While the best way to determine the effectiveness of exercise and nutrition is usually through proven scientific methods, that isn’t always the case. Many studies are published that are clearly wrong in their conclusions, and you don’t have to be a scientist to figure it out. Two recent studies with relevance to typical bodybuilding practices are good examples. Although neither study involved bodybuilders, they both focused on behavior that is widespread among bodybuilders.
The first study used mice that were divided into two groups—a high-fat, low-carb group that ate 45 percent of daily calories as fat, and a high-carb, lowfat group. Both groups were allowed to eat as much as they wanted for 14 weeks. The mice were further divided into a sedentary group and a group that got an overload stress placed on their plantaris muscle, which is a type 2 fast-twitch muscle, the kind most amenable to growth. The researchers caused the overload stress by surgically removing two other associated muscles in the mice, which resulted in more stress on the plantaris.
The mice following the high-fat diet had a blunted muscle hypertrophy, or growth, effect compared to the lowfat, high-carb mice. The effect increased with time. The authors suggest that the blunted muscle growth in the high-fat-diet mice was caused by the dietary fat’s interference with cellular signalling related to muscle protein synthesis. One possible mechanism they mentioned was increased intramuscular fat in the high-fat-diet mice.
Without thinking that through, your first impulse might be to conclude that a high-fat diet will interfere with gains made through weight training. Consider, however, that the high-fat, low-carb diet is popular among many bodybuilders, and that there’s never been any record of that type of diet inhibiting muscle growth in humans. If anything, the converse is true.
Studies have consistently shown that not eating enough fat results in a decline in anabolic hormones, especially testosterone. They also show that you need to eat about 25 to 30 percent of daily calories as fat for your body to produce the optimal amount of testosterone. Clearly, if eating a high-fat, low-carb diet actually blunted muscle growth in humans, we would know that by now, since low-carb, high-fat diets have been popular for more than 40 years.
The take-home lesson is that what applies to a mouse doesn’t always translate into humans. In addition, the way that the mice muscle was overloaded in this study—by surgically removing associated muscles—isn’t often seen in humans.
Another recent study did involve humans but reached an equally wrong conclusion. It was a cohort study that looked at the eating behavior of a large group, in this case 38,094 people. There was a 10-year follow-up on 918 cases of diabetes that turned up in the subjects. The study found that those who ate more protein in place of carbs and fat had higher rates of diabetes. While animal protein was most potent in that regard, eating any type of protein, including vegetable protein, also increased the risk of diabetes. Interestingly, while type 2 diabetes is usually linked to increased bodyfat, the high-protein effect in the study was limited to lean adults. Specifically, those who followed a high-protein diet increased their risk of diabetes by 30 percent.
As to the suggested mechanism for the effect, the authors cite studies showing that amino acids, the elemental components of protein, interfere with glucose transport and metabolism. They further suggest that the main component of protein foods that produces the diabetic effect is iron.
Once again, if a high-protein intake caused diabetes, the disease would be epidemic in bodybuilders, who eat far more protein than the average person. Yet diabetes is no more prevalent in bodybuilders than it is in any other group, regardless of how much protein is eaten. If anything, countless studies have clearly shown that focusing on protein instead of carbohydrate results in a significantly decreased risk for diabetes. The reasons for the protection include lowered bodyfat, along with lower resting glucose and insulin counts. If anything increases the risk of getting diabetes, it would be the processed junk food rich in high-fructose corn syrup and transfat that so many people eat. Those particular ingredients are rarely, if ever, included in typical bodybuilding diets. Add it all up, and you can only conclude that the study implicating a high-protein diet in diabetes is nonsense.
1 Sitneck, M., et al. (2009). Chronic high fat feeding attenuates load-induced hypertrophy in mice. J Physiol. 587(23):5753-65.
2 Sluijs, I., et al. (2010). Dietary intake of total, animal, and vegetable protein and risk of type-2 diabetes in the European Prospective Investigation into cancer and nutrition (EPIC)-NL study. Diab Care. 33:43-48.
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