The glycemic index, or GI for short, is a way to rank foods high in carbohydrate, such as pasta, rice, or cereal, according to their effect on blood sugar levels.

Although the GI is popular with diabetics who want to control their blood sugar levels, it’s also used by people who want to lose weight.

But is following a low GI diet really going to help you lose fat faster? Or is it just another dietary myth?

We'll come to that in a moment.

First, if you're not familiar with the glycemic index, here's a brief history.

Carbohydrates used to be known as either simple or complex. Foods like chocolate, fruit or cakes were classed as simple carbohydrates. Scientists used to think these foods were quickly digested, leading to a rapid rise in blood sugar.

Complex carbohydrates, such as potatoes, rice and pasta were thought to break down more slowly, producing a gradual rise in blood sugar.

That all changed in the early 1980's when Dr. David Jenkins — a professor of nutrition at the University of Toronto — set out to establish the type of foods that were best for people suffering from diabetes.

Jenkins found that foods such as potatoes — traditionally defined as a complex carbohydrate — actually led to a rapid rise in blood sugar. Some foods high in simple carbohydrates appeared to digest more slowly, leading to a gradual elevation in blood sugar. This led researchers to classify foods according to their glycemic index.

The glycemic index refers to the change in blood sugar that occurs after you eat a food high in carbohydrate. Foods with a high glycemic index lead to a bigger change in blood sugar levels over a 2-3 hour period than foods with a low GI.

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Although many people claim that eating foods with a low GI will help you lose weight, the research tells a different story.

In fact, many people are surprised to learn that eating more carbohydrate-rich foods with a low GI and fewer carbohydrate-rich foods with a high GI — without making any other change to your diet — actually has very little effect on weight loss.

A good example comes from a group of researchers from the University of Minnesota, who wanted to find out if lowering the GI of a diet already low in calories would have any further effect on weight loss [1].

They compared the effects of three low-calorie diets, each with a different glycemic index, on 29 overweight adults. All of the diets — high GI, low GI or high fat — provided the same number of calories.

After 12 weeks, all three groups lost weight. Which is pretty much what you’d expect.

But here’s the kicker - there was NO significant difference in weight loss between the groups.

Subjects on the low GI diet lost, on average, 9.9 kilograms, while those on the high GI diet lost 9.3 kilograms.

Weight loss between weeks 12 and 36 also did not differ among groups. Those on the low GI diet lost an additional 1.8 kilograms, while those on the high GI diet lost 1.6 kilograms.

"Lowering the glycemic load and glycemic index of weight reduction diets does not provide any added benefit to energy restriction in promoting weight loss in obese subjects," conclude the researchers.

Any extra weight loss on a low GI diet is very small, and can be accounted for almost entirely by a drop in calorie intake. In other words, when you eat fewer refined carbohydrates like cookies, cakes, or sweets and replace them with fruits, vegetables and protein-rich foods, you end up eating fewer calories. As a result, you lose fat.

In summary, once the basics of your diet are in place (calories and protein are set at the right level and you're getting sufficient amounts of essential fatty acids), worrying about the GI of bread, pasta, rice or potatoes is largely a waste of time and effort, and isn't going to make much of a difference as far as fat loss is concerned.

P.S. On a completely different subject, check out this video if you're in need of a bit of inspiration. He's not called the Calisthenics King for nothing you know!

Reference
Raatz, S.K., Torkelson, C.J., Redmon, J.B., Reck, K.P., Kwong, C.A., Swanson,J.E., Liu, C., Thomas, W., & Bantle, J.P. (2005). Reduced glycemic index and glycemic load diets do not increase the effects of energy restriction on weight loss and insulin sensitivity in obese men and women. Journal of Nutrition, 135, 2387-2391