This is an article from ivillage.com



Fat Burning Zone? Let's Do the Math
by Jonny Bowden, MA, CNS

I want you to go back to school with me for a minute, and review some math.

Now, when I teach this stuff to trainers, as soon as they hear "math" their eyes glaze over and they look like a collective herd of deer caught in the headlights of a Mack truck. But, honestly, how are you going to talk sensibly about calories, diets like "40/30/30," percentages of calories from protein, decoding a food label, or anything else along those lines without unfuzzy-ing up some of the basics in the math department?

Which brings me to the area of "fat burning" zones.

See, one of the biggest misunderstandings and "myth-conceptions" in the field of exercise and weight loss has been around the field of fat burning. Aerobic teachers are constantly admonishing their students to work at a slower rate so they can "burn more fat." Almost all cardio equipment in the gym has a "fat burning" program, and we fitness professionals are constantly bombarded with questions from clients about how to get their heart rate in the target "fat burning zone."

The misconceptions come from a basic confusion between percentages and absolute amounts. See, at rest, the body is always burning a mix of fuels. All other things being equal, it doesn't like to burn protein, so that leaves fats and carbohydrates (more technically, fatty acids and glucose). At rest, the "average" person burns about 70 percent fat and 30 percent carbs. As one moves from rest to activity, the percentage of fuel coming from fat decreases and the percentage coming from carbs increases. The more intense the exercise, the more carbs and the less fat in the mix, until you reach the point called the "anaerobic threshold" where you're going at about your intensity limit. At that point, 99 percent or more of your fuel is pure carbohydrate and 1 percent or less is coming from fat.

Now, this situation has led many people to assume that in order to "burn fat" they need to exercise at lower intensities. They're missing the boat. Why? Because while at rest, although a higher percentage of your calories is indeed coming from fat, you are ultimately burning a lower absolute number of calories. At higher intensity exercise, the percentage of calories from fat goes down, true -- but it is a percentage of a significantly higher number.

To illustrate this critical difference, I often ask audiences to picture Ross Perot standing next to me. Then I ask them, "Would you rather have 90 percent of all the money I have in the world, or 3 percent of all the money Mr. Perot over here has?" When they give the obvious answer, I say, "But why? 90 percent is so much higher than 3 percent!"

They get the picture.

So, let's say you're exercising at a fairly low intensity that burns, oh, 100 calories in a half-hour. Let's say that 70 percent of those calories come from fat. Your neighbor, however, is working out much harder, outside the magical "fat burning" zone: She's burning up, say 300 calories in that same half hour, but only 50 percent of those calories are from fat. Now do the math. You're burning a higher percentage of fat, but 70 percent of your 100 calories equals 70 fat calories burned. Your neighbor, on the other hand, is burning a lower percentage of fat, but she has burned up 50 percent of 300 calories, or 150 fat calories, more than twice what you've burned in the same period of time!

Thanks for posting this. I've been trying to help de-bunk the "fat burning zone" mentality in my small way, but so many people buy into this! What matters is not WHERE the calorie burn comes from, but the TOTAL amount of calories burned! I'd much rather burn 200 calories in 30 minutes than 200 calories in 45 minutes! The will both result in the same amount of fat loss, even though the longer workout may tap into fat stores during the workout itself.

Whenever I am on the elliptical, it shows me my heart rate and whether or not it is in the fat burning zone or the cardio zone. I am always blasting past the fat burning zone and stay in the cardio zone until the cool down. Of course in 30 minutes, it tells me I burn 400 calories so I'll take it I rather work my butt off and get it done with rather than trying to go at a slower pace.

Great article, Jennifer! I always heard the same thing - that those so-called fat burning and cardio zones are a bunch of hogwash. I always try to be as intense as possible when I do cardio and frequently go over the target zones for old folks my age.

I met a woman the other day who was telling me that she does 'everything right' but can't lose any weight, so I asked her in detail about what she was doing. For cardio, she's limiting herself to walking on the treadmill at 2.7 MPH so as to stay in the so-called 'fat-burning zone'. I said 'bingo' to myself and suggested that she try for more intensity - told her that what counts is the number of calories burned, not the 'zone'. I don't know about you guys, but at that speed, I'd be burning about 100 calories per hour or less ... I've got to get the treadmill up to 4 MPH and an incline of 10 or so to get my heartrate elevated at all. Which is why I use a crosstrainer or elliptical because it's a whole lot easier to get my heartrate up and keep it there. Like Nelie and Funniegrrl say - it's all about the calories you burn. And they're both very successful 'losers' and know what they're talking about!