Can we lose weight with exercise alone?

To lose 1 kg of body fat it is necessary to lose 9000 kcal. However, to lose 1 kg of body weight we will take into account that not only fat is lost, but we will probably also lose water and some muscle mass, so we will take 7000 kcal as an assumed value. That is, we must force our body to spend 7000 kcal.

To spend 7000 kcal of body reserves we can try three strategies:

1.- Dieting

2.- Exercise

3.- Combine exercise and diet.

Dieting

It basically consists of calculating our total energy needs for the day (Total Energy Expenditure, GET) and reducing the intake by enough daily calories to lose 1 kg. Assuming that our intake is 2200 kcal, if we do a 1500 kcal diet we could not ingest 700 kcal a day. In 10 days we would lose 7000 kcal, that is, 1 kg of body weight in the form of fat and some muscle and water.

Working out

We will take into account the energy expended in different physical activities. If we look at the energy expended per minute and per kilo of body weight (values taken from the Nutrition and Dietetics Manual, Carbajal et al):

Take for example a 70 kg girl who goes 2 times a week to Zumba (45 minutes each day) and swims 3 times a week (1 hour each time). In this case, you will spend 318 kcal in each Zumba class and 357 kcal in each swim class. In addition, you are probably not constantly dancing or swimming because the intensity of the exercise decreases or you take short breaks. But suppose that you do indeed perform the corresponding sport at maximum intensity all the time. If we calculate the weekly average, we get about 243 kcal / day. To spend 7000 kcal it will take about 29 days to lose 1 kg of weight.

Now suppose the case of a man, weighing 70 kg, who goes for a run for 1 hour 3 times a week and plays a football game in the neighborhood league on the weekend. You will spend 634 kcal / day of running (assuming that in 1 hour of running you are always at maximum intensity) and 863 kcal assuming that you play the 90 minutes of the match at maximum intensity. In a week you will expend 395 kcal / day, which means that to expend 7000 kcal it will take almost 18 days.

It must be taken into account that physical exercise, in the short term, produces an increase in hunger and there is the possibility that, without realizing it, we increase the intake , so that, despite spending energy on exercise, it is possible that we are consuming more calories than we should, and as a consequence we do not lose weight.

By the way, to have an increase in muscle mass by exercising it is necessary that 1) we eat enough protein to contribute it to the muscle, 2) we do strength exercise to stimulate muscle growth and 3) we provide enough energy to be able to create that muscle. On a hypocaloric diet, no muscle is generated no matter how much exercise we try to do. And if that exercise is exclusively cardiovascular type, neither.

Combine exercise and diet

When we combine exercise and caloric restriction we achieve a synergistic effect. We need to “remove” fewer calories from our diet and increase energy expenditure at the same time, making weight loss much more effective and easier. Especially in the case of people who have a low GET.

Let’s imagine a person who has a GET of 1800 kcal and a basal expenditure of 1300 kcal. This could happen in a woman 160 cm tall and 50 kg in weight, for example. Or in a person over 50 years old.

If we reduce 700 kcal from his diet, he would eat 1100 kcal, which could lead to nutritional deficiencies and there would be no energy left for him to carry out his daily activities, causing his metabolism to slow down and increase the absorption of nutrients. On the other hand, without touching your diet is unlikely that someone wants to go to the gym and lose 1 kg every 28 days. It would take 6 months to lose 5 kg, so your frustration is very likely to increase.

If, on the other hand, we reduce your diet to 1500 kcal and increase your physical exercise in the examples that we have put above, you will lose about 500-700 kcal a day and it will take approximately 10-15 days to lose 1 kg of weight, so you will lose about 5 kg in 2 months, which is a much less frustrating figure.

We must therefore understand that the best strategy to lose weight is the combination of diet and exercise, as much as we are lazy to leave the sofa.