An editorial in The Journal of Physiology explains how both high-fat diets and obesity prevent strength gain with exercise, and increase risk for diabetes heart attacks, and premature death (1).
The editorial was inspired by a study from the University of California at Davis, showing that a high-fat diet prevents exercising mice from enlarging their muscles (2) . If this study can be applied to humans, it means that not only does a high-fat diet make you fatter, it also prevents you from enlarging your muscles.
EXPERIMENT: Male mice received either unlimited : a) low fat, high carbohydrate diet or b) high fat, low carbohydrate diet for 14 weeks. Each group was divided into those who performed progressive resistance exercises with their plantaris muscles or those that did not do this exercise. Those who exercised on the low fat, high-carbohydrate diet had substantially larger muscles than those who exercised on the high-fat diet. Chemical analysis of their muscles showed that the high fat diet group had lower levels of polysomes (Akt and S6K1) necessary for making protein.
MECHANISM: Eating large amounts of saturated fats (the dominant fat in meat) turns on your immunity to cause inflammation that prevents the body from making protein necessary for enlarging muscles (3).
DELAYS RECOVERY: A high saturated-fat diet also prevents your body from responding to insulin which is necessary for muscles to heal from intense workouts. You train for cycling by taking a hard workout to damage your muscles. They feel sore the next day and you are supposed to take less intense workouts until your muscles heal and the soreness goes away. Then you take a hard workout again. Insulin drives amino acids, the protein building blocks, into muscles to help them heal faster. So blocking a muscles' ability to respond to insulin, decreases amino acid entry into muscles and delays healing so you can't recover as fast for your next workout.
WHAT IT MEANS TO YOU: All fats are classified by their chemical structures into saturated, polyunsaturated, and monounsaturated. All plants and animals have all three types of fats in their structures. The fat content of a food is classified by its dominant fat. For example, meat, coconut and palm kernel oils contains all three fats with higher levels of saturated fat. Olives contain all three fats with monounsaturated fats dominating. Nuts and most vegetables contain all three fats with polyunsaturated fats dominating. You should restrict saturated fats (meat from mammals) and eat lots of monounsaturated and polyunsaturated fats (fruits, vegetables, whole grains, beans, seeds and nuts). Deep-water fish are considered healthful because they have a type of polyunsaturated fat called omega-3 which reduces heart attack risk.
DATA SHOWING THAT SMALL MUSCLES AND EXCESS BODY FAT INCREASE RISK FOR DIABETES, HEART ATTACKS, AND PREMATURE DEATH: *Having large hip muscles prolongs life and prevents disease and having small hip muscles increases risk for heart attacks and premature death (BMJ. 2009;339:b3292) * Lack of hip muscle prevents the body from responding to insulin to cause diabetes. (J. Physiol. 2005;565:555–562) * Storing fat primarily in the belly increases risk for heart attacks, diabetes, and premature death, even in people who are not obese. (J Physiol 2009;587:5559–5568) * Lack of exercise and low levels of fitness, increase risk for heart attacks, diabetes, and premature death (J Physiol 2009;587:5559–5568) * Being fat and eating a high-fat diet, prevent muscles from enlarging maximally with heavy weight lifting. (J Physiol 2009;587:5753–5765)
1) The Journal of Physiology 2010(Jan);588;21 2) J Physiol 2009;587:5753–5765 3) J Nutr. 2009;139:1–4
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