Burning Fat: Myths and Facts

Apr 22, 2010

Fitness Handout

A popular myth is that there is a specific range of heart rates in which you must exercise to burn fat. Even many cardio machines display a “fat-burning zone” on their panels, encouraging people to exercise in a specific heart rate range. Have you ever wondered if you really have to exercise in a specific heart rate zone to lose fat? And what happens if you venture out of that zone? Jason R. Karp, PhD, a nationally recognized speaker, writer and exercise physiologist who coaches recreational runners to Olympic hopefuls through his company, RunCoachJason.com, sheds light on this issue.

Fuel Use During Exercise

You use both fat and carbohydrates for energy during exercise, with these two fuels providing that energy on a sliding scale. During exercise at a very low intensity (e.g., walking), fat accounts for most of the energy expenditure. As exercise intensity increases up to the lactate threshold (the exercise intensity that marks the transition between exercise that is almost purely aerobic and exercise that includes a significant anaerobic contribution; also considered the highest sustainable aerobic intensity), the contribution from fat decreases while the contribution from carbohydrates increases. When exercising just below the lactate threshold, you are using mostly carbohydrates. Once the intensity of exercise has risen above the lactate threshold, carbohydrates become the only fuel source.

If you exercise long enough (1.5–2 hours), your muscle carbohydrate (glycogen) content and blood glucose concentration become low. This metabolic state presents a threat to the muscles’ survival, since carbohydrates are muscles’ preferred fuel. When carbohydrates are not available, the muscles are forced to rely on fat as fuel.

Since more fat is used at low exercise intensities, people often assume that low-intensity exercise is best for burning fat, an idea that has given birth to the “fat-burning zone.” However, while only a small amount of fat is used when exercising just below the lactate threshold, the rate of caloric expenditure and the total number of calories expended are much greater than they are when exercising at a lower intensity, so the total amount of fat used is also greater.

The Bottom Line

For fat and weight loss, what matters most is the difference between the number of calories you expend and the number of calories you consume. Fat and weight loss is about burning lots of calories and cutting back on the number of calories consumed. For the purpose of losing weight, it matters little whether the calories burned during exercise come from fat or carbohydrates.

IDEA Fitness Journal, Volume 7, Issue 5

© 2010 by IDEA Health & Fitness Inc. All rights reserved. Reproduction without permission is strictly prohibited.


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  • Mark freeman

    Theres some valuable information in this article, great post! i spent over a year trying different things to lose a good amount of weight to finally find results. I really wish someone would have pointed me in the right direction from the start, that being said i would love to help anyone that is struggling to lose weight. Email me at markfreeman7@hotmail.com and ill show you my before and after pictures and share what has brought me success.
    Commented Sep 02, 2014
  • Mark freeman

    Theres some valuable information in this article, great post! i spent over a year trying different things to lose a good amount of weight to finally find results. I really wish someone would have pointed me in the right direction from the start, that being said i would love to help anyone that is struggling to lose weight. Email me at markfreeman7@hotmail.com and ill show you my before and after pictures and share what has brought me success.
    Commented Sep 02, 2014
  • Fat Loss Factor

    Hey , Thank you for your very .There is a program that helps in burning fat Like I want to share with you the program module. program by Dr. Charles Fat Loss Factor program consists of 11 authors and a free book. And 4 Videos To watch a video review : www.youtube.com/watch?v=UV7rXZmZzJk
    Commented Nov 08, 2013
  • jason springer

    Lol you have to step back and look at Olympic sprinters , hockey players , football players ect.. they all are 100% intensity of sort bursts. There all huge avg hockey player is 210lbs of soild muscle
    Commented Jul 03, 2013
  • Cynthia McGinnis

    Wow! Great comments! I try to get my clients to do something different everyday. Sometimes HIIT, sometmes long cardio bouts, weights training at least once a week, body weight training at least once a week, as well as, a mind body class. And for fuel, my rule of thumb, if it doesn't look like God made it, don't eat it. Sometimes I think we make it too complicated. Exercise fuel your body with 'real' food, have fun and you will be healthy.
    Commented Mar 23, 2012
  • narissa coleman

