A new collaborative study which included researchers from the University of Aberdeen has found that a long-term increase in exercise leads to a 28% reduction in calories burned by the body during basic activities like sleeping.
The research also showed that those with the highest body fat see just 54% of calories burned by activity translating into calories burned for the day.
The analysis, led by the University of Roehampton, found that people who take part in regular exercise burn less calories on body maintenance than people who don’t do any strenuous activity, dramatically reducing the calorie burning gains of exercise.
Using the largest global dataset on human energy expenditure, from the International Atomic Energy Agency’s Doubly-labelled water database of over 1,750 adults, researchers found that the calories the body burns to keep ticking over (known as basal energy expenditure), for example when sleeping, decreases by 28% during periods when daily exercise levels are consistently high. This means the more we exercise over the long-term, the less calories our bodies burn for the most rudimentary activities, therefore reducing the overall calories we burn per day.
Professor Lewis Halsey of the Department of Life Sciences at the University of Roehampton and Dr Vincent Careau of the University of Ottawa (Canada), who led the data analysis, also found that adults with the highest body mass index (BMI) burned even less calories in the background after an increase in activity.
The results show that only 54% of the calories burned by exercise or activity among people with the highest BMI actually translated into calories burned at the end of the day, due to their bodies reducing the energy spent on the most basic of functions. In contrast, 70% of calories burned during activity by those with the lowest body mass translated into more calories burned at the end of the day1. Overall, calories lost were no different when comparing age and sex, meaning the energy lost during activity applies equally to men and women, young and old, once their BMI is accounted for.
The research suggests that people who have a higher BMI and thus greater fat levels may burn less calories per day in response to long-term hikes in activity.
With many current weight loss programmes using additive models to calculate how many calories should be burned to reduce fat loss, and the rise of digital exercise trackers such as Fitbit and Apple Watch highlighting people’s calories burned during a day, this study debunks the belief that the calories burned from exercise easily translate into extra calories burned overall for the day.
Professor Lewis Halsey from the University of Roehampton said: “Around the world, national guidelines tend to recommend a 500-600 calorie deficit through exercising and dieting to lose weight. However, they do not take into account the reduction of calories being burned in the most basic of human functions as the body compensates for the calories burned on the exercise as shown in our research, and the variation in this compensation between people with different levels of body fat. Not only should these guidelines be revised, but there is also a need for greater personalisation of exercise plans depending upon body mass.”
Professor Speakman from the University of Aberdeen and chairman of the management group for the database adds: “This is a cruel twist for individuals who have obesity because it means for them losing weight by increasing activity is likely to be substantially harder than for a lean person where the compensation is much less, but their need to lose weight is much lower.
“This analysis using data from the DLW database shows how individuals are not all the same in the way they budget their energy use. People living with obesity may be particularly efficient at hanging onto their fat stores, making weight loss difficult.”
A copy of the research paper ‘Energy compensation and adiposity in humans’ is available to download here