Fat

Macronutrient · fatty acids

What does Fat do in your body?

Concentrated energy, building blocks for cell membranes and hormones, and the carrier for vitamins A, D, E and K.

How it works, step by step

1. Bile from the liver breaks fat into tiny droplets.
2. Pancreatic lipase splits triglycerides.
3. Products are absorbed and rebuilt in gut cells.
4. Packaged into chylomicrons, they travel via lymph to blood.

What does Fat do?

Provides about 9 kcal per gram; forms cell membranes; makes hormones; carries fat-soluble vitamins; insulates and cushions organs.

Where does Fat act in the body?

Every cell membrane, brain (about 60% fat by dry weight), adipose tissue, hormone-producing glands.

Which foods contain Fat?

Oils, nuts, seeds, avocado, fish, meat, dairy, eggs.

How much Fat do adults need?

AMDR: 20–35% of energy for adults. Saturated fat: Dietary Guidelines suggest under 10% of calories. Trans fat: as low as possible.

What happens with too little Fat?

Very low-fat diets can reduce absorption of fat-soluble vitamins and essential fatty acids.

Can you get too much Fat?

Type matters more than total: replacing saturated fat with unsaturated fat is linked to lower heart disease risk.

What does Fat interact with?

Needed to absorb vitamins A, D, E, K and carotenoids.

What is known and unknown about Fat?

Two fatty acids are essential: linoleic acid (omega-6) and alpha-linolenic acid (omega-3).

Evidence & sources

• Adults' Acceptable Macronutrient Distribution Range for fat is 20–35% of energy. Evidence: regulatory. Known: A range associated with adequate nutrient intake and reduced chronic disease risk. Unknown: Fat type matters as much as total amount. Source: National Academies (Institute of Medicine), DRIs for Energy and Macronutrients (2002/2005).

Connected topics

• Omega-3 Fats
• Saturated Fat
• Trans Fat
• Liver
• Vitamin A
• Vitamin D
• Vitamin E
• Vitamin K
• Avocado
• Salmon
• Olive Oil

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General education only, not medical advice. Drafted Oct 2026 · pending qualified expert review.