The effects of low and high glycaemic carbohydrates on endurance performance

The concept of glycaemic index (GI) was originally introduced to classify carbohydrate-rich foods, usually having an energy content of >80 % from carbohydrates, according to the differences in effects on post-meal glycaemia. The GI, which is a nutritional property of a carbohydrate-rich food, is defined as the incremental area under the blood glucose response curve following a 50 g glycaemic carbohydrate portion of a test food expressed as a percent of the response to the same amount of carbohydrates from a standard reference product taken by the same subject (FAO/WHO, 1998).

Carbohydrate-rich foods can be classified according to their GI values (glucose as the standard): high GI >70 (white bread, most white rices, corn flakes, extruded breakfast cereals, glucose); normal GI 55-70 (whole wheat products, basmati rice, sweet potato, sucrose); low GI 40-55 (most fruits and vegetables, legumes/pulses, whole grains, nuts, fructose) and very low <40.

On the other hand, is not easy to outline glycaemic index of foods rich in carbohydrates because many other factors in the diet (e.g. amount and type of dietary fibre, amount of dietary fat, energy density, physical properties, mode of preparation) are involved.

EFSA (European Food Safety Authority) expressed its negative opinion on the substantiation of health claims related to carbohydrates that induce low/reduced glycaemic responses and carbohydrates with a low glycaemic index. The claims effect was related to carbohydrates with a low glycaemic index (GI) and Impact on blood glucose / Glycaemic control / Glycaemic response or to maintain healthy cholesterol levels. The main cause of rejection of these claims was that the food constituents, carbohydrates that induce a low/reduced glycaemic response and carbohydrates with a low glycaemic index (e.g. <55), which are the subject of the health claims are not sufficiently characterised. On the other hand, there are also positive opinions concerning natural and artificial sugar replacers such as xylitol, sorbitol, mannitol, maltitol, lactitol, isomalt and sucralose for which EFSA approved the claims related to consumption of these substances and reduction of post-prandial glycaemic responses, furthermore the same opinions have been given for slowly digestible starch in starch-containing foods, beta-glucans from oats and barley and others.

Concerning this topic a recent human trial study has highlighted effects relevant to sportsmen. The study involved 10 well trained cyclists to investigate the effects of high and low glycaemic index (GI) 24 h recovery meals on the physiological responses and subsequent athletic performance, following a glycogen depleting protocol.

On day 1, subjects performed a glycogen depleting protocol after which they then consumed either high or low GI recovery diets over the next 24 h, which provided 8 g.kg BWˉ¹ of carbohydrate. On day 2, the subjects returned to the laboratory, 2-3 h postprandial, to perform a 40 km time trial (TT) on the Velotron cyclePro© ergometer. The results showed no significant differences between the two groups of subjects with respect to both physiological parameters (carbohydrate, fat oxidation and blood glucose concentration) and related to endurance performance.

The study suggests that type of carbohydrate intake (low GI or high GI carbohydrate) does not affect performance. This calls into question some long-standing formulation principles, and requires further research. The available evidence strongly supports carbohydrate intake in the context of sports; the final word on the use of low GI carbohydrates over high GI carbohydrates had not been said, and high GI carbohydrates still have a place.

Jacopo Angelucci – Sport nutrition Team

Advertisements

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google+ photo

You are commenting using your Google+ account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

%d bloggers like this: