The rise in obesity has been blamed on high and rising produce costs (erroneously), as well as increased portion sizes, cheap and appealing junk food, and inactivity. Yet, a recent study points to a simpler, behavioral factor: The number of daily snacks we consume has soared in the past three decades.

Looking at dietary data from several national surveys encompassing roughly 46,000 men and women (average age 44 years old), researchers found that overall calorie intake increased from 1,800 to 2,374 during the 30-year analysis — a dramatic 32% increase. So, what factor most significantly contributed to this increase? While portion sizes rose by about 13% during the time period, by far the most dramatic change was in snacking frequency: Back in 1977, the average adult had 3.8 meal noshes a day — by 2006, that number was 4.9, a 29% increase, which in turn accounted for an extra 570 calories a day.

Lead study author Barry Popkin, Ph.D., of the University of North Carolina at Chapel Hill, had previously determined that the amount of time we wait between snacks has shrunk by 23%, while the amount of calories consumed from extra eating has risen 23%. While certainly market and lifestyle changes may have made frequent snacking more convenient and appealing, the behavioral aspect of simply eating more often throughout the day should not be ignored. Those seeking to manage their weight may want to stick to a reasonable number of snacks — e.g., one mid-morning and one mid-afternoon. Moreover, switching out unhealthy junk snacks for a piece of fruit or a small portion of unsalted nuts can also help keep calories in check, while leveraging snacking to improve nutrition.

Bonus: Unhealthy snacking may be driving childhood obesity as well. Research shows junk food snacks account for 27% of children’s total calories consumed.

 Published August 1, 2011