Friday, April 4, 2008

Why are some people thinner than others?

Little daily habits could hold the answer

Why do some people seem to be habitually thin. Recent research suggests that higher levels of fidgeting and other non-exercise movements may be a key factor in determining which of us gain weight easily, and which of us do not.


Fidgeting, stretching, toe-tapping -- such random activities of daily life may “explain the variability in fat gain with overeating” between individuals, according to recent research

For most people excessive calorie intake beyond daily energy requirements leads to weight gain in the form of fat. However, some individuals seem to be able to indulge in calorie-rich foods without weight gain.

Researchers tried to determine whether a particular form of energy expenditure, called “nonexercise activity thermogenesis” (NEAT) might play an important role in fat accumulation. The authors define NEAT as calorie expenditure “that accompanies physical activities other than volitional exercise, such as the activities of daily living, fidgeting, spontaneous muscle contraction, and maintaining posture when not recumbent.”

The researchers placed 16 healthy volunteers, aged 25 to 36 years old, on an 8-week diet which supplied them with an extra 1,000 kilocalories above normal energy intake. Levels of voluntary exercise were restricted.

The researchers then used high-tech methods to determine daily energy expenditure allotted to basal metabolism (the energy used by the body at rest), energy expenditure associated with the digestion and storage of food, voluntary exercise, and NEAT.

What they found

They found at the end of the 8-week period, “fat gain varied 10-fold among (the) volunteers”, from between 0.36 kg (less than 0.8 pound) to 4.2 kg (over 9 pounds).

Basal metabolism, energy expenditure associated with food processing, and voluntary exercise varied little between the study subjects, the authors report, and had minimal impact on variations in weight gain.

Instead, “NEAT proved to be the principal mediator of resistance to fat gain with overfeeding”, according to the investigators. “The rate of change in NEAT in our volunteers was large”, they say. Some volunteers fidgeted and shuffled their way to a loss of over 692 kilocalories per day, they say. Others actually slowed down on the high-calorie diet -- their NEAT expenditure decreasing by up to 98 kilocalories per day.


Why some people have much less NEAT is unclear. Though it may relate to people fidgeting more or less that needs to be studied further. The important message appears to be that every little bit of activity is important because its effect becomes cumulative over time. Get rid of the TV remote and always take the stairs. The key difference between people who are overweight and those that are not relates to their respective levels of physical activity.