You already know you need to eat well and exercise regularly in order to score a killer beach body. But new research has found that your brain might be working against you.

A recent Harvard study found that we regularly think serving sizes are smaller than they actually are, leading us to eat and drink more than we realize.

In the study, researchers asked 294 people to estimate how much liquid was in a variety of cups (starting at 12 ounces and working up to a whopping 50-ouncer). Study participants consistently guessed wrong, estimating that the bigger cups held 20 to 40 percent less liquid than they actually did. (Other studies found the same results using jelly beans, popcorn, ice cream, and booze.)

What's up with that? Scientists say our brain just has trouble accurately gauging how big something is. With foods that are packaged a certain way, like drinks that have wider tops than bottoms, it becomes even harder for us.

Want make sure you're not super-sizing your portions? Eat protein servings like hamburgers, fish, omelettes, etc., that are no more than the size of your fist, and keep in mind that the standard serving size for drinks is eight to 12 ounces. When in doubt, read the label, if it's available. Your bikini bod will thank you.

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