Fitness: Energy Balance

Daily energy expenditure consists of three components:
1. Basal metabolic rate (BMR) - 60-70%,
2. Diet-induced thermogenesis (DIT) - 10% and
3. Energy cost of physical activity - 20 - 30%.

Thermic Effect of Food
-Energy required to digest, absorb, transport, and store food.
-Diet induced thermogenesis (DIT) is different for each nutrient based on the amount of ATP required for the initial steps of metabolism and storage.
-In healthy subjects with a mixed diet, where intake equals expenditure, DIT represents about 10% of the total amount of energy ingested over 24 hours

Activity
-Daily Activity
-Exercise
1. Aerobic exercise - Expends calories during exercise
2. Anaerobic exercise can increase metabolism for hours after exercise is finished

-3-14 hours: dependent upon intensity

-For every calorie expended during anaerobic activity, 9 times as much fat (per calorie expended) was metabolized as compared to aerobic activity.

Resting Metabolic Rate
1. Energy expended to maintain the body during resting conditions.
-Proportional to muscle mass
-Muscle is more metabolically active than fat
2. May account a smaller proportion of the daily caloric needs for those who have regular vigorous exercise.

Energy Balance

1. Neutral energy balance is when the calories you take in is equal to the calories expended.
-Weight is maintained.
2. Positive energy balance is when the calories you take in is greater than the calories expended.
-Weight is gained and fat stores are increased.
One pound of fat contains approximately 3500 Calories.

3. Negative energy balance: calories you take in is less than the calories expended.

-Adipose, glycogen, and muscle can be used for energy to make up the caloric deficiency.
-Ideally weight is lost and fat stores are reduced.

4. Appetite - Appetite is increased in proportion to energy expenditure over a broad range of exercise intensities and durations to maintain body weight.

-However, formerly sedentary individuals show a net loss of appetite when exercise is introduced.

The metabolism adjusts to changes in diet

1. If calories are increased
Thermo-genesis - Body heat is produced
Metabolism increases
Muscle mass may increase
2. If calories are restricted
Metabolism decreases
Muscle mass may decrease
3. A cascade of metabolic / hormonal changes allow the body to adapt