Balancing Energy Input with Energy Output

To Maintain Weight, Energy Intake Must Balance Energy Output

Recall that the macronutrients you consume are either converted to energy, stored, or used to synthesize macromolecules. A nutrient’s metabolic path is dependent upon energy balance. When you are in a positive energy balance, the excess nutrient energy will be stored or used to grow (e.g., during childhood, pregnancy, and wound healing). When you are in a negative energy balance, you aren’t taking in enough energy to meet your needs, so your body will need to use its stores to provide energy. Energy balance is achieved when the energy intake is equal to the energy expended. Weight can be thought of as a whole-body estimate of energy balance; body weight is maintained when the body is in energy balance, lost when it is in negative energy balance, and gained when it is in positive energy balance. In general, weight is a good predictor of energy balance, but many other factors also play a role in energy intake and energy expenditure. Some of these factors are under your control and others are not. Let us begin with the basics of how to estimate energy intake, energy requirement, and energy output. Then we will consider the other factors that play a role in maintaining energy balance and hence, body weight.

Estimating Energy Requirement

To maintain body weight, you must balance the calories obtained from food and beverages with the calories expended every day. Here, we will discuss how to calculate your energy needs in kilocalories per day so that you can determine whether your caloric intake falls short, meets, or exceeds your energy needs. A formula was devised for calculating your Estimated Energy Requirement (EER). It takes into account your age, sex, weight, height, and physical activity level (PA). The EER is a standardized mathematical prediction of a person’s daily energy needs in kilocalories per day required to maintain weight. It is calculated for those over 18 years of age via the following formulas:

Adult male: EER = 662 − [9.53 X age (y)] + PA X [15.91 X wt (kg) + 5.39.6 X ht (m)]

Adult female: EER = 354 − [6.91 x age (y)] + PA x [9.36 x wt (kg) + 726 x ht (m)]

Note: to convert pounds to kilograms, divide weight in pounds by 2.2. To convert feet to meters, divide height in feet by 3.3.

Estimating Caloric Intake Requirements

The numbers within the equations for the EER were derived from measurements taken from a group of people of the same sex and age with a similar body size and physical activity level. These standardized formulas are then applied to individuals whose measurements have not been taken but have similar characteristics, to estimate their energy requirements. Thus, a person’s EER, as the name suggests, is an estimate for an average person of similar characteristics. EER values are different for children, pregnant or lactating women, and overweight or obese people. It is also important to remember that the EER is calculated based on weight maintenance, not for weight loss or weight gain.

The 2015 Dietary Guidelines provides a table (Table 14.2) that gives the estimated daily calorie needs for different age groups of males and females with various activity levels. The Dietary Guidelines also state that while knowing the number of calories you need each day is useful, it is also pertinent to obtain your calories from nutrient-dense foods and consume the various macronutrients in their Acceptable Macronutrient Distribution Ranges (AMDRs) (Table 14.3).

Total Energy Expenditure (Output)

The amount of energy you expend every day includes not only the calories you burn during physical activity, but also the calories you burn while at rest (basal metabolism), and the calories you burn when you digest food. The sum of caloric expenditure is called total energy expenditure (TEE). Basal metabolism refers to those metabolic pathways necessary to support and maintain the body’s essential functions (e.g. breathing, heartbeat, liver and kidney function) while at rest. The basal metabolic rate (BMR) is the amount of energy required by the body to conduct its essential functions over a certain time period. The great majority of energy expended (between 50 and 70 percent) daily is from conducting life’s basic processes. Of all the organs, the liver requires the most energy (Table 14.4). Unfortunately, you cannot tell your liver to ramp up its activity level to expend more energy so you can lose weight. BMR is dependent on body size, body composition, sex, age, nutritional status, and genetics. People with a larger frame size have a higher BMR simply because they have more mass. Muscle tissue burns more calories than fat tissue even while at rest; thus, the more muscle mass a person has, the higher their BMR. Since females typically have less muscle mass and a smaller frame size than men, their BMRs are generally lower than men’s. As we get older, our muscle mass declines and thus, our BMR declines. Nutritional status also affects basal metabolism. Caloric restriction, as occurs while dieting, for example, causes a decline in BMR. This is because the body attempts to maintain homeostasis and will adapt by slowing down its essential functions to offset the decrease in energy intake. Body temperature and thyroid hormone levels are additional determinants of BMR.

The energy required for all the enzymatic reactions that take place during food digestion and absorption of nutrients is called the “thermic effect of food” and accounts for about 10 percent of the total energy expended per day. The other energy required during the day is for physical activity. Depending on lifestyle, the energy required for this ranges between 15 and 30 percent of the total energy expended. The primary control a person has over TEE is to increase physical activity.

How to Calculate Total Energy Expenditure

Calculating TEE can be tedious, but it has been made easier with the help of calculators available on the Web. TEE is dependent on age, sex, height, weight, and physical activity level. The equations are based on standardized formulas produced from actual measurements from groups of people with similar characteristics. To get accurate results from web-based TEE calculators, it is necessary to record your daily activities and the time spent performing them. An interactive TEE calculator can be found online at Health-calc.