Everything you need to know about human energy balance

Gaining muscle and losing fat is fundamentally a matter of energy balance. Most understand the concept of “Calories in vs. Calories out,” but this is over-simplistic for the serious trainee that wants a solid understanding of human energy balance.

This article will cover everything you need to know to understand the nuances of energy balance and how it applies to the human body. I’ll also cover some less intuitive aspects of human energy balance and supplemental topics that are often overlooked.

Human energy balance and the first law of thermodynamics

Calorie is the unit of energy typically associated with human energy balance. 1 Calorie = 1000 calories = 1 kcal. Almost every nutritional label uses the unit “Calories.” Even though many will write “calories” without a capital “C”, they mean “Calories.”

There are three components of human energy balance:

Energy Intake: The consumption of energy from food the food we eat. Energy intake is pretty straight forward and doesn’t require a long drawn out explanation. Humans only use the constituents of food for energy. Our bodies extract usable energy from the three macronutrients in food; protein, carbohydrate, and fat.

The scientist Wilbur Atwater discovered an easy and accurate way to quantify the energy content of the three macronutrients. Atwater found, regardless of the food source, 1 gram of protein contains ~4 Calories, 1 gram of carbohydrate contains ~4 Calories, and 1 gram of fat contains ~9 Calories. With this information, it is easy to determine with good accuracy how many Calories (energy) we consume over time.

Energy expenditure: How we use the available energy from the food we eat and from the energy we have stored to carry out any physiological process. Energy expenditure will be covered in more detail later.

Energy storage: Your energy intake and energy expenditure dictate whether or not you will be storing energy (energy surplus) or losing stored energy (energy deficit) over time.

To put human energy balance in simple mathematical terms:

\text{ ΔE (energy stored) } =  E_i \text{(energy intake)} - E_e \text{(energy expenditure)}\hspace15ex (1)

You can have a ΔE that is negative, positive, or 0.

Negative energy balance (ΔE<0): If you expend more energy than you consume over a period of time, your body will use stored energy to make up for the lack of energy consumed in your diet.

Positive energy balance (ΔE>0): If you consume more energy than you expend over a period of time, your body will store the excess energy.

Energy maintenance (ΔE=0): If you consume the same amount of energy as you expend over a period of time, you store no energy.

Equation (1) is formally known as the first law of thermodynamics (also referred to as the conservation of energy), modified for human energy balance. In a more general sense, the first law of thermodynamics applies to every entity in this universe. Sorry, there’s no way around it; you need to consume less energy than you expend over time to lose fat (there is a rare caveat to this, you will see when and why below).

It’s very trendy in today’s mainstream fitness industry to go against the grain of conventional and undeniable wisdom like this. As a fitness enthusiast, you’ve likely have heard contradicting advice from self-proclaimed nutrition experts or “fitness influencers” on this topic. Many of them sadly don’t even understand the fundamental physical nature of this law, so they dismiss it and suggest this law can somehow be circumvented or ignored entirely in achieving your desired body. They are all full of it. Unfortunately, lies like this are commonplace in the fitness space today, in part because they can sadly get away with such lies without having to worry much about legal issues. Another driver in fabricating these ridiculous, non-scientific claims, is to attract those who are less informed on the subject, to sell them highly profitable items (i.e., supplements) which ironically help very little, or not at all, in their journey to lose fat and gain muscle.

Many erroneously associate a surplus of energy solely as fat gain and a deficit of energy only as fat loss. In general, that is the case for the sedentary population but is over-simplistic for strength trainees that are going to put on muscle. Muscle tissue functions under the same principle; it is stored energy just like fat.

There are two components of muscle tissue that your body can use for energy:

  • The muscle proteins that make up the contractile component of the muscle.
  • Muscle glycogen, the stored form of glucose, a fuel source for the muscle.

Muscle tissue is often referred to as lean body mass (LBM). As strength trainees, resistance training allows us to skew energy balance in favor of storing energy as LBM. So, when muscle hypertrophy occurs, the new muscle tissue added to your skeletal frame is stored energy added to your body, just like fat. And just like body fat, your body can break down muscle tissue and use it for energy, which of course, is highly undesirable! Fortunately, resistance training typically signals your body to use body fat as energy rather than your precious muscle tissue.

Since we only store or lose energy as body fat or LBM, we can rewrite equation (1) as follows:

\text{ ΔE (energy stored) } =  ΔLBM + ΔBF \hspace20ex (2)

∆LBM is the change in your lean body mass-energy over time, and ∆BF is the change in your body fat mass-energy over time.

