7.4.3: Fats: Hormones, Membranes, and Essential Functions

Dietary fat is not the enemy that 1990s diet culture made it out to be. Fat is an essential macronutrient: your body cannot function properly without it. It serves as the structural backbone of every cell membrane, is required for the absorption of fat-soluble vitamins (A, D, E, K), and is a precursor for critical hormones—including testosterone and estrogen, both of which play roles in muscle growth and recovery.

Minimum intake: A commonly cited threshold for maintaining hormonal health is approximately 0.5–0.7 g/kg of bodyweight per day. Dropping below this—particularly for extended periods during aggressive diets—can lead to hormonal disruption, including suppressed testosterone in men and menstrual irregularity in women.

Types of fat:

Type	Examples	Guidance
Monounsaturated	Olive oil, avocados, nuts	Prioritise — associated with cardiovascular benefits
Polyunsaturated	Fatty fish (salmon, mackerel), walnuts, flaxseed	Prioritise — includes omega-3 (EPA/DHA) which are anti-inflammatory
Saturated	Butter, red meat, coconut oil, cheese	Keep moderate — not “toxic,” but excessive intake is associated with elevated LDL
Trans fats	Partially hydrogenated oils, some processed foods	Avoid — no safe level; directly atherogenic

Practical approach: Don’t fear fat, but respect its caloric density. At 9 kcal/g, fat is more than twice as energy-dense as protein or carbohydrate. A tablespoon of olive oil (~120 kcal) can easily go unnoticed in cooking but adds up quickly. When setting up your macros, meet the minimum fat threshold, then allocate the remaining calories to carbohydrates.