Wednesday, March 26, 2008

The environmental scourge of obesity

Last month, I was reading an article in The New Yorker about calculating carbon footprints. The article referenced an article in the New Scientist which they said "suggested that the biggest problem arising from the epidemic of obesity is the additional carbon burden that fat people—who tend to eat a lot of meat and travel mostly in cars—place on the environment." The article, which appeared in the June 30, 2007 issue of the magazine, is by Ian Roberts, a professor of public health at the London School of Hygiene and Tropical Medicine. It is only available online to subscribers to the magazine, but I think it's just as well, as it is a truly shameful excuse for science "journalism."

Here are Roberts's key points (please note that he does not cite any sources for any of this information, and much of it is either highly suspect, or I know it to be incorrect):

-The U.S. has the world's highest rate of obesity and also has the highest per capita carbon emissions, and this shows that obesity and carbon emissions are linked.

-Obese people eat 40% more calories than lean people, and food production accounts for 20% of greenhouse gas emissions

-I was going to summarize this next part, but realized that I could not possibly convey its awfulness by doing so, and so I will just reproduce it:

Consider what happens to someone on the path to obesity. It might start when he (or she, of course) decides to drive rather than walk the half mile to the office, just to get there a few minutes earlier. A year on he might have gained a kilogram of fat, and as the weight continues to pile on he eventually finds it harder to move around and is loath to walk or cycle anywhere[...]By now he'll be suffering low self-esteem, which leads to comfort eating and perhaps heavier drinking, too. He'll even notice a load on his household energy bills: his greater bulk and higher metabolic rate will cause him to feel the heat more in the globally warmed summers, and he'll be the first to turn on the energy-intensive air conditioning.

In looking for the New Scientist article, I had come across some other media reports on the environmental impact of obesity, most of them referencing this study by a University of Illinois Computer Science professor and a graduate student. Unfortunately, I wasn't able to read the original article, as none of the libraries I have access to subscribe to The Engineering Economist, but according to that press release, the study showed that weight gain by Americans since 1960 now causes us to consume an additional 938 million gallons of gasoline per year. That sounds pretty bad, right? But maybe not so much when you consider that that represents only a 0.7% increase in fuel consumption over what it would cost if Americans weighed the same now as in 1960. As the authors, McLay and Jacobson, write in the paper, "the amount of fuel consumed as a result of the rising prevalence of obesity is small compared to the increase in the amount of fuel consumed stemming from other factors such as increased car reliance and an increase in the number of drivers
" (not to mention the fact that people still opt to drive heavier and less fuel-efficient vehicles). And yet still, the article was widely reported on with headlines like "Expanding waistlines lead to pain at the pump."

It also occurs to me that even if obesity did have a significant impact on fuel consumption and carbon emissions, what would be the logical response to such a finding? Forced weight loss surgeries? Food rationing for fat people? Forcing people to pay for carbon offsets for their fat? Obviously these are all ridiculous ideas, particularly in light of the fact that there are many factors which we can control that also contribute to fuel consumption and global warming.

Although there may indeed be a link between our high-carbon lifestyle and obesity, it seems to me that we ought to be looking at this issue from the perspective of those things we can change. This study for example, finds that taking public transit is associated with an additional 8.3 minutes per day of walking, which if applied to people who now commute in their cars could dramatically reduce obesity rates (in addition to the carbon savings associated with public transit). This is a theoretical model, so its validity is not established, but if it's true, increased funding and use of public transit will result in both decreased pollution and increased health, which sounds like a win-win situation to me.

Tuesday, March 18, 2008

Can gastric banding cure diabetes? Part II.

As I mentioned in the last entry, in 1995, Pories et al. found that Roux-en-Y gastric bypass surgery normalized blood glucose in some type II diabetics within days of the operation (1). This immediate improvement in blood glucose, which preceded any significant weight loss, led some to speculate that the blood glucose changes were a result of the effects of surgery on the gut rather than a consequence of weight loss. The gastrointestinal tract has been shown to secrete a number of hormones that can influence glucose and insulin levels and insulin sensitivity (2), and people theorized that changes in the levels of those hormones following absorptive surgery might be the mechanism by which those surgeries caused improvements in diabetes (1). Indeed, a number of papers showed that absorptive weight loss surgeries caused changes in levels of many of these gut hormones, and that these changes persisted even 20 years after the surgeries (3-5).

