The collection of anthropometric data, is important for body composition analysis and contributes a great deal to the nutrition care process of individuals. Body composition involves the overall weight of an individual, with fat deposits in certain parts of the body. Several areas are also important in this regard. Those areas are, energy requirements of individuals and the components of this, methods of measuring an individual and the factors which may affect metabolic rate.
When the food we eat is broken down, we are able to harness energy stored in the food for our metabolic processes. Some of the macronutrients such as carbohydrates, proteins, fats and oils supply the energy required for daily activity. This energy allows chemical and mechanical processes to take place in the body, together with electrical processes. Which is important to keep the body functioning optimally.
Energy is defined as the “capacity to do work” (Mahan and Janice L. Raymond 2012). In humans’ energy is manufactured in the body through the use of carbohydrates, proteins and fats. Everyone has their own unique energy requirements, due to lean body mass vs body fat. Energy intake is defined as “the dietary energy intake that is required for growth or maintenance in a person of a defined age, gender, weight, height, and level of physical activity” (Mahan and Janice L. Raymond 2012).
The various components of energy requirements include basal energy expenditure (BEE) (also known as basal metabolic rate (BMR), Resting energy expenditure (REE) or resting metabolic rate (RMR), activity thermogenesis (AT) and thermic effect of food (TEF). These various components make up one’s daily total energy expenditure (TEE). The following graph shows the components of energy expenditure.
Figure 1- Graph Showing the Percentage of the Components of Energy Expenditure(Adapted from www.sciencelearn.org.nz)
BEE is the minimum amount of energy expended that is compatible with life and looks at the amount of energy used within a period of 24hours, while being physically and mentally at rest (Mahan, Escott-Stump and L. Raymond 2012). This measurement should be done before a person engages in physically activity. Ideally this should be done just as someone has awaken from sleep. It should be noted that this term is not used as much as RMR.
RMR is the energy expended in the activities necessary to sustain normal body functions and homeostasis. When a person is in a state of rest, their body still requires energy to keep functioning. Some of the functions for energy in this state are respiration and circulation, controlling body temperature, cell growth, pumping ions across membranes and contraction of muscle. Some of the factors which affect RMR include age, body composition (fat free mass of more commonly called lean body mass), body size, climate, gender, hormonal status, temperature, caffeine, nicotine and alcohol.
Consuming food also influences energy expenditure and this is called the thermic effect of food. When food is consumed energy is used to consume, digest and absorb food. The thermic effect is dependent on the size of the meal and the proportions of fat, carbohydrates and proteins. The energy required for proteins to be burnt is 30%, for simple carbohydrates 3%, complex carbohydrates will require more and fats take about 5% (Borne 2013).
Non-exercise activity thermogenesis (NEAT) is the energy expended for everything done except sleeping, eating or sports-like exercise (James A. Levine MD 2002 ). It involves simple activities such as typing, fidgeting and doing simple yard work.
Energy expenditure is measured either by direct calorimetry or indirect calorimetry. Direct calorimetry uses equipment which are specialised and expensive. Direct calorimetry measures energy expenditure by assessing body heat loss within metabolic chambers The indirect calorimetry method is more commonly used. Oxygen and carbon dioxide levels are quantified for a given timeframe. Equipment for this type of measurement is usually range from large equipment to small and can be held quite easily in one’s hand. The equipment is called a measurement cart or monitor. Smaller handheld devices are used by persons who are spontaneously breathing. Larger equipment is used in hospitals in the intensive care units. Simple calculations such as the Harris Benedict calculation or Mifflin St. Jeor can estimate energy expenditure based on age, gender, height, weight, and level of activity. The Harris Benedict method is the most popular and is used in a range of persons. Those who are normal to ill or injured. Mifflin -St. Jeor is another calculation used and was developed more for normal persons, that is persons who are not experiencing any illness or injury. Respiratory quotient is also used in the calculation of basal metabolic rate. It is calculated in relation to the amount of carbon dioxide produced to the amount of oxygen consumed. There are numerous online calculators that are used as well. These are some of the more popular methods for estimating energy expenditure.
There are many factors affecting metabolic rates. Some of these include, lean body mass, age, gender, ethnicity, stress and body size. The more lean body mass an individual has the higher their metabolism will be as muscle is more active than adipose tissue. Such as seen in athletes. As one gets older metabolic rates tend to decrease.Men tend to have a high metabolic rate than females. Stress and trauma can increase the metabolic rate as more heat is realased and hormones in response to the stress and trauma. Body size, as in more taller individuals may have a higher metabolic rate, due to more surface area for heat to be realised.