Glycemic Index and Glycemic Load at Breakfast: Burn More Fat With the Right Starches

Nutrition Performance

There is much interest in the potential of low-glycemic index (GI) foods in the management of obesity and as a tool for weight loss. Some scientists have advocated that low-GI (LGI) foods may enhance weight loss by promoting satiety and promoting fat oxidation. Dietary-induced thermogenesis (DIT) is the amount of energy required for absorption, the initial steps of metabolism, and storage of nutrients. The amount of calories burned by DIT represents about 10 percent of the total amount of energy consumed over 24 hours, but in the long term, even a small increase in calories burned can play a role in weight loss.

In a previous investigation on the role of glycemic index and fat oxidation, researchers investigated the effect of mixed high-carbohydrate (CHO) meals with different GI on fat utilization during subsequent exercise in men and females. The results suggest that meals composed of low-glycemic index carbohydrates could be more beneficial for maintaining a favorable metabolic milieu during the postprandial period by reducing plasma glucose and serum insulin concentrations, and by increasing the total amount of fat oxidized.

Eating a low-GI meal for breakfast (i.e., oatmeal) may favor fat mobilization, while eating a high-GI meal for breakfast (i.e., cereal) may reduce fat metabolism. Earlier research found that eating a low-GI meal before exercise can favor fat metabolism. Studies reported that there was a significant shift in substrate utilization from carbohydrates to fat when a low-glycemic index meal is ingested before exercise, compared to a high-glycemic index meal.

In addition to the GI of food, there is the glycemic load (GL). The GL is a ranking system for carbohydrate content in food portions based on their glycemic index (GI) and the portion size. The usefulness of glycemic load is based on the idea that a high-glycemic index food consumed in small quantities would have the same effect on blood sugar as larger quantities of a low-glycemic index food. For example, white rice has a somewhat high GI— eating 50 grams of white rice in one sitting would produce a particular glucose curve in the blood, while 25 grams of white rice would give the same curve but at half the height of the curve.

Glycemic load— which is obtained by multiplying the amount of carbohydrates by the GI— can be reduced by acting on one of these two factors. A recent study reported that a low-fat, high-carbohydrate diet induced lower postprandial dietary fatty-acid oxidation than a low-carbohydrate, high-fat diet. These authors found that high-carbohydrate diet shifted away from fat oxidation. Therefore, a high-GL meal potentially leads to greater storage of fat, reducing fat and increasing carbohydrate oxidation.

Glycemic load also has a scale. Low is 10 or less, medium is 11-19 and 20 or greater is considered high. Both GI and GL are useful for monitoring the rise in insulin and the amount of fat oxidized, but there has never been a study that examined the impact of different GI and GL on fat metabolism and insulin.

Researchers from Italy examined three breakfasts with different GI and GL and their effect on post-meal fat metabolism. Subjects consumed the following meals:

1. High-GI/High GL (high glycemic index/high glycemic load); rich in carbohydrates (81.8g/100g) and with a GI of 67. For example, white bread and jam.

2. HGI/LGL (high glycemic index/low glycemic load); carbohydrate quality was equivalent (GI of 68), but carbohydrate quantity was lower (47.4g/100g) and lipid content higher (21g/100g vs. 4.5g/100g). For example, white bread and jam and butter.

3. LGI/LGL (low glycemic index/low glycemic load); low GI (44) and thus the same glycemic load as the breakfast with higher lipid content (GL of 36 and GL of 32, respectively). Snack consisted of a biscuit bar containing 25 percent of extruded cereal and legume flour, and 30 percent extruded oat flour.

The three breakfasts were designed to assess the effect on postprandial energy metabolism of two different glycemic loads obtained with two different dietetic approaches. The first approach was to reduce the GL by acting on carbohydrate quality, i.e., reducing GI of breakfast. The second was to reduce GL by limiting carbohydrate content, keeping the breakfast energy constant by increasing fat. The three breakfasts were of equal calories with comparable protein content, but different in GI and/or GL.

The LGI-LGL breakfast consistently increased post-meal energy expenditure during the entire test period after the meal was consumed. This could be due to slower carbohydrate absorption, as a consequence of a slower gastric emptying rate of the LGI-LGL meal— with prolonged energy consumption as a consequence, for absorption and storage of carbohydrate as glycogen and fat.

However, the LGI-LGL meal shifted the respiratory quotient (fat oxidation) toward its base values after three hours, meaning there was a significant enhancement of fat utilization. This enhanced fat oxidation could be attributed to the low availability (low GI) of carbohydrates in the LGI-LGL meal, which are oxidized with a higher energy expenditure (higher DIT after one hour). After the first hour, RQ (fat oxidation) rapidly increased, indicating a decrease in carbohydrate and an increase in fat utilization of the oxidation mixture, and remained low during the rest of the test. This means that when dieting for a show, choosing a LGI-LGL meal can enhance fat oxidation for several hours after being consumed.

Glycemic load also has a scale. Low is 10 or less, medium is 11-19 and 20 or greater is considered high.

source:musculardevelopment.com