N

nutrient density The nutritional value of a par-
ticular food, generally presented as an assessment
of the quantity and quality of NUTRIENTSthe food
delivers per CALORIE. Foods that contain multiple
minerals and vitamins per calorie have high nutri-
ent density; those that do not have low nutrient
density. Generally the less processed a food is, the
higher its nutrient density. Fruits, vegetables,
legumes, seeds, whole grains, and nuts have high
nutrient density. Prepared dinners, cookies, crack-
ers, chips, candy, and other such food products
have comparatively low nutrient density. Some
prepared foods, such as cakes and pastries, have
relatively little nutritional value beyond the
energy forms (carbohydrate and fat) they deliver.
Though many prepared foods are not devoid of
nutrients, they deliver significantly more calories
for comparable nutrient levels. Foods with higher
nutrient density also tend to be more filling.
See also EATING HABITS; METABOLISM; NUTRITIONAL
NEEDS; WEIGHT LOSS AND WEIGHT MANAGEMENT.

nutrients Substances that participate in METABO-
LISM. Macronutrients deliver energy. The three
macronutrient groups are carbohydrate, fat, and
protein. Micronutrients facilitate the biochemical
actions that convert macronutrients into energy.
The main groups of micronutrients are vitamins
and minerals. Supportive nutrients include phyto-
chemicals (plant-based biochemicals such as
flavonoids and plant sterols) and the numerous
trace minerals and other chemicals that are pres-
ent in the body and have roles in metabolism,
though researchers do not fully understand those
roles. The final nutrient is water. Essential nutri-
ents are those the body must acquire from sources
outside itself, such as foods. Other nutrients,
though no less important to health, are nonessen-

tial because the body can synthesize them from

substances within it.

Macronutrients

The macronutrients—carbohydrates, fats, and pro-

teins—are the body’s energy sources. The amounts

and ratios of them that an individual needs vary

according to age, gender, activity level, and health

status. Metabolism reduces all macronutrients

ultimately to GLUCOSE. The body stores any

excesses (amounts the body does not immediately

use for energy) as glycogen and fat, regardless of

the source macronutrient. Per gram carbohydrates

and proteins yield four calories of energy; fats,

which represent stored energy, yield nine calories

per gram.

The body must use in some way all of the energy

that enters it in the form of food, either through

immediate consumption or storage. Glycogen,

which the LIVERproduces and stores, is an interme-

diate storage form that can supply about 12 hours

of energy. The liver also produces fat, which adi-

pose cells throughout the body store (body fat). The

body in healthy balance warehouses enough body

fat to supply energy for six to eight weeks.

In 2005 dietary recommendations shifted from

a percentage allocation for macronutrient con-

sumption to a stance of moderation in choice with

a focus on managing overall CALORIEintake across

the spectrum of energy nutrients. Health experts

concur that people need a wide variety of nutri-

ents and individual needs vary. Focusing on the

quality of foods within each macronutrient group

allows people to make choices that meet their per-

sonal needs and tastes, yet still meet the nutri-

tional needs of their bodies in healthful ways.

Carbohydrates Carbohydrates are chemical

structures consisting of oxygen, carbon, and

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