What Causes You to Consume Too Many Calories?

There’s no doubt that Americans continue to get fatter.  Twenty years ago, no US state had an obesity rate above 15%; today, more than two out of three states (38 in all) have obesity rates over 25%, and just one has a rate lower than 20%.  The equation “calories in – calories out = weight change” may sound simplistic, but studying the changes responsible for increased calorie intake is a useful way to spot where the trouble lies.

Chapel Hill, North Carolina, researchers have surveyed eating habits over the last 30 years, and published their findings in the online journal PLoS Medicine.  They set out to examine the combined contribution of changes in portion sizes, the caloric level of foods (caloric density), and eating frequency on total calorie consumption.  They used cross- data from the Nationwide Food Consumption Survey (1977–78), Continuing Survey of Food Intakes of Individuals (1989–91), and National Health and Nutrition Examination Surveys (1994–98 and 2003–06) for adults in their NIH-funded study.

There was an increase in daily total calorie intake and the number of daily meals/snacks between 1977–78 and 2003–06. The average portion size increased between 1977–78 and 1994–98, and then dropped slightly between 1994–98 and 2003–06.  The average caloric density of food remained steady between 1977–78 and 1989–91, and then declined slightly between 1989–91 and 1994–98.

How do the researchers interpret these findings?  Large portion sizes drove the rise in calorie intake during the early part of the study period.  But when people became aware of portion sizes, they declined somewhat.  Instead, however, the number of ‘eating occasions’ – meals and snacks – increased, and they have now taken over the driving seat.  In fact, the average number of daily meals and snacks has increased from 3.8 in 1977 to 4.8 in 2006.

This study strongly suggests that efforts to prevent obesity in US adults should focus on reducing the number of meals and snacks people consume during the day.  Of course, switching to low-calorie-dense foods and taking more exercise wouldn’t hurt, either.  And watch out for portion-size creep.