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When is Fasted Cardio Useful for Fat Loss?

Question: I’ve long seen it claimed that cardio has to be done first thing in the morning on an empty stomach (i.e. fasted cardio) for optimal fat loss, is this true?

Answer: This is probably one of the most commonly asked questions which is why it’s worth addressing. It’s worth keeping in mind that this idea usually comes out of the bodybuilding subculture, usually contest bodybuilders who, assuming their diet is working properly, are getting towards the low-end of body fat levels.  And the short-answer to your question is that the body fat of the person is going to be the main determinant of whether doing cardio fasted in the morning is important or not.

How is Bodyfat “Burned”?

To understand that, I need to cover a bit of background physiology, I’d mention that this is discussed in much more detail in both my Ultimate Diet 2.0 and The Stubborn Fat Solution for anybody who is truly interested in the topic.  But simply, there are three primary steps involved in ‘losing’ fat, they are:

  1. Mobilization
  2. Transport
  3. Oxidation (burning)

Mobilization refers to actually getting stored fat (specifically fatty acids) out of the fat cell; this process is under the primary control of insulin and the catecholamines although hormones such as growth hormone, cortisol and others play secondary or tertiary roles.

Transport refers to the actual transport of fatty acids (bound to albumin) within the bloodstream; this step can be an issue when folks are dealing with stubborn body fat (such as lower ab/low back fat in men and hip/thigh fat in women); blood flow is impaired in those areas.

Finally is oxidation which is the actual burning of fatty acids within tissues such as skeletal muscle, liver and heart.

The Impact of Bodyfat Percentage

Now, in lean individuals (where lean is around 12-15% body fat for men and about 19-22% for women), fat mobilization becomes a problem; blood flow is often an issue as well.  As folks get leaner, the body undergoes a series of adaptations that occur to make getting fat out of the fat cells more difficult.

For the most part, oxidation isn’t so much of a problem although there are strategies (such as skeletal muscle glycogen depletion) that can enhance the process; read my Ultimate Diet 2.0 for more details.

At the other extreme, that is in the very obese (here I’m talking about perhaps 35%+ body fat for men and 40%+ for women), the reverse problem is present.  There are tons of fatty acids floating around in the bloodstream, but for a variety of reasons, oxidation has become impaired.  To fully discuss this issue (along with approaches of fixing it) would require a full article an I won’t say much more about this group here.

And between those two extremes (so from about 15-35% body fat in men and ~20-40% body fat in women), there are really no issues.  Mobilization is usually not a problem since the body hasn’t started to fight back, transport isn’t an issue since stubborn fat isn’t being targeted, and oxidation is rarely a problem since the defects which show up at the extremes of obesity generally aren’t present.

When Can Fasted Cardio be Useful?

For the lean trying to get very lean (15% body fat or less for men, 22% or less for women), various strategies, including fasted cardio are probably going to be required to offset the mobilization and blood flow defects.

That’s why that specific group found decades ago that fasted morning cardio worked best.  And why I wrote The Stubborn Fat Solution since it deals with how to overcome all of the problems.

But for folks who aren’t that lean yet, the folks in the middle range of body fat levels, it really doesn’t matter.  The best time to do cardio will be whenever it will most consistently get done.  If that’s first thing in the morning, fantastic.  If not, also fantastic.  It’s more important in this situation that it gets done than when it gets done.

Again, for the extremely obese, different strategies entirely are required but, again that would take a full article to address so I won’t talk about it here.

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35 thoughts on “When is Fasted Cardio Useful for Fat Loss?

  1. And at what intensity?
    speed walking in inclined position on the treadmill for like 30-40 min 2 or 3 times per week after 200mg caffeine is a good way to start??

  2. Ah fuck….Never heard of this before. I really appreciate that. Something I was pondering, too.

  3. Hi Lyle,

    Thanks for the article (literally always appreciated).

    Considering insulin you said is the primary determinant of fat mobilization, would it be fair to say that “fasted” in this sense refers to a time basically 4 or more hours after ingestion of a normal mixed meal, when insulin levels pretty much return to baseline?

