Dietary fat
The most energy-dense macronutrient, essential for hormones and vitamin absorption.
Dietary fat is one of the three macronutrients, supplying about 9 kcal per gram, more than twice as much as protein or carbohydrate. It carries fat soluble vitamins, supplies essential fatty acids the body cannot make, forms cell membranes and is the substrate for steroid hormones.
It has a floor for that reason. Reference intakes put fat at 20 to 35% of energy, and pushing far below the bottom of that squeezes essential fatty acids and fat soluble vitamin absorption for no return, which is a real cost of the very low fat diets that were fashionable for a while.
Type matters more than total for health outcomes. Replacing saturated fat with unsaturated fat lowers LDL cholesterol, and trans fats from industrial hydrogenation are the one category with unambiguous harm, now largely removed from the food supply in the UK and EU.
Seed oils have become the current battleground and the human evidence points the opposite way from the online consensus. A pooled analysis of cohort studies found higher circulating linoleic acid, the main omega-6 in seed oils, associated with lower cardiovascular disease and lower cardiovascular mortality.
Omega-3 fats from oily fish are the ones most people genuinely under-eat, with the strongest general health case among the fats.
For body composition, fat is neither fattening nor protective in itself. Its energy density makes it easy to over-consume and easy to use deliberately when calories need to be high, which is a practical property rather than a metabolic one.
In practice, set a fat floor of roughly 20 to 25% of calories in our macro calculator, favour unsaturated sources and oily fish, and let carbohydrate take the remainder.
Sources
- Marklund M, et al. Biomarkers of Dietary Omega-6 Fatty Acids and Incident Cardiovascular Disease and Mortality: an individual-level pooled analysis of 30 cohort studies. Circulation 2019;139:2422-2436
- Institute of Medicine. Dietary Reference Intakes for Energy, Carbohydrate, Fiber, Fat, Fatty Acids, Cholesterol, Protein, and Amino Acids (2005), fat acceptable macronutrient distribution range 20 to 35% of energy