How much energy you consume -- and whether you use that energy or let it remain unused to the point of possibly unhealthy storage levels -- is largely a matter of individual choice and lifestyle. Your body uses some energy just to maintain itself, such as for normal operation of organs and the brain.
Low-intensity exercise includes slow, casual walking and light stretching. At low intensity, there are no noticeable changes in your breathing pattern and you can easily carry on a conversation. Nutrients provide the energy sources for all forms of exercise. Fat is your body's preferred source of energy for low-intensity exercise. While at rest and during low-intensity exercise, free fatty acids are the predominant energy sources. The process by which fatty acids and other sources are converted to energy during low-intensity exercise is described as aerobic.
Moderate-intensity exercise includes walking at a brisk pace, hiking or roller skating. It is an activity involving 3 to 6 METs or metabolic equivalents and 3.5 to 7 calories per minute of energy expenditure. One MET is the amount of metabolic demand -- or energy -- required to sit in a chair at rest. At moderate intensity, your breathing quickens and you develop a light sweat after 10 minutes.
As you transition from low- to moderate-intensity exercise, you begin to use a higher percentage of carbohydrate-based energy sources. Low-intensity exercise is around 40 to 50 percent of your maximum heart rate. Moderate-intensity exercise is around 50 to 70 percent of your maximum heart rate. Leonard Kravitz, an associate professor in the Department of Health, Exercise, and Sports Sciences at the University of New Mexico, found that a 191-pound student burned 60 percent fat calories and 40 percent carbohydrate calories while exercising at 55 percent of his maximum heart. At low to moderate intensity, the nutrient-to-energy conversion processes are mixed, involving mainly aerobic metabolism and fatty acid sources.
If you want to burn more fat calories, you need to burn more total calories. At higher intensities, the ratio of fat to carbohydrate calories burned decreases, but the total number of fat calories burned increases. High-intensity exercise also provides the basis for greater gains in overall conditioning. Fatty acids can be derived from the breakdown of stored fat or from dietary fat. Make healthy choices for dietary fat and for carbohydrates.
Carbohydrate is the primary fuel for most types of exercise and the most important nutrient for athletic performance. Our body runs most efficiency with a balance of protein, fat and carbohydrates, but adequate carbohydrate is a key source of energy for athletes. Carbs provide…
- Energy that fuels muscle contractions and brain function
- Stored energy for later use. (Any glucose not needed right away gets stored in the muscles and the liver in the form of glycogen.)
- An alternative energy source to protein being used for energy
During physical exercise stored carbohydrate or glycogen is converted into energy to fuel the muscles, but this supply is not endless. The amount of carbohydrate that can be stored in the body as glycogen depends on diet and the athlete’s conditioning level. Typically total glycogen stores equal 400-700 grams (75-100g in the liver and 300-600g in the muscles). An athlete consuming a high carbohydrate diet and following a solid nutrition protocol can increase these total carbohydrate reserves up to 880g. After about 60 to 90 minutes of exercise these fuels will become depleted; therefore the need to refuel for longer training.
Health Canada's "Guide for Nutrition" Recommendations advises that 55 per cent of the total energy in our diet should come from carbohydrates. For elite athletes, it is recommended that 60% to 70% of total energy be comprised of carbohydrates. Without adequate dietary carbohydrate the body is forced to rely more on fat stores and protein from our muscles, which are less efficient energy-producing pathways. As a result, the quality of training and performance may diminish. For athletes with a busy and rigorous training schedule, both carbohydrate snacks and adequate fluid intake are essential to maintain muscle glycogen and to sustain optimal energy levels.
How much carbohydrate and fluid should we consume before, during and after exercise?Figure skaters, for example, must have enough energy to endure long aerobic activities and have split-second power surges to jump. On top of eating adequate carbohydrates daily, taking in carbohydrate before during and after exercise is essential to provide enough fuel and promote recovery. The following table outlines the key guidelines for carbohydrate, protein and fluid intake pre-, during and post-training. It is important to note that the exact timing and type of food to consume can be very individualized. It is recommended that athletes trial various types of food to find out which works best for them.
Why eat carbohydrate?
Before: To top up energy stores and delay fatigue. What you eat depends on how much time you have, but aim for a light carbohydrate meal.
