Chapter 36 PP Notes.docx - 6 CLASSES OF NUTRIENTS The...

6 CLASSES OF NUTRIENTS
The science of nutrition is the study of the intake of food and how food nourishes the body. It
encompasses the study of nutrients and how they are handled by the body as well as the impact of
human behavior and environment on the process of nourishment.
Nutrients are specific biochemical substances used by the body for growth, development, activity,
reproduction, lactation, health maintenance, and recovery from illness or injury. The metabolic
processes involved in these functions are complex. Subsequently, most nutrients work better together
than they do alone. Nutrient needs change throughout the life cycle in response to changes in body size,
activity, growth, development, and state of health.
Some nutrients are considered essential because either they are not synthesized in the body or are
made in insufficient amounts. Essential nutrients must be provided in the diet or through supplements.
Essential nutrients that supply energy and build tissue (such as carbohydrates, fats, protein) are referred
to as macronutrients. Micronutrients, such as vitamins and minerals, are required in much smaller
amounts to regulate and control body processes.
Nonessential nutrients do not have to be supplied through dietary sources because they either are not
required for body functioning or are synthesized in the body in adequate amounts. Some nutrients can
be converted to others in the body. For instance, the body converts excess carbohydrates and protein
into fat and stores them as triglycerides.
Of the six classes of nutrients, three supply energy (carbohydrates, protein, lipids [fats]) and three are
needed to regulate body processes (vitamins, minerals, water).
FACTORS AFFECTING BMR
The body needs energy to function. Energy is derived or obtained from foods consumed. Energy in the
diet is measured in the form of kilocalories, commonly abbreviated as calories, or cal. Only
carbohydrates, protein, and fat provide energy. Vitamins and minerals, needed for the metabolism of
energy, do not provide calories.
Energy in the body is used to carry on any kind of activity, whether voluntary or involuntary. A person’s
total daily energy expenditure is the sum of all the calories used to perform physical activity, maintain
basal metabolism, and digest, absorb, and metabolize food.
Basal metabolism is the energy required to carry on the involuntary activities of the body at rest—the
energy needed to sustain the metabolic activities of cells and tissues. These activities include actions
such as maintaining body temperature and muscle tone, producing and releasing secretions, propelling
food through the gastrointestinal (GI) tract, inflating the lungs, and contracting the heart muscle.
Because of their larger muscle mass, men have a higher basal metabolic rate (BMR) than women.