a 4-month weight loss program did not make any difference in maintenance of weight loss. The authors attributed the lack of effect to the fact that many of the participants in the study were not comfortable using the internet.
Other: Interestingly, 2 found that unsuccessful maintainers were more likely to follow popular diet books than those who were successful at maintaining weight loss.
Anyway, I doubt any of these things are shockers, but it may be a helpful collection of information for some people!
1. Kruger J, Blanck HM, Gillespie C. Dietary Practices, Dining Out Behavior, and Physical Activity Correlates of Weight Loss Maintenance. Preventing Chronic Disease, 5:A11, 2008.
2. Befort CA, Stewart EE, Smith BK, Gibson CA, Sullvan DK, Donnelly JE. Weight maintenance, behaviors and barriers among previous participants of a university-based weight control program. International Journal of Obesity, 32: 519-526, 2008.
3. Heymsfield SB, van Mierlo CA, van der Knaap HC, Heo M, Frier HI. Weight management using a meal replacement strategy: meta and pooling analysis from six studies. International Journal of Obesity and Related Metabolic Disorders 27: 537-549, 2003.
4. Ditschuneit HH, Flechtner-Mors, M. Value of structured meals for weight management: rsk factors and long-term weight maintenance. Obesity Research 9: 284S-289S, 2001.
5. Weiss EC, Galuska DA, Khan LK, Gillespie C, Serdula M. Weight Regain in Adults Who Experienced Substantial Weight Loss, 1999-2002. American Journal of Preventative Medicine, 33: 34-40, 2007.
6. Anderson JW, Konz EC, Frederich RC, Wood CL. Long-term weight-loss maintenance: a meta-analysis of U.S. studies. American Journal of Clinical Nutrition 74: 579-584, 2001.
7. Jeffery RW, Epstein LH, Wilson GT, Drewnowski A, Stunkard AJ, Wing RR, Hill DR. Long-term maintenance of weight loss: Current status. Health Psychology 19 5-16, 2000.
8. Grodstein F, Levine R, Troy L, Spencer GA, Colditz GA, Stampfer MJ. Three-year follow-up of participants in a commercial weight loss program: can you keep it off? Archives of internal medicine 156: 1302-1306, 1996.
9. McGuire MT, Wing RR, Klem ML, Lang W, Hill JO. What predicts weight gain in a group of successful weight losers? Journal of Consulting Clinical Psychology, 67: 177-185, 1999.
10. Vogels N, Westerterp-Plantenga MS. Successful long-term weight maintenance: a 2-year follow-up. Obesity 15: 1258-1266, 2007.
11. Klem ML, Wing RR, McGuire MT, Seagle HM, Hill JO. A descriptive study of individuals successful at long-term maintenance of substantial weight loss. American Journal of Clinical Nutrition, 66: 239-246, 1997.
12. Svetkey LA, Stevens VJ, Brantley PJ, Appel LJ, Hollis JF, Loria CM, Vollmer WM, Gullion CM, Funk K, Smith P, Samuel-Hodge C, Myers V, Lien LF, Laferriere D, Kennedy B, Jerome GJ, Heinith F, Harsha DW, Evans P, Erlinger TP, Dalcin AT, Coughlin J, Charleston J, Champagne CM, Bauck A, Ard JD, Aicher K for the Weight Loss Maintenance Collaborative Research Group. Comparison of Strategies for Sustaining Weight Loss. Journal of the American Medical Association, 299: 1139-1148, 2008.
13. Cussler EC, Teixeira PJ, Going SB, Houtkooper LB, Metcalfe LL, Blew RM, Ricketts JR, Lohman J, Stanford VA, Lohman TG. Maintenance of Weight Loss in Overweight Middle-aged Women Through the Internet. Obesity, advance online publication, 2008.
14. Butryn ML, Phelan S, Hill JO, Wing RR. Consistent Self-monitoring of Weight: A Key Component of Successful Weight Loss Maintenance. Obesity 15: 3091-3096, 2007.
Many, but not all, of the studies I will mention in this post use subjects in the National Weight Control Registry (which I will refer to as the NWCR). They have a pretty detailed website, so if this subject is of interest, you might want to check it out. While this is a tremendously valuable resource in the study of successful weight loss maintenance, in general, I would say that the studies that come out of this cohort are slightly less reliable, because the analysis is retroactive in nature, meaning that the people's habits are being studied after they have lost weight and kept it off. Other studies, in contrast, have looked at people's habits immediately after losing weight and then looked to see what lifestyle factors ended up being associated with maintaining that loss. The former approach is more susceptible to something called recall bias, meaning that the fact that the people being studied have already successfully maintained their weight loss might affect their memories and perceptions of their own habits as compared to people who did not maintain weight loss. With that caveat (and you can tell which studies are NWCR-related by the authors...Rena Wing and James Hill are the founders of the registry), here is a summary of some of the major findings.
