While strength trainees often focus on their carbohydrate intake because, God forbid, if they have one low carb they they will be completely depleted and ''flat'' because of it, I often do not care about carbohydrates as much as I care about fat intake.
Even when I am setting up a diet for my clients, protein and fats are determined and optimized first, while carbohydrates are used to fill in the remaining caloric budget. There are 2 main reasons why you should care about your fat intake:
1. Increased anabolic hormone production
2. Anabolic effects of certain fatty acids.
As fat intake is directly related to anabolic hormone production such as testosterone, estrogen, growth hormone, and IGF-1, it becomes very important to optimize fat intake for maximum muscle growth.
Research shows a clear trend of an increase in testosterone in men and both testosterone and estrogen in women with higher intake of fats. The relationship with fat intake and anabolic hormones is correlated and it goes in both directions, meaning with low fat intakes, testosterone also decreases. This can have negative effects on muscle growth.
Goldin et al. (1994) did a study on women where they initially had a meal plan consisting of 40% fats. After switching to a lower fat level, which was 20-25%, there were significant decreases in serum concentrations of estrone, estrone sulfate, testosterone, androstenedione, and sex hormone binding globulin (SHBG) and near significant decreases in estradiol and free estradiol.