We know with a high degree of accuracy thanks to Hall et al. 2008, muscle tissue contains about 1820 Calories/kg (827 Calories/lb), and pure fat mass contains 9441 Calories/kg (4284 Calories/lb). However, if you lose 1 lb of body fat, you would be incorrect in saying you lost 1 lb of pure fat. Instead, you actually lost 1 pound of adipose tissue.

Adipose tissue is the biological term used to describe body fat. Adipose tissue is ~87% fat; the rest is mostly water and even a little protein. So, if you lose 1 lb of body fat, you’re losing approximately 0.87 lbs of pure fat, the rest is mostly water. Therefore, body fat contains 8260 Calories/kg (3746 Calories/lb).

So, you can determine if you were in an energy deficit or surplus over a given period of time “simply” by knowing how your body composition (you can think of body composition as the sum of your body fat and lean body mass) changed over that period of time. You don’t need to know your energy intake or energy expenditure!

Application of the first law of thermodynamics

To gain a better understanding of human energy balance, lets now apply the first law of thermodynamics (specifically, equation 2) to everyday situations in the bodybuilding/strength training world.

First and foremost, how do you know with certainty you are storing energy over time or losing energy over time?

At first glance, many people are quick to say if the number on the scale (your weight) is dropping, you are obviously in an energy deficit. However, this is another oversimplification. While this is generally true, especially for people who don’t lift weights, it is not necessarily the case for strength trainees. As strength trainees, we are not interested in losing weight, we want to lose fat, and we want to gain muscle!

For example, say an intermediate male trainee goes on a cut and starts a new optimal strength training program and loses 1lb of body fat but gains 1lb of muscle. His overall change in weight is 0. Therefore, many would erroneously conclude based on his weight not changing; he was in energy maintenance (he burned the same number of Calories as he consumed, ∆E=0) during that period. But remember, body fat has a lot more energy in it per unit weight than muscle tissue (~4.5X more energy), so he was actually in an energy deficit!

Plugging these values into the first law of thermodynamics:

∆E =∆LBM + ∆BF = 827 \frac{kcal}{lb} * (1lb) + 3746 \frac{kcal}{lb}*(-1lb) = -2,919  \text{Calories (energy deficit)}

The negative number indicates a loss of energy from the body. This is why it is crucial to not only track your weight over time but to also track your body composition over time. Losing body fat but gaining an equal amount of weight in muscle during energy deficit is excellent progress. This is known as “perfect recomposition.” If perfect recomposition is happening to you and you aren’t tracking your body composition, you may incorrectly assume you’re not in an energy deficit and needlessly lower your Calorie intake to the point where you’re in too high of a deficit!

By the way, it is absolutely possible for dedicated trainees to gain muscle during an energy deficit. The addition of muscle is an adaptation to stress. The adaptation/recovery process is influenced little by your energy intake (assuming you’re within a reasonable range), especially the more overweight you are. It takes energy to build muscle, but your body has plenty of it already. Even a 175lb guy at a lean body fat percentage of 10% has 75,000 kcal of stored fat energy! This doesn’t even include the energy consumed every day from his diet.

People who don’t gain muscle/strength or lose muscle during a Calorie deficit are often doing the “little things” wrong (not sleeping well, not controlling their stress levels well, poor nutrition, not doing an optimal training program, energy deficit is too high). Your level of training advancement and genetics (which is one aspect out of your control) are also a factor.

Nutrient partitioning is the term used to describe what your body does with excess Calories in times of energy surplus and which energy source it pulls from during an energy deficit. During an energy deficit, all of the lifestyle factors you have control over mentioned above need to be dialed to skew nutrient partitioning in favor of using fat as energy and not muscle.

Here’s another example:

Let’s say a male trainee gained 1 pound over the course of 3 weeks. He measured his body composition by getting a DXA at the beginning and the end of the three weeks. According to his two DXA scans, that 1 pound he gained was entirely muscle mass. Does this mean he was in an energy deficit, energy maintenance, or energy surplus?

The answer is energy surplus. Remember, muscle tissue stored energy, just like fat. You do not need to be gaining fat to be in an energy surplus:

∆E =∆LBM + ∆BF = 827 \frac{kcal}{lb} * (1lb) + 3746 \frac{kcal}{lb}*(0lb) = +827  \text{Calories (energy surplus)}

Weight maintenance doesn’t mean energy maintenance

Weight maintenance means your body weight did not change over a period of time. However, just because you didn’t gain or lose weight over some time does not necessarily mean you were in energy maintenance! This goes back to the perfect recomposition example above. Just because your weight isn’t changing, doesn’t mean you’re in energy maintenance.

