Losing weight, specifically fat, is a struggle for most. This article is about what I believe is the most effective cardiovascular method for shedding fat fast and retaining muscle.
People get too caught up in how many calories they burned, how long their cardio session was, and how much they sweated during a workout. Sorry, but that is only half the equation. Much of the recent research regarding mTOR and its anabolic processes as well as the interplay between AMPK and mTOR have become available in the last few years. These two pathways, and the cycle they follow, are key in understanding the way our bodies build muscle and lose fat.
In terms of losing the most fat and retaining muscle, I believe that high intensity training (HIT) is the most effective cardio you can use. This is amplified when done in a fasted state (I’ll explain). I’m not saying that “aerobic steady state” cardio can’t work. It’s just less effective, more time consuming, and more catabolic. HIT is much more intense. While some might not be able to perform it, it’s the preferred choice if fat loss is the goal. Looking strictly at the energy systems helps, but different exercises can produce unique and profound hormonal responses, some transient and some noteworthy. So here are some of the benefits.
HIT causes a severe increase in AMP-activated protein kinase (AMPK), and this is the key response. Fasting also increases AMPK, which helps to explain why it’s so effective in decreasing fat and increasing insulin sensitivity. This is also why I recommend fasted HIT cardio for fast fat loss. AMPK is often referred to as the “master metabolic switch/regulator.” In laymen’s terms, when you’re quickly running out of fuel, AMPK is activated and drives catabolic processes while inhibiting anabolic processes. It sounds bad but bear with me.
This is where some may argue that they want to avoid AMPK because it’s “catabolic” and can inhibit mTOR, an important pathway for anabolism or muscle building. That is true. AMPK is transiently catabolic, but with HIT, we’re looking for AMPK activation for a controlled amount of time, not continuous. AMPK will be inhibited as soon as we eat a meal and the AMP:ATP ratio of available fuel is raised or returned to normal.
Too much of a good thing is bad for either side. A chronic over expression of mTOR, though “anabolic,” can be detrimental. mTOR aids in the inhibition of certain hormones like hormone-sensitive lipase (HSL), which impairs the body’s ability to break down stored triglycerides. So the “perma-bulkers” can now understand why they’re always fat and have a hard time losing this fat. They’re constantly force feeding themselves and are experiencing an over expression of mTOR.
So when we activate AMPK, the body increases fat oxidation instead of glucose, thereby preventing muscle catabolism. It improves insulin sensitivity by increasing glucose uptake and inhibiting glycogen storage. During HIT, the body shifts to using fat for fuel instead of glucose. Whenever muscles contract, energy is provided through ATP. When ATP is used up faster than it can replenish itself, the AMP/ATP ratio increases and AMPK is activated. The body will sense that energy is being used faster than it can supply it, so metabolic changes will occur. If this didn’t happen, we would run out of energy and die. But this is when AMPK is activated and shifts the body from glycolysis to fat oxidation. This continues long after exercise, so it explains why AMPK has long-lasting effects on fat consumption. Low intensity exercises don’t activate AMPK to the same extent and use mainly glycolysis for fuel. Therefore, the results are slower and less effective.
I’m not saying that aerobic exercise doesn’t have its place, but in terms of fat loss, it’s less effective. According to a report by The Journal of Obesity in their study “High Intensity Intermittent Exercise and Fat Loss,” they concluded that “the effect of regular aerobic exercise on body fat is negligible.”
There is a natural rhythm or balance between AMPK and mTOR. Think of the interaction like a metronome or a pendulum. We constantly shift between the two. During times of glucose deprivation, fasting, or HIT cardio, AMPK is activated and puts us in a prime position to burn fat by using our stored energy as fuel. On the other end of the spectrum, when mTOR is activated by, say, overeating or lifting, we’re primed for cell growth and protein synthesis. This is why fasting is such a useful tool in dieting because it plays off this interaction.
