Fat Burning: A How-to Guide


We have become a society of carb burners. That is where sports nutrition has been for the past couple of decades. Of the two main food sources the body uses for energy, carbohydrates and fats, our working muscles would prefer carbs because they create ATP (energy) faster. They are “easier” to convert into energy. As a result, we just pour in the carbs. We have fuel belts and hydro packs with pockets, water bottle holders with pouches and clothes with pockets everywhere to carry hundreds of portable carbohydrate calories. But the reality is, we are already carrying thousands of calories… in the form of our own body fat.

So, what’s wrong with carbs? I personally have been encouraging athletes to include plenty of healthy carbs (whole grains, fruits and vegetables) in their race fueling, training diets and recovery snacks for years. And nothing is wrong with carbs; we just may have lost sight of one of the most important parts of our nutritional fueling: using our own fat for energy.

What if we could use our on-board energy (our own body fat) for fuel? Most trained runners are carrying about 1,500 to 2,500 calories of carbs and 80,000-plus (!) calories of fat. Even the leanest runners. Yes, we need some carbohydrates to activate enzymes in order to burn fat for energy, and also the brain is fueled on carbs. But think of it this way: more fuel is better. One fat-burning enzyme burns a little fat; a bunch of fat-burning enzymes ignites a bonfire! So the focus of this article is how to turn your body into a fat-burning engine: Metabolic Efficiency (“ME”) training. ME training builds a stockpile of fat-burning enzymes, and voilà—the ultrarunner becomes much less reliant on consuming mass amounts of carbs during the race and has less chance of GI distress.

What Is Metabolic Efficiency Training?

Also known as fat-burning, metabolic efficiency training is not a calorie-deficient diet and it is not a low-carbohydrate, Atkins like diet. You do not need to count calories and you do not need any special foods or supplements. It is rather macronutrient partitioning—or manipulating your macronutrients (carbohydrates, fats and proteins)—and exercise adaptation—or manipulating your exercise with correct intensity training—that allows us to reap the benefits of increased fat utilization. By effectively manipulating our aerobic training, we can increase mitochondrial capacity (the number of mitochondrial enzymes). By manipulating our diet to control blood sugar and our insulin response, we will be able to fuel with fewer calories during training and racing, therefore reducing our reliance on consuming simple sugars and increasing our utilization of our on-board internal body fat. The key is that you must manipulate both diet and exercise together. If executed properly, meaningful improvements can be achieved in as little as four weeks.

Exercise Training – 30% Effect

ME training conditions your body to use fats and carbohydrates more efficiently. It manipulates cellular processes through aerobic training by increasing the size and number of mitochondria (and related enzymes) in your cells that use fat for energy. It teaches your body to use more fat by creating conditions that generate high fat metabolism. Many ultrarunners ignore or “skip over” setting up an aerobic foundation because they don’t see the immediate benefits as in speed training. This is not to say that interval training, hill repeats, etc. do not produce positive changes—they do—but they just don’t improve fat burning. You will be more metabolically efficient if you work on fat-burning (aerobic exercise) first, and then add in the other training regimes. All your runs during this period will be at a lower intensity.

Of course, you can get around this by relying on a constant source of carbohydrates coming in to fuel your muscles (aid stations, carrying lots of calories, spiking your insulin by eating simple carbs… all the time!) but you will still be carrying around some of that fat on your body. Think of it this way: you know what goes through your mind when you see a runner carrying two full bottles of water during a race that they never drink. Why carry all that weight around if they don’t use it? Hmmm. Plus, an increased carbohydrate diet can be inflammatory—not great for our long-term health.

Frequency and consistency are the keys to fat-burning training. You will need at least six to seven hours per week in this low-intensity zone for results, and it is critical to have most of your training in this zone. This means going a slower, plenty-of-available-oxygen, can-speak-full-sentences pace. Training in higher intensities also contributes to adaptations—one of which is the release of adrenaline—which leads to higher lactate formation. This has an acidic effect on free fatty acid transport that reduces fat going into the mitochondria to be used for energy. Not the adaptation we are looking for. Will you lose your speed? No, this is just a base training period; remember, we are not talking about that long—four to 10 weeks.

Implementing The Nutrition Plan – 70% Effect

The nutrition component has by far the biggest effect on your fat-burning capacity, and you must make changes to your diet to see results. The bottom line is that you remove, or drastically reduce, all grains from your diet. Not “all carbohydrates,” just grains. Your nutrition during this time will consist of lean protein, good fats and plenty of fruit and vegetables. Your sports nutrition during your runs will change too (more about that later).

