Seven Signs of Fat-Burning

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These simple tips will help you assess if you are burning more fat for fuel.

As fuels for daily activities —including physical exercise — humans burn both sugar and fat, along with small quantities of protein and varying amounts of ketone bodies. In general, those with better metabolisms rely more on fat for energy, leading to improved health and fitness, including athletic performance.

Many people focus on their weight, and thus look to the scale for guidance. However, a person’s percentage of body fat is more important than total weight. This is why the scale is misleading — fat doesn’t weigh much but takes up much more space than lean body mass, such as muscle, which weighs much more.

Even more important than determining a percentage of body fat is measuring the body’s ability to burn fat.

The best way to evaluate your metabolism, especially whether you are burning more body fat and less sugar, is to be tested. While it’s becoming easier than ever to find a facility that performs metabolic testing, where fat- and sugar-burning are measured at various heart rates, the fact is, most people will not be properly tested. This includes performing the test with some regularity to monitor progress.

However, various signs and symptoms can provide a very good idea of whether we’re burning sufficient body fat. Our bodies are always signaling us about many aspects of health and fitness, and fat-burning is one of them. Here are seven common indications:

  • Clothes fitting more loosely, especially around the waist.
  • People start asking you if you’re losing weight. They often notice it in your face first, and sometimes in other places. Likewise, people may ask if you’re lifting more weights — even a slight reduction in body fat leads to more muscle definition.
  • Improved performance — increased physical energy leads to less fatigue, and more mental energy, improving creativity and reducing feelings of depression.
  • Training and racing also improves. This can also be measured by the MAF Test.
  • Increased exercise duration without the need for food intake.
  • Reduced cravings for sweets and hunger. Freedom from sugar addiction.
  • Improved health — a variety of factors related to reduced fat-burning can raise disease risk. These include increased blood fats (especially triglycerides and LDL cholesterol), blood pressure, inflammatory-related conditions, and a variety of other related conditions discussed in the white paper, Carbohydrate Intolerance.

The single common denominator that triggers the most fat-burning is the  elimination of refined carbohydrates. But training in your individualized fat-burning zone as determined by the 180 Formula also optimizes your fat-burning system. Other tips for increasing your body’s ability to use fat as fuel can be found elsewhere on this website.

Increasing your body’s fat-burning abilities is a key to improving health as well as overall human performance. Monitoring your fat-burning metabolism using these simple methods can be a key to keeping yourself on the right track.

Join the discussion 27 Comments

  • Rachel Fischer, MD, MPH says:

    It seems what often works for men, does not work for women. Specifically, I’m thinking of female athletes and lower carb/higher fat food plans. Seems a very tricky balance with complex hormones involved!

  • DR. SUNIL RAI says:

    I am a staunch follower of MAF . I strictly carry HRM while running. But I have few queries.(1). what should I do when heart rate goes beyond max aerobic heart rate? I am 51 year old with MAF kept at 130-113. I am injury free since last two years. should I increase MAF to 135? though I feel comfortable some times with 135 HR.

    • Dr. Sunil Rai:

      When your heart rate goes above MAF, it’s best to simply slow down your speed until it returns to MAF or slightly below. Once you become experienced at this, you’ll get to know the speed/effort at which you usually stay below MAF. Generally speaking, unless you are also improving in your race times, do not add 5 BPM to MAF. In any case, it’s best to err on the low end: running 8 BPM below MAF will barely reduce your training response, but running 5 BPM above may make it so that your body responds to the training in a very different way.

  • Jodi Maurici says:

    I have been following the MAF method for over a year now as a result of damaging myself in multiple ways from OTS. My body fat percent is still increasing with a stellar fitness plan and a totally clean diet of lean protein, veggies and low on the healthy carbs. Do you have any research on how I can turn body to burning fat again? Before the OTS, I was 12% body fat and less than a year later I am 20%. Thanks so much.

    • Jodi:

      Let me begin by asking: are you male or female? (I’d rather not assume).

      The reason I ask is because 20% is on the high end for women athletes, but only slightly high for a sedentary man. Whenever you are overtrained, your body has to bounce back to normal before it can start building itself up towards being an athletic body. The best way to restore fat-burning is to eat a low-glycemic diet (in both glycemic index and glycemic load), and to engage in low-intensity training. In other words, being good at burning fats is very basic, and very simple to do. For example, check out this Outside Magazine article on the fat-burning effects of thru-hiking.

