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Feb 22

Researchers give less weight to established slimming tricks

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The Irish Times - Tuesday, February 21, 2012

DICK AHLSTROM, Science Editor in Vancouver

THE OLD models of how much weight you can lose by reducing calories are seriously off the mark. It is a lot more difficult to lose weight than these models suggest, according to the authors of a mathematical approach to weight loss and obesity.

Dr Kevin Hall and Dr Carson Chow from the US National Institute of Diabetes and Digestive and Kidney Diseases improved on the old linear model that suggested a 250 kilocalorie (usually just referred to as calorie) cut in food intake would deliver a 25lb loss over a year.

This ignored the reality of human metabolism, however, they told a session at the American Association for the Advancement of Science’s annual meeting in Vancouver.

Weight loss when dieting comes quickly when you start but soon diminishes over time until finally hitting a plateau, as habitual dieters can attest. For this reason assumptions about energy intake and expenditure based on each pound of fat representing 3,500 calories was not useful for calculating energy balance, they said.

Dr Hall pointed to a US study that indicated 67 per cent of people there were overweight or obese. It suggested that if the government introduced a heavy tax on sugar-sweetened beverages this would quickly drop to 50 per cent on the basis of the older models. The researchers ran a “dynamic simulation model” on the data and found that in fact the tax would only reduce obesity to 62 per cent because of the plateau effect.

The two decided to build a new, more accurate model of energy balance and weight loss. It took into account metabolic factors including the weight to lean ratio, sex, physical activity and other factors. They also built a simpler online version so people could log on and set up a weight loss programme. ( bwsimulator.niddk.nih.gov)

This was very different from the older calculators that suggested reducing calorie intake by 500 a day would deliver a 1lb loss per week. Their calculator allows you to set goals – how much weight you want to lose over what period of time – and then does the calculations for changes to calorie intake and exercise.

A person should reduce food intake by 10 calories a day for each pound of weight change required. At that rate about half the weight change would be reached in about a year and about 95 per cent of the loss reached in about three years, the researchers calculate.

They also used their model to look at the US adult obesity epidemic. They showed that reaching the average population-based weight gain only required seven extra calories a day.

The calculations were much more sophisticated, however, and also took into account the energy demands required by an individual to carry around the extra average weight. The average person needed to burn up an extra 215 calories a day to haul around the weight. Changing the energy balance will deliver weight loss, Dr Chow said. Eating one fewer biscuit a day could deliver a 15lb weight loss over a year.

“The surprise is such a little change can deliver such a large result,” he said.

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Researchers give less weight to established slimming tricks

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