A family eating lunch together outside. Image Credit: Maria Teijeiro/Photodisc/Getty Images

A rise in the daily consumption of calories can be blamed for America's obesity epidemic. When you take in more calories than you burn, you gain weight. By 2010, Americans consumed 20 percent more calories compared to 1970, according to "The New York Times." The added calories expand America's waistline and increase the health-related costs associated with obesity.

How Much You Need

The average American adult woman needs between 1,800 and 2,400 calories per day, while the average American adult man needs between 2,400 and 3,000, according to the U.S. Department of Agriculture's 2010 Dietary Guidelines. Younger, more active folk can consume a higher number of calories and still maintain their weight. Eating just 250 more calories daily than your body requires for body functioning and exercise leads to a 26-pound weight gain in a year. A 20-ounce bottle of soda, half of a bakery cupcake and many fancy coffee drinks all contain at least 250 calories.

What People Actually Consume

The average number of calories consumed falls within the USDA guidelines, but it's unclear if these numbers -- which are self-reported -- are accurate or appropriate for the size and activity level of each person. In 2010, the average adult woman reported consuming 1,785 calories per day and adult man, 2,640 per day. The USDA suggests that these numbers are probably lower than what is consumed in reality. A study published in a 2003 issue of the "Annals of Epidemiology" found after examining the food diaries of 161,856 women, the underestimated calorie intake was 25 percent on average. If this is the case, Americans may be consuming more like 2,231 to 3,300 calories per day.

What Americans Are Eating

The calories Americans consume don't always come from healthiest sources either. Among the top five sources of calories for adults are grain-based desserts, alcoholic beverages and soda or other sugary drinks. These foods provide a lot of calories with minimal nutrition. "The New York Times" reports USDA statistics revealing that from 2005 to 2008, 20 percent of American calories were consumed from restaurants, including full-service and fast-food -- this is three times the amount consumed in restaurants from 1977 to 1978.

Knowing What You Need