Diet--The following dietary habits have been found to be associated with successful maintenance of weight loss:
-Eating five or more servings of fruits and vegetables per day (1, 2)
-Not eating at fast food restaurants (as compared to those who eat fast food at least twice a week) (1)
-Using low-calorie pre-packaged meals (2-4)
-Practicing portion control (2, 11)
-Moderating intake of fat (2, 11)
-Eating breakfast (11)
Exercise: Multiple studies have found that exercise improves one's chances of maintaining weight loss (1,2, 5-8). There is some debate, however, over how much exercise is necessary. Several studies have suggested that an hour of exercise each day is needed to improve chances of weight loss maintenance (1, 2) but at least one other study found that any amount of exercise was beneficial (5)
Weight loss as a percentage of starting weight: Multiple studies (5, 9, 10) have shown that basically, the more weight you lose, the harder it is to maintain. For this reason, many public health officials are now recommending that obese people strive to lose 10-15% of body weight and keep it off rather than trying to achieve a "normal" BMI and then rebound.
"Screen time": Television and computer use (outside of work) has been shown to be positively correlated with weight regain (5)
Consistent Monitoring of Weight: One of the characteristics identified in subjects in the NWCR was frequent weighing (11). 44% of these people said they weighed themselves daily and 31% weighed themselves weekly (11). A more detailed study also showed that subjects in the NWCR who started weighing themselves less frequently gained more weight than those who maintained their strict weighing schedule (14). However, it's not clear whether weighing itself somehow affected these people's motivation to maintain their weight or whether people who knew they'd "slipped" a bit had more trepidation about stepping on the scale regularly.
Online Support: A recent study published in JAMA (12) looked at people who had lost weight through a 6-month program of monitored diet and exercise and then looked at the efficacy of three different types of counseling in helping them to maintain their weight loss over 30 months. Following the initial weight loss period, the "self directed" group were given some literature with recommendations for diet and exercise and met with a counselor after 12 months. An "interactive technology-based intervention" group was given unlimited access to a web site which assisted them in monitoring their weights, monitoring their caloric intake and physical activity and charting their progress, as well as giving them access to a message board where they could interact with other members of that group. The third group received monthly personal contact with a counselor either over the phone or in person. While all three groups regained some weight, they found that the technology-based intervention group regained less than the self-directed group, and the personal contact group regained the least.
While personal monitoring of weight maintenance may not be widely feasible, this does suggest that support provided through the internet may assist in weight loss maintenance. However, at least one other study (13) had different findings that a (different) website they set up to support maintenance of weight loss after a 4-month weight loss program did not make any difference in maintenance of weight loss. The authors attributed the lack of effect to the fact that many of the participants in the study were not comfortable using the internet.
Other: Interestingly, 2 found that unsuccessful maintainers were more likely to follow popular diet books than those who were successful at maintaining weight loss.
Anyway, I doubt any of these things are shockers, but it may be a helpful collection of information for some people!
1. Kruger J, Blanck HM, Gillespie C. Dietary Practices, Dining Out Behavior, and Physical Activity Correlates of Weight Loss Maintenance. Preventing Chronic Disease, 5:A11, 2008.
2. Befort CA, Stewart EE, Smith BK, Gibson CA, Sullvan DK, Donnelly JE. Weight maintenance, behaviors and barriers among previous participants of a university-based weight control program. International Journal of Obesity, 32: 519-526, 2008.
3. Heymsfield SB, van Mierlo CA, van der Knaap HC, Heo M, Frier HI. Weight management using a meal replacement strategy: meta and pooling analysis from six studies. International Journal of Obesity and Related Metabolic Disorders 27: 537-549, 2003.
4. Ditschuneit HH, Flechtner-Mors, M. Value of structured meals for weight management: rsk factors and long-term weight maintenance. Obesity Research 9: 284S-289S, 2001.
5. Weiss EC, Galuska DA, Khan LK, Gillespie C, Serdula M. Weight Regain in Adults Who Experienced Substantial Weight Loss, 1999-2002. American Journal of Preventative Medicine, 33: 34-40, 2007.
6. Anderson JW, Konz EC, Frederich RC, Wood CL. Long-term weight-loss maintenance: a meta-analysis of U.S. studies. American Journal of Clinical Nutrition 74: 579-584, 2001.
7. Jeffery RW, Epstein LH, Wilson GT, Drewnowski A, Stunkard AJ, Wing RR, Hill DR. Long-term maintenance of weight loss: Current status. Health Psychology 19 5-16, 2000.
8. Grodstein F, Levine R, Troy L, Spencer GA, Colditz GA, Stampfer MJ. Three-year follow-up of participants in a commercial weight loss program: can you keep it off? Archives of internal medicine 156: 1302-1306, 1996.
