Owing to their fast rate of growth in early life, infants have much greater energy requirements than adults relative to their body weight. Fat is a rich source of energy (calories), and is critical for many body functions.
Fat provides the largest amount of energy (nine kilocalories per gram) relative to protein and carbohydrate (four kilocalories per gram each), which are the other macronutrients found in breast milk and infant formula.
Fat is also the vehicle for supplying the fat-soluble vitamins A, D, E and K, and other substances such as prostaglandins. These vitamins are absorbed in the small intestines and are primarily stored in the liver and adipose tissue1.
Newborn babies have very little fat for insulation. They also have a large surface area meaning they can lose heat rapidly. The subcutaneous layer of fat, which is found just beneath the skin and provides insulation for the body, accounts for approximately 16% of the body fat in infants compared to 30-35% in adults2. The surface area-to-body mass ratio is about three times greater in infants than adults2. So dietary fats play a key role in helping to insulate infants against heat loss by building up the subcutaneous fat stores3.