In order to use fat (Free Fatty Acids – FFA) as your main fuel, you need to exercise at low intensity (e.g. cycling, walking) so the body has the capacity to mobilize and oxidize fat (break down fat). Remember, the complete oxidation of one molecole of stearic acid (fat) requires 26 molecules of oxygen, while the complete oxidation of one molecule of glucose (carbohydrate) requires only 6 molecules of oxygen. In other words, if you want to burn fat you need more oxygen and this is the reason why you should exercise at low intensity (in theory).
Fat combustion almost totally powers exercise at 25% of aerobic capacity (it is the highest amount of oxygen consumed during maximal exercise). If you walk or cycle, at 1 hour you use 70% of carbohydrate and 30% of fat, at 2 hours 60% of carbohydrate and 40% of fat, at 3 hours 40% of carbohydrate and 60% of fat, and at 4 hours 20% of carbohydrate and 80% of fat (Generalized percentage contribution of macronutrient catabolism in relation to oxygen consumption of the leg muscles during prolonged exercise, e.g. cycling figure 2.9, page 46 – William D McArdle, Frank I Katch – Essentials of Exercise Physiology 4th edition, 2011).
As you can see exercise intensity and duration affect Fat Oxidation. You need to walk or cycle for more than 3 hours if you want to use fat as your main fuel. That’s boring and unfeasible.
Don’t worry, there is another way…
You need to increase your metabolism! The only way to increase your metabolism is resistance training ( weight lifting) in order to build up your fat-free mass (muscles). More muscles = higher metabolism at rest = more calories to burn.
Endurance training (running, cycling, rowing, etc) has a lot of beneficial effects on your heart health, cardiorespiratory function, endurance fitness, and physical well-being. However, it is important to realize that muscles are the engines of our bodies. If the engine is bigger, we burn more calories. For this reason, the only option you have to keep a big engine is …. weight lifting.
ACSM (The American College of Sports Medicine) Resistance training recommendations:
- 2-4 sets x 8-12 reps each for the major muscle groups;
- 70% – 80% of maximum resistance (8-12 reps);
- performing 8 to 10 multi joint exercises;
- two or three nonconsecutive days per week
Another option if you don’t have time to go to the gym or like now you are stuck at home due to covid19, it is high-intensity circuit training (HICT) using body weight as resistance.
HICT can be a fast and efficient way to lose excess body weight and body fat. When resistance training exercises using multiple large muscles are used with very little rest between sets, they can elicit aerobic and metabolic benefits. Research has found that these metabolic benefits can be present for up to 72 hours after a high-intensity exercise bout has been completed.
- Number of exercises 9-12
- A 30-second exercise bout
- Rest Between Exercise Bouts 30″ (6)
- Total exercise time at least 20 min ACSM guidelines (3)
HICT SAMPLE PROGRAM: The following is an example of a 12-station HICT program. Exercises are performed for 30 seconds, with 10 seconds of transition time between bouts. Total time for the entire circuit workout is approximately 7 minutes. The circuit can be repeated 2 to 3 times.
- Jumping jacks Total body
- Wall sit Lower body
- Push-up Upper body
- Abdominal crunch Core
- Step-up onto chair Total body
- Squat Lower body
- Triceps dip on chair Upper body
- Plank Core
- High knees/running in place Total body
- Lunge Lower body
- Push-up and rotation Upper body
- Side plank Core
You don’t need to walk or cycle for hours, in order to start burning fat. Everyone will give up at one point. There is a much better and quicker way. You need to do resistance training, because the secret to burn fat faster is to increase your metabolism.
- Carbohydrate and fat utilization during rest and physical activity, the European e-Journal of
Clinical Nutrition and Metabolism, 2010;
- Skeletal muscle energy metabolism during exercise, Nature metabolism, 2020;
HIGH-INTENSITY CIRCUIT TRAINING USING BODY WEIGHT: Maximum Results With Minimal Investment, ACSM, 2013;
- Intramuscular and extramuscular fuel sources (fig.2 – Skeletal muscle energy metabolism during exercise, Nature metabolism, 2020);
William D McArdle, Frank I Katch – Essentials of Exercise Physiology 4th edition, 2011, page 46, figure 2.9