Research suggests that it is more difficult to lose weight by exercising for obese people.
Initial research suggested that energy expenditures in a day were the sum of energy spent due to activity (ranging form light gardening to running marathons) and energy needed for basic functioning (what keeps our bodies ticking even though we're not doing anything, such as wound healing and immune function).
However, preliminary laboratory research suggests that this simple addition could lead to misleading estimates of daily total expenditure. These tend to be lower than the sum of activity and baseline expenditures in individuals.
This was further explored by a team of international scientists who analysed energy expenditure measurements from 1,754 adults using a dataset that had been collected over many decades and provided by the International Atomic Energy Agency.
According to the current biology study, increasing activity levels by exercising more led to each person's body compensating by limiting energy spent on basic metabolic functions over longer periods.
If you run 300 calories and your activity tracker shows that you ate nothing but a healthy meal, you might assume that your daily energy expenditure increased by 300 calories.
This may seem to be true in the short-term, but the body will eventually compensate by using less energy for other processes over time, according to Prof Lewis Halsey, University of Roehampton's lead author.
He said that it is like the government trying balance the budget by spending more on education. Then, it might have to spend less on roads.
People who are trying to lose weight may also notice this. They might lose some weight at first, but then find it becomes irritatingly slow. This could be because their body uses less energy to maintain its baseline functions.
The analysis revealed that approximately half of calories burnt in physical activity was converted to energy at the end of each day for those with the highest BMI (body weight index), while 72% of calories were used in total daily energy expenditure for those with a normal BMI.
Halsey stated that there is a greater energy compensation for people with higher BMIs, but it was not clear why.
Is it possible that these people are more heavy because they have more energy to compensate, or that their energy compensation is greater once they are heavier? We don't know.
The researchers pointed out that the key to improving public health strategies for obesity will be resolving the causality between energy compensation and body fat accumulation.
Halsey also noted that it is not clear which part of the body's baseline functioning has been lost to compensate for extra activity.
Exercise is still a good thing, even if you're trying to lose calories.
He said that if we try to lose a lot of calories through increased exercise, we might get into trouble. As our bodies compensate, we may start to notice the negative effects.
