Certain individuals possess the capacity to consume substantial amounts of food yet remain lean. However, research indicates this phenomenon is not attributable to a single determinant but rather to a combination of physiological characteristics. This conclusion was reached by scientists investigating the bodily mechanisms that govern weight regulation.
Obesity is commonly viewed as an outcome of an imbalance between energy intake and expenditure. Nevertheless, observations reveal that this equilibrium is established differently across various individuals. In 2022, researchers from the University of Aberdeen and the Chinese Academy of Sciences conducted a study, the findings of which were published in Cell Metabolism. The study involved 150 participants with a Body Mass Index below 18.5, alongside 173 individuals maintaining normal weight parameters. Direct measurement techniques were employed to assess energy expenditure.
The study authors determined that the exceedingly slender participants, on average, took in approximately 12% fewer calories compared to those with standard body weight. Furthermore, these lean individuals displayed a greater rate of energy expenditure while at rest, a tendency linked to augmented thyroid hormone activity. It was also noted that, typically, these people exhibited lower levels of general movement.
A significant role is played by what is termed the thermogenesis of non-exercise activity, or NEAT. This encompasses the energy expended on any movement outside of sleeping, eating, or formal exercise sessions. Researcher James Levine of the Mayo Clinic has pointed out that disparities in this metric among people can reach as much as 2000 calories daily. In one of his investigations, it was discovered that obese individuals spend roughly 150 minutes more per day seated than their lean counterparts.
In 2023, Levine put forward a hypothesis in the journal Frontiers in Sports and Active Living suggesting the existence of a “fidget factor”—an innate predisposition toward spontaneous physical movement that might intensify when energy intake is excessive, thus affecting total caloric burn.
Genetics also exerts an influence on body mass. Scientists at the University of Cambridge, by comparing genetic information from individuals of differing body weights, identified both known and novel gene variants associated with obesity risk. Alongside these, genetic profiles contributing to lower body weight were also uncovered.
Additional contributing elements relate to lifestyle choices. Specifically, a meta-analysis by Italian researchers, detailed in Obesity Research & Clinical Practice in 2020, demonstrated that persistent sleep deprivation elevates the likelihood of weight gain.
Overall, experts concur that no single explanation accounts for the state of leanness. It is simultaneously influenced by physical activity levels, hormonal profiles, genetic makeup, sleep routines, and even dietary habits, including the frequency of snacking.
About the Author
