Empty calories aren't just bad for your belly. They can be downright ruinous for your brain -- and the latest research shows again how people who eat the most have the highest risk of memory problems.

That means watching what you eat now could be the simplest way to avoid dementia later on.

Researchers divided some 1,200 seniors between 70 and 89 years old into three categories based on how many calories they ate each day: a third consumed between 600 and 1,526 calories a day, a third chowed down on between 1,526 and 2,143, and the final third ate between 2,143 and 6,000 calories a day.

Those in that last group had double the risk of mild cognitive impairment compared to the rest of the eaters in the study, even after adjusting for other risk factors like age, education and health history.

But if you've noticed that the last category was rather broad, you're not alone.

It seems to me there's a huge difference between someone who eats 2,200 calories a day -- which can be healthy, depending on how you get those calories -- and someone who gorges on 6,000 calories a day... which isn't healthy no matter what you eat.

Yet in this study, they're both lumped into the same group. In addition, the study was based on food frequency questionnaires -- so those numbers are guesstimates at best.

But I'm not ready to write this study off yet, either, because there's a clear link between diet and dementia -- and other studies have also found that people who weigh the most have the highest risk of the condition.

One study found that women with the biggest waistlines in middle age had double the risk of dementia in old age. Another found that men and women alike with the highest levels of abdominal fat have more than triple the risk of dementia of those with the least.

And yet another study last year found that overweight people see significant improvements in both memory and concentration when they lose weight.

But if that's not enough of a reason to drop the extra pounds, consider all the other risks that accompany obesity: heart disease, diabetes, cancer, depression and -- of course -- an early demise.

If you can avoid all that by eating a little better, I say go for it.