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Gaining muscle mass: A lean bulk or a dirty bulk?

By Fleur van Griensven

Spring has just begun and some have probably already started cutting. The winter is the perfect moment for gaining muscle mass, right? Temperatures below zero, Christmas and New Year with a lot of delicious food. Also way too cold to wear tank tops, so you can hide the gains or a little winter fluff with comfortable sweaters. This is also the reason why most people tend to use this season for bulking and start a cut before summer to see what they have built up. What should you do once you have decided that it is time to improve your physique and start a bulking period: a lean bulk or a dirty bulk (one in which you eat as much as you can)? Which one is more optimal for gaining muscle mass whilst keeping fat gain to a minimum? Read the answer here.


To optimally gain muscle mass you need to be in a caloric surplus, hence eat more calories than you burn. This means that to optimize muscle growth you need to be in a weekly caloric surplus. Those extra calories can then be used for protein synthesis and recovery. If you also apply progressive overload in the gym, you will give your body a stimulus to adapt to and grow stronger and bigger (=supercompensation). Progressive overload can be accomplished in many ways: lifting more weight, doing more reps/sets, training more frequent so you can get in more volume per muscle group etcetera. When your skeletal muscles grow bigger and stronger upon a training stimulus, you need to continue making greater demands, so they can make further adaptations. I will not go into detail about what you should do with your training during a bulk, but I briefly wanted to get you familiar with the concept of progressive overload if you have not heard of it already. I will come back to it later when I discuss the downsides of implementing a dirty bulk.

Lean bulking

If you choose to go for a lean bulk, you are going to be in a small caloric surplus every day (+/- 200-300 calories above maintenance). You will probably keep yourself accountable that things do not get out of hand: you will weigh yourself, take pictures and make sure that you can see the progress being made. A lean bulk does not give you permission to go all-out and eat as much as you can, since the main purpose of a well-executed lean bulk is like the name implies: staying relatively lean whilst putting on muscle mass. Therefore, slow and steady wins the race when we talk about a lean bulk. Next to that, there is the misconception that lean might imply that you can only eat ‘healthy’ foods. Healthy is a concept which in my opinion is made very black and white. Sure, some foods are considered more nutrient-dense and thus contain more vitamins, minerals, complex carbohydrates and healthy fats than others. Where it goes wrong is by claiming that certain foods are bad or good, but you should always look at the diet as a whole. If you do care about your health, get in enough nutrient dense foods, then do not say that your diet is unhealthy simply because you have eaten one meal which does not contribute as much to your health. Look at the big picture: the diet as a whole.

How long you can lean bulk depends on a few factors:

  • the level of leanness you start with. No need to make this one more complicated: the leaner you are the longer you can lean bulk for (provided of course you eat at a small surplus and monitor your weight so that you gain weight slowly). Being lean enough to start with provides you with more time which you can spend lean bulking.

  • your daily/weekly caloric surplus. If you keep the caloric surplus small, most of this excess of calories will contribute to building muscle mass and you will be able to lean bulk for longer since you will stay in a relatively lean shape. You will inevitably gain fat, because even in a small caloric surplus you are eating more calories than your body needs to maintain its current weight (=maintenance calories). You are basically still overfeeding your body, but doing it in a controlled way so that the fat gain will be minimal.

Dirty bulk

If you choose to go for a dirty bulk, you are going to be in a big caloric surplus every day. The term dirty bulk might also be a bit confusing. What is not meant with it is that you eat junk food all day long. Sure there are people who do this and it is possible in a dirty bulk, but dirty refers to the big caloric surplus that you are in. Dirty or unhealthy foods are often energy dense and thus contain more calories per gram. This makes it easier to end up in a big caloric surplus at the end of every day.

During a dirty bulk you create a big caloric surplus (500 calories or more above maintenance). This is an easy way to gain weight, because if you eat more and more the number on the scale will also go up rapidly. I am not implying that all this weight gain will be muscle and you will see your body fat percentage probably rise quickly too. The downside is that a long cut is waiting for you to bring your bodyfat percentage back to a point from where you can start another period of gaining muscle mass if wanted.

A common mistake is that the bigger the caloric surplus or the more you eat the more muscle mass you will gain. Seems like the perfect world, right? Eat as much as possible, get stronger and it will all be used for building muscle. In the beginning you will probably stimulate muscle growth quicker because you are 100% sure that you are eating enough to end up in a caloric surplus at the end of the week. What if you got fat after 2/3 months and need to cut already? On the long term you will lose this advantage, because you will be able to bulk for only a short period.

Another downside of a dirty bulk is that nutrient partitioning gets worse with a higher body fat percentage. For this one I have to explain something else first, namely the P-ratio, which scientists use when talking about the partitioning of calories. It represents the amount of protein gained/lost during over- or underfeeding. A high P-ratio during overfeeding means that you gained a lot of protein and very little fat, just what you ideally want if your goal is to gain as much muscle mass as possible. The P-ratio is mostly genetically determined for every individual and we can maybe control 15-20% by some other factors that control the P-ratio. The primary other predictor of the P-ratio during overfeeding is your body fat percentage. There are some implications that fatter individuals gain more fat and less muscle when overfeeding, thus the P-ratio tends to get less favorable in terms of building muscle compared to gaining fat[1]. However keep in mind that body fat percentage only plays a very small role in controlling P-ratio and it is mostly genetically determined.

Then there also is the question which comes up next: How quickly can you gain muscle mass if you are a natural and do not use anabolic steroids?

