Understanding Fat Loss

There is never a time when there is a shift from one source to the other. The two are always contributing to the energy production pathways. One may be favored or dominant, but never exclusive.

Today everyone wants to be lean and mean. We all want to, not only feel good, but look good too. Everyday we work our butts off to get there and everyday we think we are one step closer. But soon a week, a month, even a year goes by and nothing has changed. What could I possible be doing wrong, you ask?

Truth be known, you aren't doing anything wrong. You are doing exactly what you have been told time and time again. Unfortunately the information you have been given is based on research and studies that have nothing to do with what you want to accomplish.

"You have to work in the fat burning zone if you want to loose weight." We've all heard that before, right? But have you ever stopped to ask what exactly that means? Lets take a brief look at what this really means.

Fat burning is the process where free fatty acids are used for fuel as opposed to glucose (human blood sugar). During times of very low intensity (less than 50% VO2 max) the preferred fuel is fat. About 75-80% of the energy used is supplied by fat.

This does not mean that it is the only source. It just means that there is a larger contribution of energy from fat than glucose. There is never a time when there is a shift from one source to the other. The two are always contributing to the energy production pathways. One may be favored or dominant, but never exclusive.

Fat Burning Will Equate To Fat Loss

The fact of the matter is, "fat burning" has nothing to do with fat loss.[1,2,3] Fat is the preferred fuel for low intensity activity. So while you watch T.V, sit behind a desk or while you sleep! We are "burning" fat all of the time, 24 hours a day, 7 days a week.

For there to effectively be a loss of whole body fat, a negative energy balance must be maintained for a prolonged period of time. Meaning, weeks, months and years. Not minutes or hours. This is most important point to understand and it is the one that virtually every fitness buff and expert seems to neglect.

The vast majority of us will work out for about an hour and remain sedentary for the rest of the day. That's 23 hours of little to no activity. Our workouts contribute less than 10% of our total caloric output. This is where all that research comes into play.

Lower intensity exercise for long durations may burn a bit of calories, but it does nothing to your resting metabolic rate.[5,6,9] In other words, it doesn't increase the amount of energy you expend during those other 23 hours of the day. This is the critical component of fat loss that we all seem to forget about.

Do The Math

Working at a heart rate of about 120 beats per min will "burn" 8 calories per min. Because of the low intensity, 80% or 6.5 calories will be coming from fat. Working at 160 beats per minute will "burn" 18 calories a min.

Even if fat oxidation drops to 50% of the energy supplied, this is still 9 calories from fat every minute. So we can clearly see that if there was any validity to this "Fat burning zone" it really isn't burning all that much fat to begin with.

We can clearly see that working at a higher intensity would in fact "burn up" more fat, even if the relative contribution of fat energy is lower than at a lower intensity of exercise.

Lets make this clear, just because you burn more fat during the actual exercise, does NOT mean you will actually lose more body fat.[5] Isn't about time you asked why you haven't lost the weight you want by now?

What Is EPOC?

Excess Post-exercise Oxygen Consumption. How much oxygen you consume during the other 23 hours of the day. Why is that important? Well, the amount of oxygen consumed is a very accurate way to determine how many calories your are burning. Lower intensity exercise does not create this effect.[6,9]

On the other hand both High intensity cardiovascular and weight training do. When intensities reach levels of approx 85% VO2 Max, the EPOC can last for up to 2-3 days.[11,12] You metabolism will literally be a Colorado forest fire! You can work out for shorter durations (15min) and get better results.[7,8,9]

How do you know when you've reached the right level of intensity? Well to make it simple, if you can talk to someone while your are doing it, then you aren't even close! It is uncomfortable, yes. Start slow and work your way up to it. There is no point to just spinning your wheels any longer.

And no, doing 3 sets of 12-15 will not enhance fat burning or create a more defined body. This type of weight training actually conditions muscular enzymes to become more efficient at handling lactic acid. Lactic acid is basically a glucose molecule split in two, and being an acid, it burns. It is not, however, an indication that you are burning more fat.


As mentioned before, total fat loss comes down to burning off more calories than you take in. This is where the trainer can only educate and the trainee has to take over. Monitoring your food intake is very important to your overall fat loss goals. And if you have a high level of body fat, you will have to be more cautious on your food selections.

It is well documented that people with a greater amount of body fat, have a greater ability to store dietary fat. That's right, the human body loves its energy stores and its gets greedy!

You have to make a conscious effort to know how many calories you eat EVERY DAY. If you are working your butt off and you can't loose any fat, then you are most likely eating too much. However, do not confuse weight and fat.

It is very possible to loose body fat with out seeing the scale drop. So keep that in mind. In the next article, I will show you just what food selections are good, which are bad, and I'll even tell you why!


Fat oxidation, mobilization, utilization or the "Fat burning zone" have virtually nothing to do with fat loss itself. A negative calorie balance is the biggest factor that influences fat loss. High intensity (>85% VO2 max) will allow you to burn a greater amount of calories. Don't forget about the other 23 hours of the day.

Working out in the morning will help you maximize fat loss. You will have effectively cranked your metabolism through the roof and will be able to fuel the fat burning fire for the rest of the day. This does not mean it must be done on an empty stomach however. Low fat diets will accelerate fat loss, but a no-fat diet can be VERY dangerous.


  1. J. Calles-Escandon, P. J. Arciero, A. W. Gardner, C. Bauman, and E. T. Poehlman Basal fat oxidation decreases with aging in women J Appl Physiol 1995 78: 266-271.
  2. E. T. Poehlman, A. W. Gardner, P. J. Arciero, M. I. Goran, and J. Calles-Escandon Effects of endurance training on total fat oxidation in elderly persons J Appl Physiol 1994 76: 2281-2287.
  3. Anne L. Friedlander, Gretchen A. Casazza, Michael A. Horning, Anton Usaj, and George A. Brooks Endurance training increases fatty acid turnover, but not fat oxidation, in young men J Appl Physiol 1999 86: 2097-2105.
  4. H Bessesen, CL Rupp, and RH Eckel Dietary fat is shunted away from oxidation, toward storage in obese Zucker rats Obes Res 1995 3: 179-189.
  5. Bret H. Goodpaster, Robert R. Wolfe, and David E. Kelley Effects of Obesity on Substrate Utilization during Exercise Obes Res 2002 10: 575-584.
  6. Dorien P. van Aggel-Leijssen, Wim H. Saris, Anton J. Wagenmakers, Gabby B. Hul, and Marleen A. van Baak The Effect of Low-Intensity Exercise Training on Fat Metabolism of Obese Women Obes Res 2001 9: 86-96.
  7. Yohiako, M. et. al. Impact of high intensity exercise on energy expenditure, lipid oxidation and body fatness. Int. J. Obes. Relat. Metab. Disord. 2001 Mar: 25(50 p332-339.
  8. Broeder CE, et al. The effects of either high-intensity resistance or endurance training on resting metabolic rate. Am J Clin Nutr. 1992 55(4):802-10.
  9. Thornton, M. Kathleen; Potteiger, Jeffrey A Effects of resistance exercise bouts of different intensities but equal work on EPOC; Medicine and Science in Sports and Exercise v 34 no4 Apr 2002. p. 715-22
  10. Jack Wang, Blandine Laferrere, John C. Thornton, Richard N. Pierson, Jr, and F. Xavier Pi-Sunyer Regional Subcutaneous-Fat Loss Induced by Caloric Restriction in Obese Women Obes Res 2002 10: 885-890.
  11. Int J. Sport nutri and exercise Metab. v11(1) pp 109-32
  12. Eur. J. App. Physiol 86(5) 411-7