    Ok one BIG flaw with this article and the previous comments is that they do NOT cover the fact that you do need to have atleast a certain number of calories more than what you are USING in order to loose weight ... in some cases if a person consumes too few calories then i can cause the metabolisim to basically go into starvation mode where instead of burning fat or loosing weight the body instead will actually react by trying to convert every bit that it possibly can out of what is taking in for food into fat for storage.. also the more muscle mass the person has the more they do need for a minimum caloric intake in order for their body to not react this way. And this is even MORE of an issue for people who's bodies build muscle easily any time they are active.. if they are eating less than their body needs (or not eating frequently enough, hence why nutritionists actually eating 6 SMALL meals instead of 3 normal size ones) then often they will over time gradually continue to gain weight. The best way to tell if this is your issue? the best way to tell if this is your problem? figure out how many calories you usually consume per day and if it is less than 2000 a day (and especially if it is less than 1500) then try eating 6 small meals a day as is reccomended by nutritionists and up your calorie intake per day for that month, but DONT do it using junk food or soda, even diet soda .. add more healthy foods and possibly a multi-vitamin if you dont already take one, because lack of too many nessasary vitamins can also effect a body in this way.. try to avoid weighing your self the first two weeks as it will take some time for your metabolism to recover if you hadnt been consuming enough (or had been consuming all your calories in like 1 or 2 meals instead of spread out through the day) at first you may gain a little weight if the problem is your metabolism being in starvation mode, however once your body gets to a point where the metabolism has had a chance to recover (which will not happen just overnight) then if this is your problem then you will after a while begin to loose weight rather quickly.. (i myself at one point by simply eating regularly and not skipping meals and by eating MORE so that i got enough for my body to not feel it needed to store for later usually will end up loosing sometimes as much as 20 pounds in a month when i start eating the way i should be again after having lapsed back into my old habits of skipping meals when i'm busy, for me i find it tedious to remember to eat as much& as often as i should especially if i'm stressed and have lost my appetite because of it)...
    Commented Aug 12, 2011
  • Daniel Omokha

    Fat burning continues to be arguably the most highly debated and talked about issue in fitness. As personal trainers, this can often cause challenges and some frustration while designing cardio programs for our clients. In the old days, it used to be all about calories consumed versus calories burned; translation: fat and weight loss occur when calories burned is more than calories consumed. While that still holds true today, the BIG question we all face today is what exercise modality is the best? I agree with Channing Morales in the regard that anaerobic training (i.e. weight/resistance training) burns way more calories than aerobic training. A 45-minute strength training session followed by a 10-15 minute cardio workout (65%-75% of MHR) will burn more calories than a 60-minute cardio workout! But that's not to say individual cardio sessions shouldn't be performed, which then leads to this question: How should cardio be performed for the most maximizing fat-burning benefits? Steady-state cardio (moderate pace for an extended period) versus high intensity interval training or HIIT (bouts of high intensity combined with bouts of low intensity) seems to be the big debate nowadays. Both methods, while they do burn calories, are great but HIIT has garnered a lot of buzz over the last few years because of its ability to keep the body in a fat-burning zone 24 hours long after a cardio session. Walking/running on a treadmill for an extended period of time no longer seems to be the the preferred method for burning fat, although it continues to be done by lots of exercisers. I will conclude by offering my final thought and opinion on this issue. No matter the type of cardio one chooses, a strict nutrition program and a healthy diet remains the key to weight loss/fat burning. Weight training is imperatively mandatory for anyone looking to burn fat and lose weight. And finally, rather than spend 45 minutes to an hour on a treadmill or elliptical, aim for 10-15 minutes of a moderate-to-mild cardio workout (65%-75% of MHR) following every weight training session and incorporate at least one HIIT workout a week. This is jut my opinion. I'm sure some people will have an issue or two with this so I welcome your thoughts, comments and/or opinions. This topic will continue to be controversial but we can make some progress by brainstorming together. Good luck with all your fitness goals!
    Commented Mar 06, 2011
  • Channing Morales

    This theory has been proven time and time again to be false in the scheme of fat burning. Burning fat comes from a hormonal balance between cortisol, insulin, growth hormone, estrogen and testosterone (the 5 big players) not to mention countless other players in the whole process. We know for a fact that consuming a great amount of carbohydrates spikes insulin which mobilizes fat into fatty tissue. The math with consumption of calories does not equate with a simple calories in calories out to fat burn. I am also concerned this article does not stress that increasing muscle mass, which is done through strength training (and not body pump/high rep aerobic strength training - i.e. group classes), increases your resting metabolic rate to burn fat during rest. Another point with "fat burn" is that during rest your body burns 100% fat = no movement while sleeping. If you only have 3hrs during the week to dedicate to "fat burn" then strength training is KEY to fat burning. If you have 5-6 then go ahead and add the intervals, and then lastly, add the longer bouts if you are training for a specific event. Otherwise, utilize the 24-48hrs post exercise energy usage from a solid strength routine and increasing RMR by 50kcal/day with an added 1lb of muscle. Happy Training!!
    Commented Mar 03, 2011
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