I recall reading something a while ago about doing LSD type workouts (eg. long low intensity rides-below 80% of max heart rate/below 70% of power at lactate threshold) without ingesting carbohydrates before or during a ride to accelerate/teach the body to mobilize fats for energy. The author felt that these kind of workouts were important in the early stages of a periodization plan to help build a strong aerobic foudation for the rest of the season. The author's contention had nothing to do with losing weight- he felt that the body needed to be trained to efficiently use fats and this was the best way to do that.

Does anyone have any thoughts on whether it makes sense to deprive the body of carbs in order to strengthen/hasten the body's ability to mobilize fats- is there any scientific data to support this?

Ric/2lap any thoughts?

There's no data to suggest that this is useful. it's pretty much rubbish. actually, that's not true - it's complete rubbish.

Substrate utilisation depends on the relative intensity that you're riding at, your fitness, and what foodstuffs you've ingested.

As you get fitter (measured by e.g., increases of VO2 max, LT) you cover a greater amount of energy via fat oxidation than when you are less fit, when cycling at a given workload.

To maintain a certain workload, will generally depend on taking carbs while cycling (else you get depleted and suffer a drop in workload). Even cycling at low intensity for a short period of time (e.g. 60-mins @ 50% VO2 max) results in a decrease in performance in well trained cyclists.

Ric

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OK so now you have me all set at the table, ready to learn, to see what might support this claim...

Now that in essence tells me that it's possible that at some intensity if I eat carbs I'll burn carbs; if I eat fat, I'll burn fat; if I don't eat carbs, I'll burn.... fat?

This seems logical, but it doesn't do anything as far as I can tell to support your claim. I'm still seated here at the table eager to learn.

or in other words, carbs help me sustain a higher workload [because I can more readily convert them to a form my muscles can use].

Ric, did you simply state your opinion above or do you have facts to back up your claim? Mind you I know very little about nutrition, and I'm not saying you are wrong. I'm only pointing out that for this layman in particular you've done nothing to convince me the original post was rubbish.

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i'd support your library and get out a physiology text such as Astrand and Rodahl or McArdle, Katch and Katch

if you don't eat carbs, you'll be glycogen depleted, and thus you'll crawl along at a very low power output (ever 'bonked', had the 'knock', etc.?)

if you want to learn about physiology then get a text out of the library or purchase one. i think relying on myself or 2Lap (the other physiologist here -- apologies if there's more) means you'll only get a few paragraphs etc., i doubt either of us can go into enough depth so that you can truly learn (if that's what you meant)

by training harder (and therefore needing carbs) this increases the respiratory capacity of the muscle. little or no fat is oxidised during very high intensity work. however, this shifts substrate oxidation to fat at lower sub maximal intensities (even though the training for it relies totally or virtually completely on carb oxidation).

ric

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In my post I wrote: "Now that in essence tells me that it's possible that at some intensity if I eat carbs I'll burn carbs; if I eat fat, I'll burn fat; if I don't eat carbs, I'll burn.... fat?"

and you replied:
The original post refered to a lower level of intensity ["long low intensity rides-below 80% of max heart rate/below 70% of power at lactate threshold"]. Again, sorry but as far as I can tell, you're not addressing the question about whether the body could be trained to more efficiently burn fat and why you think it is rubbish.

But then you get us back on track:

OK so if I read that right you just said that fat would indeed be burned, albeit that carbohydrates would be required to bring it about. Did I get that right? It seems to follow that a body with enough carbohydrate to sustain some unspecified power level below 70% would become more reliant on fat burning. Does that follow?

If not then I'm mistaken in the conclusions I'm drawing from this discussion.

But if it does then I am becoming more convinced that it is only your opinion that it is rubbish that the body might be "trained to efficiently use fats". So far I think I've learned that I may be able to burn more fat by working out at low intensity in a somewhat, unspecified as to level, carb-depleted state. So I'm left wondering whether some residual effect might be possible.

Please note that I'm not contending that the body would or could become trained in such a way. I don't know whether it can or not. I'd like to believe it's possible but life isn't fair and it seems that when it comes to fat accumulation and fat loss, life is at it's most unfair and all the decisions go against us.

If it's only your opinion that this theory is rubbish then please tell us that. If it is indeed rubbish then please tell us why this is so.

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I have no science background here, only personal experience with a successful low-carb diet this season. Seems to me that if you stop feeding on hi-glycemic carbs the body will become more efficient at burning fat on low-intensity rides, and would utilize a higher % fat at a given low-effort level. However, it doesn't make sense to me that this is the way to achieve early-season aerobic fitness improvement. Conditioning your metabolism to burn a higher % of fat at a given level of effort wouldn't automatically cause an improvement in maximum aerobic capacity, IMO....just the ability to ride longer at low levels (60-65%) without carbs.

And also from personal experience, training in a carb-deprived state is not a good idea, since that leads to poor performance and recovery in the long run. I noticed a dramatic improvement in recovery by eating the post-ride carbs as Ric and others suggested a few months ago.

Dan

A good point Dan, which should be emphasised. It's all well and good following a low carbohydrate or low glycemic index carb diet, but you absolutely MUST use carbs during training and afterwards to restore glycogen. If you don't you will suffer in future training sessions and fail to reach the power levels you are capable of and need to reach to get a training effect.

