What's Really Making Us Fat?

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It may not be as simple as calories in, calories out. New research reveals a far more complex equation for weight gain that places at least some of the blame on organic pollutants.

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Conventional wisdom says that weight gain or loss is based on the energy balance model of "calories in, calories out," which is often reduced to the simple refrain, "eat less, and exercise more." But new research reveals a far more complex equation that appears to rest on several other important factors affecting weight gain. Researchers in a relatively new field are looking at the role of industrial chemicals and non-caloric aspects of foods -- called obesogens -- in weight gain. Scientists conducting this research believe that these substances that are now prevalent in our food supply may be altering the way our bodies store fat and regulate our metabolism. But not everyone agrees. Many scientists, nutritionists, and doctors are still firm believers in the energy balance model. A debate has ensued, leaving a rather unclear picture as to what's really at work behind our nation's spike in obesity.

Bruce Blumberg, professor of developmental and cell biology and pharmaceutical sciences at the University of California, Irvine, who coined the term "obesogen," studies the effect that organotins -- a class of persistent organic pollutants that are widely used in the manufacture of polyvinylchloride plastics, as fungicides and pesticides on crops, as slimicides in industrial water systems, as wood preservatives, and as marine antifouling agents -- have on the body's metabolism. Organotins, which he considers to be obesogens, "change how your body responds to calories," he says. "So the ones we study, tributyltin and triphenyltin, actually cause exposed animals to have more and bigger fat cells. The animals that we treat with these chemicals don't eat a different diet than the ones who don't get fat. They eat the same diet -- we're not challenging them with a high-fat or a high-carbohydrate diet. They're eating normal food, and they're getting fatter."

The CDC reports that "nearly all" Americans tested have BPA in their urine, "which indicates widespread exposure to BPA in the U.S. population."

A widely reported study that came out in January in The American Journal of Clinical Nutrition (AJCN) would seem to dispute this finding: it confirms the belief in the energy balance model, and has been cited as proof by many researchers working in the field. I asked an author of the study, Dr. George Bray, professor of medicine at Louisiana State University, about the myriad of additives and industrial ingredients in our food that were not accounted for in this study. "It doesn't make any difference," he said in a telephone interview. "Calories count. If you can show me that it doesn't work, I'd love to see it. Or anybody else who says it doesn't -- there ain't no data the other way around."

The participants in the AJCN study were given low, normal, and high amounts of protein and 1,000 more calories than needed. The study does not take into account the content and form of calories, how they were processed, or with what additives or industrial chemicals.

Bray doesn't believe that additives or how foods are processed or produced will ultimately affect the outcome of studies. In fact, he completed research in 2007 that he refers to as his "Big Mac study," which fed participants three meals a day for three days giving one group fast-food items like Big Macs and the other group foods made "from scratch." Bray says the results showed that the type of food made no difference: "At least in an acute study measuring glucose tolerance, insulin, and things -- they don't make any difference. Now, if you fed them over a longer time period, it's clearly going to be the quantity that matters, largely."

One study conducted at Princeton University indicates that types of calories do matter. Researchers found that rats drinking high fructose corn syrup (HFCS) gained significantly more weight than rats drinking sugar water, even though the amount of calories consumed was the same. The rats drinking HFCS also exhibited signs of metabolic syndrome, including abnormal weight gain, especially visceral fat around the belly, and significant increases in circulating triglycerides.

Miriam Bocarsly, the lead author of the Princeton study and a Ph.D. candidate there, said in a phone interview: "The question of calories in, calories out is a very good one and is highly debated in the field. You have traditional nutritionists who say 'energy in energy out,' but we have this result and at this point all we can really say is that this is what is happening in the rat model. Something is obviously different between HFCS and table sugar, and the next question is, What is that difference?"

Blumberg says that fructose itself is an obesogen. "Crystalline fructose doesn't exist in nature, we're making that," he says. "Fructose is not a food. People think fructose comes from fruit but it doesn't. The fructose that we eat is synthesized. Yes, it's derived from food. But cyanide is derived from food, too. Would you call it a food?"

Robert H. Lustig, a pediatric neuroendocrinologist and a professor of pediatrics at the University of California, San Francisco, also believes that fructose is an obesogen. "I personally do lump fructose in with [obesogens]," he told me in an email. "There are those who don't, because fructose is a nutrient, and they want to think of an obesogen as a foreign chemical. But because fructose tricks the brain into eating more in a free-range situation, it has some properties consistent with an obesogen."

Lustig is another researcher and doctor who finds fault in the calories in, calories out model. "I don't believe in the energy balance model, which is calorie-centric," he says. "I believe in the fat deposition model, which is insulin-centric. The reason is that by altering insulin dynamics, you can alter both caloric consumption and physical activity behavior. This has been my research for the past 16 years." What Lustig means is that by increasing circulating insulin -- often as a result of consuming too much fructose -- people become hungrier and more fatigued, which results in overeating and little motivation to exercise.

Another possible obesogen that has made headlines recently is bisphenol-A (BPA), which is found in an overwhelming number of food items and packaging material. Frederick S. vom Saal, curators' professor at the University of Missouri-Columbia, receives funding the National Institute of Environmental Health Sciences for his research on BPA. "We do animal experiments with chemicals like BPA, and we dramatically alter the way fat is regulated in those animals," vom Saal said in a phone interview. "And they're not changing their food intake."

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Kristin Wartman is food writer based in Brooklyn. Her work has appeared in The Huffington Post, Civil Eats, and Grist.

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