Other studies showed that while gastric bypass surgery altered the levels of these hormones, gastric banding surgery did not (4, 6). This makes sense, as the absorptive surgeries work by physically disconnecting some parts of the gastrointestinal tract that make the hormones, whereas the gastric banding, which is only restrictive, does not.

So, if gastric banding doesn't abate diabetes by altering gut hormone levels, how does it work? In the recent JAMA paper showing dramatic levels of diabetes remission with gastric banding, the authors found that weight loss was strongly correlated with diabetes remission, both in the gastric banding group and in the traditional diabetes therapy group (7). They conclude that "degree of weight loss, not the method, appears to be the major driver of glycemic improvement and diabetes remission in obese participants. This has important implications, as it suggests that intensive weight-loss therapy may be a more effective first step in the management of diabetes than simple lifestyle changes."

So, it seems that while gastric banding's effects on diabetes are primarily a result of its effects on weight loss, gastric bypass surgery also improves diabetes by altering levels of gut hormones that are involved in regulation of glucose and insulin. While gastric bypass surgery is generally more effective against diabetes and has a dual mechanism, the recent JAMA paper serves as evidence that with the right surgical team, gastric banding can also be very effective against diabetes in newly diagnosed patients, at least in the short term. This has generated a lot of excitement in the medical community, with some proposing gastric banding as the standard treatment for type II diabetes. However, until longer-term results have been shown, I think that assessment is a bit premature.

1. Pories WJ, Swanson MS, MacDonald KG, Long SB, Morris PG, Brown BM, Barakat HA, deRamon RA, Israel G, Dolezal JM. Who would have thought it? An operation proves to be the most effective therapy for adult-onset diabetes mellitus. Annals of Surgery 222: 339-352, 1995.

2. Drucker DJ. The role of gut hormones in glucose homeostasis. Journal of Clinical Investigations 117: 24-32, 2007.

3. Naslund E, Gryback P, Hellstrom PM, Hacobsson H, Holst JJ, Theodorsson E, Backman L. Gastrointestinal hormones and gastric emptying 20 years after jejeunoileal bypass for massive obesity. International Journal of Obesity and Related Metabolic Disorders 21: 387-392, 1997.

4. Kellum JM, Kuemmerle JF, ODorisio TM, Rayford P, Martin D, Engle K, Wolf L, Sugerman HJ. Gastrointestinal hormone responses to meals before and after gastric bypass and vertical banded gastroplasty. Annals of Surgery 211: 763-771, 1990.

5. Wilson P, Welch NT, Hinder RA, Anselmino M, Herrington MK, DeMeester TR, Adrian TE. Abnormal plasma gut hormones in pathologic duodenogastric reflux and their response to surgery. American Journal of Surgery 165: 169-177, 1993.

6. Korner J, Inabnet W, Conwell IM, Taveras C, Daud A, Olivero-Rivera L, Restuccia NL, Bessler M. Differential effects of gastric bypass and banding on circulating gut hormone and leptin levels. Obesity (Silver Spring), 14: 1553-1561, 2006.

Dixon JB, O'Brien PE, Playfair J, Chapman L, Schachter LM, Skinner S, Proietto J, Bailey M, Anderson M. Adjustable Gastric Banding and Conventional Therapy for Type 2 Diabetes. JAMA 299: 316-323, 2008.

Monday, March 17, 2008

Can gastric banding cure diabetes? Part I.

A couple of months ago, a paper published in the Journal of the American Medical Association made headlines with the claim that gastric banding surgery resulted in remission of type II diabetes in 73% of patients who had the surgery (as opposed to only 13% remission in controls).

A few obvious questions come to mind here: is it true? And if so, is the remission from diabetes just a consequence of weight loss, or does the surgery result in some other physiological change that results in diabetes remission? In this post, I'm going to write about the validity of these studies. And in Part II, which I'll post on Friday, I'll talk about the mechanisms by which weight loss surgeries are believed to affect diabetes.

