The Basics of Muscle Growth and Fat Loss
How Muscle Building Works
Protein is vital for muscle growth [1] [10] [13] [14]. Protein supplies amino acids, which are used as building blocks for muscle. When you combine protein with strength training, you create an anabolic environment for muscle hypertrophy.
Here’s how it works:
Exercise causes tiny tears in muscle fibers. Your body uses amino acids from dietary proteins to reconstruct these damaged fibers. Over time, the amino acids build larger fibers [15].
Contrary to some beliefs, muscle growth happens during recovery, not exercise. The process responsible for this is muscle protein synthesis (MPS). MPS is a mechanism where our bodies create new muscle proteins to replace damaged ones [15].
But the body also breaks down muscle proteins into amino acids, a process called muscle protein breakdown (MPB) [15].
Your body is constantly building and breaking down muscle tissue. The balance between synthesis and breakdown is vital for muscle growth. Gaining muscle mass happens when synthesis is greater than breakdown. Conversely, we lose muscle mass when breakdown surpasses synthesis [15].
This process requires energy. The best way to ensure that you’re building muscle quickly is to eat more calories than you burn [14]. This is called a calorie surplus.
But a calorie surplus isn’t needed to build muscle mass. You can also build muscle when you eat fewer calories than you need daily. This is called a calorie deficit [1] [3] [14]. We will explore this further down in the article.
How Fat Loss Works
To lose weight, you must eat fewer calories than you burn (calorie deficit) [5]. By doing so, your body taps into its stored energy, mostly body fat.
The most straightforward method to lose weight is to focus on balancing calories consumed and burned. You may have heard of CICO: Calories In, Calories Out. The idea is simple: control the calories you eat and drink while increasing the calories you burn through physical activity.
You can count calories by estimating calorie intake and calorie expenditure.
Let's start with Total Daily Energy Expenditure (TDEE). It represents the total number of calories your body burns daily.
TDEE covers your:
- Basal metabolic rate (BMR)
- Calories burned through daily activities
- Exercise energy expenditure
- The thermic effect of food.
BMR refers to the calories needed to keep your body functioning while resting, like breathing and circulation. The thermic effect of food is the energy used to digest, absorb, and metabolize nutrients.
Here's how to calculate Total Daily Energy Expenditure (TDEE):
The easiest way is to use an online TDEE calculator such as this or this. Note that these calculators are not perfectly accurate. They give you rough estimates on what your energy expenditure is. If you want an exact number, visit a metabolic lab.
Also, your TDEE varies from day to day and week to week. Factors like activity level, muscle mass, and age affect it. Increased physical activity or muscle mass raises your TDEE because your body demands more energy. On the other hand, your TDEE decreases with age as your BMR naturally drops.
TDEE also responds to how many calories you eat. The body will use more energy when you eat a calorie surplus, and less energy when you eat a calorie deficit.
The most important thing is to keep an eye on your weight. You may need to adjust your calorie intake and exercise if nothing happens.
But weight loss is never linear:
Body recomposition is an alternative to the traditional cut and bulk
Body recomposition is when you lose fat while building muscle [1].
Weightlifters, bodybuilders and athletes typically focus on losing weight (cutting) or gaining muscle (bulking). This is divided into phases, such as winter bulking or off-season bulking. Then it is followed up with a cut to prepare for the season.
Body recomposition challenges this traditional approach by working on both goals simultaneously [1]. Newer research shows that it can also be done in trained athletes [1]. This shift in perspective has gained traction in recent years.
| Fact box
A calorie deficit is when you eat fewer calories than you burn. This leads to weight loss. A calorie balance is when you eat the same amount of calories you burn. This leads to weight maintenance. A calorie surplus is when you eat more calories than you burn. This leads to weight gain. |
There are 3 types of body recomposition:
- Body recomposition in a calorie deficit: easy to lose fat, harder to gain muscle
- Body recomposition in a calorie balance: lose fat and gain muscle
- Body recomposition in a calorie surplus: hard to lose fat, easy to gain muscle
Is It Possible to Build Muscle in a Calorie Deficit?
If weight loss requires a calorie deficit, and muscle hypertrophy requires a calorie surplus, how can you do both at once?
It was once believed that these two phenomena couldn’t coincide due to “metabolic antagonism” [3]. But things have changed.
Studies show you can gain muscle while losing fat
You can build muscle while losing fat in a calorie deficit [1] [3] [14]. The studies below show the data.
Body recomposition can be a slow process
"Although it is possible to gain lean muscle in a deficit, it is quite often not fast enough to satisfy most lifters emotionally."
Allan Bacon.
Coach and Founder of Maui Athletics.
Allan Bacon.
While gaining in a calorie deficit can be appealing, it does have its limitations:
- Slower than cut/bulk cycles: Alternating between periods of caloric surplus (bulking) and caloric deficit (cutting) may give quicker results [1] [14]. Separating muscle-building and fat loss phases enables concentrated progress.
