Effective fueling for optimal gains. Your guide to the metabolic balancing act between building muscle and burning fat.

When it comes to muscle building there is a lot of confusion.

Especially around the correct approach to fueling your body for maximum gains.

Logic says that to increase our muscle mass we need to consume enough energy to support the muscle building process.

And we know it’s possible to build muscle while losing body fat. So it seems reasonable to assume that we can build muscle without gaining body fat. 

However, this fails to answer several questions relating to ‘when, why and how’ we might be able to increase muscle mass - without increasing or even decreasing fat mass.

Let’s take a closer look…

Building muscle without gaining (or even losing) fat…

Muscle growth is an energy demanding process.

But if we have sufficient fat stores, it’s likely we will be able to sustain reasonable rates of muscle growth while losing (or at least maintaining) body fat. Even in an energy deficit.

The problem is - results will are likely to be highly individual. The amount of fat mass needed to maximize muscle growth will vary person to person. As will how lean we can get before muscle growth is impaired.

When we get lean we reach a point where muscle growth starts to become inhibited. This point is likely to be largely determined by genetics.

Low levels of body fat create a stressful environment within the body. Making muscle building more difficult. It can lead to an increase in catabolic hormones and reductions in anabolic, muscle building ones.

This means that at some point rates of muscle growth will slow. And if there aren’t sufficient calories available to sustain a healthy level of body fat, we actually begin to lose muscle.

Muscle growth v fat loss

Which also points towards another important question…

Because we are able to maintain, or even lose body fat while building muscle - is this optimal for muscle growth?

Well, this is again likely to be largely determined by genetics. In some cases, it could be beneficial for muscle growth to be in a calorie deficit and to focus on losing fat mass. There is some evidence to suggest large amounts of fat mass may impede muscle growth.

This is due to negative changes in hormones as body fat converts testosterone into oestrogen, which hampers the muscle building effect.

There is also likely to be a genetic component with how much fat mass we can get away with before it hinders muscle growth potential, if indeed it does at all.

Why would we want to increase fat as well as muscle mass?

It might be the dream to increase muscle mass without gaining fat mass. But the problem with this approach is that there are only very theoretical ideas surrounding how much extra energy we need to consume in order to support muscle growth.

The factors that influence these energy requirements are so dynamic it is difficult to hit the perfect sweet spot. Muscle growth is a slow process. If we want to ensure that we are consuming enough energy to support muscle growth, then we could use increases in fat mass too. It’s a solid indicator that we are consuming enough calories to allow muscle growth to occur.

Once fat mass begins to creep up, calorie intake can then be reviewed and reduced if needed until things level off again. Hopefully then as we start to build more muscle and our metabolism increases - both at rest and especially during activity we will burn more calories – our fat mass should then start to reduce as a result.

This is why taking consistent measures of body composition - such as weight, skin fold calipers and pictures are essential to document progress. These combined with improvements in gym performance create a solid data set to monitor muscle growth.

So how can we increase muscle mass without (significant) increases in fat mass?

To answer this question, it is important to understand both the rate of muscle growth and also how much energy is needed for a certain amount of muscle to grow. If we can understand how much energy it takes to sustain this process then we can in theory, provide the correct amount of energy to maximize muscle growth without increasing fat mass.

However, this is not an exact science. The precise amount of energy required to stimulate muscle growth is not known. Nor is it known if fat stores are sufficient to provide this energy cost in its entirety.

It is entirely possible to grow muscle and lose fat at the same time. But it is not known if this could sustain an optimal rate of muscle growth. And if not, at what level of calorie deficit muscle growth would be impaired.

One study looked at the impact of an energy deficit of ~20% in people undertaking resistance training on muscle building processes, whilst consuming a moderate protein diet of 1.5 g/kg per day.

Participants ended up losing around 1 kg in weight, but this was at the expense of some muscle building processes - with a 16% reduction observed.  

Energy deficits v muscle growth

This suggests that even a moderate energy deficit can impair rates of muscle growth. However, the impact of energy restriction on muscle growth in populations consuming higher protein diets with higher levels of body fat and under different training conditions is still unknown.

Most leading experts in muscle growth suggest an energy surplus of 350-500 kcal per day to support muscle growth without increasing fat mass. This number is based around the energy composition of 1 kg muscle being in the region of 1250 kcal.

