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Carbohydrates, Proteins, and Fats

By Adrienne Youdim, MD, David Geffen School of Medicine at UCLA

Last full review/revision Aug 2019| Content last modified Aug 2019

CLICK HERE FOR THE PROFESSIONAL VERSION

Carbohydrates, proteins, and fats supply 90% of the dry weight of the diet and 100% of its energy. All three provide energy (measured in calories), but the amount of energy in 1 gram (1/28 ounce) differs:

4 calories in a gram of carbohydrate or protein

9 calories in a gram of fat

These nutrients also differ in how quickly they supply energy. Carbohydrates are the quickest, and fats are the slowest.

Carbohydrates, proteins, and fats are DIGESTED in the intestine, where they are broken down into their basic units:

Carbohydrates into sugars

Proteins into AMINO ACIDS

Fats into fatty acids and glycerol

The BODY uses these basic units to BUILD substances it needs for growth, maintenance, and activity (including other carbohydrates, proteins, and fats).