JOH: The expression energy balance describes the flow of energy through the body, and to understand the way in which body weight is regulated, it is necessary to understand this concept. Once we have a basic knowledge of how the energy balance is adjusted, we can better understand and modify the factors that cause a positive energy balance and weight gain.
What Components Intervene In The Energy Balance?
JOH: The main components of the energy balance are energy intake, energy deposits, and energy expenditure. These components are interrelated, so changes in any of these components affect others. Therefore, it is not enough to change one part and assume that the others will not change. For example, increasing exercise could lead to increases or decreases in energy intake and changes in the body’s energy. The system is regulated in the brain, although all the neurological components are still being worked on.
In What Ways Do Humans Spend Calories?
JOH: Humans spend energy through three primary forms:
1) basal metabolic rate (sometimes called resting energy expenditure or GER), which is the energy needed to maintain the body’s functions;
2) energy expenditure in physical activity;
3) energy necessary to absorb and metabolize food (thermal effect of food).
The rate of basal metabolism is a function that depends in no small extent on the size of the organism. The thermic effect of the food is relatively fixed, between 7 and 10% of the energy intake. The energy required by physical activity is the most variable component of energy expenditure and the one that most obeys voluntary control.
How important is the time during which the energy balance is maintained?
JOH: The energy balance seems to be regulated for long periods (days) vs. short periods (on the same day). Neither the energy intake nor the energy expenditure is constant from day to day, and the organism seems to be able to regulate or integrate these inputs and outputs throughout a few days.
Throughout the last decades, the majority of the population has experienced an increase in weight. Can this be explained from the energy balance and the modern lifestyle?
JOH: Totally. The body strives to achieve a balance between intake and energy expenditure. In today’s world, environmental factors such as hypercaloric diets, cheap and readily available foods, the lack of physical activity, or the attractiveness of sedentary activities, tend to increase energy intake and decrease spending. The organism adapts by increasing body fat deposits that serve to increase energy expenditure (a more substantial body increases its basal metabolic rate and the energy cost of physical activity) and restore balance. In this way, obesity should not be perceived as a defective regulation of the energy balance, but as an adaptation to the modern world.
Usually, restricting food has been considered a strategy by itself to try to lose weight. Is it right?
JOH: We have spent decades of research to show that, to reduce obesity, food restriction is not a good long-term strategy. Humans feel a strong urge to eat and are not very good at limiting food. To reduce obesity, a very common approach is to eat too little to respond to a low level of physical activity, but it rarely succeeds. Knowing the energy balance, it can be predicted that this strategy would be unsustainable for most people. Maintaining food restriction over a long period is difficult. For people to eat a reasonable amount of food without feeling limited in diet, and keep healthy body weight, it will be necessary to increase the physical activity of the population.
What is the best strategy for maintaining the long-term energy balance?
- Increase physical activity in the population.
- Encourage a more intelligent way of feeding (without food restriction). This includes being aware of the size of the rations and choosing less caloric foods (limiting the intake of sugars and fats, for example).
- Teach people energy balance techniques. Most people who do not pay attention to the energy balance are probably gaining weight. We need to teach people (starting with children) how they relate the energy of food and the power of physical activity so that they can make better conscious choices of diet and physical exercise.
From energy balance, what is easier: to avoid obesity, to reverse it when it is already present, or both.
JOH: From an energy balance point of view, it should be easier not to gain weight than to treat obesity. This is because, when obese people lose weight, the energy expenditure is reduced (perhaps in an attempt by the organism to maintain the energy balance). People who successfully keep significant weight loss have to work harder to avoid weight gain than those who have never been obese. It is possible to prevent weight gain by small changes in behavior and without triggering any compensatory change in energy expenditure.