When foods are eaten the body breaks them down into their components, and one component will be sugar. Different foods break down at different rates. Lentils, for instance, generate a long, gentle release of sugars, while foods like white bread send a sudden rush of sugar into the blood stream. Foods that release sugars rapidly are said to have a high glycaemic index, those that release it slowly have a low glycaemic index.

A team of Cochrane Researchers set out to search for carefully conducted research trials that looked at the effects of eating high and low glycaemic index foods. They found six randomised controlled trials that involved a total of 202 participants. The trials ran for between five weeks and six months.

Their conclusion was that people eating low glycaemic index diets lost a mean of one kilogram more than those on similar energy high glycaemic index diets.

"Low glycaemic index diets appear to be particularly effective for people who are obese," says lead author Dr Diana Thomas, the Scientific Director of the Centre for Evidence Based Paediatrics Gastroenterology and Nutrition, in Westmead, Australia.

"It may be easier to adhere to a low glycaemic index diet than a conventional weight loss diet, since there is less need to restrict the intake of food so long as the carbohydrates consumed have a low glycaemic index," says Thomas.

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Roberts and colleagues conclude that cravings for energy-dense foods are common. Although they caution that additional long-term studies are needed to confirm their findings, they write that their results suggest that people attempting to lose weight and maintain weight loss may benefit from advice to accept that food cravings may not decrease in frequency. Controlling the frequency of giving in to cravings, rather than suppressing them, they say, may be an important area of emphasis in future weight control programs.

This work was supported by the Agricultural Research Service of the U.S. Department of Agriculture, and by grants from the National Institutes of Health and the Boston Obesity Nutrition Research Center. For more information about ongoing recruitment for the second phase of the CALERIE study at Tufts, visit hnrc.tufts/studies/2520.shtml.

Gilhooly CH, Das SK, Golden JK, McCrory MA, Dallal GE, Saltzman E, Kramer FM, Roberts SB. International Journal of Obesity ; Advance Electronic version 26 June 2007; doi: 10.1038/sj.ijo.0803672. Food cravings and energy regulation: the characteristics of craved foods and their relationship with eating behaviors and weight change during 6 months of dietary energy restriction.

The Gerald J. and Dorothy R. Friedman School of Nutrition Science and Policy at Tufts University is the only independent school of nutrition in the United States. The school's eight centers, which focus on questions relating to famine, hunger, poverty, and communications, are renowned for the application of scientific research to national and international policy. For two decades, the Jean Mayer USDA Human Nutrition Research Center on Aging at Tufts University has studied the relationship between good nutrition and good health in aging populations. Tufts research scientists work with federal agencies to establish the USDA Dietary Guidelines, the Dietary Reference Intakes, and other significant public policies.

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