High-Carb, High-Fat Diets Superior to High-Protein Diets in Improving Cognitive Performance

Deborah Brauser

September 01, 2009

September 1, 2009 — Diets high in carbohydrates or fat can lead to significantly better cognitive-performance and inflight-testing scores in pilots than diets high in protein, according to results reported in a poster presentation at the Military Health Research Forum (MHRF) 2009 in Kansas City, Missouri.

In addition, a high-carbohydrate diet helped study pilots sleep better, and a high-fat diet appeared to lead to significantly faster short-term memory.

"We started out thinking that the high-protein diet would lead to being the sharpest afterward," said colead investigator Glenda Lindseth, RN, PhD, licensed registered dietician and professor of nursing at the University of North Dakota (UND) in Grand Forks. "But we were surprised by our findings that it was actually the high-carb or high-fat diets that were the best. Eating a diet that's high in protein just isn't going to help you perform optimally."

"As a retired air-force pilot and a pilot for over 30 years, I believe this type of study is definitely needed," said the other colead author, Paul Lindseth, PhD, professor of aviation and associate dean at the UND Odegard School of Aerospace Sciences. "This is important for pilots in the military and in combat situations, where they need to be sharp and alert."

The Lindseths report that human error has been implicated in 70% to 80% of civil- and military-aviation accidents and in up to 91% of general-aviation accidents. In addition, lack of proper nutrition was rated as the top stressor in the daily lives of professional airline pilots.

Little Research on Diet and Cognition

There is currently little research on the potential connection between dietary intake and cognition. So in this study, the investigators sought to compare diets high in carbohydrates, fat, and protein to test their effects on cognition, flight performance, and sleep patterns.

A total of 45 pilots (mean age, 20.8 years; 87% male) from the UND commercial-aviation program were enrolled in this 14-week repeated-measures crossover trial.

During the first week, participants were randomized to receive 1 of 4 diets (3 full meals and 2 snacks) for 4 days: a diet high in carbohydrates, a diet high in fat, a diet high in protein, or a control diet. After a 2-week "phase-out" period, all pilots then randomly received a different study diet. This process was repeated until all pilots had received all 4 diets.

"We made sure that each pilot, no matter which of the study plans we gave them, got what would be considered a well-balanced diet, within 95% of the US recommended daily allowances for all of the micronutrients," explained Glenda Lindseth. In addition, the pilots were tested to make sure they received the number of calories required to sustain their weight.

Worse Performance With High-Protein Diet

Flight performance scores were determined using a GATT 2 full-motion flight simulator. The Sternberg item-recognition test and the Vandenberg mental-rotation test were used to evaluate cognitive function. Sleep patterns were measured with the Actiwatch sleep watch.

Results showed that overall flight-performance scores for the pilots consuming a high-protein diet were significantly worse (< 05) than for those consuming a high-carbohydrate or a high-fat diet. A hierarchical regression analysis indicated that this was due in part to dietary protein intakes, serotonin levels, and irritability scores.

In addition, high-carbohydrate diets produced shorter sleep latencies than the other diets, especially the control diet (< .03). In fact, the researchers found that if the pilots ate the high-carbohydrate diet, they seemed to sleep better, fall asleep quicker, and wake up less often.

The response time on the Sternberg test of short-term memory was significantly faster for participants who ate the high-fat diet (< .05) than for those who ate the protein and control diets, especially at higher memory loads. No significant impact was observed on the Vandenberg test.

"We're certainly not saying you always have to eat high fat," said Glenda Lindseth. "The take-away message is that a diet that is well balanced and has a lot of carbohydrates and a reasonable amount of fat in it is best for pilots to perform well cognitively."

"These results can make significant contributions to understanding the effects of diet on cognition and performance and may, therefore, decrease the number of errors due to human factors for the war fighter," she added. The investigators are planning a follow-up study to confirm their findings.

Findings Likely Generalizeable

In an interview with Medscape Psychiatry, Karen Tountas, PhD, MHRF conference chair and the event's peer-reviewed medical research program manager, said: "I think this is a very exciting study. They've focused on working with pilots but anything we can find out about diet and its relationship to cognition [will likely] translate across all people. [This study] does open up avenues of more questions to be asked." Dr. Tountas was not associated with the trial.

She said that others reading these results should take into consideration who their particular patients are. "There are a lot of other different end points. Is it cognition that [the clinician] is looking at? Is it weight? Is it a combination of those 2? I think that it would be important for [clinicians] to get a broader picture of that before making a decision for their own patient population."

"We know the brain's primary source of energy is glucose — that is sugar, just straight sugar," Captain E. Melissa Kaime, MD, director of the Congressionally Directed Medical Research Programs (CDMRP), part of the US Army Medical Research and Materiel Command, told Medscape Psychiatry.

"In some ways it shouldn't surprise us that a diet high in carbohydrates is good for the brain because that's the glucose it needs. But we all know that there are other problems in society too, such as an obesity epidemic. So we want to certainly feed the brain but we don't want to overfeed it or the rest of the body." Captain Kaime was not involved in the study.

"Pilots use higher executive-functioning parts of their brains, and this study was testing these highly trained pilots at their maximum cognitive stress," added Captain Kaime.

"This is the first look at a new way of science, of looking to see: What does the brain need? So the next step is going to be: What dose now? What schedule? If you need glucose, is it 10 minutes before the stress test of the brain or is it a continuous diet of glucose? Like all good studies, this one brings up more questions than it answers."

"We're trying so hard to keep people healthy and we want the magic bullet — the 1 pill or the 1 vaccine that fixes everything." Captain Kaime said that this study is just 1 more that says the solution "is in your diet. And that is actually good news. Because if the solutions are . . . common sense and practical and available, [something] that you don't have to go out and buy with a prescription and that is at your fingertips anyway, that just makes it all the more powerful."

This study was funded by the CDMRP of the US Department of Defense. The Lindseths, Dr. Tountas, and Captain Kaime have disclosed no relevant financial relationships.

Military Health Research Forum (MHRF) 2009: Abstract P16-9. Presented September 1, 2009.


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