Americans are getting bigger, studies show. But it's not entirely your fault: As the number of overweight Americans goes up, so has the amount of food in a baseline portion size, Business Insider reported.

Consumers have little control over the size of meal serving portions, whether they’re from a fast food restaurant, a sit-down restaurant, or a grocery store.

But the average size of our foods has increased 138 percent since the 1970s, according to the American Journal of Public Health, the Journal of Nutrition, and the Journal of the American Medical Association.

Here are examples cited by Business Insider:

There are a variety of reasons why Americans are getting bigger, according to a study in the American Journal of Public Health by Lisa R. Young and Marion Nestle of the Department of Nutrition and Food Studies at New York University. The share of food consumed outside the home went up from 34 percent in the 1970s to 47 percent by the late 1990s, the study found.

At the same time, the portions at most restaurants exceeded what the U.S. Department of Agriculture and Food and Drug Administration deemed a normal portion size. So as more Americans ate out — a trend spurred by the improved economic stability of the 1970s — meal sizes grew beyond sensible portion sizes.

Companies also advertised larger sizes as key selling points, the study found. That applied even to diet meals such as Lean Cuisine and Weight Watchers frozen dinners.

It's a serious issue. Obesity rates currently surpass 35 percent in three states: Arkansas, West Virginia, and Mississippi, according to the State of Obesity’s latest report in September. Twenty-two states have obesity rates above 30 percent, and 45 states are above 25 percent, with the majority of the most obese states in the South and Midwest. No states had an obesity rate lower than 20 percent.

This map illustrates the increase in the obesity rate from year to year. Not a single state has seen a decrease in its obesity rate.

The State of Obesity - stateofobesity.org

Doctors advise exercising and eating right to lose weight. But you should also worry about the size of your plate — and the amount of food piled on it as well.