Your body is in the energy exchange business all the time. Here’s how it works. You balance the energy you expend with energy from the food and beverages in your did. If you do a fairly good job of equalizing input and output, your body does the rest – maintaining energy equilibrium and keeping your weight steady. But suppose you bring in more energy than your body can handle? Or assume the opposite situation – you expend much more energy than you bring in? What’s going to happen? In this article we’re going to take a closer look at the energy balance equation to see how it operates and where most misunderstandings arise.

Energy intake & Energy output

Before we start analyzing the energy balance equation, you need to become familiar with the ways your body gains and loses its energy. In our previous articles, we analyzed in detail how to estimate (calculate) your daily energy intake and your daily energy consumption, as accurately as possible. We have also discussed in detail about the key factors that affect energy consumption, as well as their contribution to total daily energy expenditure. Therefore, only when these concepts completely sink in does it make sense to continue to further study the equation of energy balance.

In a nutshell, energy intake is the amount of calories you take in through consumption of carbohydrate, protein, fat, and alcohol. Energy output is the amount of calories you expend on basic body functions, physical activity, and the processing of food.

Energy-balancing equation

The principle embodied in the energy-balancing equation is simple: as long as caloric input equals caloric output, the person does not gain or lose weight. Therefore, if a person maintains a healthy weight over time, the person is in energy balance.

energy balance equation

There are three possibilities resulting from this equation: (1) energy equilibrium, (2) positive energy balance, and (3) negative energy balance.

Energy equilibrium

People who maintain a relatively constant weight are in energy equilibrium. Within limits, your body automatically regulates your weight, thanks to its ability to balance intake and expenditure. Your body can be in energy equilibrium even if your energy intake is very high, as long as your expenditure also is high. Conversely, your body can be in energy equilibrium when you don’t expend much energy, as long as your intake also is low.

Therefore, energy equilibrium or neutral energy balance indicates that the energy intake and cellular expenditure match exactly. However, energy intake and expenditure rarely match.

energy equilibrium - energy balance

Positive energy balance

When you take in more energy than you need (expend), you have a positive energy balance. You store the surplus as fat – the major energy reserve – and as glycogen – the short-term energy/carbohydrate reserve. Pregnant women and growing children need a positive energy balance to increase energy stores. This is also the case with bodybuilders and people engaged in strength training whose main goal is increase in muscle mass. But the positive energy balance that results from overeating and inactivity, a common occurrence around major holidays, leads lo unneeded weight gain.

Therefore, positive energy balance is the consumption of more energy in food than is used by the cells.

positive energy balance

Negative energy balance

When you take in less energy than you need (expend), you have a negative energy balance. Your body uses stores of glycogen and fat for fuel (and body protein, too, if the deficit is extreme), and body weight goes down. Thus, body weight change reflects overall energy balance.

Here, obviously, there is consumption of less energy in food than is used in the cells.

negative energy balance

Losing body mass

The energy balance diagram shows that to lose body mass, it is necessary to reduce energy intake below energy use. This can be done in two ways:

  • by eating less ‘high-energy’ food, which will reduce the energy intake;
  • by taking more exercise, which will increase the energy use;

The best approach is to combine both methods, controlling the diet and also taking more exercise. Many people who rely on diet alone have great difficulty in controlling their body mass.

Gaining body mass

The energy balance diagram shows that to gain body mass, it is necessary to increase energy intake above energy use (calories burned). There are two ways to achieve this:

  • by eating more ‘high-energy’ food, which will increase the energy intake;
  • by taking less exercise, which will decrease the energy use;

Again, the best approach is to combine both methods.

Maintaining body mass

As long as caloric input equals caloric output, the person will maintain its body mass.

weight loss, weight gain, weight maintenance

Numerical example

A 29-year-old man weights 180 lb (82 kg), is 6 feet tall (183 cm), and eats an average of 3.700 kcal/day while maintaining moderate active lifestyle (he exercises 2-3x weekly). Calculate his daily energy expenditure (energy output). What can you conclude from the energy balance equation?

Total energy intake (calories from food and beverages): 3.700 kcal

BMR (basal metabolic rate) = 88.362 + (13.397 x weight in kg) + (4.799 x height in cm) – (5.677 x age in years) = 88.362 + (13.397 x 82) + (4.799 x 183) – (5.677 x 29) = 1.901 kcal/day

Total energy expenditure = BMR x physical activity factor = 1.901 kcal/day x 1,7 = 3.232 kcal/day.

Result: this men will tend to gain weight with his current exercise and meal plan, because he is consuming 468 kcal more than he is expending. Because 1 lb (0,45 kg) of body weight equals approximately 3.500 kcal, this 29-year-old man will gain approximately 1 lb (0,45 kg) every 7 days with the preceding eating and exercise routine.

One pound of fat is the equivalent of 3500 calories. If a person’s estimated energy requirement is 3232 kcal/day and that person were to decrease intake by 500 calories per day (from 3232 to 2732), it should result in a loss of one pound of fat in seven days (500 x 7 = 3500).

Closing thoughts: Energy balance equation

Energy balance is a comparison between energy intake (in the form of food) and energy use by the cells. Measuring weight and height provides very good indicators of positive or negative energy balance. There’s nothing magical about controlling weight. The amount of calories you can consume to match your body’s energy (calorie) expenditure is your daily energy allowance. Think of it as a calorie budget. For weight loss consume fewer calories than you burn each day. Either cut back on calories in, or move more. Better yet, do both! For weight gain take in more calories than your body uses. Still keep moving!

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