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Playing around with how much fat you consume may make the difference between gaining muscle mass and wallowing in bodybuilding purgatory Furthermore, scientists are beginning to unveil the effects of various levels of macro- and micronutrient intake on protein metabolism in humans.
A study published in the journal of Applied Nutrition tested the notion that a certain level of fat and certain type of calcium might affect nitrogen balance.
Why is this so important? Well, if you remember, nitrogen balance is a crude measure of the difference between the amount of nitrogen (from protein) consumed and the amount excreted (from protein breakdown). If a person takes in more nitrogen or protein than he or she excretes, then that person is in positive nitrogen balance. This is a good thing for bodybuilders since it means they could be gaining skeletal muscle mass. If they're in nitrogen balance, they'll theoretically neither gain nor lose lean body mass; if they're in negative nitrogen balance, they'll likely end tip losing lean body mass.
Subjects in this study were examined for 28 days in a cross-over research design. For two 14-day periods they consumed either a 40%- or 30%-of-calories-from-fat diet and calcium from either milk or a calcium-lactate supplement. (Okay, we know bodybuilders don't eat 40% and probably not even 30% of their calories from fat, but we think the study is informative for showing the different effects of two levels of fat consumption.) Nitrogen balance was determined by subtracting nitrogen excretion from dietary nitrogen intake.
The researchers found that calcium intake, whether from milk or calcium-lactate tablets, had no appreciable effect on nitrogen balance. So in this case, it doesn't matter what form of calcium you consume with regard to nitrogen balance. When comparing data on the 40%- vs. 30%-fat diets, however, the researchers concluded that the 30%-fat diet was superior to the 40%-fat diet with regard to nitrogen balance.
Does this mean eating 40% of your calories from fat is had for you? Maybe, maybe not. Most nutrition experts advocate keeping your fat intake around 30% of calories for better health. In the United States, at least, where fat intake can approach 40% or at least the high 30s, a 30%-fat diet is considered low-fat. Healthwise, both the type of fat and the amount of fat seem to matter. Also keep in mind that eating a higher-fat diet is common in certain cultures (for example, the Mediterranean diet) and is espoused by various "nutrition experts."
From the small sample size in this study, a lower fat intake of 30% seems better in terms of nitrogen balance than a 40%-fat diet for muscle-building potential. On the lip side is the idea that higher fat intakes correlate with higher plasma levels of the anabolic hormone testosterone. Is a 30%-fat intake high enough for optimal nitrogen balance and the maintenance of higher plasma testosterone levels? The answers aren't entirely known, but I'd speculate that 30% is adequate to meet both needs.