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ISSA, International Sports Sciences Association, Certified Personal Trainer, Fat, The Right Way to Burn Fat, Not Muscle, Nutrition

The Right Way to Burn Fat, Not Muscle

Reading Time: 4 minutes 56 seconds

DATE: 2022-02-14

To avoid losing muscle along with fat, you have to combine exercise programming with the right strategy for fueling.

As a trainer, you probably already know this, but do your clients? Your recommendations and strategies for fueling have to match the goals of your clients. Typically a client’s goal is to lose weight and look better, not to lift a certain amount of weight or be a better endurance athlete.

When you work out to lose weight, without knowing how to do it the right way, you end up creating a smaller version of your unmuscular self. You need to know how to explain to your clients about combining exercise and food to maximize fat loss and minimize muscle loss for optimal body condition. In this article, we'll break it down in a way that is fairly simple for your clients to understand, so feel free to share!

You don’t need a Ph.D. in biology to make sound recommendations to your clients, but you do need a solid knowledge of the basic principles of fueling and working out:  

Basic Principle #1: The body is a biogenetic continuum of energy systems.

Adenosine triphosphate (ATP) is our fundamental unit of energy. The body uses ATP to fuel work. The human body has enough ATP to fuel 5 to 10 seconds of work before it starts to break down stored macronutrients to manufacture more ATP.

The easiest macronutrient to burn is sugar. Exercise lasting from 10 seconds to several minutes uses predominantly glucose in the form of pyruvate, and if the exercise is intense enough, in the form of lactate.

After several minutes of work, the body will begin to burn fats for energy use.

Share This: The body will burn sugars first, always.  

Basic Principle #2: Exercise intensity determines how you fuel your body.

High-intensity workouts such as weight lifting, cross-fit, Tabata, high-intensity interval training (HIIT), and sprinting, cause physiological responses that are different from those caused by aerobic training.  

High-intensity work is anaerobic, meaning without oxygen. High-intensity work has a lot of unique effects on the body:

  • It creates an Excess post-exercise oxygen consumption (EPOC) effect—the body burns calories resynthesizing ATP.

  • The body burns calories restoring oxygen to myoglobin and the blood.

  • The body experiences an elevated core temperature and heart rate, increased respiratory rate, and thermogenic effects of fat burning hormones such as epinephrine. 


Lower intensity and endurance workouts are aerobic activities. The primary effect they have on the body is to burn fat as fuel, once you have gotten through the available sugar.

Share This: You burn fat during low intensity, aerobic workouts, but the benefit from high-intensity exercise occurs predominantly after the workout.

For more information on the role fats play, check out the ISSA's article on Explaining Fats' Function to Clients.

Fueling for the Workout: High-Intensity Days

With these things in mind, the goal of fueling should be to optimize the workout. For example, low-carbohydrate diets can be an effective strategy for weight loss. But on days of high-intensity workouts, low-carbohydrate fueling may not be the most effective strategy, especially post workout.  

The body burns sugars first. Low glycogen levels (stored carbohydrates) combined with high-intensity exercise creates opportunities for the body to burn higher amounts of muscle—not what anyone wants.

As well-known Canadian bodybuilder and strength coach Christian Thibodaux once said, those who burn up both fat and muscle create “smaller versions of their unaesthetic selves,” and this is not the goal of improving body composition. 7

Therefore, on higher intensity days the optimal situation is to create opportunities to consume protein to rebuild muscle and carbohydrates to burn as fuel.

Insulin is a power hormone that stimulates protein synthesis and it also releases blood sugar for energy use. Insulin is triggered when you eat carbohydrates.5 So, you want to eat carbs on these high-intensity days to ensure you have enough sugar to burn. This prevents the body from breaking down muscle to burn protein for energy. 

Share This: Complex carbs should be consumed well before a workout and especially after. The body needs the insulin for protein synthesis after the workout is complete.

Also, review popular protein myths with your clients so they know how much protein they need and how it will affect their bodies.

Fueling for the Workout: Low-Intensity Days

On days that you do a lower intensity, aerobic workout, fueling will be different. On these days the goal is to burn fat, so everything put into the body should be to induce lipolysis—the burning of fat for energy.