If you gained a half-pound of muscle and lost a half pound of body fat over the course of a month, you were in weight maintenance during that month, but you were not in energy maintenance. Remember, fat contains more energy per unit weight than muscle:

∆E =∆LBM + ∆BF = 827 \frac{kcal}{lb} * (0.5lb) + 3746 \frac{kcal}{lb}*(-0.5lb) = -1,460  \text{Calories (energy deficit)}

In this example of weight maintenance, you were actually in an energy deficit!

Let’s now take the above example, but instead of gaining a half-pound of muscle, you gained 2.26 pounds of muscle:

∆E =∆LBM + ∆BF = 827 \frac{kcal}{lb} * (2.26lb) + 3746 \frac{kcal}{lb}*(-0.5lb) \approx 0  \text{Calories (energy maintanence)}

So, in this case, you were in energy maintenance, but you weren’t in weight maintenance! This also illustrates that you can gain muscle or fat in energy maintenance; you need to lose an equal amount of energy in fat or muscle to make ∆E=0.

You can also be in an energy surplus when you are in weight maintenance:

∆E =∆LBM + ∆BF = 827 \frac{kcal}{lb} * (-0.5lb) + 3746 \frac{kcal}{lb}*(0.5lb) = +1,460  \text{Calories (energy surplus)}

Test your understanding

The following examples of human energy balance are rarely seen in practice. If you can answer the following questions, you have a solid understanding of human energy balance! If you were to ask a lot of personal trainers/coaches these questions (or the previous questions for that matter), many would get them wrong.

Q: Is it possible to lose fat in an energy surplus (∆E is positive)? Hint: like all of these examples, think about the first law of thermodynamics (equation 2).

Answer:

It is possible to lose fat in an energy surplus, and there are cases in which this has occurred. For ∆E to positive, while your ∆BF is negative, you need to gain at least ~4.6x more muscle than you are losing in body fat.

So, if someone gained 4.6 lbs of muscle and lost one pound of body fat over a period of time, they would have been in an energy surplus (a slight one):

∆E =∆LBM + ∆BF = 827 \frac{kcal}{lb} * (4.6lb) + 3746 \frac{kcal}{lb}*(-1lb) = +58  \text{Calories (energy surplus)}

This is a pretty extreme example and generally only happens with untrained males with exceptional genetic potential or when a trainee takes a very long layoff, loses a lot of muscle, but has “muscle memory” to gain muscle back very quickly.

People that take anabolic steroids can also see changes in body composition like this. You may think, “well, if a person is on drugs, that is an exception.” It’s not, however. Being on steroids does not somehow circumvent the first law of thermodynamics. That law applies to every single system in this universe. On a very fundamental level, steroids influence nutrient partitioning. So, a person on steroids is still obeying the first law of thermodynamics; the steroids skew what their body does with its energy.

Q: Is it possible to gain fat in an energy deficit?

Answer:

Yes, this is also possible. And if this ever happens to you, you know you’re on a terrible program or something is seriously wrong! In this case, your ∆E is negative, and you need to lose at least ~4.6x more muscle than you gain in body fat for this to occur!

∆E =∆LBM + ∆BF = 827 \frac{kcal}{lb} * (-4.6lb) + 3746 \frac{kcal}{lb}*(1lb) = -58  \text{Calories (energy deficit)}

Final question: Is it possible to gain weight during an energy deficit?

Yes, it is! Participants in this study (they were elderly, believe it or not) gained weight in a Calorie deficit. In this case, you’re not quite gaining 4.6x more muscle than you are losing in body fat.

For example:

∆E =∆LBM + ∆BF = 827 \frac{kcal}{lb} * (4lb) + 3746 \frac{kcal}{lb}*(-1lb) = -438  \text{Calories (energy deficit)}

Your change in weight is + 3lbs, but you were in an energy deficit.

Net energy balance over time

In practice, you’re constantly in a flux of energy balance throughout the day and over time. When you consume a meal, your body will be absorbing the Calories from the food over the next several hours. You’ll likely be in energy surplus over these several hours, especially if you’re relaxing on the couch. So, throughout a cut, you still have acute spikes of energy surplus when you eat your meals.

The same is true for bulking. Even though over the course of many months, you will be in a net energy surplus, you will have acute spikes in which you were in energy deficit. For example, if you consumed your last meal at 6 pm and don’t eat again until 9 am, your body will be using stored energy to fuel its energy needs during the morning hours.

Here is a graphical representation hypothetically illustrating energy balance over the course of a day with three meals and an overall loss of energy (-650 kcal):

Theoretical Energy Expenditure

Our bodies expend energy around the clock. Your body uses energy to carry out every physiological process, whether it’s physical activity (such as lifting weights), pumping blood throughout your body, or growing muscle.