During: To help to maintain blood sugar to fuel muscles during exercise. If your training session lasts longer than 90 minutes you will need additional carbohydrates to maintain energy levels. Choose easy to digest carbohydrates and aim for 30-50 g of liquid or solid sources every 30 minutes.
After: For replenishment of your energy supply after exercise, which helps guarantee the ability to last longer in the next training session or event. For optimal recovery and replenishment of glycogen stores, eat carbohydrates and protein within 60 minutes of completing your session.
| When | How much? | For Example |
| Pre-training fuel1-2 hours before* easy to digest * low fat | Carbohydrate 2 g/kgProtein 10-15 g Fluids 500 ml | 1 cup chocolate soy milk + 1 cup water + banana Or, 1 Granola bar + 1 low fat yogurt + 1 cup water |
| During training fuels | 600-1200 ml fluid/ hour(3-4 large gulps every 15-20 minutes) Carbohydrate 30-60 g/hr over 60-90 minutes | Water or sports drink 1 -2 water bottles (~500 ml each) |
| Post-training fuel * within 1 hour of session | carbohydrate 1 g/kgprotein 15-20 g fluids 600-1200 ml | 1 tetra pack soy milk + banana + 2 cups water Or, 1 cliff bar + apple + 2 cups water Or, 1 Kashi granola bar + 1 cup chocolate milk + 1 cup water |
More than one training session or game….For sports where there is more than one daily training session or back-to-back events scheduled follow these additional guidelines to ensure optimal refuelling and recovery between:
| When | What? | For Example |
| 30 minutes between games | Carbohydrate | Juice or sports drink |
| 1-2 hours between games | Carbohydrate | BananaJuiceSports drink Energy bar |
| > 2 hrs (recovery nutrition) | Carbohydrate & Protein | 1 cup chocolate milk + Nature Valley granola bar + 1 cup water Or Cliff Bar + ¾ cup yogurt + 1-2 cups water Or Peanut Butter & Jam sandwich + 1 cup soy milk Or 1 Kashi Granola Bar + 1 banana + 1-2 cups water Or 1 Apple + energy bar + 1-2 cups water Or ¾ cup yogurt + 0.25 cup dried fruit + 1-2 cups water |
What are sources of carbohydrate and fluids for exercise?
Complex carbohydrates such as whole grain pasta and cereals, legumes, fresh fruit and starchy vegetables are excellent sources because they release energy slowly, are low in fat, and are packed with nutrients and fibre. Although sports bars, gels and drinks are quick, convenient sources of energy, obtaining your energy from natural sources of food is highly recommended and more economical. For example, a medium banana and one cup of fruit yogurt supply approximately 215 calories and 40 grams of carbohydrate. A Power Bar supplies 220 kcal and 48 grams of carbohydrate. If you choose sports foods, choose those without hydrogenated or saturated fats and without additives or preservatives. There is an advantage to making your own snacks they are nutritious, unprocessed sources of carbohydrate, protein, fat, fibre, minerals, and vitamins that energize your body.
Homemade Energy Bars 1 cup old fashioned oats ½ cup unsalted raw peanuts ½ cup pumpkin seeds ½ cup sunflower seeds ¼ cup semi-sweet coconut ½ cup raisins 1/2 cup ¼ cup dried cranberries ¼ cup Family flaxseeds 1 cup bran flakes 1 ½ cup crispy rice cereal ¾ cup smooth peanut butter ¾ cup honey 2 tsp vanilla Mix dry ingredients, mix wet ingredients. Mix together. Spread in pan. Bake at 350°F (180°C). Cool & cut into 20 bars. |
Take Action
- Plan ahead! Prepare your daily snack-pack the night before. Pack it full of nutritious carbohydrate-rich snacks such as a whole grain bagel with peanut butter, yogurt, fig bars, bananas, orange slices, graham crackers and granola bars.
- Develop a complete nutrition training plan. Don't just eat and keep well hydrated during competition. Practice fuelling during training so you are accustomed to it for your events. Experiment with different quantities and sources of carbohydrate (foods and fluids) during exercise to determine what keeps your body performing at optimal levels.
- Always carry a water bottle and take regular sips during activity. Ask your coach to remind you.
Note: With even a 2 percent dehydration work capacity drops by 10-20 percent.
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