Burning fat vs burning carbs: Explain to me why it matters?

[texasdiver]

Hi everyone:

I'm pretty new to the area of exercise for weight loss but as a former HS athlete, I'm not entirely new to the concepts and principles of fitness training.

One subject I've seen repeated on various web sites including Concept2 is the idea that there is an ideal HR zone to work out at for weight loss where something like 90% of your calories will be burned as fat and that as you increase your exercise intensity you increase the proportion of calories that are burned as carbs rather than fat.

Now setting aside the notion that your body only burns carbs (As I understand it, fat is first converted to sugars (carbs) before being burned). What I'm really wondering is how this information is relevant to planning a fitness and weight loss regimen.

From what I understand, weight loss is achieved when your total calorie expenditure is higher than your total calorie intake over time. Simple as that. And that if you are eating less calories than you are spending you'll burn fat and lose weight. This happens 24 hours/day, not just during the 45 minutes that you happen to be working out.

So the real benefits of exercise during a weight loss regimen are threefold. First, to burn off additional calories that you wouldn't burn if inactive. Second, to increase your metabolism and therefore, burn still additional calories, and third, to increase your fitness which is a separate objective on its own.

Now my question is this. If I have 45-60 minutes/day in which to exercise, and all other factors are equal (same diet, same activity level during the rest of the day) then which type of workout will be better for me in the long run:

45 minutes of exercise in the max fat burning HR zone, which for me is really not much more than a walking pace where I barely break a sweat. The charts tell me that most of the calories I burn this way are fat.

45 minutes of exercise at my aerobic threshold so that I am totally whipped after the workout. The charts tell me that most of the calories I burn this way are carbs.

All other factors being equal, I can't see how the easier workout is in any way preferable to the hard workout. I will burn a lot more total calories during the hard workout and will certainly increase my overall fitness level much faster if I'm working out this way.

What am I missing?

[Bob S.]

Hi everyone:
As I understand it, fat is first converted to sugars (carbs) before being burned.

No. Fats and saccharides are both converted to the same basic body fuel, acetate (i.e vinegar, but in the form of the thioester AcetylCoA).

http://dl.clackamas.edu/ch106-06/metaboli.htm

Bob S.

[Yankeerunner]

texasdiver,

I don't think that you're missing anything. I've posed similar questions in the past and threads usually come to a crashing halt with no further responses.

One of the things I ask the advocates of "fat-burning" low intensity is: "If you can avoid burning carbohydrates during a workout, and burn only fat, then what happens to those unburned carbohydrates?" The answer, if I understand physiology textbooks, is that excess carbohydrates eventually get converted to fat so that the body can store it more efficiently. Thereby creating a vicious cycle.

The only thing you might possibly be missing is that daily workouts of 45'-60' at you threshold might be so tiring that you cannot continue training regularly due to overtraining/underresting. In that case, easier days could help you to avoid unwanted training breaks. Alternating a threshold day with an easier day might be a better way forward.

Rick

[NavigationHazard]

There's quite a bit of sensible info about combining training with weight loss, over on the UK Forum: http://www.concept2.co.uk/weightloss/ch ... _fat.php#5

IMO it would be hard to overstate the importance of adapting your food intake to match your calorie-expenditure goals. It's vital to link what you do on the erg to what you do at the table.

Good luck with your efforts.

[jamesg]

What's missing? Just maths.
A small proportion (%) of a large amount can be more than a high % of a small amount.

See also
http://www.newscientist.com/channel/hea ... 225760.900
This article suggests that the 1st Law is inescapable, but that the problem is WHY we eat too much.

[texasdiver]

texasdiver,

I don't think that you're missing anything. I've posed similar questions in the past and threads usually come to a crashing halt with no further responses.

One of the things I ask the advocates of "fat-burning" low intensity is: "If you can avoid burning carbohydrates during a workout, and burn only fat, then what happens to those unburned carbohydrates?" The answer, if I understand physiology textbooks, is that excess carbohydrates eventually get converted to fat so that the body can store it more efficiently. Thereby creating a vicious cycle.

The only thing you might possibly be missing is that daily workouts of 45'-60' at you threshold might be so tiring that you cannot continue training regularly due to overtraining/underresting. In that case, easier days could help you to avoid unwanted training breaks. Alternating a threshold day with an easier day might be a better way forward.

Rick

Thanks Rick:

For my own part I'm equally interested in fitness and weight loss and have quite a ways to go to reach either objective. So a pure weight loss program that is nothing but low intensity exercise (like mall walking with the seniors) has no interest for me.

