Body Fat Through Life

Does your body fat remain constant all through life? The answer is no. So what changes occur at some key milestones along the way?


During adolescence, your body composition changes dramatically. The differences in body composition - both fat and lean body mass - between girls and boys are very small during infancy and childhood. However, they become significant during adolescence.

Although they usually mature more slowly, boys tend to add more lean mass and less body fat than girls during adolescence.

Girls put on more body fat than boys during adolescence. This is perfectly normal and healthy. A female should always have a higher percentage of body fat than a male of equal fitness because her amount of essential fat is higher and her reproductive function requires more energy. (For more information, visit Body Fat Basics).


During adulthood, the healthy ranges of body fat differ for men and women. The body fat ranges for women are significantly higher than for men. This is both normal and healthy. One major study showed that the range of percent body fat increases slightly with age in both men and women.

Healthy Range of Body Fat
Age Female Male
18-39 21-32% 8-19%
40-59 23-33% 11-21%
60-79 24-35% 13-24%

Notice that at any age, the healthy range of body fat is significantly higher for women than for men. It is widely accepted that this is due to the reproductive function of women.


During pregnancy, a woman's body undergoes dramatic changes that are normal and necessary for a healthy baby. By the end of a normal pregnancy, a woman may gain an average of about 25 pounds. The baby accounts for only one third of that weight.

In addition to the growing baby, weight gain during pregnancy is due to changes in the placenta, amniotic fluid, uterine and breast tissue, and maternal fat. Her blood volume also increases by as much as 40 percent. The extent of these changes is markedly different from mother to mother which is why weight gain differs so much.

It is widely accepted that the fat gained during pregnancy is needed to produce milk once the baby is born. The baby also gains fat as pregnancy proceeds, especially in the last three months of the pregnancy.


During lactation, the body is in a state of change. Lactation requires even more energy than pregnancy. The body's energy needs are met by:

  • eating more calories
  • drawing on the fat that your body stored during pregnancy

Body fluids also change. Even at six months after delivery, body composition may still be different from before pregnancy, especially if the woman is exclusively breast feeding her baby. Breast feeding is recommended for the entire first year of a baby's life.

Want to build up your lean body mass? The good news is that you can increase the amount and the strength of your muscles through a regular program of strength training — also known as "resistance" training.


As you age, your body changes:

  • Body fat increases
  • Lean body mass decreases because you lose muscle mass
  • The body's water content decreases
  • Bone density is reduced, sometimes to unhealthy levels

No matter what your age, you can slow and even stop many or all of these undesirable changes.

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