There are some general formulas that estimate (more on this later) how much energy we expend over the course of a day to carry out these physiological needs. In this section, I’ll go over these formulas in some detail. You’ve probably seen some or all of the following formulas before. These formulas are used to give you a good idea as to how many Calories you burn every day so you can then determine a corresponding energy intake that is in line with your goals (i.e., fat loss).

Basal metabolic rate (BMR)

BMR is the energy your body expends to carry out its necessary daily functions to keep you living, such as brain activity, organ activity, controlling body temperature, cell growth, etc. BMR is essentially the amount of energy you would burn if you were to lay in bed all day and not move. The most well-known formula that estimates your BMR (in Calories) is the Katch-Mcardle equation:

BMR =  370 + 21.6*FFM(kg)

FFM is your fat-free mass (in Kilograms). FFM is your body weight minus all fat mass and is calculated using your body weight (BW) and body fat percentage (BF%):

FFM = BW(kg)*(1-BF\%/100)

Since most of us are not lying in bed all day, the amount of energy you expend throughout the day will be your BMR plus the energy you expend during daily physical activity and working out at the gym. Furthermore, when you consume food, your body also spends energy digesting the food.

The thermic effect of food (TEF)

TEF is how much energy you expend digesting and absorbing the nutrients from the food you eat. It is proportionate to your Calorie intake. To estimate how much energy you expend from TEF, you multiply your Calorie intake by your TEF.

How do you determine your TEF?

TEF is an educated guess. Based on the limited research we have, TEF for humans is typically 0.1 – 0.25. Overweight individuals and anyone with a poor diet (consisting of mostly processed food and low in fiber) will have a TEF closer to 0.1 (this is an appropriate number for most at first). TEF for a lean person (body fat percentage ~10% for males and ~14% for females) eating a healthy diet consisting of whole foods, lots of fiber, and sticks to eating their meals at the same time every day (yes, eating your meals at the same time every day increases your TEF) will have a TEF around 0.25, possibly higher! People who are lean and eat healthily, burn significantly more energy digesting their food on a per Calorie basis than someone who eats a poor diet with lots of processed foods, snacks often, always eats at random times and is overweight.

TEF is a highly underrated aspect of a diet. Not only do you burn more energy with a higher TEF, it also allows you to consume more food and be in the same energy deficit. It’s beneficial to consume more food from a nourishment standpoint. It’s hard to consume enough micronutrients during a fat loss diet, even if your diet is healthy. So, the more food you can have, the better the chance it gives you to hit your micronutrient needs. Many of the cookie-cutter programs out there that calculate your energy expenditure typically don’t consider your TEF.

Rest day energy expenditure (RDEE)

Putting together all variables that contribute to your daily energy expenditure allows us to calculate how much energy you expend on a day in which you are not training. This is your RDEE in Calories.

RDEE = (BMR*PAL) + (CI*TEF)

CI = Calorie intake, the total Calories you consumed for the day.

PAL = Physical activity level. PAL Typically ranges 1 – 1.5. The higher your PAL, the more active your daily life is. PAL is easy to overestimate. I recommend being conservative when choosing a value. 1 is typically a good number for someone with a sedentary office job. 1.25 could be a personal trainer that does a lot of moving all day. 1.5 could be a construction worker that is doing constant hard manual labor all day.

Your Calorie intake on a rest maintenance day (∆E=0) will be BMR x PAL. Plugging that into the formula for your RDEE gives you the following:

RDEE = BMR*PAL*(1+TEF)

Training day energy expenditure (TDEE)

To estimate the amount of energy you expend during a workout (RTEE, in Calories), use the following equation:

RTEE = 0.1*BW(kg)*T

T = time of your workout in minutes. Workouts that consist of 12 total working sets take about an hour. If it takes an hour to do three sets of squats because you waited 10 minutes between sets and were also spending time on your phone, that does not mean your workout time is 60 minutes for this calculation.

To determine your TDEE, add your RDEE to your RTEE:

TDEE = (BMR*PAL) + (CI*TEF) + RTEE

If you want to know your maintenance energy intake on a training day, substitute BMR x PAL + RTEE in for your CI:

TDEE = (BMR*PAL + RTEE)*(1+TEF)

These calculations result in a decent ballpark estimate of your daily energy expenditure. However, many people become fixated on theoretical one-size-fits-all calculations and roll with what they spit out without second-guessing their accuracy. This often leads to under/overeating, leaving many confused as to why the calculations aren’t working.

