Bad eating habits, a sedentary lifestyle and ever-larger portions of food have conspired to make the United States the fattest nation on Earth. The National Institutes of Health estimates that 97 million American adults – 55 percent of the adult population – now are overweight or obese. Public health officials say that weight problems often lead to chronic diseases, such as diabetes and high blood pressure, and contribute to as many as 300,000 deaths annually. Dieting and more exercise are the two most obvious solutions. But many Americans who lack the time or will are turning to medically assisted weight loss and diet drugs that promise to melt away pounds without significant lifestyle changes. Few of the drugs have been rigorously tested, and some have proven dangerous.