Gastric banding is a "restrictive" surgery involving the placement of a band around the stomach, restricting food intake by limiting the capacity of the stomach (1). Some other types of weight loss surgery are "absorptive" and work by limiting absorption from the gastrointestinal tract by physically bypassing parts of the gastrointestinal tract (1). And some surgical procedures are both restrictive and absorptive.

There are different advantages and disadvantages to different types of surgeries. Patients who undergo gastric banding tend to lose less weight than those who have other types of weight loss surgeries (an average of 47.5% of excess weight loss with gastric banding vs. an average 70.1% of excess weight with the duodenal switch procedure, a restrictive and absorptive surgery), however, the gastric banding procedure is faster, less invasive, and has a lower risk of complications than more invasive surgeries (1). It also has the advantage of being reversible.

Two studies in the 1990s had demonstrated that the Roux-en-Y gastric bypass surgery (which is both restrictive and malabsorptive) reduced pre-diabetic patients' risk of developing type II diabetes (2) and normalized blood glucose in some type II diabetics within days of the surgery (3) (in fact, some patients experienced an "overnormalization" of blood glucose and suffered occasional attacks of hypoglycemia).

In 2004, Ponce et al. (4) set out to see if gastric banding (ahem, excuse me, Lap-Banding ® which is just a specific brand of gastric band) produced similar results. They measured HbA1c levels, an indicator of average blood glucose over the past couple of months, in patients 12, 18, and 24 months after their surgeries. They found that glucose levels improved following surgery and maintained that improvement at 24 months. They also found that type II diabetes was resolved in a majority of patients who had been diabetic for less than 5 years prior to their surgery, but in only about a third of those who had been diabetic for more than 5 years prior to surgery.

Last year, Korenkov et al. (5), set out to look at a slightly longer follow-up period, but unfortunately, because the patients varied in their followup durations from 2 to 8 years (with an average of 5 years) it is not possible to determine based on their results if the health improvements they saw were truly stable over this period. They found that the prevalence of type II diabetes decreased from 10% pre-surgery to 4% at followup. However, they do not say how many (if any) of these patients were still diabetes free 8 years out. Another short-term study published last year (6) compared gastric band and Roux-en-Y gastric bypass surgeries and found that at 13 months post-surgery, 50% of diabetic gastric band patients and 95% of gastric bypass patients had improvements in their diabetes. However, again, it is not clear whether these effects persisted over the long term.

So the JAMA study which received so much media attention recently was really not so revolutionary. The study's subjects were all patients with a BMI <40* style="font-style: italic;">JAMA explain the discrepancy by pointing out that the surgical team participating in the study "is among the most experienced groups in the world using LAGB, and their excellent results may not be reproducible elsewhere. Their reported post-LAGB weight loss often exceeds that observed by other investigators" (8). I hope that longer-term findings will be published in the coming years, but the results this far look pretty promising. But of course, weighing the risks and benefits of any surgical procedure is something that should be the sole prerogative of patients themselves.

*The authors explain that they "believed it inappropriate to recruit those with a BMI greater than 40 into the study, because a number of observational studies have shown effectiveness of bariatric surgery in these patients." I think they're missing a "not" in there somewhere...

1. Korenkov M, Sauerland S, Junginger T. Surgery for Obesity. Current Opinions in Gastroenterology 21: 679-683, 2005.

2. Long SD, O'Brien K, MacDonald KG Jr., Leggett-Frazier N, Swanson MS, Pories WJ, Caro JF. Weight loss in severely obese subjects prevents the progression of impaired glucose tolerance to type II diabetes: a longitudinal interventional study. Diabetes Care 17: 372-275, 1994.

3. Pories WJ, Swanson MS, MacDonald KG, Long SB, Morris PG, Brown BM, Barakat HA, deRamon RA, Israel G, Dolezal JM. Who would have thought it? An operation proves to be the most effective therapy for adult-onset diabetes mellitus. Annals of Surgery 222: 339-352, 1995.

4. Ponce J, Haynes B, Paynter S, Fromm R, Lindsey B, Shafer A, Manahan E, Sutterfield C. Effect of Lap-Band®-Induced Weight Loss on Type 2 Diabetes Mellitus and Hypertension. Obesity Surgery 14:1335-1342, 2004.

5. Korenkov M, Shah S, Sauerland S, Duenschede F, Junginger T. Impact of Laparoscopic Adjustable Gastric Banding on Obesity Co-morbidities in the Medium- and Long-Term. Obesity Surgery, 17: 679-683, 2007.

