High-fat diets linked to poor mental function

Animals fed a high-fat diet for nine days could run 50 per cent less far than their counterparts fed a standard rodent diet, while they also made mistakes sooner in the maze task, suggesting that their cognitive abilities were also being affected by their diet.

The study, funded by the British Heart Foundation and published in the FASEB Journal​, has potential implications for people eating lots of high-fat foods, as well patients with metabolic disorders. It also draws attention to formulations in the food industry, with reduction of fat in products a growing area of interest to food manufacturers as consumers continue to seek out low-fat and low-calorie versions of their favourite foods.

The standard diet-fed animals obtained 7.5 per cent of their calories from fat, while the high fat diet-fed animals obtained 55 per cent of their calories from fat.

“The high-fat diet, in which 55 per cent of the calories came from fat, sounds high,”​ said lead author Dr Andrew Murray, “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 added.

Study details​

The researchers initially fed all 42 rats the standard diet, and measured their physical endurance using a treadmill, while their short-term or 'working' memory was tested in a maze. Half of the animals were then fed the high-fat diet, and their endurance and cognitive performance tested for another five days.

According to the data, after only 5 days on the high-fat diet the physical endurance of the rats decreased by 30 per cent, compared to animals on the low-fat diet. By the ninth day, the animals were running 50 per cent less far.

Furthermore, their performance in the maze task also decreased. The number of correct decisions before making a mistake dropped from over six to an average of 5 to 5.5.

“We found that rats, when switched to a high-fat diet from their standard low-fat feed, showed a surprisingly quick reduction in their physical performance,” ​said Murray. “After just nine days, they were only able to run 50 per cent as far on a treadmill as those that remained on the low-fat feed.”​

An investigation of the metabolic changes revealed increased levels of a specific protein called the ‘uncoupling protein’ in the muscle and heart cells of the high-fat diet-fed rats. This protein reportedly ‘uncouples’ the process of burning food stuffs for energy in the cells, reducing the efficiency of the heart and muscles. The researchers also noted an increase in heart size in the high-fat diet-fed animals.

Dr Murray has since moved to Cambridge University and is continuing his work in this area. His new team are now carrying out similar studies in humans, looking at the effect of a short term high-fat diet on exercise and cognitive ability.

Commenting on the study, Professor Jeremy Pearson, Associate Medical Director of the British Heart Foundation said: “We look forward to the results of the equivalent studies in human volunteers, which should tell us more about the short-term effects of high-fat foods on our hearts. We already know that to protect our heart health in the long-term, we should cut down on foods high in saturated fat.”​

Source: FASEB Journal​
Published online ahead of print, doi: 10.1096/fj.09-139691
“Deterioration of physical performance and cognitive function in rats with short-term high-fat feeding”​
Authors: A.J. Murray, N.S. Knight, L.E. Cochlin, S. McAleese, R.M.J. Deacon, J.N.P. Rawlins, K. Clarke