Top athletes make sure they know precisely what they eat every day. New England Patriot's quarterback Tom Brady follows a strict routine of 80 percent vegetables and whole grains, along with 20 percent lean meats.

But chances are you can't remember what you ate yesterday.

A couple of years ago, 75 percent of Americans told pollsters they ate healthfully, even though 90 percent fail to eat the recommended amount of fruits and vegetables, according to the Centers for Disease Control and Prevention.

It's little wonder that 70 percent of U.S. adults are overweight or obese, and don't know how they got that way.

If that's you, try this trick that's proven to work: Keep a food diary.

The act of writing down, every day, everything you put in your mouth will automatically help you eat better. That's the conclusion of a study published in the journal Obesity.

The researchers acknowledge that most people feel like keeping a food diary is an onerous task, but they show it isn't, and that it works. Over six months, study participants who lost 10 percent of their body weight spent only 14.6 minutes a day recording the calories and fat, as well as the portion sizes and preparation methods.

But don't get too obsessed. It was the frequency of making notes, not the quantity of details, that correlated with the greatest weight loss. Three or more entries a day was optimal.

So create a food diary where you can log of all the food you eat, or enlist a buddy or coach to email your food choices to daily.