9. McGuire MT, Wing RR, Klem ML, Lang W, Hill JO. What predicts weight gain in a group of successful weight losers? Journal of Consulting Clinical Psychology, 67: 177-185, 1999.
10. Vogels N, Westerterp-Plantenga MS. Successful long-term weight maintenance: a 2-year follow-up. Obesity 15: 1258-1266, 2007.
11. Klem ML, Wing RR, McGuire MT, Seagle HM, Hill JO. A descriptive study of individuals successful at long-term maintenance of substantial weight loss. American Journal of Clinical Nutrition, 66: 239-246, 1997.
12. Svetkey LA, Stevens VJ, Brantley PJ, Appel LJ, Hollis JF, Loria CM, Vollmer WM, Gullion CM, Funk K, Smith P, Samuel-Hodge C, Myers V, Lien LF, Laferriere D, Kennedy B, Jerome GJ, Heinith F, Harsha DW, Evans P, Erlinger TP, Dalcin AT, Coughlin J, Charleston J, Champagne CM, Bauck A, Ard JD, Aicher K for the Weight Loss Maintenance Collaborative Research Group. Comparison of Strategies for Sustaining Weight Loss. Journal of the American Medical Association, 299: 1139-1148, 2008.
13. Cussler EC, Teixeira PJ, Going SB, Houtkooper LB, Metcalfe LL, Blew RM, Ricketts JR, Lohman J, Stanford VA, Lohman TG. Maintenance of Weight Loss in Overweight Middle-aged Women Through the Internet. Obesity, advance online publication, 2008.
14. Butryn ML, Phelan S, Hill JO, Wing RR. Consistent Self-monitoring of Weight: A Key Component of Successful Weight Loss Maintenance. Obesity 15: 3091-3096, 2007.
Monday, April 14, 2008
Weight loss success: a teaser
In the "requests" posts, someone asked me to write about the issue of the success rate for weight loss maintenance. This is something I wondered about myself. I'd heard the factoid that "95% of dieters regain the weight within five years" but was not familiar with the actual scientific literature on the subject.
Now, having familiarized myself somewhat...I still have no idea what the success rate is for weight loss. The literature is a mess.
A big part of the problem is that different studies use different measures of "significant weight loss" and "long term." Is "significant weight loss" a certain number of pounds, maybe 20, or 30, or 50? Or a certain percentage of your starting body weight? And is "long term" one year, or two, or ten? There are also qualitative differences in studies looking at different kinds of weight loss. Some studies look at people who started out morbidly obese and others looked at weight loss in those who started out merely overweight. Some studies look at weight loss through diet alone, others through exercise alone, and some through a combination of the two. Some of the diets studied are moderate, and some actually involve medically-supervised fasting conditions. The weight loss interventions studied vary in their durations, as well.
So some studies say that the rate of long-term weight loss success is 2% (1) and others say it is 20% (2). At any rate, I think it's safe to say that the rate of success at long-term maintenance of significant weight loss is greater than 0% and less than 100% and instead of further dissecting the matter, I think it's more instructive to focus on studies looking at variables that predict success in long term maintenance of weight loss. Weight loss maintenance may truly not be feasible for all or even most people, but I still think dissecting out factors that can contribute to maintenance of long-term weight loss is useful.
And that's what I'm going to post about on Monday...
1. Stunkard AJ, McLaren-Hume M. The results of treatment for obesity. Archives of Internal Medicine 103: 79-85, 1985.
2. Wing RR and Phelan S. Long-term weight loss maintenance. American Journal of Clinical Nutrition, 82: 222S-225S, 2005.
Now, having familiarized myself somewhat...I still have no idea what the success rate is for weight loss. The literature is a mess.
A big part of the problem is that different studies use different measures of "significant weight loss" and "long term." Is "significant weight loss" a certain number of pounds, maybe 20, or 30, or 50? Or a certain percentage of your starting body weight? And is "long term" one year, or two, or ten? There are also qualitative differences in studies looking at different kinds of weight loss. Some studies look at people who started out morbidly obese and others looked at weight loss in those who started out merely overweight. Some studies look at weight loss through diet alone, others through exercise alone, and some through a combination of the two. Some of the diets studied are moderate, and some actually involve medically-supervised fasting conditions. The weight loss interventions studied vary in their durations, as well.
So some studies say that the rate of long-term weight loss success is 2% (1) and others say it is 20% (2). At any rate, I think it's safe to say that the rate of success at long-term maintenance of significant weight loss is greater than 0% and less than 100% and instead of further dissecting the matter, I think it's more instructive to focus on studies looking at variables that predict success in long term maintenance of weight loss. Weight loss maintenance may truly not be feasible for all or even most people, but I still think dissecting out factors that can contribute to maintenance of long-term weight loss is useful.
And that's what I'm going to post about on Monday...
