Fatty acids must be available in the body to create cholesterol, which is eventually converted to testosterone. If fat intake is too low, there won’t be enough fatty acids available for optimal testosterone production.
This leads to lower testosterone levels, which lead to greater muscle loss during prep. The two combine to lower your metabolic rate.
The body also has a built-in adaptive response to chronically low dietary fat intake. When it senses an extremely low intake of fat, your body naturally tries to hold on to body fat stores, since fats are at a premium. Moderate amounts of fat intake will ensure that calories are low enough for fat loss, but that the body does not perceive starvation.
By Neale Cranwell