A diet that scores low on the “glycaemic index” helps overweight people lose body fat while also reducing levels of “bad” cholesterol that contributes to the risk of heart attack and stroke, a study shows.
The glycaemic index (GI) measures the impact of carbohydrates on blood sugar levels. Food with a high GI score, like a biscuit, causes sharper peaks in sugar levels than a low GI food, such as pasta. Earlier research has shown that low GI foods make people feel fuller for longer, and may promote the breakdown of fat. These foods also tend to contain more soluble fibre, which reduces total and low density lipoprotein (LDL), or “bad” cholesterol.In a study of 189 overweight and obese adults, Joanna McMillan-Price at the University of Sydney, Australia, and colleagues found that a diet high in either protein or carbohydrates, but with a low total GI score, brought about the biggest reduction of body fat. They also found that a high-carbohydrate and low GI diet caused the greatest drop in total and LDL cholesterol levels.Risk factors: “This study provides evidence-and there hasn’t been much before-that a low GI carbohydrate diet is as good as a high protein diet in terms of weight loss,” says Peter Clifton, director of the CSIRO Nutrition Clinic in Adelaide, Australia. The Atkins diet, for instance, advocates high protein and very low levels of carbohydrate.The research also helps to clear up confusion over whether changing the total GI rating of a diet can affect risk factors for cardiovascular disease, says Simin Liu, of the University of California in Los Angeles, US, in a related editorial.McMillan-Price and colleagues studied men and women aged 18 to 40. Subjects were randomly assigned to one of four reduced-calorie and reduced-fat diets for 12 weeks. The first diet was high in carbohydrate (55% of total energy) but scored low on the GI index. The second was high-carbohydrate and had a high GI rating. The third was high in protein (25% of total energy) with a high GI score, while the fourth was high-protein and low-GI. Red meat: After three months, all the volunteers lost a statistically similar amount of weight: between 4.2% and 6.2% of body weight. But those on the low GI diets lost the most body fat. For example, those on the high-carb, low-GI diet lost about 80% more body fat than those on the high-carb, high-GI diet.When it came to cholesterol levels, however, the effect of each diet varied. Those eating the high-protein, high-GI diet saw their LDL cholesterol level increase while those on the high-protein, low GI regimen, saw cholesterol levels go down slightly. “So it seems that you can eat a lot of red meat-but it’s important that you combine it with low GI foods in order to have the best heart health,” says McMillan-Price.People on the high-carbohydrate, low-GI diet, saw total and LDL cholesterol levels decreased significantly, compared with levels at the start of the study. “I think that’s because low GI foods have such intrinsically high levels of soluble fibre-and that has the effect of lowering cholesterol,” McMillan-Price says.(Source: Archives of Internal Medicine: University of Sydney: July 2006).