Gaining Muscle While Losing Fat with Flexible Dieting

gain muscle lose fat

One of the most frequent questions we receive is from someone wanting to know if they can gain muscle and lose fat at the same time with flexible dieting or IIFYM.

This can be a bit tricky, but it can be accomplished with flexible dieting as long as people are patient and willing to put in a little extra effort with the nutrition and fitness aspect of the flexible diet.

First, let’s take a quick look at the physiology regarding fat loss and muscle gain and then we can apply those principles in some practical ways.

Fat Loss

Most people understand that fat storage is a survival mechanism that the body uses to store energy in case of periods of famine. Thousands of years ago this mechanism was vital to our survival as a species because since we hunted and gathered for food, sometimes humans would have to go days or even a week before adequate food was obtained.

Now fast forward to our modern times where food is abundant and little energy is expended to get that food beyond pushing a cart around the grocery store. Our bodies are still hardwired the way they were a thousand years ago.

  • Excess food energy gets stored in the form of fat.
  • Fat stores are broken down when the body needs energy it isn’t getting from enough food.

Unfortunately, the body doesn’t have an off switch and fat storage is accumulative. What’s worse, it is far easier to store fat than it is to release fat because we are hardwired to enjoy food as a way to also ensure our survival.

So, to lose fat you have to be taking in less energy than you are expending during any given day.

To make up for the calorie deficit that you are in, your body has to begin breaking down fat for the energy required. There are a few caveats to this and I’ll address those a little later, but in a basic sense this is why we store fat and how we lose it.

Muscle Growth

Biologically, muscle tissue is functional tissue in that it exists to serve a purpose and the extent at which it exists is dependant on the body’s need of it.

The body has no interest in partitioning energy to muscle growth and development unless it believes that the extra muscle is required for our survival, whether in reality or artificially contrived (the gym).

Thousands of years ago humans had to work hard for their survival; hunting, building, farming, laboring etc. and muscle development occurred more naturally.

Today, while some do still labor, most of us have more sedentary type lives which means that the minimal amount of skeletal muscle is required for our survival.

This means that simply eating more will not result in muscle gain. Since more muscle isn’t needed, extra energy will be stored as fat like I previously described.

In order for muscle to grow1 it has to be stimulated in a way that breaks or injures muscle fibers (muscle trauma), so that they are rebuilt stronger with the help of key hormones and amino acids (protein syntheseis)2.

Also, the rate of muscle protein synthesis has to be greater than the rate of muscle protein breakdown caused by the trauma, therefore a person’s diet must contain the raw materials needed for protein synthesis.

Since most of us don’t naturally undergo the type of activity that causes muscle trauma in our jobs, we have to simulate this at the gym with strength training and/or weight training.

Therefore, muscle growth in its basic sense requires the right diet and the right exercise.

Build Muscle, Lose Fat in Conjunction

Traditional bodybuilders use two phases to build muscle and then lose fat:

  • Bulking: which is to eat a calorie surplus while engaging in comprehensive weight training with some fat also being gained.
  • Cutting: which involves reducing calories drastically and often includes either a very low fat diet or ketogenic type diet while engaging in comprehensive weight training.

The above method can grow muscle relatively quickly and can also remove fat relatively quickly, but it probably isn’t realistic for most, especially those who are not athletic and already have a fair amount of fat to lose.

Most of us want to gain muscle and lose fat at the same time instead of in two separate steps. This is possible as long as you do things correctly.

First, you must maintain a sensible calorie deficit. Too drastic and your muscles won’t grow, too little and fat loss will be extremely slow.

Secondly, you have to have a comprehensive weight training program in place. This can be weight training, Crossfit, boot camps etc. but you have to be constantly breaking down muscle tissue, giving them time to repair, and then pushing them harder to break tissue down again.

Third, your diet must contain the raw materials for muscle growth. Adequate protein and nutrition that will cause protein synthesis to outweigh protein breakdown.

Lastly, your hormonal levels must be in balance. Both fat loss and muscle growth rely on hormones to release fat stores and to build muscle tissue. The best way to achieve healthy hormones is to eat a healthy nutrient dense diet, get plenty of sleep, and to exercise regularly.

How Flexible Dieting Helps

protein rich spaghetti and meatballs

I’ve had great success using flexible dieting or IIFYM to lose fat and build muscle simultaneously. (You can read my story here.)

Flexible dieting is conducive to this process for several reasons.

  1. It places you in a moderate calorie deficit based on your exercise adjusted TDEE: This amount encourages the breakdown of fat for extra energy.
  2. It allows you to adjust your protein amount in a way that provides muscle tissue the raw materials needed for growth.
  3. It adequately fuels your muscles so that your workouts can stress your muscles to the point of muscle trauma, which is essential for growth.

While the flexible diet fuels your transformation, I can’t stress the importance of proper exercise. Weight bearing exercise actually enhances fat loss as well promotes muscle growth.

Research reveals3,4 that exercised muscle causes the hormone irisin to be released, which in turn, causes the formation of brown fat. Brown fat5 actually burns fat instead of storing it.

Therefore, a weight training program of some sort has to be used in conjunction with the dietary recommendations of the flexible diet.

Measuring Progress

Using a scale isn’t the best measure of your progress concerning how well you are losing fat and gaining muscle.

