Staying active is critical to a healthy lifestyle, but long-term exercise may reduce the amount of calories we burn during "body maintenance".
The NHS recommends adults be moderately active for at least 150 minutes a week, which could include brisk walking, gentle cycling or even pushing a lawn mower. If time-pressed, be vigorously active for 75 minutes via jogging, cycling briskly or skipping rope.
Aside from helping you stay slim, exercise has been linked to a reduced risk of depression, certain cancers and even a premature death.
Nevertheless, scientists from the University of Roehampton have reported that when a person's daily exercise level is "consistently high", they burn 28% fewer calories while carrying out essential daily functions, like sleeping.
This may then reduce the overall calories an active person burns in a day, added the team.
"Around the world, national guidelines tend to recommend a 500-600 calorie deficit through exercising and dieting to lose weight," said lead author Professor Lewis Halsey.
"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."
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The scientists analysed more than 1,750 participants of the International Atomic Energy Agency, all of whom were "living normal lives".
Results – published in the journal Current Biology – reveal those who exercised vigorously every day burned fewer calories while their body "ticked over".
This was particularly true among the participants with the highest body mass index (BMI).
Among those who were overweight or obese, only 54% of the calories burned while exercising translated into the overall calories burned at the end of the day. This is compared to 70% among the participants with the lowest BMI.
Many weight loss programmes calculate the number of calories that need to be burned to reduce our BMI.
Exercise trackers like Fitbit and Apple Watch estimate the calories burned in a given day. The Roehampton study suggests, however, the calories burned from exercise may not easily translate into the overall calories that we shed in a day.
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