The Calorie Control Council is having a bad month. The group, which represents "the low-calorie and reduced-fat food and beverage industry" has got to be hurting after a couple of high-profile studies getting media coverage in the last month cast doubt on the healthfulness of some of these products.
The first of these studies, by Lutsey et al. (1) showed that higher consumption of diet soda was associated with an increased risk of metabolic syndrome. What is metabolic syndrome? It's when you have three or more of the following: waist circumference >102 cm in men or >88 cm for women; triglycerides >150 mg/dl, HDL cholesterol <>130 mm Hg, diastolic blood pressure >85 mm Hg or use of antihypertensive medication; and fasting glucose > 100 mg/dl or treatment for elevated glucose. These things are of concern because they confer a heightened risk for heart disease and type II diabetes.
What these authors did was looked at a group of people who didn't have Metabolic Syndrome and gave them a long quiz about how much they consumed of 66 different foods and beverages. Then they looked for associations between people eating more or less of certain foods and whether they had developed Metabolic Syndrome after 9 years of followup. I will refer to Metabolic Syndrome as "MetSyn" for the rest of this blog post because I am a bit of a lazy typist.
The authors found that a "Western dietary pattern" and high consumption of meat (especially hamburgers and hot dogs), fried foods, and, surprisingly diet soda were associated with increased rates of MetSyn, and high consumption of dairy was associated with a lower risk. The authors were also surprised that they didn't see any association of MetSyn risk with whole grain or fruit and vegetable intake. They say the dairy (2-4) and diet soda (5) findings were also found in previously published studies by other groups. They controlled for age, race, sex, education, total caloric intake, baseline overweight, smoking, exercise, and what seem to me to be all the other obvious possible cofactors.
So what can we say about the health risks of diet soda? This is an epidemiologic study, so it just establishes an association, not a causal relationship or a mechanism. It may be that some component of diet soda has a biological effect on people who drink it that makes them more prone to MetSyn. Or it could be that some other behavior or genetic variant that predisposes people to drink more diet soda also predisposes them towards MetSyn. At any rate, it's quite a strong association. The authors of this study found that people who drank the most diet soda had a 34% higher risk of developing metabolic syndrome than people who drank the least. They say that data from the Framingham Heart study showed that drinking 1 or more diet sodas a day increases your risk of metabolic syndrome by 56% (5). They didn't see any association with sweetened beverages.
These data seem pretty striking, although it is notable that a lot of things you might expect to be associated with Metabolic Syndrome risk weren't, according to their study (like fruits and vegetables and whole grains, which are supposed to be protective against obesity). As the authors say, "[a]dditional research on the relation between diet soda and incident MetSyn is clearly warranted."
The second study is not yet published but is slated to appear in next month's issue of Behavioral Neuroscience. In this study, they divided male rats into two groups: one group was fed yogurt sweetened with glucose (sugar) in addition to their normal chow, and the other was fed yogurt sweetened with saccharin along with chow. They apparently found that the rats in the saccharin group ate more calories, gained more weight and body fat, and had a decreased metabolic response to food, indicating that saccharin somehow predisposes rats (and possibly their human cousins) to weight gain.
While there are still a lot of unanswered questions resulting from these studies (particularly from the latter one, which has still not even been published, meaning that what we know about it comes from a press release), I know that this news made me think twice about my own Diet Coke habit. But are artificial sweeteners to blame for the increased risk of MS with diet soda consumption? Are all artificial sweeteners alike? Do humans and rats respond the same way to artificial sweeteners, particularly given that humans have access to a much more varied diet than lab rats?
For now, I've cut way back on the Diet Coke...it's more expensive than water or tea anyway and there's no reason why I need to drink it.
1. Lutsey PL, Steffen LM, Stevens J. Dietary Intake and the Development of the Metabolic Syndrome. The Atherosclerosis Risk in Communities Study. Circulation e-pub ahead of print, January 22, 2008.
2. Azadbakht L, Mirmiran P, Esmillzadeh A, Azizi F. Dairy consumption is inversely associated with the prevalence of the metabolic syndrome in Tehranian adults. American Journal of Clinical Nutrition 82:523-530, 2005.
3. Mennen LI, Lafay L, Feskens EJM, Novak M, Lepinay P, Balkau B. Possible protective effect of bread and dairy products on the risk of metabolic syndrome. Nutrition Research 20: 335-347, 2000.
4. Pereira MA, Jacobs DR Jr., Van Horn L, Slattery ML, Kartashov AI, Ludwig DS. Dairy consumption, obesity, and the insulin resistance syndrom in young adults: the CARDIA Study. Journal of the American Medical Association 287: 2081-2089, 2002.
5. Dhingra R, Sullivan L, Jacques PF, Wang TJ, Fox CS, Meigs JB, D'Agostino RB, Gaziano JM, Vasan RS. Soft drink consumption and risk of developing cardiometabolic risk factors and the metabolic syndrome in middle-aged adults in the community. Circulation 116: 480-488, 2007.