Another area that has some scientists excited is the question of how weight gain is linked to chemicals we are exposed to every day--things like the bisphenol A (BPA) found in linings of canned-food containers and cash-register receipts, the flame retardants in sofas and mattresses, the pesticide residues on our food and the phthalates found in plastics and cosmetics. What these chemicals have in common is their ability to mimic human hormones, and some scientists worry they may be wreaking havoc on the delicate endocrine system, driving fat storage.
"The old paradigm was that poor diet and lack of exercise are underpinning obesity, but now we understand that chemical exposures are an important third factor in the origin of the obesity epidemic," says Dr. Leonardo Trasande, an associate professor of pediatrics, environmental medicine and population health at New York University's School of Medicine. "Chemicals can disrupt hormones and metabolism, which can contribute to disease and disability."
Another frontier scientists are exploring is how the microbiome--the trillions of bacteria that live inside and on the surface of the human body--may be influencing how the body metabolizes certain foods. Dr. Eran Elinav and Eran Segal, researchers for the Personalized Nutrition Project at the Weizmann Institute of Science in Israel, believe the variation in diet success may lie in the way people's microbiomes react to different foods.