- Physics limits endless progress: As fat decreases and muscle increases, the energy needed to support both muscle gain and fat loss becomes harder to maintain. Diminishing returns make it impossible to carry on this process forever.
- Muscle maintenance, fat loss: Some may only preserve their current muscle mass while burning fat. This outcome still improves body composition [9].
For these reasons, you need to make sure you’re setting yourself up to succeed. In the following section we share our best evidence-based advice.
“Most people want to see quick results and fast changes. With regular gaining, you hardly do. Let alone deficit gaining!”
Coach and Nutritionist.
Ruby Cherie.
How to Build Muscle in a Calorie Deficit
#1 - Avoid rapid weight loss
Rapid weight loss is when you drastically cut calories For example, you reduce calories to 1500 kcal per day when your caloric need is 2500 kcal.
While rapid weight loss can look good on the scale, it can lead to muscle loss [2] [4] [7] [8] [11]. The deeper the caloric deficit, the higher the risk of losing muscle mass.
The graph below shows the correlation between calorie intake (x-axis) and changes in lean mass (y-axis).
“Relationship between estimated energy deficit and change in lean mass. The shaded area on either side of the regression line represents the 95% confidence interval for the regression” [11] The y-axis shows the effect size and should not be interpreted as kilograms.
For this reason, researchers recommend limiting energy deficit to ≤500kcal per day [10] [11]. I.e. If you need 2500 kcal per day to maintain weight, you should cut calories to no more than 2000 kcal per day. Another way to calculate it is to aim for a 10-20% calorie deficit.
Note that the body dynamically adjusts its energy needs. You might need 2500 kcal a day at the start of your weight loss, but after some months, the energy need may decrease to 2300 kcal. The body does this to prevent weight loss. This reaction is known as adaptive thermogenesis.
#2 - Eat a high protein diet
Protein is the most important macronutrient for preserving and gaining muscle mass. The scientific literature recommends eating a high protein diet when in a caloric deficit [1] [10] [12] [13].
Aim for 1.6g to 2.2g of protein per kilogram of bodyweight [13].
#3 - Do strength training with progressive overload
Strength training protects muscle mass when you cut calories [9].
Progressive overload is gradually increasing the weight, volume, or intensity of your workouts over time. Aim for at least 3 training sessions per week [1].
#4 - Get proper recovery and sleep
Sleep is often overlooked as a variable for fat loss and muscle gain. A lack of sleep can slow down fat loss, and speed up muscle loss [1] [13]. It can also affect your progress by increasing hunger and fatigue. So you eat more and train less.
7-9 hours is the recommended amount of sleep [6].
#5 - Do it while its effective
There is a limit to how long you can do body recomposition effectively. It could be months, or years.
At some point, you may start spinning your wheels. So keep a track of your progress. If it slows down, consider switching to bulking and cutting.
Who Has the Best Chances of Gaining Muscle While Losing Fat?
The 3 factors that make deficit gaining easier
- High body fat percentage: This allows your body to prioritize fat as an energy source. It spares muscle tissue from being broken down. As a result, you can continue to build muscle even as you lose weight [14].
- Beginner / newbie gains: When you first start strength training, the body is highly responsive. This responsiveness allows you to build muscle while losing fat, even in a caloric deficit [14].
- Retraining (muscle memory): Athletes or lifters who come back from a break, can easily do body recomposition. Muscle memory is when muscles “remember their former glory”. This memory comes from nuclei in muscle cells, which remain intact even after muscle loss. When you start training again, your muscles quickly regain their previous size and strength.
Deficit gaining is harder for trained lifters and elite athletes
For trained lifters and athletes with low body fat %, body recomposition becomes harder.
Here's how it works:
Low body fat
A low body fat percentage means there is less stored energy available for the body to use. When the body has limited energy reserves, it may use muscle protein as a source of energy [10].
Additionally, low body fat levels can result in hormonal changes that can affect muscle growth and fat loss [4]. For example, bodybuilders have reduced levels of leptin, a hormone that regulates energy balance and appetite [4].
Bodybuilders preparing for a contest often do not achieve body recomposition[1] [4]. Their body fat percentage is very low (4-7%), which is one of the main reasons. [1] [4].
Closer to genetic ceiling
Trained lifters and elite athletes have likely reached or are approaching their genetic ceiling. As you get closer to your genetic potential, it takes more work to progress.
"Deficit gaining doesn't make sense, in my opinion, for those who want to optimize their progress in a given period of time, those who are lean, or highly experienced trainees."
Coach and Founder of Maui Athletics.
Recommendations
Are you a trained weightlifter, athlete or bodybuilder with a low body fat %? If so, you might spin your wheels with body recomposition. Traditional cuts and bulks may yield more sustained progress.
The exception is if you’re coming back from a break. In which case, studies have shown that deficit gaining is much more likely.
Gaining Muscle Mass in a Deficit vs. Bulking (Research Review)
Can we gain in a deficit? How much should you eat to reach your goals? This article applies to you whether you’re a beginner or advanced lifter.