Nutrition and The Life Stages

Macronutrient energy sources, micronutrients, EFA, and EAA are required at every life stage. Additionally, each stage has specific nutrition needs.
A. Infancy, childhood, and adolescence
The rapid growth and development in infancy (birth to age 1 year) and childhood (age 1 year to adolescence) necessitate higher energy and protein needs relative to body size than are required in subsequent life stages. In adolescence, the marked increases in height and weight that occur increase nutritional needs. Growth charts (Fig. 1) are used to compare an individual’s stature (height) and/or weight to the expected values for others of the same age (≤20 years) and sex. They are based on data from large numbers of normal individuals over time. [Note: Deviations from the expected growth curve, as reflected in the crossing of two or more percentile lines, raise concern.]

Figure 1:  Clinical growth chart of stature-for-age for boys age 2–5 years from the Centers for Disease Control and Prevention (CDC) (see https://www.cdc.gov/growthcharts/). Charts for girls are pink.
1. Infants: Ideal infant nutrition is based on human breast milk because it provides calories and most micronutrients in amounts appropriate for the human infant. Carbohydrates, protein, and fat are present in a 7:3:1 ratio.
[Note: In addition to the disaccharide lactose, human milk contains nearly 200 unique oligosaccharides. About 90% of the microbiota (the population of microbes) in the breast-fed infant’s intestine is represented by one type, Bifidobacterium infantis, which expresses all the enzymes needed to degrade these complex sugars. The sugars, in turn, act as prebiotics that support the growth of B. infantis, a probiotic (helpful bacteria).] Breast milk is low in vitamin D, however, and exclusively breast-fed babies require vitamin D supplementation. [Note: Human milk provides antibodies and other proteins that reduce the risk of infection.]
The microbiota in and on the human body plus their genomes are referred to as the microbiome. It is acquired at birth from the environment and changes with the life stages. The gut microbiome influences host nutrition by facilitating processing of food consumed and is itself influenced by that food. Its relationship with undernutrition, obesity, and diabetes is under investigation.
2. Children: As with infants, children have increased need for calories and nutrients. The primary concerns in this stage, however, are deficiencies of iron and calcium.
3. Adolescents: In the teen years, the increases in height and weight increase the need for calories, protein, calcium, iron, and phosphorus. Eating patterns in this stage can result in overconsumption of fat, sodium, and sugar and underconsumption of vitamin A, thiamine, and folic acid. [Note: Eating disorders and obesity are concerns in this age group.]
B. Adulthood
Overnutrition is a concern in young adults, whereas malnutrition is a concern in older adults.
1. Young adults: Nutrition in young adults focuses on the maintenance of good health and the prevention of disease. The goal is a diet rich in plantbased foods (with a focus on fiber and whole grains), limited intake of saturated fat and trans fatty acids, and balanced intake of ω-3 and ω-6 PUFA.
2. Pregnant or lactating women: The requirements for calories, protein, and virtually all micronutrients increase in pregnancy and lactation. Supplementation with folic acid (to prevent neural tube defects ), vitamin D, calcium, iron, iodine, and DHA is typically recommended.
3. Older adults: Aging increases the risk of malnutrition. Decreased appetite resulting from a reduced sense of taste (dysgeusia) and smell (hyposmia) decreases nutrient intake. [Note: Physical limitations, including problems with dentition, and psychosocial factors, such as isolation, may also play a role in reduced intake.] Inadequate intake of protein, calcium, and vitamins D and B12 is common. B12 deficiency can result from decreased absorption caused by achlorhydria (reduced stomach acid). In aging, lean muscle mass decreases and fat increases, resulting in decreased RMR. [Note: Drug–nutrient interactions can occur at any life stage but are more common as the number of medications increases as in aging.]
Monoamine oxidase inhibitors (MAOI), used to treat depression and early Parkinson disease, can interact with tyramine-containing foods. Tyramine is a monoamine derived from the decarboxylation of tyrosine during the curing, aging, or fermentation of food (Fig. 2). It causes the release of norepinephrine, increasing blood pressure and heart rate. Patients who take an MAOI and consume such foods are at risk for a hypertensive crisis.

Figure 2:  Decarboxylation of tyrosine to tyramine. CO2 = carbon dioxide.