A quick statistics lesson

Whenever a single calculation is used to determine a value (for example, your BMR) for an entire population, the calculation will be accurate on average for a given individual. For example, if we were to take every guy that is 175 lbs at 10% body fat, they would all theoretically have the same BMR per the Katch-Mcardle equation. However, if you were to measure the BMR of a large group of them (this is possible by the way, using a method called indirect calorimetry), you would get varying values of BMR. If you were to plot the BMR of the entire group of people on a graph, it would look something like this:

Those who are familiar with statistics will recognize this type of plot. The plot is known as a normal distribution (often referred to as a bell curve). This type of plot for a given set of data occurs everywhere in nature. Some examples include the height of men, the weight of apples in a grocery store, 1 RM bench press in intermediate male trainees, and the mass of stars in the universe. This type of plot even exists for the amount of training volume one should do for optimal results.

As you can see from the plot, if you are 175lbs with 10% body fat, your BMR will probably be around 1900 kcal (which is the average in this plot). To put this another way, if you randomly picked one person that is 175lbs at 10%, odds are, they will have a BMR close to 1900 kcal. As you move further away from the center of the bell curve toward the “tails,” it becomes less likely a random person you pick from this population will have a BMR at either tail end of the curve.

Along with your BMR, your TEF, PAL, and RTEE are also an educated guess that further contribute to error. This is why the above theoretical one-size-fits-all calculations can only offer a decent idea as to what your energy expenditure will be. You won’t know where you specifically fall on the bell curve until you start collecting data that is specific to you.

Let’s look at an example.

A male trainee weighs 175 lbs (79.5 kg) at 10% body fat and eats an excellent diet consisting of mostly whole foods with plenty of fruits and vegetables. He also eats his meals at the same time every day. He has an office job. His training sessions are 60 minutes long, and he has five training sessions a week. Determine his weekly maintenance energy intake.

First, calculate his BMR:

FFM = BW(kg)*(1-BF\%/100) = 79.5kg*(1-10\%/100) = 71.6 kg

BMR =  370 + 21.6*FFM(kg) = 370+21.6*71.6kg \approx \text{1,900 Calories }

He has an office job, so let’s go with a PAL of 1. He’s also lean, eats healthy, and sticks to a meal schedule, so we’ll go with a TEF of 0.25.

His rest day maintenance energy intake is:

RDEE = BMR*PAL*(1+TEF) = 1,900*1*(1+0.25) = \text{ 2,375 Calories }

His resistance training energy expenditure is:

RTEE = 0.1*BW(kg)*T = 0.1*79.5kg*60 = \text{ 477 Calories }

Notice that resistance training burns a good number of Calories.

His training day maintenance energy expenditure is:

TDEE = (BMR*PAL + RTEE)*(1+TEF) = \text{2,971 Calories}

His theoretical weekly maintenance energy intake is:

(2,971*5)+(2,375*2) \approx \text{19,600 Calories }

This is when tracking your body composition and energy intake comes into play to determine your actual energy expenditure, and thus, your target energy intake. Say the trainee in this example wanted to be in energy maintenance and consumed 19,600 kcal each week, for four weeks in a row. He weighed himself daily and recorded his body composition throughout the four weeks using skin fold caliper readings. By the end of the four weeks, his strength in the gym went up, his weight was the same, but his skin fold readings dropped, indicating he lost fat. Again, this is another example of a perfect body recomposition; he more or less lost the same amount of weight in fat as he gained in muscle, meaning he was actually in energy deficit over that time. So, it’s obvious the calculations above were off. His weekly maintenance energy intake is actually higher than 19,600 Calories.

Let’s say he gained 2 lbs of muscle and lost 2 lbs of body fat during those four weeks. Calculating his energy deficit:

∆E =∆LBM + ∆BF = 827 \frac{kcal}{lb} * (2lb) + 3746 \frac{kcal}{lb}*(-2lb) = -5,838  \text{Calories (energy deficit)}

5,838 Calories of energy were lost from his body over the four weeks, so his actual maintenance energy intake during those four weeks was approximately:

19,600 \frac{kcal}{week}*4weeks+5,838*(1+TEF) \approx \text{85,700 Calories }

Notice how you need to add in the additional energy you will expend from consuming the extra Calories via TEF.

In practice, you likely won’t know the exact amount of muscle and fat you lost/gained over time unless you get a DXA scan (which still isn’t 100% accurate) or are very good at self accessing your body composition.

If you’re a beginner, you’ll use the above theoretical formulas to determine your approximate energy expenditure, which dictates what your target energy intake will be based on those calculations and your goals (i.e., cutting, bulking, or maintaining). Once you calculate your target energy intake, you need to track your body composition and make slight adjustments (if necessary) to your energy intake as you go until your body composition is changing the way you want it.

