What’s the best method for burning fat – long & slow or short & fast?

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A number of years ago, you may remember many fitness professionals prescribing lower intensity activity to maximize fat loss. Many fit people lowered the intensity of their workouts fearful that they were not burning fat. Unfortunately, they were misled and many people still believe that low intensity activity is the best way to maximize fat loss. In fact, I just heard a well-known doctor (mind you a psychologist not a physiologist) recommending that if people want to burn fat they need to slow down! So it caused me to want to include the following information in today’s blog. I hope it helps to clarify the issue for you.

The reality is that the activity that expends the most amount of calories will lead to the most amount of fat burned.

Yes, during lower intensity activity you will burn a higher percentage of fat and during higher intensity activity you will burn a higher percentage of carbohydrates or sugars. But the important point to note is that during low intensity activity you are burning fat at a higher percentage of a lower amount of calories. When you exercise at a lower intensity you are definitely expending less calories. The selective use of fat as a fuel, specifically at lower intensities, does not translate into greater fat loss, regardless of how tempting it is to draw this conclusion. The more important focus with regard to calories expended, is not the percentage of energy coming from fat, but rather the total volume of fat used and the total number of calories expended. Let’s look at the math.

At 60% max heart rate (easier intensity)
• Approximately 50% of calories come from fat (50% from sugars)
• Approximately 8 kcal/min are expended
• 60 minutes x 8 kcal/min = 480 total calories
• 50% x 480 kcal = 240 fat calories

At 80% max heart rate (more vigorous intensity)
• Approximately 40% of calories come from fat (60% from sugars)
• Approximately 11 kcal/min are expended
• 60 minutes x 11 kcal/min = 640 total calories
• 40% x 640 kcal = 264 fat calories

From these figures you can see how fitness leaders could have been misled. If you were to examine only the first line, the percentage of fat being burned as fuel, you would definitely prescribe lower intensity activity. However, if you examine the whole picture, it is clear that higher intensity activity definitely expends more calories and also more fat. Here are some more statistics to convince you.

It takes approximately 3,500 calories to burn one pound of fat. Compare the following exercise programs.

Program A – Easier intensity (approximately 5kcal/min) – For example, easy walking
• 30 minutes of activity 3x/week
• 150kcal/session x 3x/week
• 450kcal/week
• It would take 8 weeks to burn 1 pound of fat

Program B – Same intensity as above but for a longer duration
• 60 minutes of activity 3x/week
• 300kcal/session x 3x/week
• 900 kcal expended per week
• It would take 4 weeks to burn 1 pound of fat

Program C – More vigorous intensity (approximately 10 kcal/min) – For example, jogging or power walking up and down hills
• 60 minutes of activity 3x/week
• 600kcal/session x 3x/week
• 1800 kcal expended per week
• It would take 2 weeks to burn 1 pound of fat

If you followed Program A, it would take you eight weeks to burn one pound of fat! Most people would give up by then. If you could easily handle the higher intensity of Program C, wouldn’t you prefer to just wait 2 weeks to burn off that pound of fat deposited around your waist, hips or thighs? Remember though, if you can’t handle the higher intensity of Program C, follow Program B which means you can maintain the easier intensity but you just have to go longer.

Time is definitely an issue for a lot of exercisers and most don’t want to spend hours in the gym if they can get the same results in a shorter period of time. Consider this. At 60% of your max heart rate, it would take you approximately 40 minutes to burn off 300 kcal. If you could handle a higher intensity and were able to exercise at 80% of your max heart rate, it would only take you approximately 27 minutes to burn the same 300 kcal. If time is a factor and you do not have a lot of time to waste, would you rather exercise for 40 or 27 minutes and still burn the same amount of calories?

If I have not convinced you yet, consider this. Did you know that the highest percentage of fat that you burn during any activity is during rest! At rest, you are using approximately 50% fat as your fuel – that is the highest % of fat you can burn – you are never burning 100% fat. That’s right, just sitting here reading this blog, you are burning the highest percentage of fat you could possibly burn. That is because your body can only store a limited supply of carbohydrates (sugars) and so during rest, the demand on your body is low and your body wants to spare your precious sugar stores. Since you have an unlimited supply of fat stores, your body would rather burn fat during rest.

