Caveat Eater: Rice, Bread, Pasta -- Oh My!

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The craze for high-protein, low-carbohydrate diets is on the wane. One sure sign is that Atkins Nutritionals, the company that produces Atkins Diet-related products, declared bankruptcy this summer. Another is that the number of low-carb foods introduced this year was down compared to the past two years. But not everyone has given up the extreme approach to shedding pounds. So, if you're on a high-protein, low-carb diet, watch out: You may be courting a nasty case of "Um ... er ... ah, what was I saying?" in front of an unforgiving classroom of students. According to nutritionists, diets too low in carbs can affect brain power, not to mention energy, bone mass, and kidney function.

On a low-carb diet, "you'll have problems with word recall, and you'll feel less sharp," says Diane Stadler, research assistant professor in the Oregon Health and Science University's Health Promotion and Sports Medicine Division.

Dietary reference tables published this year by the Institute of Medicine indicate that to achieve and maintain normal brain function, adults and children need 130 grams of carbohydrates a day. On the Atkins Diet or similar regimens, you're allowed to eat about 20 grams of carbs daily at first; you can later nudge up the intake, but never to the minimum amount nutritionists recommend.

"Restricting carbs like that is going to have an effect on the brain," Stadler warns. She adds that a high-protein/low-carb diet can also whittle away at your bone mass, regardless of your age or relative health. Diets high in meat raise the acid level of blood, increasing excretion of calcium and phosphorus from the bone, which leads to early loss of bone density and accelerating osteoporosis. High-protein diets that rely on meat also decrease levels of urinary citrate, which can cause kidney stones.

As distance runners know, carbs are fuel, so if your lifestyle includes intense cardio workouts or you plan to start an exercise program at the same time you begin a high-protein diet, you may lack the stamina for even thirty minutes on an elliptical machine.

"Even going up a flight of stairs, not just working out, you're going to have some fatigue," says Stadler. And though you may be okay during short workouts with weights, Stadler adds that the potassium concentration of a high-protein diet is more likely to cause muscle cramps.

Diet guru Dr. Dean Ornish also worries about the effect of such diets on the kidneys. "High total protein intake, particularly animal protein, may accelerate renal-function decline," says Ornish.

More dangerous possible consequences exist, such as raised levels of bad cholesterol, as does a less dire but socially embarrassing side effect: bad breath. But losing focus while trying to hold students' attention is a professional downside that even a rapid drop in weight can't justify. Working to get yourself in better shape is a worthy goal, but when shape trumps sharpness, something's got to give. So cook yourself a veggie stir fry on rice, whip up a plate of pasta primavera, or have a slice of whole-grain bread with your soup. Carbs are back. Your brain is hungry for them.