There are different opinions about the rate of muscle gain per year depending on the years of training or on your level of training (beginner, intermediate, advanced). Keep in mind that these data I am going to present in a bit apply to male lifters, since data on females are much harder to find. Most research indicates that women can gain the same percentage of muscle mass compared to men during strength training [2+3]. This still is a bit of a controversial topic and the research is ongoing. More often or not women have a different body composition to start with, so less muscle mass and more fat mass compared to men. I have addressed this topic in the article ‘Do women naturally have less muscle building potential than men?’. If you want to know more about it, check out this link

Lyle McDonald came up with a model that considers the years of proper training. In the first year of training the potential to build muscle mass is the highest and it decreases with the years. You have to take into account that this is an average which you can expect with proper training. There are other factors such as age which interfere with it. Older individuals may gain more slowly than younger ones

Table 1: Lyle McDonald model for rate of muscle gain [4].

Years of Proper Training / Potential Rate of Muscle Gain per Year

1 / 20-25 pounds (2 pounds per month)

2 / 10-12 pounds (1 pound per month)

3 / 5-6 pounds (0.5 pound per month)

4+/ 2-3 pounds (not worth calculating)

Alan Aragon came up with a model in which he considers the level of training (beginner, intermediate and advanced). The results end up being pretty similar to the ones from Lyle McDonald presented above.

Table 2: Alan Aragon model for rate of muscle gain [4].

Category Rate of Muscle Gain

Beginner 1-1.5% total body weight per month

Intermediate 0.5-1% total body weight per month

Advanced 0.25-0.5% total body weight per month

Concluding here: gaining muscle mass takes time, you can not force-feed muscle gains and the potential rate of muscle gain decreases with the years. Beginners can probably get away with a dirty bulk, since they can gain 9-11 kilograms in their first year of training [3]. The closer you get to your genetic potential the less muscle mass you will be able to build and it is not smart to do a dirty bulk, since the potential for muscle growth is low and you will gain a significant amount of body fat.


There are different ways to set up your own bulk. The dirty bulk is on the long term less effective, because your body fat percentage will go up quick in comparison to the amount of muscle mass you will be able to build. Also, you will not be able to bulk long and thus limit the amount of time spend in a caloric surplus building muscle. Next to that, if you carry a higher body fat percentage nutrient partitioning probably gets worse. There are implications that fatter individuals gain more fat and less muscle when overfeeding, even though for the biggest part the P-ratio is genetically determined for every individual.

An optimal bulk is one in which most of the gained body weight is muscle mass and one in which you keep fat gain to a minimum. For most individuals this will be a lean bulk in which you eat a controlled small caloric surplus to stay in a relatively lean shape whilst putting on muscle mass and improving your physique.

Don’t end up spinning your wheels between short bulk and cycles. Get progressively stronger, enjoy more food and more flexibility during a lean bulk and you will be happily living the bulk life for a long time!

My own experience

I myself have done both a dirty bulk and just finished a very long lean bulk (13 months). I learned my lesson during the first time that I decided to do a bulk. I just started training and lacked the knowledge that I do have today. I started eating as much as I could. In the beginning it all went fine: the weight on the scale went up, i gained strength like crazy and I saw some improvements in my physique. However, it did not take long before I started to lose the motivation to hit the gym, because I saw myself getting fatter and I did not feel 100% comfortable looking at myself in the mirror or wearing gym clothes. After bulking for around 4 months I gained a total of 10 kilograms. Safe to say I just got fat. It was a real eye-opener when a friend of mine told me straight in my face that I have let this bulk gone way too far. I did not want to believe it myself up until that point, but I knew this was not the way (at least for me) to gain muscle mass. I gained a lot of  body fat and little to no muscle mass. I started cutting at 72 kilograms and got back to 60 kilograms only to conclude that I was at the same point where is started bulking earlier. Not to mention the cut was long and demotivating having to lose quite a significant amount of weight.

After I finished my cut at 60 kilograms in February 2017 I started a lean bulk. I had a proper plan and promised myself two things: I wanted to be in a caloric surplus for at least one year and gain a maximum of 10 kilograms whilst being happy with my shape at the end of the lean bulk. By now I am still happy with my shape even though I gained those 10 kilograms. I can see the progress that I have made and even though I am really curious to start a cut to see what I’ve built up, I also know that I have been able to keep the body fat gain during this lean bulk to a very minimum. This is how I will always set up a bulk for myself. I know a smallfat gain is inevitable and I do feel a little bit more ‘fluffy’ from time to time. I remember then that there is a huge difference between getting fat and gaining a little bit of fat whilst being in a caloric surplus for quite some time already. I prefer the last one because I would rather feel good in my own skin year-round whilst being able to put on muscle mass, than getting fat during the winter only to conclude next summer that I did not make any improvements.


[1] McDonald, L (2008). Calorie Partitioning part 1. Retrieved from:

[2] Roth, SM (2001). Muscle size responses to strength training in young and older men and women. Journal of the American Geriatrics Society, 49(11), 1428-33.

[3] Smith, I (2012). Similar muscle protein synthesis rates in young men and women: men aren’t from Mars and women aren’t from Venus. Journal of Applied Physiology, 112(11), 1803-1804.

[4] McDonald, L (2008). What’s my genetic muscular potential? Retrieved from: Https://Www.Bodyrecomposition.Com/Muscle-Gain/Whats-My-Genetic-Muscular-Potential.Html/

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