1. Stunkard AJ, McLaren-Hume M. The results of treatment for obesity. Archives of Internal Medicine 103: 79-85, 1985.
2. Wing RR and Phelan S. Long-term weight loss maintenance. American Journal of Clinical Nutrition, 82: 222S-225S, 2005.
Artificial sweeteners, part deux
I just wanted to post an update about artificial sweeteners, because one of the papers I mentioned in my earlier post on the subject was at that time still in press and now it has been published.
This article (1) is by a pair of researchers in the Department of Psychology at Purdue University, Susan Swithers and Terry Davidson. In their first experiment, they compared the weight gain of rats fed non-fat yogurt sweetened with glucose (a sweetener that has the same sweetness and number of calories as table sugar) vs. rats fed yogurt sweetened with saccharin. Each group got sweetened yogurt three days a week, unsweetened yogurt three days a week and chow one day a week. The rats stayed on the diets for 5 weeks while the researchers monitored their food intake and body weight. At the end of the study, they also measured the animals' body fat content.
The researchers found that all of the animals gained quite a bit of weight (about 20% over their starting weight) . However, they found that the animals which got saccharin yogurt gained slightly more weight than rats that got glucose yogurt in three out of the five weeks of testing, for an overall statistically significant effect*. They also found that the saccharin group had slightly more body fat. However, the researchers did not find a statistically significant difference in total calorie intake between the groups.
For a second experiment, the researchers sought to do a more detailed analysis of the effects of artificial sweetener on food intake. During a "training" period, rats were given normal chow along with yogurt for 14 days. On half of the days, each animal was given plain yogurt, and on the other half of the days one group of animals got glucose-sweetened yogurt and the other group got saccharin yogurt.
After the 14 day training period, they fed the animals chow and water for 1 day (presumably to "flush out" any short term effects of their yogurt diets), followed by an overnight fast (presumably to make the rats hungry...rats are nocturnal so they normally do most of their eating at night). Then half the rats in each group were given a "premeal" of Chocolate Ensure Plus** for 30 minutes, and then normal lab chow was given back to all the rats and their food intake was measured.
The researchers found that the rats that got the glucose yogurt ate slightly less during the 14-day training period than the rats that got saccharin yogurt. As in the first experiment, both groups gained weight, about 10% of their starting weight, but the saccharin group gained slightly more. During the testing period, they found that the glucose rats who got the premeal ate slightly less than those that didn't, but the saccharin rats ate the same amount, regardless of whether they ate a premeal. However, there does not appear to be an overall difference in chow intake in the testing period between the glucose and saccharin groups.
For their third and final experiment, the researchers sought to establish a physiological basis for the differences between the glucose and saccharin groups. In this experiment they look at the well established phenomenon of "postprandial thermogenesis,": when you eat food, it causes a small, temporary increase in body temperature. Studies have shown that when food is tasted, but not swallowed, it tends to cause a bigger increase in body temperature than if the food were actually eaten (2,3), whereas if food is delivered directly to the gut via a tube and not tasted, the increase in body temperature is smaller (2,4). The authors hypothesized here that since the saccharin rats have been trained to eat something that tastes sweet, but without the calories of sugar, that they might also see decreased body temperature in response to a meal compared with the rats whose bodies "expect" the calories associated with sugar. (n.b. Thanks to anonymous, who pointed out that my original interpretation of their hypothesis made no sense, and I have corrected this post accordingly. Sometimes I read stuff too fast!)
For this experiment, all the rats were surgically implanted with thermometers that transmitted temperature readings to a receiver, so the researchers were able to continuously monitor the temperature of each rat. Then they did the same 14-day training with glucose- or saccharin-sweetened yogurt as in the previous experiment. Then all rats were fasted overnight, and then given a premeal of chocolate Ensure, followed by ad lib access to chow.
They found that during the first hour of the 14-day training period that both the glucose and saccharin groups increased their body temperature after eating the yogurt, but the glucose group's temperature came down more slowly after the meal. Then during testing, they found that the glucose group's temperature went up slightly more in response to the Ensure than the saccharin group's, although both groups increased their body temperature.
Anyway, the authors' interpretation of this all is that there is a Pavlovian conditioning phenomenon occurring here. They believe that when rats eat yogurt sweetened with sugar, their bodies learn that sugary taste is associated with the intake of calories, and they adjust their diet accordingly when presented with things that are sweet. In contrast, rats that eat saccharin yogurt do not develop this association, and so when they are presented with sweet foods their bodies don't expect them to have any calories. They believe that the temperature differences following glucose- and saccharin-sweetened foods are part of the mechanism by which animals make these adaptations, but things get a little hand-wavy at this point for me.
This paper is kind of intriguing, but I think there are a few big leaps between the findings of the paper and the conclusions the authors draw. I think the biggest caveat is that they are assuming that saccharin's effects are due to the fact that it is an artificial sweetener and not due to some other possible effect of this chemical on the rats' bodies. A good way to test for this would be to look and see if other types of artificial sweeteners have the same effect.