Processed or refined carbs (and even whole grains) cause an insulin response or spike. As insulin increases, fat breakdown and oxidation (burning) significantly decreases and eventually turns “off” while this same insulin increase turns “up” the increase of carb oxidation. This causes the athlete to seek out more carbs and end fat burning. Controlling blood sugar through proper food selection is the key nutrition take-home message. Oxidizing more fat for energy means delaying the accumulation of lactate, which means runners will be able to maintain higher paces longer without having to take in more carbohydrates.

Remember, this is not a low-carb diet; it is a balanced diet. This means your meals will look different than the usual bagels, oatmeal and pasta. Breakfast may be black beans, spinach and eggs (or egg whites) microwaved to resemble an omelet, with some feta cheese or salsa on top. Or it may be yogurt with lots of berries and nuts added. Lunch and/or dinner may be a huge salad with steak, salmon or tofu on top. Or it may be a lean piece of meat with lots of vegetables and some fruit and a small bit of cheese for dessert. If you cannot go cold turkey on grains, then add a small bit of quinoa or brown rice to your dinner, but this will delay results somewhat. Snacks can be cut-up veggies with a yogurt-based dip. Soups, chili, stew, lettuce wraps—be creative!

What about during your workout? If we can’t use simple carbohydrates—sports drinks, gels, bars and pretty much everything we normally eat—what can we consume? Water and electrolytes. Yikes. What about “one gram of carb per minute… 240 calories an hour.”

Will I bonk? Will I die? No. You will burn and lose fat. Your fat. Why? Because you are not going at a high intensity, remember? You are not going through your carb stores; you are fat burning! The only reason you would bonk is if you are going too fast—or you run out of (your) fat. If you are running over two hours or so, you can add some non-grain based carbohydrate such as fruit, dried fruit, Lara bars, Justin’s or Pocket Fuel nut butters.

After finishing a run, you might usually hurry to make that “30-minute window” for refueling. Not necessary! You did not deplete your carb stores; you only made a dent in your fat stores. So rehydrate and have a balanced snack or meal.

Fat-burning training can help you stabilize your blood sugars, improve insulin sensitivity, lower cholesterol and LDLs, give you steady energy, lose body fat and allow you to run faster at a lower heart rate. All great results, plus putting your body into an anti-inflammatory state and able to fuel on the run with fewer calories, relying less on simple sugars. Try training first thing in the morning, fasted. Take in water and electrolytes if needed, and do not go out too fast (or too long). Remember, you want your pace to be slow enough to mobilize your own body fat for energy, and not bonk because you ran low on carbs. Daily consistency with paired nutrition and training will set a solid increased fat-burning base for big results down the line. When your speed starts to ramp up and you introduce hill repeats and speed endurance training, slowly add the carbs back into your diet, especially during races (i.e. gels) and in the recovery foods you ingest after hard sessions. That’s the time to replace the glycogen (carb) stores, not when you are primarily fat-burning in your ME training phase.


About Author

Sunny Blende, M.S. is a Sports Nutritionist who writes and counsels individuals and teams on fueling for enhanced performance and making healthy food choices. Currently she writes the nutrition column for UltraRunning magazine and runs ultras herself. She has presented at the National RRCA Convention, the National Rowing Convention, Nike San Francisco Marathon Expo, and the Runners World San Francisco Marathon and worked as an assistant with the Los Angeles Marathon Association. An avid master competitor herself, she trains and competes in the San Francisco Bay Area and beyond. Sunny received her Bachelor of Science degree from University of Southern California and her Masters in Human Nutrition degree from University of New Haven. (Photo at left, by Luis Escobar).


  1. Very interesting. Going grain-free has been extremely difficult for me in the past. I have a hard time finding replacements for brown rice/quinoa/pasta, which tend to be big staples in my diet. Any suggestions?

  2. Erik Meyer on

    If I am able remove grain, I am unclear as to the best way to establish the required low pace zone…is that decided by heart rate? Given a particular max rate, how is it calculated? Thank You.

    • Sunny Blende on

      This is usually done at a lab – it is a SUB MAXIMAL test (as opposed to a Max HR test), that measures, at your particular heart rates, how much carbs and how much fat you are burning. At low HR, you will burn more fat than carb and as you go to max-effort, you will be burning almost all carbs. BUT YOU CHANGE your amount of fat used (to using more at higher HR) by ME training – that’s the point. Phil Maffetone also has a formula that is accurate for “most” of the population”, but it is not as accurate as your own test on a treadmill. Check out your local gyms and/or universitiy to see if they offer a test on a “Metabolic Cart”.

  3. Jessica Whiting on

    Hi! Just wondering what you would suggest for taking in electrolytes without simple sugars. Most of the electrolyte products im familiar with contain simple sugars as well.