    Also, do you know if there would be much, if any, applicable difference between cardio ~4-5 hours after a mixed meal versus cardio after a full overnight fast, or some fast of 7-10 hours?

    Thanks again for the updates and articles.

  4. Adam: It would depend to some degree on the macronutrient content and size of the meal in questions but, for the most part, I have suggested that people do cardio 3-4 hours after a meal IF they are trying to somewhat mimick the morning fasted condition but can’t do it at that time of the day for some reason.

  5. Lyle:
    Thanks for providing this valuable information on this webpage and the support forums.

    A question about BCAA (yet again) and your SFP 2.0.

    Okay, in order not to inhibit fat mobilization/ transportation, we do not want to consume any BCAAs prior to SFP 2.0.

    However, at bf levels <10% muscle catabolism might be a concern under fasting conditions.

    So, would consuming BCAAs during the second phase of the SFP help in preventing muscle catabolism?

  6. “Again, for the extremely obese, different strategies entirely are required but, again that would take a full article to address so I won’t talk about it here.”

    Are you going to do an article on that, I am curious?!!!

  7. What about muscle loss?

  8. does body fat only get mobilized when muscle/liver glycogen gets below a certain level? it would seem there would be no reason to draw on fat stores at all if glycogen is present. or is muscle glycogen only used as an anaerobic fuel? for instance, i’m doing low intensity fasted cardio with 50% glycogen stores—is any of the glycogen being burned?

  9. This is getting stored in my favourites!

    I’m curious about the strategies that the obese might use to improve oxidation. Can’t wait to read that article (assuming it’s coming).

  10. Lyle –

    Great article, as always.

    It’s a shame that more people don’t focus on these 3 issues, rather than the same old calories-in vs. calories-out meme.

  11. RFL dieter benefit from this as well?

    Fasted as in digestion of food or store glycogen, because RFL pretty much means depletion & total digestion of food is mostly protein.

  12. Biggie: Muscle glycogen plays an indirect role in that it affects fuel selection by skeletal muscle. This is the reason I recommend glycogen depletion in UD2, to enhance whole body fat oxidation. Liver glycogen needn’t be depleted for fat mobilization to occur. YOu simply need a lipolytic stimuli.

    T-warrior: What about it?

    Thania: Yes, in the future.

    Matt: BCAA raises insulin.

    Max: Calories in vs. calorie out still matters. There are simply other issues of relevance. nothing I talked about in this article dismisses the realities of thermodynamics or energy balance. But there is also fat balance to consider (e.g. fat intake – oxidation) and the whole issue of calorie partitioning is discussed elsewhere on the site.

  13. Great article. You are no doubt aware of Alan’s usual objections to fasted cardio, summarized here:

    What do you think of his comments here:

    “Further supporting the evidence in favor of fed cardio in trained men, Febbraio’s team investigated the effects of carb ingestion pre & during training in easily one of the best-designed trials on this topic [23]. Subjects exercised for 2 hrs at an intensity level of 63% VO2 max, which is now known as the point of maximal fat oxidation during exercise [1]. Result? Pre & during-training carbs increased performance – and there was no difference in total fat oxidation between the fasted and fed subjects. Despite the elevated insulin levels in the carb-fueled groups, there was no difference in fat availability or fat utilization.”

    There are apparently quite a few studies that show that performance ability is enhanced when cardio workouts are fed, thus leading to a greater energy expenditure. The benefit of the enhanced mobilization, in your view, outweighs this benefit…?

    Also, the stuff in the above quote about fat oxidation you already dealt with, but I’m not sure if the term “fat utilization” at the end refers to mobilization as well? It seems as though Alan is suggesting that these studies had not hinted at greater fat mobilization during fasted cardio as well.

  14. But what is the physiological mechanism that would explain why fasted cardio would be better than say having a small meal prior. It doesn’t seem likely that it would effect the blood flow issue. Is it glycogen depletion (which you briefly mentioned)? Shouldn’t you also factor in the fact that one can probably do less fasted cardio than non-fasted for the simple reason that you run out of energy faster if you’re fasted?

  15. Lyle:
    1) What’s the lowest and highest percentage of MHR for low intensity steady state cardio?
    2) What’s the percentage of MHR that’s at lactate threshold level?
    3) Low intensity steady state cardio can be done daily, how about moderate intensity steady state cardio?

