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Wild Headlines: High-Fat Diets Make You Stupid and Lazy

Written by: Tom Nikkola – Director of Nutrition & Weight Management

If you were paying attention to nutrition headlines in the news over the past week, you undoubtedly saw the Time Magazine article discussing exercise and weight loss. Another confusing headline that found its way into many media sources was the headline "High-fat diets may make you stupid and lazy." To avoid confusion about exactly what this headline means, we'll take a look at the study and discuss whether it should affect the dietary choices you make. In the end, hopefully you will avoid going to your refrigerator and tossing all of your fat-containing foods. You'll probably realize that the headline was...not that smart.

The Study

The Department of Physiology, Anatomy and Genetics and the Department of Experimental Psychology at the University of Oxford published a study entitled Deterioration of physical performance and cognitive function in rats with short-term high-fat feeding on August 10, 2009. Researchers wanted to find out if there would be a drop in physical performance and cognition of rats who followed a low-fat high carbohydrate diet followed by a high-fat diet for nine days. Before you take the conclusions from the study too seriously, there are some important points you should understand. If a friend brings up the headline, you'll have more facts about the actual study and can share your knowledge.

  • The study was done on rats. Rat studies are often a good first step toward seeing whether a theory may be applicable to humans, but in no way, is it good science, to use one rat study and form a conclusion applicable to humans. Oftentimes these studies do not make headlines, but when they seem to support the idea of a low-fat diet, they often do. Even if the study had been done on humans, there were several other considerations in the design that should make you pause before applying the results to your own nutrition plan.
  • The original diet the rats were on was excessively high in carbohydrates.The original diet was composed of 7.5% fat, 75% carbohydrate and 17.5% protein. The rats were fed this diet for two months after they were introduced to the lab, so their bodies would have likely become accustomed to this type of diet. It would be expected that switching them to a high fat (55% fat, 29% protein, 16% carbohydrate) diet would require a period of transition for their bodies to become adapted to the new diet. However, the study only lasted nine days. In humans, the adaptation period from a mixed diet to a low-carb or ketogenic diet often takes ten days to three weeks to adapt, much longer than the study allowed. The decreases in performance and cognition during that time could have easily been the result of the adaptation period. Studies have shown that for some people, once they are through the adaptation period their performance and cognition are better than they were on the previous diet, but they will almost always see a short-term decrease.
  • The high-fat group consumed 51% more calories than the low-fat group. Both the low-fat and high-fat groups gained weight during the study. The low-fat, sedentary group averaged an 8% gain in weight and the low-fat, exercising group gained an average of 6% body weight. The high-fat, sedentary group averaged a 10% weight gain and the exercising high-fat group averaged a 15% increase in weight. Those are important statistics the were not emphasized. The low-fat group averaged a 6-8% increase in weight, while the high-fat groups averaged 10-15% increases in weight, while eating 50% more calories! In human terms, imagine how you would perform and feel if you suddenly had to consume 50% more calories every day for a week and a half, and gained weight at twice the rate of those around you! It is possible the weight gain and/or additional calories by themselves could have been part of the problem.


The most accurate conclusion that can be drawn from this study is that no conclusion can be drawn. There are some deeper-level issues with the study as well, but I've just included some of the points that are easier to remember. The idea of low-fat dieting being the answer to health and wellness is fading more each year. While the answer may not be a high-fat diet either, there is plenty of evidence to support the need for natural fats in the diet. There is also a lack of evidence to support the philosophy of low-fat dieting. A great article to complement this would be Skimming the Truth, found in the latest issue of Experience Life.

It is also important to consider the meaning of a "high-fat diet." If this means the way that most Americans eat, which also includes a lot of refined carbohydrates and added fats, there's no doubt that such a diet is unhealthy. However, diets high in fat and low in carbohydrates can be beneficial for certain individuals and athletes, and certain amounts of fat are essential for everyone.

In the end, the proper mix of carbohydrates, fat and protein is as individualized as each person's metabolism. Low-er fat is sometimes necessary, as is high-er fat. For the sake of your health, don't turn away from fat in your diet. It plays a critical role to health and wellness. Just be sure to make wise choices in where you get it from. And stay away from refined carbohydrate foods, which make the consumption of fat far less healthy.


Murray A, Knight N, Cochlin L, McAleese S, Deacon R, Rawlins JN, Clarke K. Deterioration of physical performance and cognitive function in rats with short-term high-fat feeding. The FASEB Journal. fj.09-139691. 2009

Helgoe C. Skimming the Truth. Experience Life Magazine. September 2009

Cordain, Loren. The Paleo Diet. Rodale Publishing:New York, NY. 2005

McDonald, Lyle. The Ketogenic Diet. Morris Publishing: Kearney, NE

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