Another important aspect in the HIT versus low intensity steady state (LISS) is HIT’s ability to generate a profound increase in catecholamine production. In a study observing individuals who ran twenty-second wind gate sprints, the catecholamine response was shown to be significantly elevated in both the men and women after exercise. The catecholamines, epinephrine and norepinephrine, were notably raised and are effective in fat burning. Epinephrine has been shown to drive lipolysis, the breakdown of fat for energy, and plays a role in fat release from subcutaneous and intramuscular fat stores.
So the net result of HIT is faster fat loss and increased muscle, as AMPK increases glucose uptake in the liver and muscle tissue, increases fatty acid oxidation, and reduces glucose and fatty acid synthesis. The problem is that it’s slightly harder to perform than slow steady pace cardio and it’s very stressful to the central nervous system.
It may seem like you can’t lose fat and gain muscle technically at the exact same time, but that doesn’t mean that you can’t over the course of a diet. It is possible. I’ve had clients lose body fat and increase lean tissue over the course of a diet. It’s not possible if you’re looking for an excuse to stuff your fat ass with Krispy Kremes hoping to gain twenty pounds and magically develop abdominals at the same time by adding cardio. You need to maximize fat loss during times where AMPK is elevated. This is why fasted HIT cardio is effective. You should also try to maximize anabolism during times of mTOR expression. This is why I like to focus certain days on either fat loss or muscle gain, sometimes even during certain periods of the day. If you’re careful and detailed in your approach, you can achieve your body composition goals at the same time.
John Meadows — NOT the legs of a marathon runner
Here’s a sample. During AMPK stimulation, a fat loss day might start like this:
- Water and black coffee plus leucine (your choice here)
- HIT cardio (8–10 sprints of 20 seconds max effort or 10–15 minutes where the first 40 seconds are moderate and the last 20 seconds are maximal sprints)
- You can add more leucine here or not; it does generate an insulin response, but it’s your choice.
- Fast until 12:00 p.m. or 1:00 p.m. (depending on how you feel as well as on how much you ate the night before)
- Light pre-workout meal with protein, leucine, and a higher GI carb source
- Intra-workout (I prefer a drink with leucine, glycine, beta-alanine, and citrulline malate.)
- Post-workout (This is when you shift from fat loss to muscle gain. From here out, I have 2–3 quite large protein and low to moderate GI meals, though you can get away with some higher GI carbs in the first meal post-workout as well. If maximum fat loss is your goal, start with a post-workout shake with leucine plus whey and go zero carb for an extra 1–2 hours.)
In closing, stop holding back your own progress by thinking that you need to exclusively bulk or cut. Find a diet and exercise program that works for you and use a well thought out plan to achieve your goal. Throw in some fasts, use some HIT cardio, lift with intensity, and let the rest play out.
Here are some studies that echo this information. Check it out and then make the decision for yourself:
- http://www.ncbi.nlm.nih.gov/pubmed/8028502
- “High intensity intermittent exercise and fat loss”
- “Just HIT it! A time-efficient exercise strategy to improve muscle insulin sensitivity”
- “Metabolic adaptations to short-term, high-intensity interval training: A little pain for a lot of gain?”
References
- Bolster DR (2002) AMP-activated protein kinase suppresses protein synthesis in rat skeletal muscle through down-regulated mammalian target of rapomyacin (mTOR) signaling. J Biol Chem 277:23977–980.
- Minokoshi Y, et. al. (2004) AMP-kinase regulates food intake by responding to hormonal and nutrient signals in the hypothalamus. Nature 428:569–74.
- Saks VA (2007) Molecular System Bioenergetics: Energy for Life. Weinheim: Wiley-VCH.
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Fred Duncan is a Doctor of Chiropractic graduate student and Personal Trainer/Nutrition consultant/Performance coach at the New York Sports Center. He specializes in weight loss/muscle gain and body recomposition. He is a former division 1 athlete and has since worked extensively under strength and conditioning coach Buddy Morris. You can access more information from his website: www.NYScenter.com 
thanks for the article, good stuff.
interesting topic, good thoughts based on science.
Looks a lot like CBL.
