People with exceptionally low BMI are not more active they are simply less hungry

Chinese researchers revealed that persons with extraordinarily low BMIs had a distinct approach. Contrary to popular opinion, these individuals are much less active than those with a BMI in the normal range, while having a metabolism that normally causes them to be more active. Furthermore, they consume less food than persons with a normal BMI. The study’s findings were published in the journal Cell Metabolism.

They utilised pre-existing questionnaires to screen out persons with eating disorders, those who stated they purposefully restricted their food, and those who were HIV-positive. They also eliminated anyone who had lost weight in the previous six months due to sickness or were taking any form of medication. They did not exclude individuals who stated that they “exercised in a driven manner,” yet just 4 of 150 stated that they did.

For two weeks, the subjects were observed. The doubly-labeled water approach, which estimates energy expenditure based on the difference in the turnover rates of hydrogen and oxygen in body water as a function of carbon dioxide generation, was used to quantify their food consumption.

An accelerometry-based motion detector was used to monitor their physical activity.

The researchers discovered that when compared to a control group with normal BMIs, the healthy underweight individuals consumed 13% less food. They were also significantly less active, by 23%. At the same time, these people exhibited greater resting metabolic rates, as well as increased resting energy expenditure and thyroid activity.

“Despite their modest levels of exercise, these extremely slender persons had really good measures of heart health, including cholesterol and blood pressure,” explains first author Sumei Hu, who is presently a student at Beijing Technology and Business University. “This shows that when it comes to long-term repercussions, low body fat may outweigh physical exercise.”

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The researchers admit certain limitations with this study, such as the fact that, while they measured food intake, they did not examine what the subjects really ate or their sensations of satiation or satisfaction.

The team is now broadening their research to include trials including these metrics. They also intend to investigate genetic variations between normal weight and healthy underweight people. Preliminary study indicates that single nucleotide polymorphisms in certain genes may play an impact. When these genetic modifications were duplicated in mice, the animals exhibited some of the behaviour found in humans.

“The next stage is to understand more about the phenotypic itself and the mechanisms that create it,” Speakman adds.

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