Bisphenol A (BPA), an extraordinarily common chemical found in items such as food and drink cans, plastic containers and paper receipts and tickets, may be to blame. In the online journal PLoS One, Spanish researchers reported that exposing human pancreatic cells to minute amounts of BPA caused them to release nearly double the insulin necessary to metabolize a meal. Over time, this excess insulin may encourage the body to store more calories as fat, boosting your waistline. Most Americans probably have BPA circulating at higher levels in the blood than the amount in the study, says Hugh Taylor, MD, a reproductive endocrinologist at Yale University. To reduce your exposure to the chemical, choose fresh foods over canned goods, reheat leftovers in nonplastic containers and order tickets online so you can print them at home on BPA-free paper.