Fat

What Is Fat?

Almost all fat in food is triglyceride: three fatty acids joined to a glycerol backbone. The fatty acids decide what kind of fat it is. With no double bonds in the chain it is saturated; with one, monounsaturated; with two or more, polyunsaturated. Every food fat is a mix of all three, named after the one that dominates.

What Fat Does in the Body

Fat is part of every cell membrane and of the myelin that insulates nerves. It carries the fat-soluble vitamins A, D, E and K from the gut into the body; a meal with almost no fat absorbs them poorly. Fatty acids are also the raw material for signaling molecules that help control inflammation and blood clotting.

Two fatty acids are essential because the body cannot make them: linoleic acid, an omega-6, and alpha-linolenic acid, an omega-3. Their own pages cover where they come from and how much is needed.

Body fat is the energy store. Fat eaten beyond what the body burns is kept in fat tissue, and so is energy from extra carbohydrate and protein. Because each gram holds 9 kcal, fat stores far more energy in less weight than glycogen does.

Butter vs. Olive Oil: Fat per Tablespoon

A tablespoon (14 g) of olive oil has 14 g of fat, of which 2.2 g is saturated. The same spoon of butter has 11.5 g of fat, of which 6.4 g is saturated. Butter has less fat in total, because part of it is water, but nearly three times the saturated fat.

Where a Day's Fat Comes From

An ordinary day from our library, in usual portions. Count the cooking fat: it is easy to forget and often the largest amount.

The butter and olive oil alone give 26 g, about 40% of the day's fat.

Who Gets Too Little or Too Much Fat

Shortfalls are rare in high-income countries. They show up on very low-fat diets, which can leave too little of the essential fatty acids and the fat-soluble vitamins, and in conditions that block fat absorption, such as cystic fibrosis, some liver and pancreas diseases, and after some weight-loss surgery.

The more common pattern is the opposite: more saturated fat than the WHO limit of 10% of calories, from fatty meat, butter, cheese, pastries and snack foods.

Common Fat Mistakes

Thinking healthy fats have fewer calories. Olive oil and lard both hold about 9 kcal per gram. The type of fat changes its effect on cholesterol, not its energy.

Calling a food by one fat. Olive oil is mostly monounsaturated, yet still about 15% saturated.

Forgetting the oil. A tablespoon poured into a pan is about 120 kcal, more than a medium apple, and it rarely gets logged.