Is it true that you can burn more fat and calories by doing a certain type of exercise? The answer is “yes” and “no”! The reality is that it depends on a few key variables. When you exercise, you burn calories mainly coming from fat and carbohydrates. If you walk at a very slow pace you burn more “fat” calories per minute than carbohydrate calories, but fewer overall calories per minute than if you exercise at a harder level. As you begin to walk faster and move into a more “moderately” intense workout, your body will shift from burning a greater concentration of fat into burning a greater concentration of carbohydrates, and burn a greater number of overall calories per minute.
Carbohydrates, fat and protein are our three main energy sources from food that we use to exercise. These nutrients are found in different amounts in foods and are broken down by the body to provide energy. Fat is the richest food coming in at nine calories per gram. Alcohol is second in calorie count with seven calories per gram, followed by carbohydrates and proteins at four calories per gram. Now that you know how many calories are in each food and/or drink source, you can better appreciate how “quickly” one can gain weight by eating high fat food or drinking too much alcohol. One serving of food rich in fat such as ice cream is twice the calorie count as the same serving size of a protein rich food such as yogurt. However, one gram of fat releases twice as much energy as one gram of carbohydrate or protein — but this doesn’t mean it’s the best fuel for exercise! That depends on the type of exercise and how long you exercise.
The most ideal fuel for working your muscles is glucose, especially as your exercise intensity increases. Glucose is formed by the breakdown of carbohydrates (sugars and starches) in your diet and is stored as glycogen in the muscles and liver. Your body, however, can only store a limited amount of glycogen.
The amount of each fuel — carbohydrates, fat and protein — you use during exercise depends on various factors:
- Past eating habits
- Current fitness level
- Type of exercise
- Intensity of exercise
- Length of workout
- Frequency of workouts
Anaerobic exercise — defined as shorter duration, higher intensity exercise — uses mainly carbohydrates broken down into glucose, whereas aerobic exercise uses all three fuels, with protein used to a lesser extent than glucose and fat.
During low intensity exercise, which uses less than 300 calories per hour, you use a greater proportion of fat, a smaller proportion of glucose and fewer calories. As you increase your exercise intensity, your body will gradually use less fat, but more glucose and more calories. Therefore, most of the energy used during moderate and high intensity exercise will come from glucose.
If you continue to exercise aerobically for a longer period of time, your body will gradually use more fat and less glucose in an attempt to conserve your body’s limited glucose stores. The fitter you are, the more efficiently your muscles use fat and the longer you can work out.
Your body does burn a higher percentage of calories from fat in the “fat burning zone”, or at lower intensities. But at higher intensities, you burn a greater number of overall calories which is what you should be concerned about if you’re trying to lose weight. Remember, a calorie is a calorie, so your goal is not necessarily to worry about the “type” of calories you burn, but rather focusing on your goal of burning as many calories as possible, to achieve a calorie loss of 3,500 calories, which translates into one pound of fat loss!
The chart below explains total calories and fat calories expended by a 130 lb. woman during cardio exercise.
 |
Low Intensity 60-65% Maximum Heart Rate |
High Intensity 80-85% Maximum Heart Rate |
| Total calories expended per minute | 4.86 | 6.86 |
| Fat calories expended per minute | 2.43 | 2.7 |
| Total calories expended in 30 minutes | 146 | 206 |
| Total fat calories expended in 30 minutes | 73 | 82 |
| Percentage of fat calories burned | 50% | 39.85% |
From The 24/5 Complete Personal Training Manual, 24 Hour Fitness, 2000
The woman in the above example burns more total calories but fewer fat calories at a higher intensity. However, again remember that your goal is to burn as many calories as possible to achieve your overall weight loss goal. Your workout programs should be a combination of longer duration, slower endurance workouts along with shorter, higher intensity workouts, which are a great way to burn more calories in a shorter period of time and build endurance.
In this example, the woman burns more total calories but fewer fat calories at a higher intensity. This isn’t to say that high intensity exercise doesn’t have its place. Longer duration, slower endurance workouts should be a staple of a complete fitness program along with shorter, higher intensity workouts which are a great way to burn more calories in a shorter period of time and build endurance. To figure out your own intensity levels, start by calculating your target heart rate zone.
Your Target Heart Rate and Personal Fat Burning Zone
To discover your ideal personal fat burning zone you need to calculate your Target Heart Rate Training Zone. The American College of Sports Medicine recommends healthy adults exercise within a range of 60-80 percent of their Heart Rate Reserve. Your optimal heart rate training zone may vary depending on your health and physical fitness status and any medications you are taking.
Now that you know the type of exercise that will give you the greatest calorie burn for your time spent you can have confidence in your exercise program. You now know that even if you can only fit in 20 minutes on a busy day, you can use that 20 minutes exercising at a moderate or higher intensity. For example, power walking on a break at work is better than a leisurely stroll to gain the greatest calorie burn in the short period of time you have available. By applying these simple exercise physiology principles and maximizing the math inside your body you will achieve the greatest benefit from your workouts!