After restocking muscle/liver glycogen by ingesting sufficient carbs, you can later return to your preferred diet style.

Ric, thanks.

What you and dnk (in the post below) say makes sense. If I am understanding you correctly fat oxidation is a function of intensity more than a function of blood/muscle glycogen levels. I have from time to time gotten up in the morning not eaten breakfast and gone out for my rides with only water in my bottle. If I had only modest levels of carbs the night before the workouts are almost a waste. I have no edge and concentration suffers. Over extended periods of time with low carb diets I also notice that I am more likely to injure myself. Recently my knees started to ache after inadvertently letting my carb levels drop to low for a week. I suspect that my hamstrings and quads were not recovering from the long rides I was subjecting them to. Both legs felt dead and stiff even with prodigious stretching. The tight musculature , I believe, was causing the knees to (ever so slightly) track in a somehat unnatural path. After a day off and refueling with a carb rich diet and some easy spinning over a tw0 day period everything seems to have returned to normal.

I have a completely torn medial miniscus and these days it doesn't take much to cause problems. I am debating having surgery on the knee (Dr.'s have no strong view one way or the other since they tell me the only option is removal of half the miniscus).

Art

"Fat burns in the fire of carbohydrate". That is basic physiology. The mechanism by which the body burns fat for energy requires some carbohydrate. Without carbohydrate, ie. in a bonked state, your body cannot make good use of fat hardly at all. Check out a physiology textbook and you will learn. What Ric says is true.

As far as burning "fat" for weight loss, the actual statistics for fat use during exercise are extremely de-motivating in this respect. Ric will step in here and correct the figures if I am wrong, but in a decent pace ride buring 600 cals / hr, I believe fat usage would only be 60 grams / hr. Yes, a measily 60 grams of fat usage in 1 hour. Go weep! Of course the only way to lose weight is to exercise to create a calorie deficit then do not replace all the calories, creating a 200-500 cal deficit per day.

The body does seem very efficient at doing work vs [my] ability to eat and store calories....and age doesn't seem to help at all. But, isn't 60 gms of fat worth 540 calories? If so that's 90% of the 600 calories burned in the hour.

For me, watching the carbs and fat intake is every bit as tough as doing the training; especially during the holiday time of year.

Dan




Dan

I think you got me wrong. There isn't anything in this paragraph that I disagree with as far as the physiology goes. It's pretty much phys 101.

Now the part about what Ric says being true, there's where I still don't believe we have an answer as it applies to the original post and Ric's response. See, my question was, and still is, whether it was only Ric's opinion that the the body cannot be trained to use fat more efficiently or whether it is as he states, a fact that it cannot (Actually he said the idea that it could was rubbish, which is about the same thing, no?). To me this question of training a body to do so is a much more advanced question, and it has little or nothing to do with bonking, working out at high intensity, or maintaining a high power output level.

Maybe the question is not so advanced. Maybe the whole idea is rubbish. I don't know. What I do know is the very idea was dismissed without a second thought and to me at least it's too complex an idea to just accept a pat answer without asking "why".

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A great article on exactly what you are asking about. Here's a couple of paragraphs going right to the heart of the matter.

"Endogenous carbohydrate reserves are limited, and muscle and liver glycogen depletion often coincides with fatigue during endurance events and many team sports (2). Consequently, methods that promote fatty acid oxidation and conserve carbohydrate stores might improve exercise capacity. Both endurance training and nutrition strategies are used in pursuit of this goal.

The effects of endurance training on fat metabolism are well documented: it enhances total fatty acid oxidation by increasing intramuscular triglyceride storage and maximal fatty acid flux. These processes conserve endogenous carbohydrate stores and prolong intense exercise."

http://www.physsportsmed.com/issues/...sep/hawley.htm

Thanks David. I think I might have seen this somewhere before, or maybe I've read excerpts somewhere. It looks familiar to me.

I read it from start to finish. The author, Hawley, investigates what happens to fat burning during exercise as a function of diet and ergogenics. Perhaps diet and supplementation are the keys to getting more efficient use of fat stores in exercise. Certainly he posits that nutrition can be used as a tool to steer metabolism towards fat buring. Unfortunately he doesn't delve into any adaptive process, or training effect, that might take place.

It's certainly on the right track though. Thanks for the lead.

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Rics original response was in answer to the original question re-depleting carb stores to enhance/train fat metabolism. If you also read his post again, he does say that fat metabolism is increased with fitness. Not sure where the problem is here
That was not what Ric posted, he posted...
"As you get fitter (measured by e.g., increases of VO2 max, LT) you cover a greater amount of energy via fat oxidation than when you are less fit, when cycling at a given workload."
This infact states that as you get fitter, fat metabolism increases. People usualy get fitter by training and therefore we can reason that training increases fat metabolism!!!!
Not sure what you mean here. Training in a glycogen depleted state is a bad idea due to (1) specificity and (2) training must be done at a low intensity (i.e. low stimulous for adaptation).
I personaly thought Rics post was well rounded and hopefully I have added to his post.

Just so its clear... fat metabolism can be imporved with training, however training in a glycogen depleted state is a bad way to go.

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i'm glad someone found it useful! thanks 2Lap

ric

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