But remember that although you are burning a higher percentage of fat at rest, you are expending very few calories (approximately 1kcal/min) so overall you are not burning a lot of fat. If type of fuel utilized was the critical factor for fat loss, then we would be prescribing more rest because this is when we burn the highest percentage of fat as fuel. But it is a higher percentage of a lower number of calories. So, of course, we know it is ridiculous to even consider rest or sleep as a high fat burning activity.

One last note. Examine elite level athletes like sprinters. The majority of their training sessions involve high intensity, sugar-burning activity. But have you ever seen a fat sprinter? Of course not. Although, they are burning a lot of carbohydrates or sugars during their training sessions, they are also expending a lot of calories and a lot of fat. In fact, some sprinters eat over 5000-6000kcal/day without gaining any fat!

The benefits of higher intensity exercise are as follows:
• Expends more calories per minute
• More efficient – burns more calories in less time
• Most effective method for improving fitness conditioning
• Most effective method for raising anaerobic threshold. Your anaerobic threshold is the stage of exercise where you feel very tired and feel the need to either stop or slow down. You may feel dizzy or nauseous if you stay at this level too long. By incorporating higher intensity activity into your exercise workouts, you raise your anaerobic threshold. This means that you can exercise at a higher intensity before you start to experience those uncomfortable sensations.
• Most effective method for inducing training adaptations. Incorporating this type of training into your program will enable your body to handle the higher intensities more easily. You will find that intensities that used to leave you breathless and fatigued, no longer challenge you anymore. Soon, you will be able to expend more calories per minute compared to when you first started exercise. When people first initiate an exercise program, a comfortable calorie burning level is approximately 5cal/min. Elite athletes can expend more than 20cal/min and sustain it for over 2 hours! As a result, it takes them a lot less time to burn one pound of fat.
• Most effective method for increasing fat mobilization. This means that as you get fitter, you actually get better at burning fat. Inside of your fat cells, you have enzymes called hormone sensitive lipase and lipoprotein lipase. Hormone sensitive lipase, the “good guys”, are responsible for releasing fat from a fall cell to be used for energy. Lipoprotein lipase, the “bad guys”, are responsible for the uptake of fat from the blood stream into fat cells to be stored. Lipoprotein lipase functions to develop our unwanted bulges. If you have lived a sedentary lifestyle and have eaten a poor diet all your life, you will have a lot of the “bad guys” and they will be very good at their job. You will have fewer “good guys” and they will not be so competent with their responsibilities. The goal is to get more good guys doing their job. But changing the internal chemistry inside of your fat cells may take years. So in the beginning you may not be experiencing results as quickly as you want because you body is actually working against you. But with consistency in your training program, your body will soon start to work for you. Soon you will have increased your ability to mobilize and use fat as a fuel. Training in a high intensity zone will make you fit quick and enable you to enjoy this wonderful training benefit. Soon you will be burning more fat during and after exercise. You will become a fat burning machine!
• Experience a higher EPOC (excess post oxygen consumption). Have you ever wondered why you continue to breathe heavy and sweat after your workout is done? Why doesn’t your breathing and body temperature go back to normal immediately? After exercise you consume a greater amount of oxygen to assist your body in recovering from the stress of the workout and the demands it placed on your body. It is important to know that EPOC uses fat as its fuel. At higher intensities, your EPOC is greater translating into a greater caloric and fat expenditure post activity. Although the effects of EPOC are small, if you expended an additional 100 calories post exercise as a result of a high intensity exercise session, within 100 workouts (5 months), you would have burned an extra 10,000 calories or 3 pounds of fat!
• Intervals are the best way to add intensity to a workout by adding brief, high-energy outputs followed by active recovery phases which will avoid fatigue and injury.

So, the bottom line is that everyone can benefit from incorporating high intensity training into their program once they have completed about 2 months of initial level base conditioning. Please note however, that every workout should not be a high-intensity workout. Doing so could result in burn-out, over-training and injury. The recommended fitness prescription is one that includes all intensity training zones. That is, sometimes you go easy and long and other times you go hard and fast. This will ensure you train all of your energy systems and minimize overtraining. Reminder – Don’t start a new fitness program with high intensity exercise. Complete a couple months of easier, base conditioning first and then slowly start to add your intervals.

Yours in health and fitness,

Sherri McMillan

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