A new report says obesity in the United States has reached what it describes as epidemic proportions.

The report -- in the latest issue of Science Magazine -- says the number of overweight people has risen dramatically over the past twenty years.

The author, Dr James Hill , the director of Clinical Nutrition Research United at the University of Colorado, says that if the trend continues, the entire American population could be overweight within a few generations.

Dr Hill blames high-fat and high-calorie diets, and says the current epidemic of obesity is caused largely by an environment which promotes excessive food intake and discourages physical activity.