6. Gan SSH, Talbot ML, Jorgensen JO. Efficacy of Surgery in the Management of Obesity-Related Type 2 Diabetes Mellitus. ANZ Journal of Surgery, 77:958-962, 2007.

7. Dixon JB, O'Brien PE, Playfair J, Chapman L, Schachter LM, Skinner S, Proietto J, Bailey M, Anderson M. Adjustable Gastric Banding and Conventional Therapy for Type 2 Diabetes. JAMA 299: 316-323, 2008.

8. Cummings DE, Flum DR. Gastrointestinal Surgery as a Treatment for Diabetes. JAMA 299: 341-343, 2008.

Sunday, March 16, 2008

Health at Every Size

The "Health at Every Size" (HAES) program has attracted a lot of positive attention among fat acceptance groups, and has been touted as an alternative to weight loss programs for obese people. The program was developed by the Association for Size Diversity and Health (ASDAH), a non-profit self-described "international professional organization." I put that phrase in quotes not to be snarky, but because the board of directors is comprised of a mix of people, some of whom have professional training in psychology and nutrition, and some of whom don't, and membership in the organization is open to anyone who is willing to pay for it. The program is based around five basic principles:
  1. Accepting and respecting the diversity of body shapes and sizes
  2. Recognizing that health and well-being are multi-dimensional and that they include physical, social, spiritual, occupational, emotional, and intellectual aspects
  3. Promoting all aspects of health and well-being for people of all sizes
  4. Promoting eating in a manner which balances individual nutritional needs, hunger, satiety, appetite, and pleasure
  5. Promoting individually appropriate, enjoyable, life-enhancing physical activity, rather than exercise that is focused on a goal of weight loss
HAES is a relatively new program, and as a result, the published research about this program per se is still fairly scant. However, there are a few studies of non-dieting psychological interventions in obese patients dating back to the 1990s that likely formed the basis for this program. Ciliska (1) looked at the effects of "education intervention" and "psychoeducational intervention" in obese women (the "education" group had classroom-style lectures about the etiology and health consequences of obesity and the "psychoeducation" group had small discussion group-format meetings about HAES principles). While weight and blood pressure did not change in either of these groups, the psychoeducation group improved in measures of "self-esteem, restraint, and body dissatisfaction." The education intervention group showed no change. Another study (2) looked at the effects of "cognitive treatment" and "behavioural treatment" in obese binge eaters and obese non-binge-eaters. They found that both treatments had statistically significant positive effects on "shape concern, weight concern and eating concern, binge eating, self-esteem, and depression." However, there was little effect on weight loss with those in the behavior treatment group losing 3 kg (6.6 lbs) at the 1 year followup and those in the cognitive treatment group losing 0.3 kg (0.66 lbs). Interestingly, they found that participants who gained weight had equal improvement in their psychological well-being as those who lost weight.

In 2002, Bacon et al. (3) did the first study comparing a HAES-type program to a traditional weight-loss-centered diet program. They looked at subjects they described as "Obese, Caucasian, female, chronic dieters, ages 30-45." These women were divided into two groups, one of which participated in a HAES-type program, with the others following a traditional diet program. Both groups received 6 months of weekly group intervention followed by 6 months of monthly after-care group support. After this year, they found that both groups had demonstrated significant improvements in metabolic fitness, psychological variables and eating behaviors. While they reported that attrition was high in the diet group (41%) compared to the HAES group (8%), the diet group showed significant weight loss (5.8 kg or 13 pounds) the HAES group did not. The authors concluded from this that the main advantage of HAES over traditional dieting is the lack of attrition.

In 2005 Bacon's group at Davis published another study, the first one to actually use the term "Health at Every Size" (4). While this study was very similar in methodology to the first one they had published, the results were quite different. While the HAES group did not show any significant change in weight throughout the study period, members of the diet group lost an average of 5.8 kg in the initial six months, however, in the six month followup period they gained back some of that weight, and they found the net change in weight (3.2 kg, or 7 pounds) to be statistically insignificant. They found that the HAES group improved their total cholesterol, HDL, LDL and systolic blood pressure scores, whereas the diet group did not. They also found that the HAES group had significant long-term improvement (this was measured 2 years out) in a number of measures of psychological well being and eating disordered behavior, whereas the diet group showed long-term improvement in only a couple of these measures.

