Dividing carbohydrates into 'good' and 'bad' carbs is misleading, and cannot be used as a measurement to prevent overweight and obesity, according to a review of scientific literature on the contentious topic.
Conducted by University of Virginia professor Glenn Gaesser and published in this month's issue of the Journal of the American Dietetic Association, the review analyzes peer-reviewed research on carbohydrate consumption, glycemic index and body weight.
It claims to be the first detailed review of literature on the link between carbohydrate consumption and body weight, with its findings running counter to the current consensus on the effects of 'good' and 'bad' carbohydrates.
According to Gaesser, diets high in carbohydrates are almost universally associated with slimmer bodies.
Additionally, his review found that consuming high levels of high-glycemic foods is not associated with higher body weights. On the contrary, he said, several large studies in the United States revealed that high-glycemic diets were linked to better weight control.
"There is no reason to be eating fewer carbs - they're not the enemy," he said.
The description of carbohydrates as 'good' or 'bad' is based on glycemic index (GI), a measure of the quality of the carbohydrate in terms of how much it raises blood sugar.
The glycemic index measures how quickly certain foods release carbohydrates into the body, which then raise consumers' blood glucose levels. High GI foods, including white bread, white rice, many prepared breakfast cereals and concentrated sugar, are considered by many as 'bad' carbs, as they cause blood sugar levels to rise more rapidly. Low GI foods include most vegetables, fruits, beans and unprocessed grains, and are considered 'good' carbs.
As science emerges showing that low-GI foods can help control weight and more certainly, help reduce the risk of diabetes and related conditions, a wider cross-section of consumers is selecting foods based on the GI index.
However, a major obstacle when it comes to using GI as a measure of a product's health benefits is that this is not consistent. Scientific literature remains mixed and insufficient, and results in fuelling confusion rather than providing reliable guidance.
Indeed, according to a group of industry and science experts, the glycemic index equation is not quite as simple as "low GI= good and high GI= bad." For example, chocolate cake has what is considered a low GI, while some whole grain cereals can have a medium to high GI.
In the US, the Glycemic (Net) Carbohydrate Definition Committee of the American Association of Cereal Chemists (AACC) International, last year approved a new set of definitions related to glycemic carbohydrates in an effort to find a compromise on a complex and inconsistent issue.
The Committee settled on four definitions designed to "provide a measurable definition that will enable manufacturers to communicate the glycemic response in grams per serving of food." These were: 'available carbohydrate', 'glycemic response', glycemic carbohydrate', and 'glycemic impact'.
According to Gaesser's recent review, GI itself is not a reliable description of carbohydrate quality, despite its use by a number of popular low-carb diets.
"Digestion is a complicated process. It's very difficult to determine the GI of a whole meal, for instance, so it doesn't really make sense to use GI or 'glycemic load' - the glycemic index multiplied by the quantity ingested - as a guide to eating."
Following his review of "hundreds" of articles on large-scale studies using surveys or randomized, controlled trials, Gaesser said they show that "people who consume high-carb diets tend to be slimmer, and often healthier, than people who consume low-carb diets."
"Even high-glycemic foods have a place in the diet, attributing that to the overall higher quality of a high-carb diet, which includes more fiber-rich and other nutritional foods."
The general consensus of the scientific community is that more science is necessary to determine the health outcomes of the glycemic index, and until that is available it urges caution in the use of GI labels and claims.
In an attempt to better understand the glycaemic index, researchers from the Jean Mayer USDA Human Nutrition Research Center on Aging at Tufts University (USDA HNRCA) recently used a simple test food, white bread, to show that a relatively high level of inter-individual (among different individuals), and intra-individual (within the same individual) variability occurs on consumption of white bread.
They found that individual variations in the glycaemic index (GI) of white bread, stated as 70 in the literature, may range from 44 to 132, which again highlights the complexity of the GI system of measurement.