Body composition and categories of nutrients

Body composition and categories of nutrients
The average human body contains about 20 % of fat, 15% protein, much smaller amounts of carbohydrate (perhaps I %) and large amounts of water. It also contains substantial amounts of the “major minerals,” from calcium and phosphorus down to sulfur and magnesium as well as trace quantities of most elements. The human diet reflects this compositional need, and consists of large quantities of water containing, proteinaceous, fatty, and carbohydrate foods, as well as others rich in the minerals.

The trace elements are found in connection with these other nutrients, except where extensive processing and purification has occurred. In all, one may partition the nutrients into six categories: proteins, carbohydrates, lipids, vitamins, major minerals, and trace elements. This excludes a consideration of water and oxygen as nutrients, since no special efforts are required to produce and provide them.
Body composition and categories of nutrients

Age Changes in Body Composition

Age Changes in Body Composition
Even though the water content of the lean body mass in adults is very constant at 75% that of newborn infants and fetuses is somewhat greater. Indeed there is a “drying out” of the body age, as well as change in the intra and extra cellular distribution of water.

The overall fat concentration of the body increases during gestation until birth, and the water content declines from birth to adulthood. If the infant is premature, there is an additional loss of water with age related to the change in fat content. Although the water content declines, the nitrogen content increases, reflecting a higher protein concentration in adult tissues as compared with that of the newborn infant or fetus. The changes from a greater to a lesser extracellular fluid volume with growth and development are reflected in the decreased sodium concentration of body tissue with age and increase in potassium concentrations. The overall contributions of calcium, magnesium and phosphorus, most of which are present in the bone, also increase dramatically from birth to adulthood, coinciding with the process of body “mineralization”.

While the proportion of the body water in the central nervous system, skin and subcutaneous tissue decline that most other organs increase, especially in the muscles. Perhaps more of the organ systems including muscle and parenchymal tissues, increase their proportion of intracellular water, where as the opposite is true of the skin and subcutaneous tissue.

These trends continue during aging. Western adult slowly losses lean body mass and accumulates more fat onward from early adulthood. The loss of lean body mass is more evident in men than women until after menopause, when it accelerates. This change is ascribable mainly to loss of cellular versus extracellular mass, reflected in losses of potassium and nitrogen that average 22.5% and 17.5%, respectively from 25 to 75 (for both sexes).
Age Changes in Body Composition