Call IT Fattergate. Americans are getting scandalously big for their britches (and shirts and skirts and dresses and suits). And scientists would like to know why, so they can make it stop. After all, this sharp trend toward a well-rounded population has some pretty hefty (and heinous) consequences for public health.
There's a simple explanation for the weight gain, of course: People consume more calories than they burn. The favorite explanation: They eat bigger portions of less nutritional foods at easier-to-get-to fast food places, even as they hunker down more and more faithfully in front of their TV and computer screens. "Most of us say it is a combination of reduced energy expenditures plus dietary intake not declining enough," says Barry Popkin, a nutrition professor at the University of North Carolina at Chapel Hill.
But why does that happen far more often now than 30 years ago? It's not obvious, says Susan Roberts, a senior scientist at the Human Nutrition Research Center on Aging at Tufts University in Boston: "There is definitely no definitive answer on 'what went wrong.' "
Even as researchers try to refine the eat-too-much-move-too-little theory, some are entertaining other ideas (obesity virus, anyone?). Read on for some of their theories, as well as a weigh-in from our panel of obesity researchers.
HIGH-FRUCTOSE CORN SYRUP
The theory: High-fructose corn syrup (HFCS) was introduced in the 1970s, about the time the obesity epidemic was first taking off. Maybe the syrup has some special, inimical quality that makes it wreak havoc with our fat cells.
The research: Made from corn, HFCS comes in two forms, 42% fructose or 55% fructose, the rest being primarily glucose. Regular table sugar (sucrose) is 50% fructose and 50% glucose.
Consumption of HFCS took off like a shot when it was introduced, but because it generally replaced sugar in foods and beverages, stats from the U.S. Department of Agriculture show that consumption of sugar dropped just about the same amount, says HFCSfacts.com, a website dedicated to all things HFCS and associated with the Corn Refiners Assn. Because the composition of sugar and HFCS is quite similar, the mix of glucose and fructose in foods and beverages is close to what it was 30 years ago, according to the site.
There have been several reviews of the HFCS-obesity link. Last month, the American Medical Assn. issued a report on HFCS and obesity after conducting a review of articles published through 2007. The authors concluded the evidence didn't support a special obesity link and wrote, "Because the composition of HFCS and sucrose are so similar, particularly on absorption by the body, it appears unlikely that HFCS contributes more to obesity or other conditions than sucrose." Some recent data raise new questions. Peter Havel of UC Davis presented a study at an Endocrine Society meeting last month in which he followed 33 overweight and obese adults as they dieted for 12 weeks. During the last 10 weeks, half of them got 25% of their calories from fructose, and half got 25% from glucose. Though both groups gained the same amount of weight -- 3.3 pounds -- those who had the fructose had an increase in the least-desirable fat (the kind that wraps around internal organs, causes a pot belly and is linked to higher risk of diabetes and heart disease) while the others did not.
The fructose-eaters (but not the glucose-eaters) also had heightened levels of triglycerides and cholesterol and decreased insulin sensitivity, a danger sign for diabetes.
Our experts weigh in: "A number of recent studies . . . have convinced me that HFCS does not affect weight gain," says Barry Popkin of the University of North Carolina, who was an early proponent of the HFCS-obesity hypothesis. "At the same time, there is a new body of research that suggested HFCS might be linked with higher triglyceride levels and other health effects. This research is too preliminary to make any conclusion."
Adds Dr. Julie Lumeng of the University of Michigan: "By exposing children to more sweet foods . . . you may be inducing a long-term preference for sweets that leads to excessive caloric consumption."
TOXINS AND POLLUTION
The theory: The pollution in our environment can poison our chances to lose weight.
The research: In a 2004 study published in the International Journal of Obesity, 15 obese people lost an average of 23 pounds on a 15-week diet. When researchers compared blood samples at the end of the diet with ones taken before the diet began, they found two differences: Concentrations of leptin -- the hormone that usually keeps hunger in check -- were 33% lower. And concentrations of industrial chemicals called organochlorines were 23% higher.