The University of Minnesota has turned to U.S. food supply sources for information about Americans' food consumption instead of traditionally asking the American public when it comes to such matters. Results show that dining out, convenience foods and large portions play a major role in the obesity of Americans.

Studies in the past have surveyed the American people, only to find that few are honest when reporting what they actually eat. Social pressure and guilt often influence participants to lie in the surveys about the quantity and type of food they consume. The new study produced some alarming statistics revealing factors contributing to overweight Americans.

Portion sizes are increasing and more restaurants are marketing meals that include more than a single serving.

The percentage of food dollars spent on food eaten away from home increased from about 20 percent in the 1970s to 38 percent in 1992.

Fast-food restaurants are growing at about 7 percent annually, while the restaurant industry as a whole increases at only 3 percent.

Americans are spending less time preparing meals at home, and supermarkets are increasing their selection of prepared foods.

"We investigated data regarding the quantities and types of foods available for potential consumption by Americans from 1970 to 1998 on a per capita basis. Assuming that food spoilage and waste remain constant over time, our findings indicate that total energy intake has increased substantially and is likely the cause of higher average body weight," said Lisa J. Harnack is the author of the study that was published in the American Journal of Clinical Nutrition.