I haven't put together any real systematic regimen so far. Instead I am rowing 6x week, running 3x week and cycling 1 or 2 times/wk for a hard ride on the weekends. Before buying the concept2 I was attempting to get back into serious running but found my weight was preventing me from getting adequate exercise running. Too much joint and knee pain. So I backed way off the running and brought in the concept2. Now I do a medium to hard run of 3-5 miles on M/W/F followed by an easy 20-25 minute 5k row. On days that I don't run I do a hard 45 minute row at a 2:05 to 2:10 pace. On weekends I do a hard ride of about 2 hours on the mountain bike. Whenever I work out I usually do so fairly rigorously but below my aerobic threshold. In other words, I'm pushing myself but not into the red. And I usually pick up the pace at the end just to really put a stamp on the workout. Old habit I guess.

I think I'm a long ways from overtraining at this point. I'm seeing good progress in both the weightloss and fitness. At some point down the road when I'm approaching where I'd really like to be I figure I will need to get more sophisticated about training. I just want to be all-over fit and strong in the do-anything Navy Seal sort of way rather than specialized fit in one specific type of activity.

What I do need to figure out is what sort of weights or calisthenics I should add to the rowing/running/cycling to round-out my fitness regime. I do pushups and ab routines but nothing else at this point. I'm thinking about getting a pull-up and dip bar frame for the room where I have the rower. But I'm open to other ideas. I don't have room for a lot of weights and don't live close enough to a gym to make that practical. So I gotta keep it simple.

[todd]

I'm with you. It's my understanding that you will burn the highest proportion of fat vs. carbs while you are sitting still. I've done a lot of sitting still so I guess I burn much more fat than the average athlete, but I weigh in at nearly 270 lbs at 5 feet 8 inches. So you can see my efforts at losing fat by sitting on my rear-end hasn't been very successful.

I realize that somebody who weighs nearly 270 lbs isn't probably the best person to take diet and exercise tips from, but I have lost nearly 60 lbs since March and I can tell you what has worked for me. I don't know if you've heard of Dean Karnazes aka Ultramarathon Man. He runs better than a hundred miles at a stretch and does marathons like I do a walk around the block. He's got like six percent body fat and I'm pretty sure he hasn't done any of these things by keeping his heart rate in the optimum fat burning range. I once read a book where a guy said you need to turn your body into a better butter burner. If you just sit around all the time, your body doesn't need to crank up the calorie burning oven, but if you exercise as hard as you can as frequently as you can, your body will be on high alert and fire up that oven whenever you start any sort of exercise, because it isn't sure if you are going run a marathon or tie your shoes. Another thing to consider about fat burning, is the after exercise burn that happens. You don't burn 800 calories an hour while you are on the erg to have it revert immediately back to your resting rate. You'll keep on burning at an accelarated rate for some time.

In addition to working out hard, I have had to reduce my sugar intake. It seems like I can eat just about anything in dang near any amount and lose weight while I'm working out like I am. But if I add any substantial amount of sugar to my diet, everything will come to a screeching halt.

I also believe that you can not successfully take off weight and maintain it without developing muscle. If I lose weight simply through diet, I lose muscle. Your body burns calories maintaining muscle. So as I lose weight by starving myself, I am also lowering the number of calories that I need. Even if I reach my target, I am going to put back on fat when I start eating again. Weight lifting and lots of protein seems to work for many successful big losers. You can get a full workout with just dumbbells. There are numerous sites that can give example workouts.

Finally (at last) here is a link to another forum that has a bunch of information you might find useful http://forum.bodybuilding.com/forumdisplay.php?f=16

[margaret]

I've weighed as much as 50 pounds over my ideal weight (40%) and am currently down to 20 pounds extra. I agree that more strenuous exercise burns more calories. There is one caveat I have personally experienced. A few times I attempted fairly intense (i.e. probably slightly anearobic) exercise on an empty stomach, and experienced a sudden loss of stamina, shakiness, and dizziness. This was not exercise beyond my normal range, but on an empty stomach. It seemed a lot like what my husband described as "hitting the wall" running a marathon. I attributed it to my body switching from burning fat or readily available calories to burning muscle. Which of course is not what I want to burn to lose weight.

I usually exercise, and lose weight, burning in the anerobic zone and only experienced this twice when my last meal was long since burned off...and my body let me know it!

I wish you success.

[Citroen]

45 minutes of exercise in the max fat burning HR zone, which for me is really not much more than a walking pace where I barely break a sweat. The charts tell me that most of the calories I burn this way are fat.

45 minutes of exercise at my aerobic threshold so that I am totally whipped after the workout. The charts tell me that most of the calories I burn this way are carbs.

The answer is to do both. As has been said excess carbs are converted to fat. You need to removed refined sugars (corn syrup) and transfats from your diet.

