When an individual is in energy balance , energy intake equals energy expenditure, and weight should remain stable. Positive energy balance occurs when energy intake is greater than energy expenditure, usually resulting in weight gain.

Negative energy balance is when energy intake is less than energy expenditure, usually resulting in weight loss.

Energy intake is made up of the calories we consume from food and beverages. These calories come from the macronutrients carbohydrates, proteins, and fats and alcohol. Remember that when the body has a surplus of energy, this energy can be stored as fat. In theory, if you consume 3, more calories than your body needs, you could potentially gain about one pound, because a pound of fat is equal to about 3, calories.

If you expend 3, more calories than you take in, you could potentially lose about a pound, as your body turns to this stored energy to compensate for the energy deficit. However, in practice, how individuals respond to an excess or deficit of calories can be quite variable, and over time, the body adapts to these conditions and resists changes in body weight.

The sum of caloric expenditure is referred to as total energy expenditure TEE. There are three main components of TEE:. Figure 7. Components of total energy expenditure include basal metabolism, the thermic effect of food, and physical activity. BMR is the energy expended by the body when at rest.

These are the behind-the-scenes activities that are required to sustain life. Examples include:. Basal metabolic rate does not include the energy required for digestion or physical activity.

If a person is sedentary or moderately active, BMR is the largest component of energy expenditure, making up about 60 to 75 percent of total energy output.

For example, a sedentary person might need about calories in a day, with about of them being for BMR. Components of energy expenditure and their percent contribution to the total in sedentary to moderately active people. BMR can vary widely among individuals. This means that a muscular person expends more energy than a person of similar weight with more fat.

Likewise, increasing your muscle mass can cause an increase in your BMR. However, skeletal muscle at rest only accounts for about 18 percent of the total energy expended by lean mass. Most is used to meet the energy needs of vital organs.

The liver and brain, for example, together account for nearly half of the energy expenditure by lean mass. Energy expenditure of organs.

BMR depends not only on body composition but also on body size, sex, age, nutritional status, genetics, body temperature, and hormones Table 9. People with a larger frame size have a higher BMR simply because they have more mass.

On average, women have a lower BMR than men, because they typically have a smaller frame size and less muscle mass. As we get older, muscle mass declines, and therefore BMR declines as well. Nutritional status also affects basal metabolism. If someone is fasting or starving, or even just cutting their caloric intake for a diet, their BMR will decrease.

This is because the body attempts to maintain homeostasis and adapts by slowing down its basic functions BMR to help preserve energy and balance the decrease in energy intake.

This is a protective mechanism during times of food shortages, but it also makes intentional weight loss more difficult.

Factors That Increase BMR. Factors That Decrease BMR. Higher lean body mass. Lower lean body mass. Larger frame size. Smaller frame size. Younger age.

Older age. Male sex. Female sex. Stress, fever, illness. Starvation or fasting. Pregnancy or lactation. Stimulants such as caffeine and tobacco. Table 7. Factors that Impact BMR. This is the energy needed to digest, absorb, and store the nutrients in foods. Search site Search Search.

Go back to previous article. Sign in. Learning Objectives Describe energy balance. Define basal metabolism and explain the factors that affect basal metabolic rate. Summarize factors that affect energy intake and energy output. Energy Balance Recall that the macronutrients you consume are either converted to energy, stored, or used to synthesize macromolecules.

Energy Intake The amount of energy taken in each day comes from the foods you eat and the beverages you drink. An estimate of your BMR can be determined using the appropriate formula below: males: weight in kg x 1.

Factors Affecting Energy Intake Physiological Influences How much we eat and what we eat is controlled not only by our own desires, but is also regulated physiologically. Genetic Influences Genetics certainly play a role in body fatness and weight and also affects food intake.

Societal Influences Food preferences, cultural customs, and religious practices are just a few of the societal influences that can impact energy intake.

Factors Affecting Energy Expenditure Physiological and Genetic Influences Why is it so difficult for some people to lose weight and for others to gain weight?

There are several theories that attempt to explain the impact of physiological and genetic influences including: Set Point Theory. This "set point" works to maintain our weight within a narrow range by triggering changes in energy intake or expenditure to maintain body weight within the target range.

Some believe that this theory provides an explanation as to why after dieting, most people return to their original weight not long after stopping the diet. Thrifty Gene Theory. The thrifty gene theory proposes that a gene or genes causes people to be energetically thrifty.

In theory, people with this gene expend less energy than other people and therefore may gain weight more easily and be more resistant to weight loss. FTO Gene. Although it is likely that there is no one 'obesity gene', there are some genes that have been identified - such as the fat mass and obesity FTO gene.

Gut Microbiome. Several microorganisms within the gastrointestinal tract or "gut" have been identified as related to obesity. Due to the complexity and diversity of the microorganisms within the gut the "gut microbiome , the mechanism by which the gut microbiome induces obesity still needs to be further studied.

This hypothesis proposes that the body has a fixed daily dietary protein target that must be reached. The hypothesis suggests that overeating may occur because our diets are proportionally higher in carbohydrate and fat and lower in protein.

Drifty Gene Hypothesis. The drifty gene hypothesis proposes that random mutation and drift in genes control the upper limit of body fatness. Individuals with "drifty genes" are prone to obesity because the genes do not control the upper limit of body fatness.

Societal Influences In the United States, many societal factors influence the number of calories burned in a day. Key Takeaways Energy balance is achieved when energy intake is equal to energy expended. The amount of energy you expend every day includes not only the calories you burn during physical activity, but also the calories you burn at rest basal metabolism , and the calories you burn when you digest food.

Basal metabolic rate BMR is dependent on body size, body composition, sex, age, nutritional status, genetics, body temperature, and thyroid hormone levels.

Energy intake and energy expenditure are regulated by complex physiological responses and are influenced by genetics, behavior, and society. References Liu BN, Liu XT, Liang ZH, Wang JH. Gut microbiota in obesity.

World J Gastroenterol. doi: The Dietary Guidelines for Americans recommendations are based upon scientific evidence. E: Exercises. Manchester Community College - Introduction to Nutrition.

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