I created a calculation page that runs the calculations for you. However, it’s still important to understand the application and limitations of these formulas.

Determining your energy balance

In the bodybuilding world, you often hear people refer to energy balance as a percentage, which is simply a ratio of your energy intake to energy expenditure:

\%(EB) = \Big(\dfrac{E_i}{E_e} -1 \Big)*100

For example, maintenance energy intake (Ei = Ee) is an energy balance of 0%:

\%(EB) = \Big(\dfrac{E_i}{E_e} -1 \Big)*100=(1-1)*100=0\%

Since most trainees are cutting or bulking, determining an appropriate energy balance is important.

What’s a proper energy balance? It shouldn’t come as too much of a surprise; it depends on the individual. Don’t worry, though, determining a target energy balance is relatively simple.

If you are cutting, use this chart as a guideline for your target energy balance:

Notice the ranges given for each corresponding body fat percentage range. Again, the deficit that is right for you depends on the “little things” I mentioned earlier. If you’re not sleeping well and always stressed out, you won’t be able to handle as large of a Calorie deficit. The goal of a cut is to lose fat as quickly as possible so you can get back on a lean bulk ASAP. However, this shouldn’t come at the expense of a loss in strength, which is one of the culprits of being in too high of an energy deficit based on your lifestyle factors. Your genetics also play a factor; some people can handle a larger energy deficit without suffering muscle and strength loss. It’s all about finding the right sweet spot for you.

For bulking, use this chart as a guideline for your target energy balance:

Again, the ranges in the chart are based on the same lifestyle factors. If you don’t sleep well and have poor control of your stress, you don’t want to be in as high of a surplus; the extra energy intake will likely be partitioned as fat.

How do you determine your training status? The best way to estimate your training status is by using the strength tables developed by the folks at exrx.net. The strength tables for each exercise are 1 RM weights with corresponding body weights. Wherever you fall on the chart is the training status for the muscles involved in the exercise. Don’t be overly critical with this; the differences in energy balance between each training status is not too significant. Most trainees are intermediates.

The target energy balance for bulking is a pretty low surplus. The typical intermediate trainee that burns 3000 calories per day should only be consuming ~150 calories more than they expend per day during a bulk. A common mistake many trainees make is “dreamer bulking.” Dreamer bulking is when the trainee above consumes closer to 4000 calories per day, a whopping +33% energy surplus.

Many think more is better. However, based on the research we have along with anecdotal evidence, most of that additional surplus of energy will go to fat storage rather than muscle growth. Minimizing fat gain during a bulk has brought about the new school bodybuilding term “lean bulking.”

Lean bulking puts you in a slight energy surplus, allowing you to bulk for many months while gaining a minimal amount of fat but still maximizing (or very close to it) muscle growth. When done correctly, your lean bulks should be long, and your cuts should be short. For example, a male trainee that starts a lean bulk at 9% body fat should be able to lean bulk for 8 – 10 months, gain a minimal amount of fat and end his bulk around 15% body fat. He should still have visible abs once he has finished his bulk and starts to cut!

The rut many put themselves into when cutting and bulking is dreamer bulking up to a very high body fat % and then having to spend an equal amount of time cutting to remove the body fat. Don’t be that person!

Should you cut or bulk?

Here is a chart to use as a guideline to begin your bulk and when you should end it:

If you’re above 15% for a male and above 25% for a female, you need to start in a deficit and cut down to the ‘begin bulk’ body fat %. The ranges of body fat % in the chart are associated with optimal hormone levels, insulin sensitivity, and low chronic inflammation levels. High levels of chronic inflammation blunt the inflammatory signal caused by your workout that your body uses to begin the muscle repair process. Thus, your body is most anabolic when it’s within these ranges of body fat %. Further decreasing your body fat % beyond the lower limits in the chart also removes you from optimal hormone levels. Ask anyone in contest prep that’s at 5%; they don’t feel that great.

If a woman loses her period, that generally means she is at the lower end of the optimal range and should begin lean bulking.

Tracking your body composition

Hopefully, by now, you understand the importance of tracking your body composition. There are various ways to track your body composition. The easiest and cheapest way is by measuring your weight and measuring the skin fold thickness (essentially, the thickness of the subcutaneous fat) at various sites on your body (the more sites, the better).

How your skin fold thickness changes over time will give you an indication of how your body fat levels are changing. If the sum of the skin fold sites you measure decreases over time, you’re losing fat. If the sum of the skin fold site increases over time, you’re gaining fat. Your change in body weight, skin fold readings, and strength in the gym is a pretty good and objective way to determine how your body composition is changing over time.

For locations of each skin fold, click here.

Here are instructions on how to use skin fold calipers.