Another big caveat is that the results in this study are mostly pretty subtle, and these studies were all done in rats that had been raised on a diet of lab chow...in other words, these experiments were the rats' first experience with sweet-tasting food. This makes me wonder about the applicability of the study in humans, since most people eat a combination of natural and artificial sweeteners, so we are not being "trained" in the same way as the rats.
A third caveat is the fact that their proposed mechanism is pretty vague. They don't identify an neural pathways or hormones or brain areas that might be implicated in this Pavlovian response. They merely show a difference in the effects on body temperature, which again, could be due to some specific effect of saccharin. I think a really interesting test of their hypothesis would be to train rats on glucose yogurt and then give them a pre-meal sweetened with saccharin and see if that caused them to eat less subsequently. Maybe that will be in their next paper.
In conclusion, I think this paper has some significant flaws (among which is the fact that they issued a press release about the paper before it was published so the results were reported in the media without any scrutiny). But I also think there might be something there. I think it's just not quite clear yet exactly what that is.
*These researchers do something I've never seen before with their statistics, which is that for the measures they say are statistically significant, they just say that the p-value is less than 0.05, they don't tell you what the p-value actually is. For the nonsignificant measures, they do tell you the actual p-value. Has anyone else ever heard of this? Is there any reason to do it other than my suspicion that these p-values were all very close to 0.05, and they wanted to downplay this by just called 0.05 the cutoff and then claiming that their data fit that criterion?
**Ensure is often used to fatten laboratory rats, and I used to work next door to a lab that did this a lot. As you can imagine, it definitely colored my view of those TV commercials for Ensure where people talk about how they give their senior citizen parents Ensure because they care about them so much.
1. Swithers SE, Davidson TL. A Role for Sweet Taste: Calorie Predictive Relations in Energy Regulation by Rats. Behavioral Neuroscience 122: 161-173, 2008.
2. Diamond P, Brondel L, LeBlanc J. Palatability and postprandial thermogenesis in dogs. American Journal of Physiology 248: E75-E79, 1985.
3. LeBlanc J, Cabanac M. Cephalic postprandial thermogenesis in human subjects. Physiology and Behavior 46: 479-482, 1989.
4. LeBlanc J, Cabanac M, Samson P. Reduced postprandial heat production with gavage as compared with meal feeding in human subjects. American Journal of Physiology 246: E95-E101, 1984.
This article (1) is by a pair of researchers in the Department of Psychology at Purdue University, Susan Swithers and Terry Davidson. In their first experiment, they compared the weight gain of rats fed non-fat yogurt sweetened with glucose (a sweetener that has the same sweetness and number of calories as table sugar) vs. rats fed yogurt sweetened with saccharin. Each group got sweetened yogurt three days a week, unsweetened yogurt three days a week and chow one day a week. The rats stayed on the diets for 5 weeks while the researchers monitored their food intake and body weight. At the end of the study, they also measured the animals' body fat content.
The researchers found that all of the animals gained quite a bit of weight (about 20% over their starting weight) . However, they found that the animals which got saccharin yogurt gained slightly more weight than rats that got glucose yogurt in three out of the five weeks of testing, for an overall statistically significant effect*. They also found that the saccharin group had slightly more body fat. However, the researchers did not find a statistically significant difference in total calorie intake between the groups.
For a second experiment, the researchers sought to do a more detailed analysis of the effects of artificial sweetener on food intake. During a "training" period, rats were given normal chow along with yogurt for 14 days. On half of the days, each animal was given plain yogurt, and on the other half of the days one group of animals got glucose-sweetened yogurt and the other group got saccharin yogurt.
After the 14 day training period, they fed the animals chow and water for 1 day (presumably to "flush out" any short term effects of their yogurt diets), followed by an overnight fast (presumably to make the rats hungry...rats are nocturnal so they normally do most of their eating at night). Then half the rats in each group were given a "premeal" of Chocolate Ensure Plus** for 30 minutes, and then normal lab chow was given back to all the rats and their food intake was measured.
The researchers found that the rats that got the glucose yogurt ate slightly less during the 14-day training period than the rats that got saccharin yogurt. As in the first experiment, both groups gained weight, about 10% of their starting weight, but the saccharin group gained slightly more. During the testing period, they found that the glucose rats who got the premeal ate slightly less than those that didn't, but the saccharin rats ate the same amount, regardless of whether they ate a premeal. However, there does not appear to be an overall difference in chow intake in the testing period between the glucose and saccharin groups.
