Healthy body weight is defined as a balance between the energy ingested and the energy expended. This balance does not mean exactly zero or complete satisfaction. The ideal BMI (Body Mass Index) for each person will depend on several factors such as sex, age, bone structure … However, it can be said that in general, this will vary in the range of 19-25. It is necessary to set the average healthy BMI at around 20-25.
We can now consider three scenarios:
1. Energy Intake
If we increase the intake of calories (energy) without modifying our metabolism (i.e., if we eat the same foods and quantities as before), this will cause an increase in adiposity (fatness).
This is why energy intake should be considered as a limiting factor; it determines both fat gain and weight gain. Of course, we could say this is an incorrect approach since in principle our total daily energy expenditure (TDEE) determines how much weight we gain or lose. However, because of the nature of the processes involved and to avoid confusion, we will continue to focus only on the role of energy intake for now.
2. Basal Metabolism
By “basal metabolism” we mean the energy expended when at rest in a comfortable environment. If the energy intake remains constant but there is an increase in basal metabolism, weight loss will occur.
However, this will not be proportional to the increase in basal metabolism. Indeed, if for example, our eating habits change and we decide to eat more vegetables, the energy expenditure will increase but not to the same extent as the calories ingested because of compensatory phenomena.
3. Physical activity
Physical activity is any muscular work that requires energy expenditure above rest. For example, walking would be a type of physical activity. An increase in physical activity beyond usual daily activities without increasing energy intake will result in weight loss.
On the other hand, if energy intake is constant, an increase in physical activity will not be able to cause weight gain.
However, it does occur together with high dietary protein content or supplementation that can promote muscle mass gain by increasing lean mass below certain thresholds of energy intake and physical activity intensity. Thus during periods of high physical activity, the body will increase the energy expenditure and reduce it when this is lower.
Aerobic exercise can also help us burn more calories than we consume, but only if we do not compensate for them by eating more.
Effective body composition is closely related to our basal metabolism. Indeed, muscle mass (in addition to fat tissue) has a higher metabolic rate than adipose tissue. Therefore the more lean mass we have, the higher our energy expenditure will be. Hence it follows that increasing our muscle mass should contribute to improving body composition and controlling weight gain.
However, the difference will not be as significant as it may seem at first glance. Whether we are talking about muscle mass or fat mass, what matters is the total amount of adipose tissue in our body because this determines how much energy is available to us. The increase in lean mass that accompanies physical activity leads to increased basal metabolism, but this improvement is much less than that caused by an increase in adipose tissue as a result of an increase in energy intake.