    Thank you.

  16. First quick question : will ingestion of pure citrulline malate (a dose being about 4-6 g) before fasted cardio affect insulin levels, and thereby affecting lipolysis negatively?
    Second question (even quicker): in a fasted state, will ingestion of creatine affect insulin and thereby lipolysis?

  17. Kenny: I have no idea what you’re asking but eating anything will raise insulin.

    Raidho: No and no, in that order.

    1. I’d keep it at the low end of things, 60-70% max.
    2. Depends on the individual and there’s no single answer.

    Mike: 63% VO2 is about 75% max heart rate (so figure 150 for a max of 200), which is higher than most would do low intensity cardio at (see response to Travis directly above). As I recall from Alan’s literature review, at lower intensities, pre-workout food/carbs have different effects.

    And I’m not talking about performance here, that’s a different issue.

  18. Lyle, I’m asking is their muscle loss? Layne Norton is against against fasted cardio because of this reason.

    ALSO, what about taking BCAAs prior to your fasted cardio? It’s zero cal and could help revent muscle loss. This is what Martin of does.

  19. Interesting article. With respect to fat mobilization, would niacin help since it causes blood vessel dilation?

  20. Niacin exerts a rather large acute blunting of FFA mobilization, this is part of how it improves blood lipid levels. So the short answer is no. However, there is a later time point a big FFA rebound when the niacin clears, I don’t recall the time frame offhand. At one point I had the bright idea of trying to harness this, took a big dose of niacin like 90 minutes before cardio.

    Here’s the problem: niacin is known for causing a massive histamine flush. That itching tingling scrape your skin off feeling. That’s what happened. So while it was an interesting idea, I consider it unusable. Or at least intolerable.

    Various approaches (dietary and otherwise) for improving blood flow are discussed in detail in The Stubborn Fat solution.

  21. ” niacin is known for causing a massive histamine flush. That itching tingling scrape your skin off feeling. That’s what happened. So while it was an interesting idea, I consider it unusable. Or at least intolerable.”

    Are we talking worse/different than that experienced by beta-alanine? I must say the first time I took about 3g of beta-alanine on an empty stocmach I felt truly freaked out. Such a uniquely uncomfortable skin sensation. But then it feels soothing to stretch the skin after about 5 mins of agony!

  22. Having never taken that much beta-alanine at once (there’s no point), I can’t tell you. But it’s the same mechanism and really unpleasant.

  23. Question about optimal fat oxidation during exercise. Let’s start by saying a person has fasted overnight, but then has a small 200 kcal meal 1 hr before exercise, and muscle glycogen stores are high.

    The subject has 1.5 hrs to exercise. What is the optimal routine to mobilize/transport/oxidize body fat? Would a constant 75% max heart rate be best, or what about intense training during the first 30-45 minutes to deplete glycogen and mobilize fatty acids, then lower intensity to oxidize them?

  24. I’m a big believer in morning cardio. Not only has it enabled me to shed a lot of fat in a short amount of time, it’s provided me with a number of other benefits as well. On the days that I do morning cardio, my overall mood is better, I have an easier time concentrating at work, I’m in a healthier mindset for the rest of the day which makes eating healthy easier, and if something comes up in the evening that prevents me from working out or I want to do weights or intervals, I know that I at least got some cardio in for the day. A lot of people, like the intervals-only crowd, say morning cardio will cause you to lose muscle. I didn’t experience that, probably cause I kept careful tabs on my diet. I realize that a lot of people can’t do morning cardio and I agree that isn’t necessary for most people. But if you can and if you make sure to take in enough calories, I think you’ll find the fat will just melt right off and you won’t end up looking like a marathoner.

  25. Im a huge fan of training on an empty stomach when it comes to fat-loss.
    Ive used both fasted and non-fasted techniques and have found eating anything before a workout has provided little more than an upset stomach (even with an hour window).

  26. This tends to be an individual thing, some need an empty stomach to train effectively, I’ve seen others who could eat a big meal and have no problems. A lot of it is individual variance and there is also the aspect of what is being done in the gym (e.g. low vs. high reps). There is also some indication that you can ‘train the gut’ to handle more nutrients before or during workout simply by doing it.

