A Low-Carb Diet Can Hurt Your Memory

Repeatedly gaining and losing weight (yo-yo dieting) can slow metabolism and pose risks to your overall health. Now, scienctific studies are questioning whether these diets are dangerous to your brain's memory function, too.


Low-carbohydrate diets are notoriously difficult to adhere to for long periods of time. Many of my patients have tried a low-carb diet and lost weight, some over 100 pounds, but most often the weight came back... and then some. Repeatedly gaining and losing weight (yo-yo dieting) can slow metabolism and pose risks to your overall health. Now, scientific studies are questioning whether these diets are dangerous to your brain's memory function, too.

Slower brain functions

Researchers at Tufts University have found that dieters who strive to eliminate most carbohydrates from their diets scored significantly lower on memory-based tasks than did subjects who simply reduced the amount of calories they ate.

The study subjects included 19 women ages 22 to 55, 9 of whom were put on a low-carbohydrate diet and 10 on a low-calorie but balanced diet. All subjects attended 5 memory-testing sessions in which their spatial memory, attention, cognitive skills, and short and long-term memory were assessed. These sessions were conducted throughout the 3 weeks of the study.

After 1 week of severe carbohydrate restriction, memory performance among the low-carb group, especially when dealing with difficult tasks, gradually decreased compared with the low-calorie group. In addition, the low-carb dieters had slower reaction times and faltered during tests of their visual-spatial memory.

Feeding the brain

The brain uses glucose as its main fuel but has no way of storing it for future use. The nerve cells use glucose immediately for energy, and if they cannot get this fuel, they aren't able to operate at peak capacity -- potentially leaving you feeling forgetful or unable to concentrate.

I read a study recently that found students and others who continually challenge their minds actually require more carbohydrates, and thus, seem to crave carbohydrate foods in direct proportion to how much they have to exert their brains. Perhaps carbohydrate cravings in such cases are the body's way of getting the brain the fuel it needs.

This study only tracked the dieters for 3 weeks and the study's sample size was small, but the authors suggest that, although low-carb diets can affect weight, they result in a lack of glucose to the brain that may be detrimental to learning, memory, and thinking.

According to the Tufts study, the popular low-carb diets—and particularly the "no-carb" diets—have the biggest potential for decreasing the ability to think and concentrate, and may also negatively affect overall mood. This could be one of the reasons many people have a hard time sticking with a no-carb meal plan.

What you need to know

  • Although carb-free diets may seem appealing, aim for at least a moderate amount of carbohydrate in your diet. In my weight-loss/nutrition practice at Johns Hopkins Bayview Medical Center, I refer to clinical research findings that suggest that for optimal function the human brain needs a minimum of 125 grams of carbohydrate each day.

    To put this into perspective, 1 medium piece of fruit or a slice of bread is about 15 grams of carbohydrate. So if you aim for 6 servings of whole grains per day for a balanced diet, that's 90 grams right there. Similarly, 1 cup of cooked rice provides 3 servings of starch or 45 grams of carbohydrate, while an 8-ounce glass of milk will give you another 12 grams of carbs.

    If you aimed for 3 starches, 3 fruits, 4 vegetables, and 1 (8-oz) glass of milk a day, you're right around the 125-gram goal, which should keep your brain clear and your body energized -- and will supply plenty of vitamins, minerals, and fiber for a healthy, balanced diet. To find healthy meal guidelines, go to the USDA's MyPyramid Web site, or see a registered dietitian who can provide you with an individualized meal plan.
  • It's a good idea to limit the carbs from processed foods, such as those little snack packs containing 100 calories. They may seem like a bargain but they're generally devoid of vitamins, minerals, and fiber and leave you feeling even hungrier an hour later.
  • If you're not sure if your brain is really hankering for carbs or you're just bored, wait about 30 minutes before you eat and see if you feel either true physical signs of hunger or signs of carb deprivation (e.g., irritability, feelings stemming from low blood sugar, and shakiness or dizziness).

I'd love to hear your thoughts and experiences with low-carb diets, dear readers.


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