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Research shows metabolic benefits of low-carb diet

27-Jun-2005

The high-protein, low-carb approach to weight loss has been underpinned by new research from Australia showing that it can provide overweight women with greater nutritional and metabolic benefits than a high-carbohydrate diet, reports Jess Halliday.

Despite the erstwhile popularity of low-carb diets like Atkins , interest has tailed off in the past 18 months, with dire consequences for food companies that had sought to satisfy the appetite of devotees for convenient low-carb products.

Rather, dieters are veering towards low-glycemic diets, which do not advocate cutting out all carbohydrates but instead focus on those that release energy into the blood stream slowly, such as oats, whole grains, most fruits, vegetables, nuts and legumes.

 

Carbohydrates that are rapidly digested and that raise blood sugar and insulin to high levels, such as white bread, refined breakfast cereals and concentrated sugars, are discouraged.

 

For the study published in the American Journal of Clinical Nutrition (2005 81: 1253-1254), researchers at the Commonwealth Scientific and Industrial Research Organisation in Adelaide randomly assigned 100 overweight or obese women aged 40 to 58 years, with a body mass index of between 28 and 38, to one of two isocaloric 5600kJ diets for a 12-week period.

 

The diets were in parallel design, but one was high-protein and the other high-carbohydrate.

 

The participants in both groups achieved the same weight loss success, of between 7.0 and 7.6 kg, and both also experienced a decrease in LDL-cholesterol, HDL-cholesterol, glucose, insulin, free fatty acid, and C-reactive protein concentrations with weight loss.

 

Folate and vitamin B-6 levels increased with both diets.

 

But the benefits of the high-protein diet were evident in participants with high serum triacylglycerol (a risk factor for atherosclerosis and coronary heart disease), who lost more fat mass on the high-protein diet than on the high-carbohydrate diet (5.7 to 7.1kg and 2.7 to 4.1kg respectively).

 

Triacylglycerol concentrations decreased more in both high- and normal- serum triacylglycerol patients with the high-protein diet than with the high-carbohydrate diet.

 

Serum vitamin B-12 levels also increased 9 percent with the high-protein diet and decreased 13 percent with the high-carbohydrate diet.

 

"An energy-restricted, high-protein, low-fat diet provides nutritional and metabolic benefits that are equal to and sometimes greater than those observed with a high-carbohydrate diet," concluded the researchers.

 

In March of this year the leading low-carb diet company Atkins Nutritionals announced that it was shutting down operations in the UK, which had been its biggest European market, amid claims that although more than 3 million Britons tried the diet in 2004, most had difficulty in sticking to it.

 

Atkins has also recently incorporated a glycemic measurement into its program and reformulated some of its products in a move that makes it closer aligned with its main competitor the South Beach Diet, an early low-glycemic proponent.

 

Other companies whose financials have been hit by the low-carb fall-out include NBTY's US wholesale division, whose sales fell four percent in 2Q 2005 (also said to be a consequence of negative reports about vitamin E), and natural foods distributor Tree of Life, the North American subsidiary of Wessanen, which announced restructuring measures in February to raise $15 million to offset falling sales of low-carb products.

 

But whether the new study will be enough to woo consumers back to the straight low-carb approach is doubtful. Its scope as not significantly wide to assess the relative benefits of low-glycemic carbohydrates, whereas low-g has been validated by research into its effect on insulin sensitivity as a means to reduce the risk or control the management of diseases such as diabetes and heart disease.

 

Food marketers and retailers have been quick to board the low-g bandwagon. UK supermarket Tesco has published a booklet explaining the diet to consumers and has started labeling some of its foods 'low-GI' or 'medium-GI'.

 

But some voices in the scientific community have risen against the trend, saying that not enough research has been carried out amongst mainstream dieters.

 

"I remain skeptical for the broader use of the GI as a weight-loss diet label. A low GI diet is extremely hard to adhere to, and there have not been sufficiently large or controlled studies in free living individuals in order to promote its use, Professor Tom Sanders of King's College London told NutraIngredients-USA.com's sister site, BakeryAndSnacks.com.

 

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