For their third and final experiment, the researchers sought to establish a physiological basis for the differences between the glucose and saccharin groups. In this experiment they look at the well established phenomenon of "postprandial thermogenesis,": when you eat food, it causes a small, temporary increase in body temperature. Studies have shown that when food is tasted, but not swallowed, it tends to cause a bigger increase in body temperature than if the food were actually eaten (2,3), whereas if food is delivered directly to the gut via a tube and not tasted, the increase in body temperature is smaller (2,4). The authors hypothesized here that since the saccharin rats have been trained to eat something that tastes sweet, but without the calories of sugar, that they might also see decreased body temperature in response to a meal compared with the rats whose bodies "expect" the calories associated with sugar. (n.b. Thanks to anonymous, who pointed out that my original interpretation of their hypothesis made no sense, and I have corrected this post accordingly. Sometimes I read stuff too fast!)
For this experiment, all the rats were surgically implanted with thermometers that transmitted temperature readings to a receiver, so the researchers were able to continuously monitor the temperature of each rat. Then they did the same 14-day training with glucose- or saccharin-sweetened yogurt as in the previous experiment. Then all rats were fasted overnight, and then given a premeal of chocolate Ensure, followed by ad lib access to chow.
They found that during the first hour of the 14-day training period that both the glucose and saccharin groups increased their body temperature after eating the yogurt, but the glucose group's temperature came down more slowly after the meal. Then during testing, they found that the glucose group's temperature went up slightly more in response to the Ensure than the saccharin group's, although both groups increased their body temperature.
Anyway, the authors' interpretation of this all is that there is a Pavlovian conditioning phenomenon occurring here. They believe that when rats eat yogurt sweetened with sugar, their bodies learn that sugary taste is associated with the intake of calories, and they adjust their diet accordingly when presented with things that are sweet. In contrast, rats that eat saccharin yogurt do not develop this association, and so when they are presented with sweet foods their bodies don't expect them to have any calories. They believe that the temperature differences following glucose- and saccharin-sweetened foods are part of the mechanism by which animals make these adaptations, but things get a little hand-wavy at this point for me.
This paper is kind of intriguing, but I think there are a few big leaps between the findings of the paper and the conclusions the authors draw. I think the biggest caveat is that they are assuming that saccharin's effects are due to the fact that it is an artificial sweetener and not due to some other possible effect of this chemical on the rats' bodies. A good way to test for this would be to look and see if other types of artificial sweeteners have the same effect.
Another big caveat is that the results in this study are mostly pretty subtle, and these studies were all done in rats that had been raised on a diet of lab chow...in other words, these experiments were the rats' first experience with sweet-tasting food. This makes me wonder about the applicability of the study in humans, since most people eat a combination of natural and artificial sweeteners, so we are not being "trained" in the same way as the rats.
A third caveat is the fact that their proposed mechanism is pretty vague. They don't identify an neural pathways or hormones or brain areas that might be implicated in this Pavlovian response. They merely show a difference in the effects on body temperature, which again, could be due to some specific effect of saccharin. I think a really interesting test of their hypothesis would be to train rats on glucose yogurt and then give them a pre-meal sweetened with saccharin and see if that caused them to eat less subsequently. Maybe that will be in their next paper.
In conclusion, I think this paper has some significant flaws (among which is the fact that they issued a press release about the paper before it was published so the results were reported in the media without any scrutiny). But I also think there might be something there. I think it's just not quite clear yet exactly what that is.
*These researchers do something I've never seen before with their statistics, which is that for the measures they say are statistically significant, they just say that the p-value is less than 0.05, they don't tell you what the p-value actually is. For the nonsignificant measures, they do tell you the actual p-value. Has anyone else ever heard of this? Is there any reason to do it other than my suspicion that these p-values were all very close to 0.05, and they wanted to downplay this by just called 0.05 the cutoff and then claiming that their data fit that criterion?
**Ensure is often used to fatten laboratory rats, and I used to work next door to a lab that did this a lot. As you can imagine, it definitely colored my view of those TV commercials for Ensure where people talk about how they give their senior citizen parents Ensure because they care about them so much.
1. Swithers SE, Davidson TL. A Role for Sweet Taste: Calorie Predictive Relations in Energy Regulation by Rats. Behavioral Neuroscience 122: 161-173, 2008.
2. Diamond P, Brondel L, LeBlanc J. Palatability and postprandial thermogenesis in dogs. American Journal of Physiology 248: E75-E79, 1985.
3. LeBlanc J, Cabanac M. Cephalic postprandial thermogenesis in human subjects. Physiology and Behavior 46: 479-482, 1989.
4. LeBlanc J, Cabanac M, Samson P. Reduced postprandial heat production with gavage as compared with meal feeding in human subjects. American Journal of Physiology 246: E95-E101, 1984.
Sunday, April 6, 2008
Book review: In Defense of Food
Michael Pollan's The Omnivore's Dilemma, which explores the moral, ecological and health impact of the food we choose to eat, was a life-altering book for me. So I was very excited to receive his follow-up book, In Defense of Food as a birthday gift. Unfortunately, as I read the book, I became gradually less thrilled, and now my Pollan-love has abated somewhat. But overall, I think Pollan and I come to the same conclusions, but perhaps for different reasons.