Skin fold calipers often come with a chart that uses a formula to determine your body fat % based on one or several skin fold sites. In my experience, these charts are usually way off and significantly underestimate body fat %. If you are good (most people aren’t) at visually estimating body fat % that is generally much more accurate than those crappy charts. It isn’t critical you know your exact body fat %, however. What’s important during a cut is seeing your skin fold caliper recordings drop over time.

The most crucial part of using the calipers is consistency with the location you are pinching. You can use permanent marks on your skin as an indicator to ensure you’re grabbing the same area every time. As with everything, it takes practice to become adept at pinching the same amount of skin and the same location each time. Correctly using the calipers takes practice. Don’t worry; it’s not like learning how to squat with proper technique.

There are also other methods such as DXA scans, electrical impedance, and others that can be useful as a way of determining your body composition. However, those methods have their limitations in accuracy (DXA probably being the most accurate), cost more, and are less convenient than simply owning a pair of body fat calipers.

During a cut, the sum of your skin fold readings should drop just about every week (assuming you can handle such a deficit without losing strength). If not, that is an indication you are consuming too much energy. Unfortunately, it isn’t practical (unless you have the money) to get a weekly DXA scan.

Pictures can also be telling of your body composition change, but only over a much more extended period. Photos of yourself two weeks apart are often not objective. Even if you take the picture in the same lighting and time of day (which is very important, even changing the lighting a little bit can make you look more muscular and leaner), it’s hard to see any noticeable difference. Bloating can also make you look leaner between two short periods even though your body composition didn’t (or hardly) changed.

The same goes for a workout pump. A pump can make it look like you’ve gained 5 lbs of muscle since the morning. It’s incredible how different you can look at the beginning of the day when you have no pump in your muscles, you’re in poor lighting and are bloated compared to later that day after your workout in an environment with good “selfie” lighting. All of these factors are one reason you need to take transformation pictures with a grain of salt. Often, people use all of these factors to their advantage to give the appearance they lost more fat and gained more muscle than they did.

Adaptive thermogenesis

There is one last piece of the puzzle that will affect your energy expenditure and, thus, your energy intake over the course of a cut and bulk. This other factor is called adaptive thermogenesis. Adaptive thermogenesis is a mechanism your body uses to prevent too much fat loss or to prevent too much fat gain.

When you are losing fat in a caloric deficit, your body has an intricate way of becoming more efficient with its energy. Your body thinks food is scarce (even though in today’s world, you are probably a few feet away from food most of the time). Lean individuals that are in a caloric deficit will be less fidgety, get cold more easily, and generally have less spontaneous movement. The opposite of this is the case when someone is in a caloric surplus. In a surplus, you generally have more spontaneous movement. Your body will also be radiating more energy as heat to burn Calories.

For example, let’s take a 175lb trainee at 10% body fat and put him on the breakfast, lunch, and dinner fast-food diet and get him up to 20% body fat. For the sake of argument, assume his FFM didn’t change and also assume his physical activity and TEF are precisely the same as well after getting up to 20%. Based on this, and what you’ve learned up to his point about energy expenditure, you would expect him to be expending the same number of Calories every day as he was at 10% body fat. However, you’d likely be wrong, and this is because of adaptive thermogenesis. He would likely be burning more Calories.

So, lets say you start a cut at a target energy deficit of 20% (your maintenance energy intake multiplied by 0.8). Once you start the cut, your body fat will decrease. If you’re diligent about tracking your Calorie intake and monitoring your body composition, it’s likely after some time you will no longer be losing fat at the same rate as you were initially because of adaptive thermogenesis. This is when you need to readjust your Calorie intake to put yourself back in a 20% deficit. The same holds when you are bulking. When you are bulking, you will eventually need to add more Calories to your weekly total to stay in the desired energy surplus.

There is no way to estimate the degree of adaptive thermogenesis you will have; it varies a considerable amount between people. Some people can start a cut and stay in their desired deficit for quite a long time, only having to make minor adjustments in their Calorie intake to remain in the same deficit for the entire duration of their cut. Others will need to drop their Calorie intake much more and with higher frequency. However, the person that has to reduce their Calorie intake significantly over the course of a cut will also have to increase their Calorie intake considerably over the course of a bulk. It works both ways.

By the way, this is one of the reasons why Yo-Yo dieting often occurs in the sedentary population. People who have a high degree of adaptive thermogenesis won’t be able to eat much food without quickly gaining back the fat they lost. And since sedentary people don’t add muscle when they lose fat, this further limits the number of calories they can have. It’s not surprising why so many people fall victim to Yo-Yo dieting. All else equal, the lean muscular version of you will always be burning more Calories than the skinny-fat version of you.

