No fat burn first 20 mins of exercise?

So I've heard this one repeated quite a few times and I was wondering if it's actually true or if it's just an urban myth. I can't seem to find any real evidence... does anyone have a proper scientific explaination of why this would be true? 

Burning calories is the goal for weightloss and you start burning more calories per minute as soon as your heart rate starts to increase.

Did you ever play that game telephone as a kid? The one where one kid comes up with a message and whispers it to the next kid who whispers it to the next kid and so on until the end, and whatever the last kid heard was usually totally different from the original message? I think that's proably what happened here.


So, your body has 2 broad ways of making energy, anerobic and areobic. Anerobic is very quick, but not very effecient and only lasts a few seconds before the areobic system has to kick in. The areobic is what's used for most long term activities and is the only way to burn fat directly, anerobic only can use glucose.

However, even with areobic respiration, using glucose is preferred, it's just easier to use than fats. And glucose is stored in the muscles as glycogen, which is used first (both anerobically and areobically). So, your body doesn't use a whole lot of fat while there's still plenty of glycogen around, but once that gets low, the body will begin to use more fat. I don't know where 20 minutes came from, because it all depends on how fast you deplete your glycogen stores, and it'll be a gradual change from burning mostly glucose to mostly fat, but I think that's where that story comes from. 

However, the net effect isn't dependent on the amount of fat you burn during exercise. Imagine if you did a workout, burned 200 calories, but your body only used glycogen stores, and no fat, for its energy. Well, after your workout, your glycogen is depleted, so guess what your body wants to do? It wants to refill it, so then, after the workout, the body uses the fat it has stored to restore the glycogen that was lost.

Hope that helps, and if you need a clarification, don't hesitate to ask.

 Mostly a myth - your body always use all three possible fuel sources(carbs, fat, protein) at any given moment, the only thing that changes is your fuel mix.

 Which fuel source predominates depens as much on the exercise as on the duration - strength work can only use glycogen, low-impact cardio like walking uses virtually no carbs from the get-go.

 High-impact aerobic activities will initially use mostly carbs; in a controlled lab setting you'll see that the proportion of carb-to-fat in the fuel mix falls as time goes by and at the 20-minute mark carb reserves get depleted enough that fat burn predominates.

 Which really, truly doesn't matter for your results, for weight loss it's all about the calories in and out.  Over a 24-hour period your body will regulate the proportion of fuels burnt so that it all evens out - burn more fat during exercise, and your body will use proprotionally more carbs for fuel the rest of the day to make it back up to the 'normal' average fuel mix. Burn more carbs during the workout, and your body will save carbs and use more fat for fuel post-workout.

 This probably partially explains why weight lifting - a pure carb/anaerobic activity - is so much more effective for fat loss than cardio is. Not the whole story - if you're trhawley and spend 1-4 hours on your bike your energy turnover is so high that you'd grow leaner even in a calorie balance. Which means that if you've got the time and the inclination to do multi-hour cardio like that it's probably your best bet for fat loss; however, if you don't have several hours each day to work out you should go for the most intens workout you can stand. 

Here's a non-scientific way to look at it.

http://www.calorie-count.com/calories/communi ty/dlog.php

i have indeed heard this urban myth as well - but i am inclined to not believe it :)

I am confused, it sounds like melkor is saying that walking doesn't do anything for you for fat loss? Please help, because it is the ONE thing I can do due to my COPD that doesn't make me fall down out of breath!

It's not that walking isn't good, it still burns calories - just at a slower rate than running. But if you can't run, then walk - it certainly burns more calories than sitting on the couch! I walk and run - the difference is that to burn the same amount of calories you have to walk for about twice as long ... but if it's a nice day out, who cares!

Walking also does help build muscle, again just at a slower rate than running. I love walking and regularly walk with a group anywhere from 10 - 25K (1:30 - 4:30 hours of walking) and have seen excellent results in myself as well as others in my walking group.

 Actually - walking is so low impact that it doesn't need to use much of the quick energy from carbs, so you're burning proportionally more fat. Thing is, since your body always regulates the fuel sources so that it evens out, it doesn't really matter what kind of fuel you're using during the exercise, what matters is your overall calorie balance and what your body does in response to the adaptive stress from your exercise.

 So walking is absolutely good for fat loss - the only thing you need to lose weight is a negative energy balance and it'll help you create that.

 The only long-term problem with solely relying on walking is that it's low-impact enough that there's not much adaptive stress on your body from it. So over the long term you'll plateu in terms of physical developement a bit faster than you would when running or doing something else for exercise. But plateus are nice, I've enjoyed the view from them many a time - and worrying over the long term when you start out is kinda pointless. If you plateau, then it's time to see what your options are. Personally I started with walking for the first 8 months of my workout program, and only progressed to other forms of exercise later.

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Here's a non-scientific way to look at it.

http://www.calorie-count.com/calories/communi ty/dlog.php

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This doesn't work for me, anyone else have success?

http://www.fatburn.com/article_show.asp?artic le_id=13

edit: The link showed carbohydrates and Fats burned at different time intervals. I should have just posted the numbers. I need to learn how to post a link here too, :)

Jeff

If walking for 20 minutes is all you can do then do it.  Any type of physical exercise is better than sitting on your tukus getting fatter.

I lost 55# just by eating less calories and walking- no running - no hiit no weights just old fashioned hitting the pavement and walking around the block.  Its very possible to lose fat and weight and get healthier just by walking.  Do what you can and be happy and healthy!!