      But in OTS, the body becomes hurt in a very similar way in which a bone becomes broken. One cannot just ask the arm to keep its muscle mass and functionality while the bone heals. It’ll become far thinner for the duration of the process. Similarly, the athletic capabilities of the aerobic system won’t even have an opportunity to begin to be restored up until the point where the basic health of the aerobic system is also restored. (It’s not uncommon for someone to take a year or more to heal from a moderate case of overtraining).

      In summary, once the aerobic system fully heals and its capabilities (including fat-burning) begin expanding again, you can expect to see your fat begin to return to athlete levels.

      • “…totally clean diet of lean protein, veggies and low on the healthy carbs.”

        Maybe not enough fat in the diet. The “lean protein” is always a potential clue.

        Just a thought.

        • Jerry:

          Could be. I need more information (sex being the main one) to make a hypothesis on that. If you don’t have a lot of carbs in the diet, you’re unlikely to gain fat mass like that. You’re more likely to lose fat mass and—in extreme cases—become chronically ill because of it. But that doesn’t strike me as being the case with Jodi. I put my money on the fact that Jodi is recovering from OTS, (and has a body and aerobic base that are still healing and haven’t gotten any kind of strong yet).

          • Completely agree. It’s just been my experience (mainly anecdotal and nowhere near as extensive as yours) that “lean protein” is another way of saying fat-phobic.

            I’ve found some people who intellectually are on board with low-carb/paleo/real food/etc. still have a strong aversion to embracing “high fat.” As a result, they’re either over consuming “healthy” carbs, or are in a caloric deficit relative to their body’s needs and are depressing their metabolism.

            I’d also be interested in the composition of what Jodi describes as a stellar fitness plan. The word “stellar” is what has me curious, as opposed to “relaxed,” “balanced,” “rejuvenating,” or something that indicated (at least a temporary) major cutback in volume.

            Mentally, someone who was used to a regimen that led to OTS may have an extremely hard time downshifting enough for healing. There’s a general theme in comments threads on this site on how hard it is for people to slow down enough to stay in the MAF zone. If you’ve got a damaged system from OTS, I doubt embracing the MAF method will mean healing if you’re still doing 80 miles a week or are on the road or in the gym 6 days a week.

            Cheers

  • Grant says:

    Hi Ivan,

    Really interesting article!

    It does raise a question for me. If MAF HR correlates nicely with an RQ (RER) of 0.85 the crossover point.

    Then the athlete is in the article who is 35 years old should have a MAF HR of 145. From the metabolic efficiency testing and data in the article this lines up fairly well (Before data). 145HR = 52% fat and 48% carbs or 153HR being 0.85 (50/50).

    As they completed the month of walking / trekking their aerobic engine developed superbly. Upon retesting they now had a HR of 168 at an RQ of 0.85. If 0.85 correlates with MAF this HR value is now well outside of range of the MAF formula. E.g. 23 beats per minute greater than 145 (even if we gave the athlete an extra 5) this would still be 18 beats above MAF HR.

    So my question is as you improve in your ability to burn fat (greater aerobic engine / dietary changes etc) this appears to impact where the aerobic threshold sits. Hence for best aerobic development you suggest training around 10 beats below and up to MAF HR. However it would appear that the greatest aerobic training would now sit at a HR of 168 or within 10 beats (158-168).

    I know MAF formula is just that and does not substitute for actual metabolic testing and determining an exact RQ. However how does it compensate or how do you factor in that as you become a better and better fat burner that your MAF HR might not actually be eliciting the best training effect anymore. E.g. this athlete would now be better served now training closer to their new RQ of 0.85 (168bpm).

    Obviosuly their MAF tests would continue to improve at 145 as they are now burning 70% fat at 145HR, but they would start to see a plateau and might supplement say 2 week blocks of intensity / strength before returning to MAF. However it could be that they would actually just benefit from training some more at a 0.85 RQ still aerobic right?

    As an athlete improves how do you handle this? Let’s assume we are not all going to go get metabolic testing.

    Cheers

    • Grant:

      The MAF HR tends to correlate with the crossover point with less aerobically fit athletes. As you become more aerobically fit, the MAF HR occurs at 65,75,85% fat-burning.

      The crossover point has no real physiological significance. It’s just a nice thing that we humans use because we like to split things neatly into halves. What matters is whether or not there is anaerobic function—no anaerobic function is the important part (which is why we also refer to it as the aerobic threshold).

      So, what you see is this: let’s say that 2 athletes are burning 10 units of sugar per minute at the aerobic threshold. And one of them is a bad fat-burner, who is burning 10 units of fat per minute. So this person is burning 50-50 at the aerobic threshold. But the second athlete is burning 30 units of fat at the aerobic threshold, so they’re burning 75% fats, 25% sugars. So the second athlete is burning 40 total units of fuel, while the first athlete is burning 20.

