Unless you've been living under a rock, you're probably aware of the low-carb craze. With fad diets such as Atkins and Paleo making the rounds, carbohydrates have gotten a seriously bad rap. But just as science grapples with the effects of cutting carbs, along comes a brand-new reason to put down the pasta fork: brain health.

A recent study published in the Journal of Alzheimer's Disease found that people on high-carbohydrate diets had four times the risk of mild cognitive impairment, or MCI. MCI often strikes before Alzheimer's disease, meaning that too many carbs could potentially lead to this debilitating illness. With 5.2 million Americans already suffering from Alzheimer's, many more may develop this disease as baby boomers grow older in the next decades.

Some scientists, like neurologist Dr. David Perlmutter, are taking a hard-line approach against carbs. Perlmutter is the editor-in-chief of Brain and Gut Journal, and believes that humans are not meant to eat grains or other high-carbohydrate foods at all. He advocates a diet of mainly proteins, fats and vegetables, claiming in his book Grain Brain that carbs are bad news for your IQ.

But as usual, the reality might not be quite so simple. Carbohydrates provide glucose, which is your brain's main source of energy. And when you severely limit carbohydrates, your body produces substances called ketones to provide alternative fuel. Over time, this creates a condition called ketosis, which can cause upset stomach, bad breath and possible kidney damage.

Most health experts recommend choosing carbs from whole-grain sources rather than shunning them altogether. Whole-wheat bread, whole-wheat pasta, brown rice, popcorn and oatmeal may be better for your brain than refined white grains because they don't cause the same spike in blood glucose.

The author of the aforementioned study, Professor Rosebud Roberts of the Mayo Clinic, noted that moderate carbohydrate intake is healthy and provides needed brain fuel. However, eating too many carbs actually prevents the brain from using that fuel, which may explain the decline in cognitive function.

Interestingly, the study also found that people who ate the most unsaturated fats, like those from nuts, canola oil and olive oil, were 42 percent less likely to get MIC. People on high-protein diets also had reduced risk, but only by an average of 21 percent.

Despite the research, the causes of Alzheimer's remain a mystery. Although it may be possible to reduce your risk with dietary changes, experts still don't fully understand how to prevent this disease. What you eat is probably just one factor among many, such as exercise habits and how often you engage in mental challenges.

Until we get more hard facts, your best bet is to stick with recommendations from the 2010 Dietary Guidelines for Americans. They advise getting between 45 and 65 percent of your total daily calories from carbohydrates, 10 to 35 percent of your calories from protein and 20 to 35 percent of your calories from fat. Many protein sources, such as red meat and cheese, are laden with unhealthy saturated fat; therefore, choose lean proteins such as egg whites and beans, and get your fat from almonds, canola oil, avocados and other plant foods. Following this plan will help your brain stay energized, and just may help keep you sharp as you grow older.