Determining your actual energy balance over time

Knowing your change in body composition over time allows you to calculate your energy balance over time using the first law of thermodynamics (equation 2). If you collect accurate self data (your energy intake and change in body composition) over time, you can calculate your actual % energy balance over a given time frame using the following equation:

\%(EB) = \bigg(\dfrac{E_i}{E_i-(∆LBM + ∆BF)} -1 \bigg)*100

Once you calculate your actual energy balance using this equation, you can then back out what your maintenance energy intake is. Furthermore, you can determine what your new target energy intake should be based on a new target energy balance. This way, you aren’t relying on a one-size-fits-all calculation; you’re using data that is specific to you.

I’ve put all of the calculations required to do this on the same page as the theoretical calculator. Click here to go to the calculator. You can compare the calculations that use your actual data to the theoretical calculations to see what kind of difference you get. Make sure your target energy balance is the same for each case.

The calculations also take into account the difference in energy expenditure from TEF (that’s why you need to make sure you select a TEF that best matches you). So, when you transition from a bulk to a cut, you’ll be expending less energy right off the bat because you’ll be consuming less food. When you finish a cut and go on a bulk, you expend more energy from the start because of your increase in energy intake.

Using the calculator

For the calculator to have any practical significance, your energy intake and change in body composition data you plug in need to accurate. If you plug garbage data into a calculation, you get garbage data out. Some error is acceptable, though. The data you have will never be 100% accurate, and it doesn’t need to be for this to give you a better idea of what your energy intake should be based on a new target energy balance. You can play with the numbers. If you’re a little off on how much muscle/fat you gained or lost, it doesn’t affect the outcome too much.

Since DXA scans typically record pure fat mass instead of adipose tissue, you need to make sure you’re using your change in fat mass with the calculator (this is different from the above examples that used change in body fat). I’ve included a converter on the calculator page.

Objectively determining your change in fat mass and LBM isn’t easy without a spectral imaging device such as DXA. If you don’t have access to DXA, you can make an educated guess yourself. Based on your change in weight, change in strength and fat caliper readings, you can probably get a good enough estimate if you’re experienced. However, many are prone to assuming they gained more muscle while underestimating the amount of fat gained over the course of a bulk.

What about changes in glycogen?

As mentioned earlier, glycogen is a substrate your body can use as energy. Once you start a fat loss diet, your body will use some glycogen as energy, initially, until it reaches a new baseline level. However, this generally happens during the first week or so of a cut and is minimal. Similarly, your body will increase its glycogen stores to a new baseline level over the first week or so of a bulk.

Technically, the change in glycogen baseline storage should be factored into the calculation if you include the first week of a cut or bulk, but it’s hard to know exactly how much glycogen you lost or gained. Glycogen binds to a similar amount of water per unit weight as protein and, therefore, has similar mass-energy density (827 Calories/lb). So, if you include the first week or so of data of a transition from a cut to a bulk or a bulk to a cut, it’s a good idea to assume at least one (if you’re a smaller male or a female) or two (average size to larger males) pounds of your total weight change came from the change in glycogen storage levels. Include this weight as LBM in the calculator.

Food in the GI tract

The amount of food in your GI tract also makes an initial contribution to your total weight change when making a transition from a cut to a bulk or vice versa. When a male transitions from a cut to a bulk, he can gain 1-2 pounds or so in weight just from the increase in the amount of food he’s eating. The weight change from food in the GI tract should be left out if your estimation of your change in LBM and fat mass based on your total weight change.

It’s harder to make an accurate assessment of your body composition change if you include the data from the start of a bulk or cut because of these factors. That’s why it’s best to leave the first couple weeks or so out of the calculation unless you know what you’re doing.

Adaptive thermogenesis

If you’re someone with a high degree of adaptive thermogenesis and you plug in data over a significant time frame, the calculation of your new target energy intake will likely be a bit further off than if you use data within a more narrow time frame. For example, if you have accurate data over the last three months of a bulk, that will give you a more precise answer than if you used data over the entire nine-month duration of your bulk. This is because your body will be expending more energy near the end of your bulk due to adaptive thermogenesis and from LBM gain, so the last three months of data will better capture that change in energy expenditure. The same is true for a cut. If you use the last month or so of data, that will be better than using the entire duration of your cut.

Physical activity

The calculations also assume your total physical activity (your PAL and resistance training energy expenditure) will remain relatively constant. For example, if you plug in 9 months of data from which you were working a sedentary office job but are now working at a job that has you moving around all day, this will need to be factored in to determine your new energy intake.

I’m here to help, please comment below if you have any questions regarding the material contained in this article.

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