Professor Jennie Brand-Miller answers your questions
‘What is the latest research on low GI carbs for exercise? Is the intensity of exercise important?’
Whether you are a professional athlete, exercising for health and fitness or aiming to lose weight, the type, timing and amount of food you eat before and after exercise will help you achieve your goals, whatever they are. When you are exercising, your muscles rely on carbohydrate and fat as their main sources of fuel.
The relative contribution of carbohydrate and fat as fuel while you are exercising depends on both the intensity and length of your exercise session. Generally, your body’s use of carbohydrate as fuel increases as your exercise intensity increases, and decreases the longer your exercise session lasts. Aerobic training and fitness increase your body’s ability to use fat as a fuel source. This is a plus, as it conserves your limited carbohydrate stores, allowing you to exercise for longer or at a higher intensity.
- Carbohydrate is stored in your muscles as glycogen, but the stores are limited and about 90 minutes of high intensity exercise will deplete them.
- Fat, which provides the largest nutrient store in the body, can fuel 100–200 hours of exertion, but at a lower intensity.
Our colleague, Dr Emma Stevenson from Nottingham University, does a lot of work in this area. She says: ‘Our research has continually showed that consuming low GI carbs in the hours before exercise can increase the rate at which you burn fat during exercise and also will help to maintain a more sustained blood glucose level. Eating a meal or snack containing low GI carbs 2–4 hours before exercise is what’s usually recommended. The type of carbohydrates that you consume during recovery from exercise depends on the length of time before your next training session. If your recovery time is more than 4 hours then it doesn’t matter what type of carbohydrate you eat or drink as long as you consume enough of it! If recovery time is short, then high GI carbs are useful to replace muscle glycogen concentrations quickly and efficiently. However, research has shown that consuming low GI carbs over a 24-hour recovery period can improve endurance capacity the next day.’
In GI News over the years we have reported several studies that found that milk can be just as effective as sports drinks to aid recovery in athletes. Skim or reduced fat milk (plain or chocolate) also has a low GI and so can be a healthier alternative to sports drinks (yes, even with the added sugar in the chocolate drink).
GI testing by an accredited laboratory North America
Dr Alexandra Jenkins
Glycemic Index Laboratories
20 Victoria Street, Suite 300
Toronto, Ontario M5C 298 Canada
Phone +1 416 861 0506
Research Manager, Sydney University Glycemic Index Research Service (SUGiRS)
Human Nutrition Unit, School of Molecular and Microbial Biosciences
NSW 2006 Australia
Phone + 61 2 9351 6018
Fax: + 61 2 9351 6022
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