  4. We are lucky to have Sunny tell us the truth. There is a lot of influence coming from the sport nutrition industry and within her own profession that discourages being critical of sugar and grains’ place in sport nutrition. The article is great. She has gone out on a limb to tell us the truth. A few brave dieticians and nutritionists are back tracking on decades of a low-fat high-carbohydrate mantra that has had grave consequences on both performance and health.

    I would just take Sunny’s take on ME a step further. Sunny is careful to not call this a low-carbohydrate diet, but it is a carbohydrate restricted diet, therefore, relatively speaking it is a low-carbohydrate diet. At least compared to what marathoners have been encouraged to eat in the conventional sense. This seems to downplay the importance of carbohydrate restriction, which is so important.

    Once the nutrient poor carbohydrates (grains & sugars) are removed as an energy source, something else needs to be added as an energy source. And that is fat. To suggest that “lean” meats and egg whites (without the yolks) have a place in a carbohydrate restricted way of eating seems nonsensical. It is these very fats that are dense with energy and nutrition.

    ME, while certainly achievable on low intensity running, it also seems nonsensical to not deplete glycogen stores at times during the period of “keto-adaptation,” that time when efficient us of ketones for energy has yet to happen. Leaving your sugary gels at home, and allow glycogen stores to be depleted will foster the adaption to being a fat burner. Performance during high intensity work will suffer of course, but I haven’t seen any resarch that suggests it will delay progressing through keto-adaptation, and into the bright world of fat burning nirvana.

    • Wesley Hurrell on

      I concur with Todd’s comments. It is particularly important to up fat intake once you drop carb intake – especially if you are a relatively lean athlete. For athletes that are overweight, it is not as important in the short term, as the body naturally taps its fat stores, but overtime it becomes more and more important to up fat intake if carb intake remains low. Dr Stephen Phinney talks about this issue in this lecture (https://youtu.be/2KYYnEAYCGk?list=PLuMDPCITxYNgwGvoAAJUuuVzWL7XsauT_) see minute 3:30 to 7min. I made the switch to LCHF for my first ironman last year and blogged about it (http://www.nutriscience.com.au/sports-nutrition/low-carb-high-fat/) with reference to metabolic testing and food diaries etc.

    • Sunny Blende on

      Thanks Todd for noticing new trends and taking the time to open your mind to them. It is true – I sometimes get “flack” 🙂 And yes, ME is NOT a calorie restricted diet. If you are cutting out grain carbs (and maybe all carbs somewhat), you must eat more fat (along with a bit more protein) in order to keep your caloric intake even. Performance during this stage is not the goal; it is changing your body into a “machine” that can use its own on-board energy without having to ingest outside calories. If you have a key race coming up, then you may need to ingest some gels, etc. (usually later than usual) if you are not fully adapted yet in order to stay competitive.

  5. Hi!
    I’m just wondering how grain-free one’s diet should remain after the initial 4-10 week “training period?” Are there any additional changes to one’s weekly run schedule in order to maintain this ME base?
    I’m so intrigued! I have so many questions! I should probably subscribe to the magazine.

    • Sunny Blende on

      Subscribe to the magazine…SO many great articles!
      And, good question. When you have a rest day, or an easy run that you are doing in a ME heart rate zone, then restrict your grain carbs. But if you are racing or doing intervals or a “hard” workout, then take in carbs during the run and in the meal afterwards. You may find that you need “less” grain carbs, but still some.

    • Sunny Blende on

      Thanks Wesley! This is an important new study….done by great scientists Noakes and Phinney. We are finally seeing more studies on this concept.

  6. Donna Mcissac on

    I’ve found that harnessing the power of the metabolism is the greatest way to lose huge amounts of weight. The best program I’ve found so far is The Metabolic Cookbook! Its full of delicious recipes that don’t deprive you of calories like many other diets! check out my review at http://truehealthreport.com/metabolic-cookbook-review/

  7. Rick Riedel on

    Small Correction: Your brain does not depend completely on sugar. You can use Ketones. It is possible to stick to the ketogenic diet which is useful for defeating cancer (cancer cells really can ONLY metabolize sugar) or for recovering from a serious brain injury and getting rid of seizures. I’ve been running ultras for 34 years and have found that weaning away from grains is not so hard. I eat what I describe as the “High fat, low carb, no sugar diet” I can run all day on just plain water and maybe an electrolyte tablet or two. I never take snacks. No weight issues, even energy all day, running or not. Carbs are really unnatural. Analysis of petrified feces from prehistoric people shows 90% meat and the rest roots and whatever they can find. Saturated fat is where it’s at!