Muscle tissue is far more dense than fat tissue, so the same volume of muscle weighs much more than the same volume of fat. Therefore, the numbers on the scale may only be going down ever so slightly as you build muscle or vice versa.

Taking progress pictures as well as measuring your body fat percentage are a much better gauge of your progress. Get yourself a cheap set of body calipers and use this body fat percentage calculator. Take selfies in the mirror or get your friend or partner to take the pics using the same settings and location each time.

Also, make sure you have realistic goals in place. Here’s how body fat percentage breaks down in both men and women.

body fat percentage

Some Challenges to Consider

If you are coming from years of low calorie dieting or yoyo dieting, your hormones could be out of balance especially the leptin group6. It can take a period of normal, healthy eating for things to normalize again. Be patient during this process.

Flexible dieting isn’t “one size fits all” so you may have to spend some time adjusting your TDEE and macros until you find YOUR personal sweet spot for muscle growth and fat loss.

Our calculator gives you just a great starting point.

For me, that means eating according to how much activity I do each day opposed to eating the same activity averaged set of macros each and every day. On rest days I eat at my sedentary weight loss levels.

At the gym you need to be adamant about continually challenging and pushing your muscle groups. This usually means adding more weight to your movements consistently. Doing a lot of reps increases endurance and strength, but doing more weight increases size, so if size is what you’re after, focus on the later.

I’m also a fan of full body workouts as opposed to isolating muscle groups when trying to build muscle and lose fat at the same time. Here’s my theory as to why. Since you are in a calorie deficit you have to be careful that your body doesn’t break down muscle tissue for resources7 instead of fat. Working out only arms could put you at risk of your body cannibalising your legs for extra energy/protein for example.

By doing whole body workouts you are stressing almost all your muscle groups, so your body will be less likely to rob Peter to pay Paul so to speak. Consuming adequate protein also helps prevent this and is essential. I also like to have 2 days of rest in between my whole body workouts and on those days I do cardio type activities.

Overall, I can’t stress the importance of being patient. Flexible dieting is designed to produce slow and steady results and the same is true for the process of losing fat and gaining muscle at the same time.

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    Scientific References:

  2. Kumar, V., Atherton, P., Smith, K., & Rennie, M. J. (2009). Human muscle protein synthesis and breakdown during and after exercise. Journal of Applied Physiology, 106(6), 2026-2039.
  3. Timmons, J. A., Baar, K., Davidsen, P. K., & Atherton, P. J. (2012). Is irisin a human exercise gene?. Nature, 488(7413), E9-E10.
  4. Havel, P. J. (2004). Update on adipocyte hormones regulation of energy balance and carbohydrate/lipid metabolism. Diabetes, 53(suppl 1), S143-S151.
  5. Harms, M., & Seale, P. (2013). Brown and beige fat: development, function and therapeutic potential. Nature medicine, 19(10), 1252-1263.
  7. Tipton, K., & Wolfe, R. R. (2001). Exercise, protein metabolism, and muscle growth.
  8. Lead image: Flickr


  1. Daniel Wagle

    I really appreciate that you stress the importance of exercise. I do some weight training, but I mainly do cardiovascular exercise by bicycling everywhere I go. But I agree that weight training is important to preserve and grow muscle mass. I am mainly interested in keeping up my strength, but I don’t really want to gain muscle weight. Many times when people do a “just diet” approach, much of their weight loss will be from muscle. This will slow down the metabolism. I have maintained my 100 pound loss going on 5 years now and my weight still trends down. I sort of do flexible dieting in that I count calories, but I don’t track macros. I don’t think, however, that my diet is really low carb or low fat and it isn’t that low in total calories either. I eat mainly plants, but I try to make sure I get protein sources, such as beans and nuts.

  2. Jacob Emerson

    Hey JamesF I agree that more protein doesn’t help. My view on the subject is for losing fat, you need to eat at a deficit, but for gaining muscle, you need to eat at a can do both at the same time contrary to popular belief. But your body doesn’t really need that much extra calorie to build muscle. It is about 100 calories at most. For gaining muscle and losing fat, you really just need to eat at your maintenance or maybe 100 calorie above your maintenance and make sure you are taking in enough protein. Of course you need to lift very heavy in the gym (go to failure in every set), then you will definitely see muscle gain and fat loss. It will be slower than if you are at a 500 calorie surplus, but when you gain muscle fast, you might gain a bit of fat nothing to worry about though. You need to also get into a routine I can’t stress this enough! be consistent! if you need help getting a routine check helped improve my gains 10 fold!

    Hopefully this helps!

    • Ted

      Hi Jacob, This may work for you and it’s great that it does! nice work! But you can gain and lose at the same time. I’m living proof as well are countless other people that have done it . Many of which do flexible dieting. More protein does make a difference and I’ve experienced great gains since I’ve started tracking my protein intake. Anyway, keep up the great work.

  3. JamesF

    Great post. I also wonder how genetics play a role, and how for many it is an unrealistic expectation to simultaneously grow muscle and burn fat. In my own seasons of intensive exercise and managed diet, I found it extremely difficult to maintain muscle while losing fat (let alone gaining). It seemed to me that my body always preferred to catabolize muscle in preference to burning fat.

    I also found that high amounts of protein didn’t necessarily help. So a lot of experimentation is needed along with realistic goals.