      The reason the aerobic threshold doesn’t climb along with the crossover point is because increased sugar-burning takes you towards anaerobic function. So if either of those athletes were to start burning 12 units of sugar, and then 15, and then 18, both athletes would burn that sugar anaerobically. Why? Because the hormone that ramps up sugar utilization (insulin) suppresses fat utilization. So you can’t really ramp up sugar utilization and not start exceeding the aerobic threshold. So what you see is that aerobically very fit athletes tend to hit their crossover point not a few beats above what the 180-formula would predict is the aerobic threshold, but actually quite close to their maximum heart rate (sometimes well beyond their anaerobic threshold).

      So by the time these powerful aerobic athletes hit 50% fat/50% sugar, they have a massive amount of anaerobic activity: lactate is already rapidly accumulating even beyond the maximum lactate steady state (MLSS), and they’re getting all the kinds of stresses on their body that you would see with 20% fat:80% sugar in an aerobically weak athlete.

      • Grant says:

        Thanks Ivan that is really helpful and well explained.

        However how do you then measure the point of primarily becoming anaerobic if not from RQ. I believe I have read other comments on other articles which referenced the 0.85 crossover point as the measure of switching to largely anaerobic. However as you state some aerobically fit athletes only hit their cross over much higher. Such as the example in the article where a 168 HR is now and RQ of 0.85.

        So if you wanted to actually validate the MAF formula to determine the exact point I ramped up sugar burning and became primarily anaerobic how would I do so if metabolic testing and an RQ of 0.85 does not demonstrate this. Lactate testing? I believe I have read Phil does not think it of much value.

        Also when we say 75% fat and 25% sugar vs 50% fat and 50% sugar the fat units are significantly more calorie dense (37kj per gram). So if we say an athlete now burns 75% fat and 25% sugar, the sugar grams would actually be 2.3125 times more than the grams of fat contributing to the energy output. As 1 gram of sugar is 16kj and 1 gram of fat is 37kj. So 50% fat equates to less grams of fat than 50% sugar. Is this correct?

        • Grant:

          Fat max. What laboratories do is calculate the point at which you reach the maximum rate of fat-burning (fatmax) by correlating your level of caloric expenditure, power output, and RER/RQ. You can also find fat max through lactate testing—of a different sort—by figuring out the point just below when blood lactate begins to rise.

          That’s right. So the fat utilization curves don’t symbolize the weight of the fuel you’re utilizing, but rather the amount of energy expenditure attributed to each fuel source. Imagine a hybrid submarine that uses both nuclear and diesel fuel. You could be going at 99% nuclear and 1% diesel, but if you discuss that same fuel utilization by weight, you might be saying that the sub is being fueled 85% by diesel and 15% by nuclear. So any ratios of fuel utilization that you see have to do with the caloric output from each of those fuel sources, rather than the weight.

  • James says:

    Go to most endurance races these days and there is a lot of overfat athletes who put in good performances. Is this due to them being anaerobically efficient and aerobically deficient? Then you have the opposite end of the spectrum – people who are lean yet not aerobically fit – they would drift up above MAHR at even the slowest of jogs.

    • James:

      Yes. Part of being anaerobically powerful is that you can push yourself very hard—the body’s “emergency systems” are overdeveloped, so you can push yourself beyond the brink of injury and illness habitually.

  • Slomoshun says:

    At age 60 after a not very active working life I took up cycling and was advised when purchasing the bike to use the Maffetone method. Train with MAF HR and reduce carbs to 100-125 grams/day and eliminate sugar. Took a while but slowly the monthly MAF test improved cycling got easier and weight dropped 40 pounds so swimming and running were added and small triathlons were entered. This year though I took 4 months off to travel in UK and Europe so now it is back to start again at age 65. My MAF HR max. is 115 . I am injury free and no medications. It is undulating where I live and the 50km course I use has a few short hills which even with dilligence push HR to 125 for a few minutes then rapidly drops back after cresting the rise. The question is do these short spikes in HR effect fat burning adaption??

    • Slomoshun:

      They do affect it. In essence, those increases in HR turn the experience into interval training. However, the less they rise, the more you are able to remain in fat-burning, and the more your body’s training response reflects it.

  • Sheilah Hure says:

    Hi, apologies for the length, hopefully you can offer some advice…

    I’m a 53yo female triathlete from Sydney Australia. I’ve been doing triathlons (starting with enticer, sprint, olympic and 70.3 x2) for 11 years and always had an accredited triathlon coach.

