Sunday, September 2, 2007

Does napping after a meal cause weight gain?

1 Sep 2007, ST

WEIGHT change is a relatively slow process over long periods. It depends on many factors and sleep itself does not cause weight gain. The key is balancing energy intake and energy use over time.

Energy input comes from food and drinks and is usually measured in kilocalories (kcal). The United States Department of Agriculture assigns calorie levels based on an individual's sex, age and activity level.

The intake quantities range from 3,000 kcal for active males aged 19 and 20 to 2,000 kcal for sedentary men aged 76 and up. It is 2,400 kcal for active females aged 19 and 20 and 1,600 kcal for sedentary women aged 76 and up.

When energy intake exceeds use, the body stores the excess as fat.

Energy expenditure consists of resting metabolic rate, or energy the body uses to maintain normal functions; diet induced thermogenesis, or energy needed to digest, absorb, transport, metabolise and store food and drink; and physical activity.

Our bodies expend energy all the time. Even when sleeping, the body needs energy to fuel the multitude of complex functions that keep us alive.

Since 0.45kg of body fat is equivalent to about 3,500 kcal of energy, the energy balance equation suggests that an increase in food intake or a decrease in energy expenditure equal to 3,500 kcal will result in a weight gain of 0.45kg.

But there are other significant individual differences to account for when predicting either weight gain or loss.

It is true to say though, that if someone went for a brisk walk rather than take a nap after eating, he would have used more energy during the walk.

And recent studies indicate that individuals who suffer from sleep deprivation could be more susceptible to weight gain. It appears that a lack of sleep leads to decreased release of the hormone leptin, which usually makes a person feel full.

Sleep loss also increases levels of the hormone grehlin, which makes people feel more hungry.

Answer provided by Dr Li Changming, head of Bioengineering, School of Chemical and Biomedical Engineering, at the Nanyang Technological University.

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