Pollan begins the book with his catchy new mantra: "Eat food. Not too much. Mostly plants" (I haven't seen this on a t-shirt yet, but fear that it is only a matter of time). Most of the first part of the book is devoted to his distinguishing food from what he calls "edible food-like substances," i.e. foods that have been heavily processed. I was with him this far, but he began to lose me with his forays into critique of food science.
Pollan is often sloppy or unclear in his treatment of the subject. On page 69, in talking about the placebo effect, he says "About a third of Americans are what researchers call responders–people who will respond to a treatment or intervention regardless of whether they've actually received it." I cringed when I read this, for several reasons. For one thing, he makes it sound as though responders are a fixed (and apparently highly suggestible) segment of the population that will respond to anything. This is not the case, nor is it the case that people respond equally to all placebos. He unfortunately does not provide a citation for this particular factoid. The book throughout is rather poorly sourced, with only a few of his claims having more than one citation to back them up.
His main critique of nutrition science is that research in that field has focused on the effects of single nutrients. This, he argues, is problematic because we do not eat nutrients, we eat foods with different combinations of nutrients that may interact with one another and thereby affect our health in ways that would not be predicted from single-nutrient studies. This is a fair enough criticism, but uses this argument to basically reject the entire field of nutrition science (except for those studies which back up his conclusions). In rejecting nutrition science as overly reductionist, he also neglects to acknowledge that the most important discoveries of nutrition science and those which have arguably had the greatest health impact were the identification and treatment of diseases resulting from deficiencies of single nutrients, such as scurvy, rickets, and beriberi.
I do agree with Pollan that nutrition science is not sufficiently advanced that we ought to eat food which has been stripped of its nutritional content through processing and then re-fortified with vitamins, or that we can depend on vitamin supplementation to balance out a diet that is not nutritionally sound. But I imagine most nutrition scientists would also agree with this...unless they work for Frito-Lay, maybe.
Interestingly, for all his talk about reductionism, Pollan does seem to be convinced as to the miraculous health properties of one nutrient: omega-3 fatty acids. He does not attempt to address the apparent contradiction between his criticism of studies that look at single nutrients, and his belief in those exact types of studies about omega-3s. He even manages to sneak in a little anti-science jab when he writes "I have been specifically warned by scientists allied with the carbohydrate camp not to 'fall under the spell of the omega-3 cult.' Cult? There is a lot more religion in science than you might expect." Sounds to me like an advanced case of the pot calling the kettle black!
Another of Pollan's main claims is that the "Western" diet is inherently unhealthy (I agree with him here) and that virtually all "traditional" diets are superior in their health effects. Here, he relies heavily on the work of a dentist, Weston Price, who conducted studies in the 1930s of traditional diets and dental health. Pollan acknowledges that Price "could sometimes come across as a bit of a crackpot," but embraces his conclusions nonetheless.
To be fair, he also looks at other studies of traditional diets, in each case finding that people eating the diets their ancestors had consumed over the past several hundred years were healthier than people who had changed their traditional diets. Even the Masai people, whose diet consisted of meat, blood, milk and virtually no plant foods were deemed to be healthier than people eating a modern Western diet. He quotes one nutritionist as saying "Just don't eat anything your Neolithic ancestors wouldn't have recognized and you'll be OK."
The obvious (to me, anyway) problem with this philosophy is that like most Americans, my Neolithic ancestors were scattered (in my case around Europe) and likely ate vastly different diets from one another. If traditional diets are truly healthier, it seems to me that we much accept one of two explanations: either various cultures were able, through trial and error, to develop optimally healthy diets from the available foods over a period of hundreds of years, OR alternatively, people may have genetically adapted to the diets to which they had access over those hundreds of years to get optimum health out of the foods available to them. Neither of these hypotheses is proven, but given the tremendous variation of the content of healthy traditional diets, the latter seems vastly more likely to me.
Pollan does talk about people adapting to their diets a few times, saying, for example, that "our bodies have a long-standing and sustainable relationship to corn that they do not have to high-fructose corn syrup. Such a relationship with corn sytrup might develop someday (as people evolve superhuman insulin systems to cope with regular floods of pure fructose and glucose)." But he never makes the leap to confront the politically incorrect notion that if people have to adapt to their diets over centuries, the ethnically heterogeneous among us might just be screwed.
That being said, while I disagree with some of Pollan's reasoning and analysis, in the end, we pretty much arrive at the same place. I found the dietary principles he espouses at the end of the book to be sound. In fact, in that part of the book, I felt the flame of Pollan-love starting to come back to life. Overall, I think the book is worth a read...with a bit of skepticism reserved.