In other words, these are your low-fat days. Total fat intake should not exceed 20% of total calories and the same goes for carbohydrates. There are two enemies of lipolysis and fat burning:

  1. Insulin Remember that the body’s natural response is to burn sugar first. It may be helpful to think of fat and sugar use for energy as two separate faucets: when sugar is available, the body will turn down the volume of fat burn on one faucet and increase the sugar burn of the other faucet. This is related to insulin. When the pancreas releases insulin, lipolysis is inhibited [4].

Share This: On longer, slower aerobic days, foods that trigger insulin release, namely simple carbohydrates, should be avoided completely.

  1. Lactate - According to research, another inhibitor of lipolysis and fat burn is lactate. 4

      Lactate is present in muscles for energy use at rest and during high-intensity exercise. Lactate is either used by slow twitch muscles for energy or it gets recycled to the liver for glycogen storage. [4] The body prefers to reserve it for energy use.  So, the more lactate has accumulated in the body, the less fat will be burned during aerobic exercise. High-intensity exercise causes large increases in lactate production and therefore should be avoided on low-intensity days designed to burn fat.The lower the exercise intensity, the higher the percentage of fat that is burned. [5] Sure, higher aerobic intensity will cause fat to be burned but also will cause higher amounts of muscle to be burned.

Share This: Aim to maintain a heart rate between 105 and 125 during exercise on low-intensity days.  

Alternate High- and Low-Intensity Days and Fuel Accordingly

The major takeaway—and the basic information you want to relay to your clients—is that to lose weight while gaining, or at least not losing, muscle, you need to alternate your workouts between high-intensity, anaerobic exercises, and low-intensity aerobic work. And then fuel accordingly on those days:

  • On high-intensity days, acquire or preserve muscle by eating more and including carbohydrates.

  • On low-intensity days, burn fat without losing muscle by truly keeping the workout intensity low and by avoiding carbohydrates, especially simple carbs.

Burning fat and maintaining muscle is both difficult and time-consuming. No quick fix exists. Encourage your clients to use the slow and steady, proven approach and to avoid fad cleanses and other diets based on drastic caloric restrictions.

These types of fueling strategies combined with exercise rich programming can cause immediate drops in clothing size and win on the scale, but over the long-term, they do more harm than good. Always focus on the long, slow, disciplined, and healthy approach to exercise and fueling.

Intrigued by the relationship between food and fitness? Boost your knowledge and build a money-making career with the ISSA'S Nutritionist course. Learn how to help clients amplify their progress with optimal nutrition and hit their fitness goals faster!


1. Brooks, G. (2000). Intra- and extra-cellular lactate shuttles.  Medicine & Science in Sport & Exercise, 32(4), 790 – 799.
2. Donovan, C, & Pagliassotti, M. (1998). Quantitative assessment of pathways for lactate disposal in skeletal muscle fiber types.  Medicine & Science in Sports & Exercise.
3. Gladden, B. (1998).  Muscle as a consumer lactate.  Medicine & Science in Sports & Exercise.  
4. Gualano, A., Bozza, T., Lopes, D., Roschel, H., Costa, D., Marquezi, L., Benatti, F., & Herbert, J. (2011). Branched-chain amino acids supplementation enhances exercise capacity and lipid oxidation during exercise after muscle glycogen depletion.  Journal of Sports Medicine Physical Fitness, 51(1), 82 – 88.
5. Jeukendrup, A., Saris, W., & Wagenmakers, J. (1998).  Fat metabolism during exercise: A review part 1: Fatty acid mobilization and muscle metabolismInternational Journal of Sports Medicine, 19, 231 - 244.
6. McArdle, W., Katch, F., & Katch, V. (2010). Exercise physiology. Seventh Edition.  Lippincott Williams and Wilkins: Philadelphia, PA.
7. Thibaudeau, C. (2016). Fasted cardio eats muscle. Plus 6 other fat loss mistakes. T-Nation.
8. Verkhoshansky, Y., & Siff, M. (2009). Supertraining. Sixth Edition.  Verkhoshansky: Rome.


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