What about those of us that use the 8 hour feeding window,ie IF? I train first thing in the morning due to schedule. I cannot start my eating until noon. Is this hurting my training not eating for six hours post workout?
as a natural bodybuilder preparing for a contest would you have any weekly templates or at least just a 1 week sample template to work off of as I set up this plan for fat loss, thanks!
Brandon: Thanks for reading the article. It may sound familiar to CBL but I assure you it’s not. I don’t agree with everything in cbl, especially being able to eat pizza and ice cream every night and get lean. If it works for someone, I’m happy and jealous of them, but for most it doesn’t work that way. CBL is a daily thing, I think that you only need to perform the layout I posted a couple times a week to get the benefit of fat loss. I don’t propose doing it every single day, it’s more about trying to change the way we view gaining muscle and losing fat. By maximizing times of AMPK and mTOR expression we can try to recomp the body more efficiently.
Jay: Thanks for reading. I actually just finished another article for elite where I discuss Peri-workout nutrition and give options for those who fast. I’m not opposed to fasted training but I’m not sure that I agree with nothing pre-workout and then nothing post-workout for 6 hours. I save fasted lifting for restorative or light days because I’ve found that fasted lifting can effect peak strength. I think just some whey (20-30g) and leucine before your lift would allow you to have a more productive lift and then you can wait 6 hours until your meal because pre-workout protein can actually be MORE beneficial than post-workout protein alone. But if the current formula has been working for you then there’s no reason to mess with it. There’s some contradicting research on the “anabolic window” and what is needed and when, I tackle that in the next article.
Fred thanks for your article. I found it very informational.
Thanks for the article — it was a good read. I followed up the discussion on eliteFTS fb page.
Marc: Thanks for the question. Setting this up for a week would depend on where you currently are in terms of leanness and where you are trying to be. So some examples might be: If you lift every other day you could do this type of set up on each off day or restorative day. Or you could start by implementing this twice a week and track progress. You wouldn’t want to start off by doing it every single day because then after a while what’s next? If you start with 2 times a week you can then bump to 3 if fat loss stalls a bit. Now the diet layout could be done everyday, but as I think we all know sprinting is pretty taxing and stressful for the central nervous system so It would be hard to perform HIT every single day. You can still perform aerobic steady state cardio while fasted on some of the days. So, again it’s hard to tell without seeing you, but I’d star with this 2-3 times a week. My next article on here will discuss fasted weight lifting a bit too which I think would be useful for you as well. Not everyday but in a planned manner.
I see how this info applies to athletes that already have a strong training base. How would you start someone on a program like this that has no significant training base, i.e. sprints are out of the question, and is heavily overweight? Will this program be as effective without supplements such as leucine? Thanks for the article!
Seth: Thanks for reading. Sprints in terms of maximal sprints on a track may be out of the question, I agree. But the other option can be done on any piece of cardio equipment, so let’s use a recumbent bike for example. The person can ride the first 40 seconds at a very light/moderate pace and then the last 15-20 seconds go as fast as they can. They can start with 5-10 minutes of this interval training and maybe work up to 15-20. In my opinion with all that we know about lecuine and it’s effects on muscle protein synthesis it should be used by everyone regardless of goals. In my upcoming article I dig a little deeper into the benefits of lecuine and how it is even superior to bcaa’s. So I feel that this program can still apply to the out of shape person, though you are right that it is tailored a bit more for someone with a base. I think fasted cardio and fasting can be beneficial for everyone, out of shape or in shape.
As a female Figure Competitor I have tried this every other day via Fred’s advice and was amazed at the results- Much better than the traditional routes of counting calories & cutting carbs!!!
Dr Duncan,
This is great info. I have used HIIT in the past to really knock down my BF%. My question is about timing. I have two windows to train: Before 7am or after 7pm. How would you you modify the nutrient timing protocol if training occurs 12+ hrs after morning HIIT?
