Low-Carb Diet May Improve Memory in People with Cognitive Problems, Small Study Suggests

Marisa Wexler, MS avatar

by Marisa Wexler, MS |

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diet and cognition

A diet low in carbohydrates may have cognitive benefits for older adults with mild cognitive impairment, a small study suggests.

Preliminary Report on the Feasibility and Efficacy of the Modified Atkins Diet for Treatment of Mild Cognitive Impairment and Early Alzheimer’s Disease” was published in the Journal of Alzheimer’s Disease.

The brain needs a lot of fuel to run, and mostly, it runs on the sugar molecule called glucose. However, the brain in people with Alzheimer’s disease can’t use glucose as efficiently — but it can use ketones, which are molecules formed when dietary fat breaks down.

When a person is on a ketogenic diet — lots of fat and very few sugars and starches, with the Atkins diet being the most well-known example — the brain tends to use ketones as a source of energy instead of glucose.

That’s the rationale for testing this kind of diet in people with mild cognitive impairment, which can be an early indication of developing Alzheimer’s.

In the study, Johns Hopkins University School of Medicine researchers hoped to compare a modified Atkins diet, in which carb intake is restricted to 20 grams or less each day, to a National Institute of Aging control diet, which is similar to a Mediterranean diet. That’s a diet with no specific restrictions on carbs, but lots of fruits, veggies, low-fat dairy, and lean protein.

In two and a half years of recruitment efforts, the researchers enrolled 27 people. So far, 14 have completed the 12-week study: 9 on the modified Atkins diet, 5 on the National Institute of Aging diet. Half the participants were female, with an average age of 71, and all were white except one.

Participants kept food diaries, and they were required to have a study partner — usually a spouse — to help them keep their eating on-track.

Prior to the study, participants in the Atkins group were eating an average of 158 grams of carbs per day. (For context, the average American eats 200–300 grams of carbs per day.) Six weeks into the study, the average carb intake in the modified Atkins group was 38.5 grams, and rose at 12 weeks to 53 grams. This is well above the 20 gram-per-day goal, but still lower than the control group, which continued to eat over 100 grams of carbs per day throughout the study.

Although diet adherence was not ideal, there were noticeable cognitive benefits observed in the modified Atkins group. Participants were given memory tests at the study’s start, and at six and 12 weeks in. In tests of delayed recall (the ability to remember something they were told or shown a few minutes earlier) participants on the modified Atkins diet improved, on average, by about 15% of the total score, while those on the control diet had a slight decline in memory scores. But these memory differences did not reach statistical significance.

Urine tests confirmed that these slight improvements were associated with increased ketone production; ketones were detectable in the urine of over half of the people on the modified Atkin’s diet and in none of those on the control diet.

These data suggest that cutting out carbs — even without great adherence to a diet — could be beneficial for people in the early stages of Alzheimer’s.

Of course, it’s well and good to suggest this as a concept, but as the researchers discovered, getting people to change their diet — and stick to that change — can pose a major hurdle.

“Many people would rather take a pill that causes them all kinds of nasty side effects than change their diet,” Jason Brandt, PhD, a Johns Hopkins professor and study co-author, said in a press release. “Older people often say that eating the foods they love is one of the few pleasures they still enjoy in life, and they aren’t willing to give that up.”

It’s worth stressing that this was a very small study, and the results should be interpreted appropriately. Still, they justify further study with larger groups.

“If we can confirm these preliminary findings, using dietary changes to mitigate cognitive loss in early-stage dementia would be a real game-changer,” Brandt said.