Follow our easy tips to make sure you're serving yourself the proper portions of food by checking labels, learning portion sizes, and splitting up meals and snacks.

Portion distortion: We tend to think of everything on our plates as a single portion.

RODALE NEWS, EMMAUS, PA—Could you tell how many calories were in the breakfast you had today? Probably not, but that's normal, suggests a study presented this month at the annual American Psychological Association. But not knowing how many calories we eat may be a big reason that obesity rates are risk, experts say.

THE DETAILS: In the study, college students were shown three portions—small, medium (two times the size of “small”), and large (three times the size of “small”)—of six junk foods (a Snickers bar, a cookie, Skittles candies, Red Vines licorice, a brownie, and peanuts) and asked to estimate the number of calories in each portion. The study authors write: “As hypothesized, the participants were insensitive to sample size. On average, as the portion size tripled, participants’ calorie estimates increased by only about 50 percent.” When it came to the peanuts, the students were off even more: They gave roughly the same calorie estimate for all three portions.

WHAT IT MEANS: Even if we know overeating is unhealthy, the human brain doesn't seem wired to calculate calories or portion sizes. "Research has shown unequivocally that people eat the entirety of what they’re served and consider what they’re served a single portion, no matter how large what they’re served happens to be,” says Yale University psychologist Andrew Geier, PhD, an expert on portion control. What's more, he says, the abundance of food that most of us have access to leads us to focus more on value—how much we’re getting for our money—than simply how much we’re getting, period. “We’re so focused on value in America that we really have to make a point of reteaching ourselves that personal health, as a priority, trumps value,” says portion-control expert Andrew Geier, PhD. “Besides, start to lose your health, and you’ll quickly find out how expensive that is.”

But you can change all that: The trick is not only to control what you’re served, but to know exactly how much you should be served in the first place.