Hey Fred Duncan. I loved this article, I am a huge fan of sprinting. I was curious what your thoughts were on Lyle McDonalds 3-part article about interval training vs steady state cardio though? http://www.bodyrecomposition.com/fat-loss/steady-state-and-interval-training-part-1.html
Evan: Thanks for the comments. I do believe I read his article in the past. If I remember correctly he posts positives and negatives for both. I tend to agree that both can have use, depending on the situation. In terms of using more fat for fuel I think he agrees that HIT is preferred. It is very demanding and can’t be performed every single day. I don’t want people to get the wrong impression with this article and think that I only advise intervals or sprints. Aerobic work most definitely has its place and can be used. As I briefly mentioned I tend to have certain days or parts of the week where I focus on fat loss and then other days where maximizing recovery and muscle gain is the focus. I also think it’s important for people to remember that nutrition or training is specific to the individual. But in terms of losing fat fast, I believe this to be the fastest way. I’ve actually done intervals up to 4-5 times a week and it was very difficult and taxing. You should be able to program them in so that you can reap their benefits but also recover from them optimally. If this means doing intervals twice a week and then adding some aerobic work on the other days, that can work too. I know the HIT vs LISS debate will always continue because you will always find people who prefer one to the other.
Kristof: Thanks for reading! I just finished part 1 of my Peri-workout nutrition article for Elite so it should be up at some point, it may be of some interest to you. I discuss pre, intra, post workout nutrition options. Depending on your goals there’s a couple different routes you can go. For fat loss you have a few options. One might be to perform your cardio fasted (with or without leucine) and pulse leucine afterwards until you feel as though you need your next meal. I don’t like saying exactly when to eat like, you must eat at 1pm, etc. If you are dying by 12 then eat, if you feel ok going until 2 then so be it. But 1 seems to be popular because of LeanGains so let’s use it as an example. At 1 you could stay carbless (protein + fat meals only) up until your pre-workout meal where you would then would have a fast acting protein and hi/med gi carb for your lift. The post workout could then be the same as outlined above. You could also start carbing up for your lift when you decide to break the fast with protein/low GI carb meals. In that case if fat loss was still the goal you would then alter the post workout feeding. Stay tuned for the next article for a lot more detail on this.
Nice article. Good read and good advice.
Very minor point, but why are you taking beta-alanine intra workout? Or indeed anywhere near training?
Cheers
I train fasted (water and coffee) in the AM. Could I follow this same protocol for fatloss and use sprints after training? Or would it be better to do this on nontraining days? Thanks!
Ian: Thanks for the question. I get a bit more in depth on the intra-workout choices in my next article for Elite. But in short the alanine is part of the intra-workout drink which plays a role in cellular hydration. During exercise cell volume decreases and certain things then happen (increase in muscle protein breakdown, increase in the removal of glutamine and alanine from the muscle, decrease in glycogen synthesis, etc). So the drink is meant to keep cell volume increased to reap the benefits of proper cell hydration (dec in protein breakdown, inc in protein synthesis, etc.) I have played around with pre and intra drinks for a while and this is what I have found works.
Great article Fred. Well written and science backed. You just convinced me to give this a shot and I look forward to your next article.
GG: Thanks for the question. If you still feel up to it after fasted lifting then I suppose you can give it a go. I would hope you are having some lecuine somewhere in the mix. But it’s also important that you gauge how you feel and how you are recovering from this. If you find that it’s too draining (which you very well may) then switch it to your off days or “lighter” days. Sprints don’t need to be done every single day, I feel as though their powerful fat burning effects can allow you to use them less frequently with good results. I think you might be better off doing it on off days but you won’t know until you try so start with 1-2 times a week after your lift and see how it goes.
Jeff: Thanks for the kind words. I hope this is something that you can find useful as a fat burning tool in your arsenal!
Thanks for the reply Fred. Off course beta-alanine is not alanine and is not invloived in same metabolic pathways. I have never heard of beta-alanine being invloved in cell volume. However you always ‘live and learn’ and look foward to your article reg intra wo drinks. I have to admit I have yet to be convinced on its importance for most trainees though :)
Cheers
Would some coconut oil and cream in the coffee before the sprints be detrimental?