  27. Lyle I was just wondering how long after a meal does it take to be in the fasted state?

  28. Lyle, you amaze me the way you answer so many specific questions! You deserve a sainthood.

    This is the best answer to the question i’ve heard. And it makes sense. Getting really lean is a journey, and I have found it’s an individual thing. Maybe like pregnancy – there are common things, but everyone’s different. And the same women can have different experiences with consecutive pregnancies. I think it can be the same with successive times of getting lean.

    This is off the subject, but the different stage of body fat can also be difficult in terms of appearance. Sometimes you can look or feel better at a slightly higher body fat. I think of it as a something filled with air deflating. Things can sometimes look worse before they look better. And I’m sure some people lose different proportions of visceral fat/ subcutaneous fat than other people, and that can make things look different too.

    Very impressed.

  29. Thank you so much for this. I have been working on getting very lean for 5 years now following the usual advice only to find that fasted morning cardio does the trick only to be told I shouldn’t be doing it! Now I know why this works for me I can move forward.

  30. Hello great article but very frustrating for the very obese you refer to also qould like some direction… why are we always ignored. I respect thin people have their own (sometimes laughable weight loss issues) but they get like 99% of the attention while the rest of us sweat as much and get nothing. I want everyone to have the body they need but sh*t can we get some love too? the one sentence we got is “I’m not going there” sigh…. such a tease! at least one or two cardio techniques to target our issues. you are one of only two blogs I’ve seen to mention the reduced blood flow so I’m very intrigued.. please do a part 2. JUST FOR US!

  31. great article man! right now at 12 BM. not looking to get very ripped. but that being said. I would love to get down to 11-12%. I do a morning 20min swim and drink green-tea before so that i remain hydrated. I have a mixed green smothie with whey for breafast and have a huge meal at (i undereat fruit and nuts before and after) 5ish, then ggym/ yoga at 7 for another 20, i feel that this ‘regimen’ works really well for me! but will it get me to 12% destination. also ow long will it take?

  32. Lyle,

    This article makes sense to me. In the morning I will find myself in a state of glycogen depletion. Thus, if I am an individual at 10% BF and want to get even leaner still, it makes sense I do some fasted cardio as my body will find fat as it’s primary source of energy in that state. I’m talking about an hour on a spin bike at a moderate intensity, not looking necessarily for a “quality workout.”

    If I am looking to hit certain numbers and want to have a really good quality workout session, I would consider ingesting some a small meal before, as my focus here would not be to lose fat.

    However, I ran into this article which, as you can see, has a different point of view.

    Any thoughts?

  33. T-nation is full of stupid. The amount of protein even potentially lost during a typical morning cardio fasted session of any sort is utterly irrelevant. Most of any amino acids oxidized from from the free pool anyhow. It’s not even muscle breakdown.

  34. Hi Lyle-
    thanks for this great information.
    can i ask, do you think there would be a significant difference between the effectiveness of fully fasted cardio, ie nothing ingested in morning at all, versus cardio with a cup of coffee with artifiical sweetner and about 1/4 a cup of unsweetened soy milk (say 20 cal, 1 g fat, less than 1 g carb, 2 g protein)?
    and, i guess to better fully understand this:
    1) i would imagine the main issue in the fat mobilization issue is, as you have been saying, insulin, so the answer to the question depends on how much insulin this drink (caffeine, artificial sweetener, very small amount of food) triggers?
    2) do you know or have a thought on whether the better fat mobilization in fasted cardio is something that is discrete, ie you are either fully fasted with no insulin or you are non-fasted with some insulin; or is it an issue of degrees, ie the more fasted you are / the less insulin in your bloodstream the more fat-mobilization you will benefit from during cardio?

    i will probably continue my little sweetened coffee cause i like it in the morning, but just curious if the effect of the little coffee is gradual and just 20 calories worth of an effect, or if it will in a discrete manner kick me out of the optimal fat-mobilization state you describe.
    hope i have understood this right. thank you!!

  35. Fasted means fasted and you’ll live by taking your coffee black.

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