    I’m seeking your advice on one thing that has now becoming a hassle when MAF training… perimenopause, am still getting my period regularly. I’m in tune with my body when it comes to my cycle and know when I’m going through the different phases. My training is nowhere near as intense as it was 12 months ago. My sleep habits are mostly good but some nights, not so good – so on these nights I don’t do anything strenuous for the next 2-3 days, usually yoga. My diet has been predominately Paleo also 11 years, but this too now isn’t as easy as it once was to stay Paleo, my hunger hormones are being dictated to by perimenopausal hormones – resulting in pregnancy like cravings of bread, rice, potatoes and crisps – which is weird as I’ve never been pregnant?! The result of these “cravings” has been an extra 10kgs of extra weight!!

    But I digress…
    I stumbled across this method of training when searching for podcasts on endurance training for women my “vintage”. I heard Dr Maffeton on both Primal Endurance and Endurance Planet – became intrigued with MAF method of training – bought the books (yellow one) – as well as Brad Kearns/Mark Sisson’s book. To my disbelief after reading both, realise I was the textbook overtrained endurance athlete. Thought I should give this a try. Thankfully the number of sessions and intensity per week, have been dramatically reduced. Obviously putting this theory into practice was always going to be a challenge for me – requiring commitment and patience – extreme patience, which I was/am prepared to do – as I enjoy doing this stuff.

    I took 3-4 months to recover after completing my last 70.3 (Nov 2015). And haven’t “raced” since then. All “training” sessions are done at a very easy pace – basically, going through the motions. Which is what my body was telling me to do before I stumbled across this method of training. But… I now realise I WAS – overtrained.

    I’ve been using MAF training since April this year – spent 10 weeks building my aerobic base training with MAF for swim and cycle which has been my focus as I’m getting over plantar fasciitis (PF) which developed training for during my second 70.3 in 2015. So now my body is trying to become familiar with training “aerobically and not anaerobically”… huge learning curve.

    I am confident that I’ve spent sufficient time rebuilding my aerobic base since I got the books (April). So then embarked and adopted on this principle of training. Some days when training, my HR is bang on within MAF (127-133bpm). Other days depending on where I am in my cycle, it spikes as high as 170pm. So I stop and wait for my HR to drop back down to 120bpm before restarting – which can sometimes take 15mins!! Some rides are entirely in the small ring easy gear – just spinning. Swimming HR training is always good as I just swim at an easy pace. For running, I was doing water running in the pool but that too done at an easy pace. Other days, it does the opposite and takes ages for my HR to get anywhere near 127bpm… go figure!

    Based on the MAF principles, we’re supposed to stop the activity altogether when the HR spikes. However due to my age, I really believe, because my body is going through hormonal changes which are natural and unique to those of us of the predominantly “X” chromosome – this is causing my HR to spike whenever I go through the different phases of menstrual cycle…every day is different for both training and dieting – sooo frustrating!!!

    So my question is…
    Can you offer any advice if women going through perimenopause… should we train or not train? I assume that any exercise is better than none but am getting disheartened when the HR spikes but it seems being perimenopausal is making this mountain so much hard to climb. To the point, I think maybe I’ve picked the wrong time to train for endurance sports (triathlon) – the MAF way! Should I have waited until my body goes through the process?

    Look forward to any insight you can offer, or anywhere you can refer me to check any peer-reviewed articles or research on the subject. Using my skills to do literature reviews, there’s not much on the subject – other than maintaining physical activity and healthy lifestyle is a must, as both are the best for medicine for perimenopause and menopause.

    Regards

    Sheilah ☺

    • Sheilah:

      Thanks for your comment. It’s very interesting, and I hope I can help.

      I may be telling you exactly what you already know in the next few sentences. I write them so that I’m certain that we share crucial bits of knowledge before we get into the discussion.

      The best way to begin is by saying that menopause, perimenopause, and any other unique endocrine state has its own unique set of benefits and challenges, much like you outlined. What’s also important to keep in mind is that the heart rate responds reliably to changes in endocrine states, and its responses have pretty much the same meaning across states. So, if a heart rate rises because of endocrine states that are caused by perimenopause, the fact that it rises tells you pretty much the same thing that it would when the cause is not perimenopause.

      What this means is that a heart rate rise due to perimenopause means more sugar-burning and less fat-burning, just like in any other case. Of course, this doesn’t mean that the benefits of habitual fat-burning and dangers of habitual sugar-burning are any smaller for perimenopause, just because perimenopause tends to send you towards a sugar-burning state. If anything, it means that more care should be taken to burn fats and keep the heart rate at aerobic levels.

