Pizza, pasta and Hodgdon muffins are often among the first to go when beginning a weight-loss diet. However, think again before you congratulate yourself for having only a cup of coffee for breakfast for the third day in a row. An unbalanced diet affects more than just your body weight.
A recent study conducted by members of the Tufts psychology department found that cutting out carbohydrates in a diet can have immediate impacts on memory and thinking.
The study, "Low-carbohydrate weight-loss diets: Effects on cognition and mood," appeared in the February 2009 edition of the journal Appetite. Psychology Professor Holly Taylor led the study in collaboration with Psychology Professor Robin Kanarek, former undergraduate Kara Watts and Research Associate Kristen D'Anci.
The group followed 19 women aged 22 to 49, 10 of whom began a traditional low-carb diet and nine of whom began a balanced, reduced-calorie diet. Throughout the study, the researchers compared the women's cognitive performance levels by conducting a series of tests on short-term and long-term memory, spatial memory and visual attention.
During the first week of the diet, the women on the low-carb diet had slower reaction times and showed a gradual decrease in performance on memory tests compared to those on the low-calorie diet.
"We used fairly standard tests of memory. A digit-span test: forward order or a backward order, spatial learning tasks … All tests that are well-validated for testing memory and thinking," Kanarek said.
"What we did was we first tested all the women … before they started the diets so we had a baseline," Taylor said. "For the first week they had to eliminate all carbohydrates from their diet like any [low-carb] diet. We then looked at their memory and attention three days after, a week after and two weeks after."
"The women were allowed to introduce a few carbs like fruits and whole grains in week two. [We noted that] when they reintroduced some carbs into their diets, the women returned to normal levels," she said.
"Basically after the women on the low-carb diet reintroduced a few carbs into their diets, the difference in the memory test results between the two groups weren't that big anymore," Kanarek said.
As to why low-carb diets affected memory, the researchers point to the fact that severe carbohydrate restriction reduces the amount of available glucose — the brain's primary fuel — in the body. Glucose is not stored, but produced when the body breaks down carbohydrates. The converted carbohydrates are then immediately used as energy by nerve cells in the brain.
"The reason we started with [this] hypothesis is because we knew the brain uses carbohydrates, especially glucose, as fuel. And we thought if we eliminated the fuel source, people would do poorer cognitively," Kanarek said.
Although the reaction times and memory performances of the low-carb dieters were poorer than those of the low-calorie dieters, the low-carb dieters demonstrated better results in attention-related tasks. These results are consistent with other studies that show that high-protein or high-fat diets can improve attention in the short-term.
Many students' impressions of how carbohydrates affect mental performance seem to support the study's conclusions.
"Isn't the normal study-crave food pizza, chips or anything carb-related?" Sarah Gregg, a junior at Santa Clara University, asked. "At least for me, my downfall during finals is Wheat Thins."
When asked why researchers only tested women in the study, Taylor explained that women are the ones who are more likely to go on diets.
"It was a senior honors thesis and it was easier to get women than men for the study. [So], we tested only women for practical reasons," Kanarek said. "But it would be important to look at men as well. [However], I think it's a fairly general conclusion that we all need a healthy amount of carbs in our diet."
"Although the study had a modest sample size, the results showed a clear difference in cognitive performance as a function of diet," Taylor said in a public press release.
Nancy Shrodes, a Tufts junior who has tried diets that include regulated carbohydrate consumption, said that although she did not notice any specific cognitive effects, she has noticed some other physical effects as a result of the diet.
"I felt weaker and maybe less energetic … and I wasn't lifting the same amount of weight that I normally could," she said. "It was really frustrating and I'm pretty sure it was because of the diet."
However, some students feel that carbohydrates do not always benefit the mind.
"I agree that [carbs take away from studying and doing homework], but I also feel like if I over-carb, I actually have more trouble completing tasks because I crash from the sugar rush," Elizabeth Houston, a junior at Pennsylvania State University, said. "When I'm not in training [for sports], I really don't need a lot [of carbs]."
According to Kanarek, the U.S. government has not released an official recommended allowance of daily carbohydrates. However, it is clear to researchers that carbohydrates are crucial for people to function normally.
"Basically, we need to have some carbs in our diet. We need them to think," Taylor said.
"The basic take-away point is ... not to go on these really extreme diets," Kanarek said. "[This is because of] several problems: people can't maintain them, and the diets don't give them the variety of food they need. And it appears that it impairs cognitive performance. So the study indicates that it could have some influence on learning."
