During the years 1976 through 1980, 15 percent of U.S. adults were obese. Today, about 40 percent of adults are obese. Another 33 percent are overweight. Coinciding with this increase in weight are ever-rising rates of heart disease, diabetes, cancer and health complications caused by obesity, such as hypertension. Even Alzheimer’s disease may be partly attributable to obesity and physical inactivity. In a study published Thursday in the journal Current Biology, researchers demonstrate that the pleasure center of the brain that produces the chemical dopamine, and the brain’s separate biological clock that regulates daily physiological rhythms, are linked, and that high-calorie foods — which bring pleasure — disrupt normal feeding schedules, resulting in overconsumption. Using mice as study models, the researchers mimicked the 24/7 availability of a high-fat diet, and showed that anytime snacking eventually results in obesity and related health problems. The National Institute of General Medical Sciences and University of Virginia Brain Institute funded the research.