So how should these conflicting findings be interpreted? The papers by Bacon's group at UC Davis seem particularly confusing, as their two studies were carried out under very similar conditions but had quite different results. This may have been a result of their small sample size (after attrition, there were only 19 women left in the diet group in their second study). It also may have been a result of demographic differences between the two groups in that second study. While the authors do not mention this explicitly, a table in the paper shows that in the HAES group, 89.5% of women were married or in a domestic partnership, whereas only 68% of the women in the diet group were in such relationships. The two groups also differed in their education levels: 53% of the HAES group were college graduates, whereas 63% of the diet group were. These disparities may have resulted from the attrition in the diet group, but they are probably an important factor to consider in assessing the results of this study.

Another problem with studying interventions like HAES counseling is that it is subject to significant observer bias. If you are studying, say, a drug, you can do a double-blind study where both the doctors who are scoring the outcomes of the study and the subjects themselves are unaware whether they are being treated with the drug in question or a placebo. If you are comparing two types of counseling that is obviously not possible. In these studies, it is possible that the HAES counselors were simply better or more enthusiastic than the counselors leading the control groups.

Clearly, many questions remain about HAES. A few things do seem to be consistent from study to study, though. There seems to be reasonable evidence that HAES improves self-esteem. Its effects on weight loss, binge eating, and other physical measures are less clear.

1. Ciliska D. Evaluation of two nondieting interventions for obese women. Western Journal of Nursing Research 20: 119-135, 1998.

2. Nauta H, Hospers H, Jansen A. One-year follow-up effects of two obesity treatments on psychological well-being and weight. British Journal of Health Psychology 6: 271-284, 2001.

3. Bacon L, Keim NL, Van Loan MD, Derricote M, Gale B, Kazaks A, Stern JS. Evaluating a "non-diet" wellness intervention for improvement of metabolic fitness, psychological well-being and eating and activity behaviors. International Journal of Obesity and Related Metabolic Disorders, 26: 854-865, 2002.

4. Bacon L, Stern JS, Van Loan MD, Keim NL. Size Acceptance and Intuitive Eating Improve Health for Obese, Female Chronic Dieters. Journal of the American Dietetic Association 105: 929-936, 2005.

Thursday, March 6, 2008

I take requests...

Just wanted to mention that while I do have a list of topics I eventually hope to cover here, I am also happy to write about things that people are curious about. So please feel free to post to the comments if there's something you have in mind!

John Godfrey Saxe neatly summarizes scientific inquiry

I've always thought that the John Godfrey Saxe poem Six Blind Men & the Elephant was a great metaphor for scientific inquiry.

You are probably familiar with the poem, but to summarize it, six blind men go to visit an elephant and each explores a different part of the elephant with his hands and comes to a different conclusion about what the elephant looks like. The first man feels the elephant's side and concludes that the elephant is like a wall. The second feels a tusk and concludes that the elephant is like a spear. The third feels the trunk and declares than the elephant is like a snake. The fourth feels the elephant's knee and declares the creature to be tree-like. The fifth touches the elephant's ear and says it is like a fan. And the sixth feels the tail and says it is like a rope.

Of course, they are all partially right and yet also wrong. Ideally, the next step would be for all six men to discuss their findings and to thereby collectively come to a broader understanding of the elephant. That obviously doesn't happen in the poem and it doesn't always happen in science, either. I think it also doesn't help that media accounts of science tend to focus on single studies rather than on the body of knowledge in a given field (news report: Elephants are like spears!).

I guess what I am really trying to say here is that while every study is limited in its scope, those limitations don't necessarily make a study "wrong." One particular example I encounter a lot in reading blogs is that people frequently critique epidemiologic studies (studies looking at behavioral and disease trends in large populations) by pointing out that correlation and causation are not the same thing. That is a fair enough point, but that doesn't mean that correlation is not a useful piece of information. It's often a great jumping-off point for further studies that may establish causation.

So, basically, it's a good thing to be aware of any study's limitations. But a limitation doesn't necessarily mean that the findings are invalid.