By Brierley Wright, M.S., R.D. , June 25, 2009 - 4:36am
It’s the time of year when my friends and I are trying to get—or keep—a slim and sexy body, be it to rock my new bikini at the beach or a bridesmaid dress in my friend’s wedding. We all go about it in a different way, though none of us thinks that dieting could fog our brains, even on the sunniest day. I prefer to tack a few more miles onto a run when I’m trying to slim down. (Get more exercise ideas and tips here. ) But most of my friends find it easier to cut back on how many calories they’re eating. Both methods will you get slim, but some diets may muddle your memory, according to new research reported by Rachael Moeller Gorman in EatingWell’s June issue. (Read the full story here. )
In a new study from Tufts University, 19 overweight women followed either a “low-carbohydrate” or a “low-calorie” diet, based on American Dietetic Association guidelines, for three weeks. After the first week, people in the low-carbohydrate group, who were told to completely eliminate carbohydrates from their diets, did worse on tests of working memory (i.e., why did I walk into this room?) and visuospatial memory (remembering locations on a map) than people in the low-calorie group. (Find 25+ delicious low-calorie recipes here. ) Fortunately for the study subjects, “memory performance returned to normal when we re-introduced carbohydrates in the second week of the study,” says Holly Taylor, Ph.D., cognitive psychologist at Tufts and co-lead investigator on the study. A piece of fruit or one-quarter of a slice of bread seemed to be enough.
Another study, published in The American Journal of Clinical Nutrition in 2007, showed that people on a higher-carbohydrate diet processed information more quickly than those on a low-carbohydrate diet.
Why? “The brain’s primary fuel is glucose,” says Taylor. Eating carbohydrate-rich foods—grains, fruits, vegetables—is by far the most efficient way of keeping the brain’s glucose supply on “full.” Try these recipes for a healthy mind—and memory.  But the body can only store one to two days’ worth of glucose, and when these stores are gone, glucose levels in the blood (also known as “blood sugar”) drop. Fats and proteins can be backup fuel sources, but they don’t provide the glucose needed to sustain peak brain power.
The good news: All diets don’t dampen brain power. A balanced, low-calorie diet, like the EatingWell Diet , may, in fact, boost it. A study in the Proceedings of the National Academy of Sciences earlier this year showed that restricting total calories by up to 30 percent for three months actually increased verbal memory scores (i.e., how many words were remembered 30 minutes after seeing them) in a group of elderly people. Researchers suspect that losing weight improved the body’s ability to use glucose, and that this allowed the brain to work more smoothly.
Bottom Line: Be cautious about striking carbohydrates from your diet: you may lose more than just a few pounds. The Recommended Dietary Allowance for carbohydrates is 130 grams per day, a number based on the amount of glucose the brain needs to function optimally. What does 130 grams look like? A cup of oatmeal, plus an apple, two slices of whole-wheat bread and 3/4 cup of cooked pasta.