      In regards to the specifics of how to train during perimenopause, it’s important to realize that walking as a form of training has benefits as immense for the elite runner as it does for the normally active person. In other words, walking is real training. Why do I say this? If you have to walk to lower your heart rate (you never have to stop completely, even when your heart rate goes above MAF), then walk.

      One of the most important adaptations that the body goes through in the process of becoming more aerobically fit is known as “aerobic coupling.” This is not so much about the strengthening of the various parts of the aerobic system, but rather reinforcing their ability to work as a team. One of the biggest indicators that the body is becoming aerobically coupled is that the heart rate corresponds to power output. In other words, the mere fact that the heart rate flies up and down of its own accord indicates the need for more aerobic training. Similarly, one of the ways in which you’ll know you’re becoming more aerobically developed will not just be the increase in speed, but an increase in your aerobic coupling. In other words, the heart rate will fluctuate only in accordance to your exertion.

      I bring up aerobic coupling because it is often a gateway to greater aerobic development. When the body is not aerobically coupled (or “decoupled), it’s as if the pieces of the aerobic system don’t fit together well. And it’s very difficult to train an aerobic system that doesn’t fit together well. So, training it to fit together well is a first step to becoming more aerobically powerful. And how do you train that? By increasingly staying at a level of exertion where the heart rate does NOT fly off on its own accord.

      And if walking helps you stay at this level (and it almost always does), then walking can be an excellent form of aerobic training. (And it will serve as the gateway to begin running aerobically.)

  • Teri Smith says:

    I am a 51 year old female. I have been jogging/running using the 180 formula, and enjoying my running again. However, I find that my pace is really slow – 9minutes/kilometre. How do I increase my pace? Thanks, Teri

    • Teri:

      By continuing to train, and giving it time. The aerobic system is the long-term energy system, meaning that it not only gives you energy over a long-period of time. but it also takes longer to train than muscle power. So the first improvements usually come within 60 days (unless you’re overtrained, under major stress, or dealing with burnout), and they can continue to improve for years.

  • Chad Myers says:

    I’ve noticed all of these, but the other thing i’ve noticed is a higher heart rate. My resting HR is still pretty normal, but my exercise HR seems to be higher at a similar effort as in the past. I’ve been doing this since around Mid December now. Is that normal? Could I be eating too much fat?

  • Paddy Hirsch says:

    I’ve been running with an HRM for nearly a year now, following the MAF diet, warming up and down before workouts three or four times a week and running monthly MAF tests, but I’ve seen absolutely zero progress. I am 49 years old, but at a 131 max heart rate, I started shuffling along at about 4.5 mph when I commenced the program, and nine months later, I’m still unable to crack five miles in an hour, even on a treadmill in a (very cold) air-conditioned gym. My monthly MAF test are a disaster, in terms of seeing speed gain: in fact, I’m seeing a net loss over time. Every month I get a few seconds slower on every mile and my overall time for the three miles has declined steadily.
    This is irritating, and it’s making me feel as though I’ve wasted nearly an entire year. I’ve been running middle distance my entire life, and I particularly enjoy trail running. Under this regime, I can’t even walk up a hill without my HRM going off. That means I haven’t been able to get into the hills, even once, because I’ve stuck to the directive to not raise my heart rate under any circumstances. I can’t even imagine what I’d be like on the hill today.
    So this regime has really killed the joy of running for me, and while I haven’t gained any weight, I don’t feel any fitter than when I started. In fact I feel less fit, and certainly a lot slower. I wonder if you have any advice for me, because I’m just … about … done.

    • Paddy:

      One of the things that comes to mind is that the 180-Formula doesn’t work for the entirety of the population. It works for the supermajority—upwards of 80%, but not for everyone. This is to say, there’s a chance that the 180-Formula is underestimating your aerobic threshold (which is what your MAF HR intends to point to).

      Since there may be health consequences to simply supposing that your number is higher and aiming for that, I suggest to people in cases like yours that you get lab tested for your aerobic threshold, also known as FAT MAX (heart rate at the maximum rate of fat-burning). FAT MAX is the metric that specifically gets at what your MAF HR should be; metabolically nonspecific tests such as VO2 MAX don’t get at this number.

      The reason we propose people use the 180-Formula is because it is a very good ballpark estimate (for the majority), which can be calculated without significant expense of time and money. But a laboratory measure will always be more accurate.

      I hope this helps,

      Ivan

  • Diane Huffman says:

    Does this work well with the Galloway run/walk program?

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