Fat burns faster after low glycemic breakfast

low glycemic eating

A low glycemic-index breakfast enhanced the fat-burning effects of moderate exercise in sedentary women, according to a small British study.

Fat oxidation increased significantly during a 60-minute walk when the women consumed low glycemic-index carbohydrates for breakfast, Emma Stevenson, Ph.D., of the University of Nottingham, and colleagues reported online in the Journal of Nutrition.

Carbohydrates with a low glycemic index have less impact on blood glucose levels and insulin response than carbohydrates with a higher glycemic index. LGI foods include cereals made from oats, barley, and bran, along with whole grain breads and most vegetables other than potatoes.

In the Nottingham study, fat oxidation remained significantly higher for three hours after a breakfast with a low glycemic-index versus high glycemic-index breakfast. Oxidation was also increased in the LGI breakfast group after exercise.

Varying the nutritional content of lunch had no effect on fat metabolism, but participants said they felt fuller after a low carbohydrate-index lunch.

“The glycemic index of the diet could be an important factor influencing daily substrate oxidation and this could have important implications for substrate storage and weight management,” the authors concluded.

“Further studies are required to investigate the potential long-term benefits of the combination of exercise and carbohydrates that elicit a reduced glycemic response.”

Researchers had already demonstrated that glycemic response to carbohydrates influences substrate metabolism during exercise in trained individuals. A lower glycemic response leads to increased fat oxidation and reduced carbohydrate oxidation during exercise.

The authors previously reported that active women who consumed a low glycemic-index breakfast three hours before a 60-minute run increased fat oxidation by about 55% compared with a high glycemic-index breakfast.

Whether the findings applied to sedentary women and low-intensity exercise had not been determined. To examine the issues, the authors studied eight healthy, sedentary young women (mean age 24) whose body mass index averaged 21.3 kg/m2.

Participant completed two assessments, each of which began with breakfast after an overnight fast. During one assessment, the women consumed a low or high glycemic-index breakfast, and during the second assessment they consumed the opposite breakfast.

Low and high glycemic-index foods were chosen on the basis of the International Table of GI and Glycemic Load Values. The low glycemic-index breakfast had an index rating of 44 compared with 78 for the high glycemic-index breakfast.

Otherwise, the meals were matched with respect to carbohydrate, protein, and fat content and were designed to provide 30% of the daily energy requirement for participants.

Best breakfasts for each group totaled 265 calories. The LGI breakfast consisted of museli, skim milk, apple juice, an apple, canned peaches and yogurt. The HGI breakfast included corn flakes, white bread, jam, skim milk, margarine and a carbonated glucose drink (Lucozade).

Overall fiber content of the LGI breakfast was considerably higher, 3.5 grams versus 1.5 grams for the HGI meal.

After breakfast participants remained at rest for three hours, and the authors periodically obtained blood and expired-air samples.

Following the three-hour postprandial period, the women performed a monitored 60-minute walk on a treadmill, calibrated to achieve 50% of an individual’s peak VO2.

Study participants consumed a standardized lunch consisting of pasta, tomato-based pasta sauce, and grated cheese.

After breakfast, plasma glucose concentrations increased rapidly with both types of meal and peaked at 30 minutes. The high glycemic-index breakfast was associated with a higher peak glucose value (P<0.005) that remained significantly higher throughout the three-hour postprandial period (P=0.05).

Serum insulin peaked at 45 minutes after breakfast but was higher after consumption of the high glycemic-index diet (P<0.05) and remained higher until the end of the postprandial period (P<0.05).

Fat oxidation was low during the postprandial period but statistically greater after the low glycemic-index breakfast (P<0.05).

Levels of the satiety hormones ghrelin, PYY, and GLP-1 did not change significantly after either breakfast.

During exercise, total fat oxidation was twice as great after the low glycemic-index breakfast than after the high glycemic-index breakfast (7.4 versus 3.7 g/h, P<0.001). Total carbohydrate oxidation was significantly greater after the high glycemic-index breakfast (51.6 versus 42.5 g/h, P<0.005).

Levels of the satiety hormones ghrelin, PYY, and GLP-1 did not change significantly in the postprandial period following either breakfast.

Following lunch, neither fat oxidation nor carbohydrate oxidation differed during either assessment. However, participants reported feeling fuller after lunch when they consumed the low glycemic-index breakfast (P<0.05). Measures of hunger and desire to eat did not differ between the two assessment periods.

Source: Medpage today


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