Cautious praise for low-GI diet21st March 2007
For most of the past half century, the US Government and many official health agencies have advocated a low-fat diet for the prevention and treatment of obesity, diabetes, and heart disease, writes David S. Ludwig, who proceeds to test out the merits of the low-glycaemic index (low-GI) diet in this commentary in The Lancet.
"The effects of total fat on bodyweight and health have been called into question in recent years. And the prevalence of obesity has increased strikingly in the USA and Europe, as the proportion of fat in the diet has decreased," writes Ludwig, citing significant short-term weight loss on diets which cut carbohydrates.
He says the glycaemic index (GI) constitutes an empirical system for classifying carbohydrate-containing foods.
"Most varieties of bread, rice, breakfast cereals, and potato products have a high GI because processing methods allow the starch to become fully hydrated and therefore rapidly hydrolysed into glucose in the human digestive tract. By contrast, non-starchy vegetables, legumes, nuts, and fruits have a low GI. Whole kernel and traditionally processed grain products, such as stoneground breads, steelcut oats, and pasta, tend to have a moderate GI."
He notes that the needs of the human brain for glucose holds the key to understanding the GI approach, because complex hormonal systems exist for the regulation of glucose in the blood through the ups and downs of feeding and exercise.
"With domestication of cereal grains, the GI of human diets increased substantially. In the past few decades, prevailing diets in the USA and Europe have become even higher in GI and GL because of increases in carbohydrate consumption and the processing of that carbohydrate," writes Ludwig.
The high-GI diet challenges the balance of glucose in the blood, while many studies have shown beneficial effects of a low-GI diet, he says, while questions remain about consistency of data and the applicability of the benefits of low-GI eating to everyday life.
"Diets that restrict one major nutrient, either fat or carbohydrate, have produced poor long-term results," he concludes.
"The low-GI diet, with its focus on carbohydrate quality rather than quantity, aims to address an underlying physiological cause of diseases arising from excessive swings in postprandial glycaemia. Because this diet does not restrict either fat or carbohydrate, it may also be more behaviourally sustainable."
"Additional well-controlled and adequately powered studies are needed to examine the long-term effects of a low-GI diet on human health. Pending results of those studies, the clinician should consider a low-GI diet to be a prudent approach to the prevention and treatment of diabetes, heart disease, and obesity," Ludwig concludes.
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