In a recent study mice were given free access to a nutritionally balanced diet or a diet that was high (61% of calories!) in fat. Some mice were allowed total access to the food at all times; others were only allowed access for an 8-hour window during the early phase of their normal active period. Mice given total all-day access to a high-fat diet (the standard American diet) developed obesity, diabetes, and metabolic syndrome and poor sleep-wake rhythms. Now for the good news! The mice that had time-restricted access to the high-fat diet were significantly healthier than the mice given all-day access to the same diet. These lucky mice lost body fat and had normal glucose tolerance, reduced serum cholesterol, improved motor function, and normal sleep cycles. Most surprising, the daily caloric intake of all groups did not differ, regardless of their diet or feeding schedule. Therefore, it truly does matter when you eat. The take-home message is eat early, skip dinner, and never have late-night snacks. Skipping breakfast and then overeating in the evening play a significant role in weight gain and obesity.