Final answer:
Newborn infants have a significant amount of body fat, which varies by individual but is essential for warmth and energy storage through mechanisms like nonshivering thermogenesis using brown fat.
Step-by-step explanation:
Newborns' average body fat percentages can vary, but generally speaking, human infants have body fat percentages between 12% and 15% at birth. This fat in the body serves a number of purposes, such as temperature regulation, energy storage, and general growth.
Human infants are born with a varying amount of body fat, which is essential for thermoregulation and energy storage. Newborns utilize a special method for generating heat known as non-shivering thermogenesis, which depends on the breakdown of brown adipose tissue, or brown fat. This brown fat is mainly located over the infant's back, chest, and shoulders. Unlike adults, newborns have a higher water content and more body fat, which contrasts with the body composition at other stages of life.
As the fetus develops, it continues to accumulate subcutaneous fat, which fills out the hypodermis. By the time of birth, the newborn's fat contributes to their total weight, which normally ranges from 2.5 to 4 kg (5.5–8.8 lbs) and is a significant part of their body composition. The fat deposited in a newborn's body not only provides insulation but also serves as an energy reserve for their growth and development during infancy.