Suche
Mein Konto
Lean people don't exercise more than the rest of us - they just eat less, a study suggests.
It has long been assumed that naturally thin people exercise more so they can eat whatever they want.
But researchers have found that the opposite is true - they actually exercise less and eat less.
They examined the diets and energy levels of 150 “super-slim” people and compared them to 173 people of normal weight.
During the two-week study, naturally thin people did 23 percent less physical activity and spent more time sitting or lying down. They also ate 12 percent less food.
However, they have been found to have a faster resting metabolism, which can help them burn more calories while idling than the average person.
Thin people don't exercise more than the rest of us - they just eat less, study finds (File)
Professor John Speakman, who led the study from the University of Aberdeen, said: “The results were a real surprise.
“When people talk to super-slim people, they often say they can eat whatever they want.
“But our work has shown that they actually eat much less than people in the normal body mass index (BMI) range.”
The study, published in the journal Cell Metabolism, recruited naturally thin people with an average BMI of 17.
A BMI below 18.5 is considered underweight, and the people in the study appeared to be naturally slim, with researchers making sure they were not dieting, had not lost weight through illness and did not have an eating disorder.
Surprisingly, these naturally thin people were found to spend 96 percent of their time sedentary or doing only light physical activity.
But they appeared to eat significantly less than normal-weight people whose BMI was below 25 - the threshold for overweight - and above 21.5.
To find out whether naturally well-groomed people could really eat whatever they wanted, researchers didn't ask them to keep food diaries, which people could misremember and get wrong, but instead calculated their calorie intake directly based on how much energy they burned.
People's energy expenditure was calculated by giving them water to drink daily that contained heavy isotopes of hydrogen and oxygen.
These are measured in urine because they are excreted in the body at different rates depending on how many calories someone burns and converts into carbon dioxide.
Using this energy expenditure as measured by physical activity, the researchers suggest that naturally thin people in the study must have eaten an average of 12 percent less than people of normal weight.
But they were also lucky in that they burned more energy just sitting still and had faster metabolisms than people of normal weight.
In fact, their metabolism was 22 percent higher than expected based on their body fat levels.
This has been linked to higher thyroid hormone levels, which may help people feel less hungry and stay slim.
Researchers are now studying whether naturally thin people have higher metabolisms and elevated thyroid hormones because of their genes, and have already found some genetic peculiarities that may help explain how people avoid gaining weight.
There is evidence that around 1.7 percent of people are underweight.
While some have eating disorders or have lost weight through illness, many are perfectly healthy but simply remain thin.
The current study only looked at Chinese people, and other naturally thin people not involved in the study may be more active.
But the results suggest that naturally thin people can get away with not exercising much because of their low body weight and diet, as study participants tend to have lower bad cholesterol levels than people of normal weight.
Dr. Sumei Hu, co-lead author of the study from the University of Aberdeen, said: “It was a big shock to me that the super-slim people were much less active than people in the normal BMI range.
“I always thought super-slim people had to be very active to maintain low body weight, but our results showed the opposite.”