My routine is 6 days a week.
Day 1: sprint intervals (8*500 3½mins rest, for example)
Day 2: long steady distance (between 8K and 15K or 30mins to an hour)
Day 3: same as day 2
Day 4: endurance intervals (4*2K 5mins rest, for example)
Day 5: long steady distance same as day 2
Day 6: hard 10K
Day 7: rest (or cycling)

You need to build variety into your program or you will get very bored. You also need to have a positive plan of what to do each session or you'll tend to just do the same favourite workout everytime at the same steady pace and same stroke rate.

I dislike doing intervals (the only thing I hate more is a pyramid workout) so the intervals days are important - do something you dislike and do it well and you get a much better session.

You need to work hard enough to break a sweat every day. But you don't want to be working at your "AT" level everyday.

Try the Concept2 weightloss program: http://www.concept2.co.uk/weightloss/interactive.php
[Note: 1 stone == 14lb; so, for example, if you weigh 216lb that's 15st 6lb or 98.2Kg]

[Yankeerunner]

I've weighed as much as 50 pounds over my ideal weight (40%) and am currently down to 20 pounds extra. I agree that more strenuous exercise burns more calories. There is one caveat I have personally experienced. A few times I attempted fairly intense (i.e. probably slightly anearobic) exercise on an empty stomach, and experienced a sudden loss of stamina, shakiness, and dizziness. This was not exercise beyond my normal range, but on an empty stomach. It seemed a lot like what my husband described as "hitting the wall" running a marathon. I attributed it to my body switching from burning fat or readily available calories to burning muscle. Which of course is not what I want to burn to lose weight.

I usually exercise, and lose weight, burning in the anerobic zone and only experienced this twice when my last meal was long since burned off...and my body let me know it!

I wish you success.

Margaret, there is no need to worry about burning muscle.

At the risk of qualified physiologists shaking their heads at me I'll try to put it in the simplist layman's terms. Muscle gets burned only as a last resort, as in anorexia or concentration camp starvation, only when the body has run out of available glycogen (carbohydrate) and fat. At 20 lbs over ideal weight you still have perhaps 30-40 lbs of fat to burn through (20 lbs over ideal plus 10-20 lbs necessary fat) before risking your muscle.

What you experienced, as happens when running marathons, was likely ketosis. That is the point at which the body has run out of glycogen (carbohydrate) and has to convert fat into ketones so that the body can burn them much the way it burns glycogen. This process is very taxing to the body and requires far more oxygen (meaning you have to breathe much harder) than rapidly burning glycogen. It's not dangerous, just uncomfortable.

It's your body's way of saying "Margaret, eat more carbohydrates (as part of a balanced diet, of course)."

Rick

[margaret]

Rick

Thanks for the interesting clarification. It's good to know even when we don't understand the physiology, our bodies will cue us in.

[Yankeerunner]

Cheers Margaret,

For a view from a more authoritative source see:

http://www.nhsdirect.nhs.uk/articles/ar ... icleId=221

They are more concerned about it being dangerous than I'd been led to believe in the past. Much more info can be found by typing ketosis into google or some other search engine. The bottom line.....eat enough carbs.

Rick

[igoeja]

I'd disagree about removing simple sugars, at least entirely. I remember reading a David Costill (carboloading, taper, physiologist/coach at Ball State) interview, and he mentioned that simple sugars are still necessary for refueling muscles post exercise, and I believe he recommended an even balance of simpler (pasta, bread) and more complex carbs (fruit, veg, whole grains).

For the average person, particularly the non-fit, complex carbs make the most sense, but for people burning a larger number of calories in exercise, particularly athletes, the restriction might be ruinous. As for my moderately fit self, most of my carbs are fairly complex, vegetables and whole rye cracker, and I tend to eat a lot of low-fat protein. Because of my caloric balance, I worry about having enough carbs for my workouts to avoid burnout .

[cityeast]

I agree with Citroen, a good mix is the best for several reasons.

Firstly, if you have only a low intensity regime, your body will adapt quickly and the benefits will taper off.

In order to maintain benefit gains, one has to challenge ones body and constantly improve strength and endurance. Intervals and short,hard rows up to 2k are great for strength. Rows of 30-60min really improve your endurance base. Mix the 2 and you are covered.

Either way, I always try to finish a row with nothing left in the tank. That forces my body to become "a bigger tank". Intervals or finishing bursts at 90-100% HR also seem to help increase V02, thereby allowing me to burn more fat at more sustainable HR (?)

Even for weight loss I don't like doing cardio of more than 30min or so without some carbs in the previous 3 hours. As has been mentioned before, in the end it is your calorie benefit or deficit, and the types of foods that provide those calories, that make a big difference.

[BobD]

Carbs go first because they are easier to burn, then the fat. But a burned calorie is a burned calorie no matter where it came from.

After about 30 minutes of strenuous exercise your body has burned it's carbs (glycogen stored in the liver and muscles) and then it starts working on the fat.

When you are overweight the kilo can be from beer or chocolate or steak but it's still a kilo of fat.