Exercise & Weight Loss

Below is an excerpt from Part Two of

The 2004 Multi-Diet

by Anderson A. Anonymous, M.D., Ph.D.

What Kind of Exercise Burns Fat?

All exercise burns Calories. (Well duhh!!J) But since you already know that, I won’t waste your time blathering about the science of how and why. For weight loss purposes the only important thing you probably don’t know about it is the actual numbers of Calories that various activities will burn. You can look this up in Table 25: Calories Expended in Various Activities. For now let’s just continue to discuss what kind of calories various exercises burn—because obviously, we would like to make sure they are mostly fat calories.

Physiologists consider a measurement called “VO2 max” to be the most accurate single measure of “aerobic fitness” (which is the body’s ability to produce energy by “burning” fuel). The more oxygen your body is capable of using (when needed), the better your level of aerobic fitness is, and the higher your “VO2 max” will be. You don’t really need to know anything about VO2 max except that it’s easily and routinely measured and is a good scientific measure of how much energy is being produced and whether the energy is coming from fat or glycogen or protein.

“VO2” means the volume (V) of oxygen (O2) in liters that the body consumes per minute per kilogram of body weight. VO2 “max” means the maximum amount of oxygen your body is capable of using. This amount depends on your fitness level. We couch potatoes have a much lower VO2 max than highly trained athletes. However, even though your VO2 max is probably pitiful compared to Michael Jordan’s, this is not the most important issue in weight-loss exercising (fortunately). The important issue is the relative intensity level you exercise at.

To put this in somewhat more useful terms:

• Low-intensity exercise uses about 25% of your VO2 max (whatever yours happens to be). This is about the exercise intensity represented by walking outdoors at a speed you find brisk but still comfortable. If you are healthy and the other vital factors are balanced properly, you can maintain this rate for many hours. At this exercise intensity level your muscles are burning almost entirely fat.
• Moderate-intensity exercise uses about 55% to 65% of your VO2 max. This is about the intensity of the standard aerobics class (not “power aerobics”). It is also the rate usually used in athletic training programs designed to increase aerobic fitness. It can normally be continuously maintained for between one and three hours. At this exercise intensity level your muscles are using about ½ fat and ½ stored glycogen for energy.

• High-intensity exercise uses 85% or above of your VO2 max. This intensity level is typical during most athletic competition. It can usually be continuously maintained for no more than 30 to 60 minutes. At this exercise intensity level your muscles are using almost exclusively stored glycogen for energy.

Obviously, to lose fat, we want to exercise in the low-to-moderate intensity range of exertion since this is where the most fat is being burned (relative to total energy expenditure).

But WAIT! There’s MORE!!

Although low-intensity exercise directly burns fat, and this is great, it has a potentially even more useful metabolic effect.

Even low-intensity exercise does burn a small amount of glucose. Therefore, it tends to slowly push your blood glucose levels down toward the low end of the “normal” range. As we found out in more on… energy metabolism & storage, a low-normal blood glucose level lowers your blood insulin level, which in turn allows your fat cells to release more fatty acids into your bloodstream to be used for energy by the rest of your body. This low–normal blood insulin level will persist even after you stop exercising (unless you go eat a lot of carbohydrate). Low-intensity exercise therefore tends to promote fat-burning even after you stop exercising. This is obviously a good thing for dieters!

Of course, it is theoretically possible to maintain this low-normal blood glucose level even without exercise by making sure you routinely eat only low-glycemic-index carbohydrate and only just enough of it to keep your brain and nervous system happy. However, you will find that you have better control by using both the Exercise Factor and the Carbohydrate Factor to manage this insulin issue. (See more on… carbohydrate.)

It is also obviously “rather easy” to eat too much carbohydrate at any given meal (or snack ). This shuts off fat burning until the excess carbohydrate has been used up (See more on… energy metabolism & storage). So if you think you may have done this, it’s a good idea to take a brisk walk around the block once or twice (or more) to “burn it off” so your fat-burning can resume. (Of course, you must also stay off the Liar’s Diet—you’d have to walk for hours to burn off a slice or two of chocolate cheesecake. )

In other words, one of the best uses of exercise is to help control blood glucose and insulin levels so that fat burning can take place both during and after the exercise. This is also a reason to make sure your exercise is of the low-intensity “lite” variety. Intense exercise can lower blood glucose too far because it forces your muscles to use a lot of stored glucose for energy. When levels of blood glucose go too low the brain and nervous system don't have enough for their needs and they naturally wake The Beast to make you go eat.