Pollan begins the book with his catchy new mantra: "Eat food. Not too much. Mostly plants" (I haven't seen this on a t-shirt yet, but fear that it is only a matter of time). Most of the first part of the book is devoted to his distinguishing food from what he calls "edible food-like substances," i.e. foods that have been heavily processed. I was with him this far, but he began to lose me with his forays into critique of food science.
Pollan is often sloppy or unclear in his treatment of the subject. On page 69, in talking about the placebo effect, he says "About a third of Americans are what researchers call responders–people who will respond to a treatment or intervention regardless of whether they've actually received it." I cringed when I read this, for several reasons. For one thing, he makes it sound as though responders are a fixed (and apparently highly suggestible) segment of the population that will respond to anything. This is not the case, nor is it the case that people respond equally to all placebos. He unfortunately does not provide a citation for this particular factoid. The book throughout is rather poorly sourced, with only a few of his claims having more than one citation to back them up.
His main critique of nutrition science is that research in that field has focused on the effects of single nutrients. This, he argues, is problematic because we do not eat nutrients, we eat foods with different combinations of nutrients that may interact with one another and thereby affect our health in ways that would not be predicted from single-nutrient studies. This is a fair enough criticism, but uses this argument to basically reject the entire field of nutrition science (except for those studies which back up his conclusions). In rejecting nutrition science as overly reductionist, he also neglects to acknowledge that the most important discoveries of nutrition science and those which have arguably had the greatest health impact were the identification and treatment of diseases resulting from deficiencies of single nutrients, such as scurvy, rickets, and beriberi.
I do agree with Pollan that nutrition science is not sufficiently advanced that we ought to eat food which has been stripped of its nutritional content through processing and then re-fortified with vitamins, or that we can depend on vitamin supplementation to balance out a diet that is not nutritionally sound. But I imagine most nutrition scientists would also agree with this...unless they work for Frito-Lay, maybe.
Interestingly, for all his talk about reductionism, Pollan does seem to be convinced as to the miraculous health properties of one nutrient: omega-3 fatty acids. He does not attempt to address the apparent contradiction between his criticism of studies that look at single nutrients, and his belief in those exact types of studies about omega-3s. He even manages to sneak in a little anti-science jab when he writes "I have been specifically warned by scientists allied with the carbohydrate camp not to 'fall under the spell of the omega-3 cult.' Cult? There is a lot more religion in science than you might expect." Sounds to me like an advanced case of the pot calling the kettle black!
Another of Pollan's main claims is that the "Western" diet is inherently unhealthy (I agree with him here) and that virtually all "traditional" diets are superior in their health effects. Here, he relies heavily on the work of a dentist, Weston Price, who conducted studies in the 1930s of traditional diets and dental health. Pollan acknowledges that Price "could sometimes come across as a bit of a crackpot," but embraces his conclusions nonetheless.
To be fair, he also looks at other studies of traditional diets, in each case finding that people eating the diets their ancestors had consumed over the past several hundred years were healthier than people who had changed their traditional diets. Even the Masai people, whose diet consisted of meat, blood, milk and virtually no plant foods were deemed to be healthier than people eating a modern Western diet. He quotes one nutritionist as saying "Just don't eat anything your Neolithic ancestors wouldn't have recognized and you'll be OK."
The obvious (to me, anyway) problem with this philosophy is that like most Americans, my Neolithic ancestors were scattered (in my case around Europe) and likely ate vastly different diets from one another. If traditional diets are truly healthier, it seems to me that we much accept one of two explanations: either various cultures were able, through trial and error, to develop optimally healthy diets from the available foods over a period of hundreds of years, OR alternatively, people may have genetically adapted to the diets to which they had access over those hundreds of years to get optimum health out of the foods available to them. Neither of these hypotheses is proven, but given the tremendous variation of the content of healthy traditional diets, the latter seems vastly more likely to me.
Pollan does talk about people adapting to their diets a few times, saying, for example, that "our bodies have a long-standing and sustainable relationship to corn that they do not have to high-fructose corn syrup. Such a relationship with corn sytrup might develop someday (as people evolve superhuman insulin systems to cope with regular floods of pure fructose and glucose)." But he never makes the leap to confront the politically incorrect notion that if people have to adapt to their diets over centuries, the ethnically heterogeneous among us might just be screwed.
That being said, while I disagree with some of Pollan's reasoning and analysis, in the end, we pretty much arrive at the same place. I found the dietary principles he espouses at the end of the book to be sound. In fact, in that part of the book, I felt the flame of Pollan-love starting to come back to life. Overall, I think the book is worth a read...with a bit of skepticism reserved.
Friday, April 4, 2008
No new post this week
It's been a hectic week, but I'll be back on Monday with a book report on Michael Pollan's In Defense of Food.
Subscribe to:
Posts (Atom)
