I set out two days ago to see what updated research I could find on diet and cognition. I found a bewildering array of items, some somewhat contradictory. It has been a cognitive challenge to make sense of them, especially while having to deal with variety of other challenges like figuring out how to bring two virus-infected computers back to life, what to tell my investment adviser, how to take care of the house given that a big tree branch has crashed through a window, keeping things going during a couple of storm-related power outages, and what I need to do to continue keeping a bunch of family members happy. The question at hand is “What is the impact of diet on cognitive functioning and memory, especially for older people?” So I report on a few selected 2009 studies and end up giving my own bottom line.
Mediterranean diet and risk of dementia
The August 2009 report in JAMA Adherence to a Mediterranean Diet, Cognitive Decline, and Risk of Dementia. “ Objective: To investigate the association of a Mediterranean diet with change in cognitive performance and risk for dementia in elderly French persons. Design, Setting, and Participants: Prospective cohort study of 1410 adults (65 years) from Bordeaux, France, — Adherence to a Mediterranean diet (scored as 0 to 9) was computed from a food frequency questionnaire and 24-hour recall. Main Outcome Measures” Cognitive performance was assessed on 4 neuropsychological tests: Main Outcome Measures: Cognitive performance was assessed on 4 neuropsychological tests: the Mini-Mental State Examination (MMSE), Isaacs Set Test (IST), Benton Visual Retention Test (BVRT), and Free and Cued Selective Reminding Test (FCSRT). Incident cases of dementia (n = 99) were validated by an independent expert committee of neurologists. – Conclusions: Higher adherence to a Mediterranean diet was associated with slower MMSE cognitive decline but not consistently with other cognitive tests. Higher adherence was not associated with risk for incident dementia.” At least one commentary on the article in JAMA suggested that at least one of the other rests also may also indicate cognitive decline(ref). Not much surprise here.
The DASH diet may slow cognitive decline – it you can get people to follow it
There is not much surprise for me in this July 2009 item either. “A diet rich in fruits and vegetables and low in salt, sweets, and red meats — the Dietary Approaches to Stop Hypertension (DASH) model — appears to slow cognitive decline, researchers said here at the International Conference on Alzheimer’s Disease(ref).” “The patients received a score based on how closely they followed the diet, which requires seven to eight servings of grains; four to five servings of fruit; four to five servings of vegetables, two to three servings of low fat dairy, two or fewer servings of meat a day, and five servings of nuts or legumes or seeds a week.”
“The groups were divided into quintiles, and the results showed that those patients in the highest quintile — the individuals who were closest in following the diet — had the slowest decline in cognitive functioning, while the patients in the lowest quintiles had the most rapid decline in functioning. — Over the 11-year time frame of the study, the difference between the most diet-adherent individuals was about 3.73 points (P<0.001) on the Modified Mini Mental State Examination, a standard instrument that measures cognitive decline. The examinations were given at baseline and as many as four times during the study period.”
I think that the proponents of this diet are correct in pointing out that getting compliance with it is likely to be very difficult, even if it does offer benefits.
Rats on junk food become lazy and stupid
The August 2009 study Deterioration of physical performance and cognitive function in rats with short-term high-fat feeding seems to say that for rats at least, a high-fat diet leads not only to long-term cognitive decline but also to short-term decline as well. “We found that rats ran 35% less far on a treadmill and showed cognitive impairment in a maze test with 9 d of high-fat feeding, with respiratory uncoupling in skeletal muscle mitochondria, associated with increased uncoupling protein (UCP3) levels. Our results suggest that high-fat feeding, even over short periods of time, alters skeletal muscle UCP3 expression, affecting energy production and physical performance.”
The Science Daily coverage of the research is headlined Do High-Fat Diets Make Us Stupid And Lazy? Physical And Memory Abilities Of Rats Affected After 9 Days. According to it “All 42 rats were initially fed a standard feed with a low fat content of 7.5 per cent. Their physical endurance was measured by how long they could run on a treadmill and their short-term or ‘working’ memory was measured in a maze task. Half of the rats were then switched to a high-fat diet where 55 per cent of the calories came from fat. After four days of getting used to the new diet, the endurance and cognitive performance of the rats on the low- and high-fat diets was compared for another five days. — “With the standard feed, 7.5 per cent of the calories come from fat. That’s a pretty low-fat diet, much like humans eating nothing but muesli,” says Dr Murray. “The high-fat diet, in which 55 per cent of the calories came from fat, sounds high but it’s actually not extraordinarily high by human standards. A junk food diet would come close to that. — Some high-fat, low-carb diets for weight loss can even have fat contents as high as 60 per cent. However, it’s not clear how many direct conclusions can be drawn from our work for these diets, as the high-fat diet we used was not particularly low in carbs,” he adds. — On the fifth day of the high-fat diet (the first day back on the treadmill), the rats were already running 30 per cent less far than those remaining on the low-fat diet. By the ninth day, the last of the experiment, they were running 50 per cent less far. — The rats on the high-fat diet were also making mistakes sooner in the maze task, suggesting that their cognitive abilities were also being affected by their diet. The number of correct decisions before making a mistake dropped from over six to an average of 5 to 5.5.”
So, if people’s metabolisms are like rat’s, a steady diet of junk food could make us fat and lazy. Some times when I am in a junk food chain late at night and noticing that everyone in sight is obese, I have had the same thought, a thought I quickly repress as being politically incorrect.
Unlike rats, airline pilots cognition is made better with a high fat or high carb diet
This next report is a mind-bender because it seems to contradict the previous one and to go against what we think we know. The report is entitled High-Carb, High-Fat Diets Superior to High-Protein Diets in Improving Cognitive Performance.* “Diets high in carbohydrates or fat can lead to significantly better cognitive-performance and in-flight-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. — Eating a diet that’s high in protein just isn’t going to help you perform optimally. Results showed that overall flight-performance scores for the pilots consuming a high-protein diet were significantly worse (P < 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. — The response time on the Sternberg test of short-term memory was significantly faster for participants who ate the high-fat diet (P < .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.”
So does a high fat diet make cognition worse or improve it? Hmm. Perhaps airline pilots can get smarter on junk food and rats can’t? I doubt it. Reminds me of the climate change studies. Most of these say that CO2 is responsible for global warming, but a few say the opposite. And I remember the old days when most research reports said cigarette smoking was very harmful and a few said the opposite. In any event the presenter tempered the findings a bit. “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(ref).”
What do I make of these reports? Basically that nutrition research marches on, and that in general a single study or research report an important theory does not prove or disprove. I think that there is plenty of additional evidence that the Mediterranean diet offers many health benefits likely to include increased cognitive clarity, and that high-fat diets are likely to create health problems. See the blog post Recent research on the Mediterranean diet. So most of these studies tend to confirm what is already known except for the airline pilot study. Either that study will provide a breakthrough new perspective if the results are supported by additional studies, or additional research will cast doubt on or significantly narrow its conclusions.
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