(1 kg muscle = ~ 800 kcal of protein, ~350 kcal of fat, and ~100 kcal from glycogen).

Rates of muscle growth are commonly in the region of 0.25-0.5% of bodyweight per week. A 100 kg person may expect to grow only 25 g-50 g of muscle per week. On face value current recommendations to consume an extra 350-500 kcal per day might not make much sense if we consider that an extra 50 g of muscle contains only 62.5 kcal of energy!

We also need to consider that we have to compensate for the energy of training, muscle repair and remodeling. Which is much more demanding than simply providing the equivalent amount of energy found in newly created muscle.  

Attempts have been made to estimate the exact amount of energy required to grow muscle. However, these estimates are somewhat crude.

Metabolism is very dynamic. The bigger we get the more calories we burn at rest and during activity. Short-term overfeeding can cause compensatory increases in metabolism and training experience.

But genetics will influence how much energy can be directed to muscle growth. So as we (hopefully) grow after each session this will have a direct impact on all of the above factors. And to accurately estimate our needs, we would need to calculate all of these variables on a daily basis and adjust intakes accordingly. Which simply isn’t practical.

So what DO we know about efficient muscle building?

Research has shown that high protein diets are essential for muscle growth, maxing our growth potential at around 2 g/kg of body weight per day. To maximize muscle growth you can split your total protein need into 4-5 meals per day, spaced around 3-5 hours apart. Including protein rich meal before bed.

This will ensure the body’s muscle building process is fully switched on and will also provide an abundance of amino acids to support muscle growth throughout the day and night.

Interestingly though, if we push calorie intake into a surplus and increase protein intake above 3 g/kg per day. There appears to be a favorable effect on muscle size without significantly increasing fat mass - even when overfeeding by up to 1000 kcal per day!

Any excess protein energy consumed does not easily convert to body fat which may be explained by an increase in metabolism. Or because the conversion of amino acids from protein into fat is an energy inefficient process.

Finding your muscle building sweet spot

Although potentially a crude estimate, many coaches do appear to use the 350 kcal-500 kcal per day approach a useful and effective starting point. But it is important to play around with and monitor many variables to find the sweet spot. These include the level of surplus and deficit, training volume, rest and recovery and dietary composition.

It is also important to ensure that we have adequate amounts of carbohydrate in the diet to fuel our training. Around 5-7 g/kg of body weight should do it for most people.

We also need adequate fat to sustain health and hormonal function. Around 1 g per kg of body weight should do it.

However, if you have an active job or exceptionally high training volumes. Or if you cross-train with lots of extra cardio, then it’s important to increase your carbohydrate intake to meet your specific demands.

How this might look in practice…

A 100 kg male, training 5 days per week has a total daily energy expenditure of 3500 kcal on training days.

Note. Online calculators can give you a rough estimate of your daily maintenance calories as a starting point.

To create lean muscle growth this is an intake of ~4000 kcal per day.

We are going to target 2 g/kg of protein, 1 g/kg of fat with the remaining intake from carbohydrate.

Protein has 4 kcal per gram, fat 9 kcal per gram and carbohydrate 4 kcal per gram.

Calculating calorie amounts for protein and fat….

Total Protein Calories = 2 g/kg x 100 kg x 4 kcal/g = 800 kcal

Total Fat Calories = 1 g/kg x 100 kg x 9 kcal/g = 900 kcal

Now we calculate carbohydrate calories from what’s left…

Carbohydrate calories = 4000 kcal – 800 kcal – 900 kcal =2300 kcal

Finally, we calculate carbohydrate intake by dividing by 4 g/kg…

Total carb intake = 2300/4 = 575 g!

That’s a total nutrient intake of:

  • 200 g of protein (2 g/kg x 100)
  • 100 g of fat (1 g/kg x 100)
  • 575 g of carbohydrate (5.75 g/kg of body weight)


Further reading:

  1. Is an Energy Surplus Required to Maximize Skeletal Muscle Hypertrophy Associated With Resistance Training? https://doi.org/10.3389/fnut.2019.00131
  2. Dietary protein requirements and adaptive advantages in athletes - https://doi.org/10.1017/S0007114512002516 
  3. The effects of consuming a high protein diet (4.4 g/kg/d) on body composition in resistance-trained individuals - https://jissn.biomedcentral.com/articles/10.1186/1550-2783-11-19