A “lean bulk” is the intention of gaining bodyweight through increasing muscle mass without gaining body fat.
Anecdotally (gym locker room chat from about 10 years ago) this is achieved by lifting heavy (to build muscle), eating high amounts of protein (because eating protein doesn’t make you gain fat) while maintaining high amounts of cardio (because cardio “burns fat”).
To new fitness and gym attendees, this may sound logical, but unfortunately, the science only seems to hold up with correlation-based studies (1).
The main finding in this study was that bodybuilders who ate higher protein intakes (up to 3.1g/kg body weight) during their off-season (the other group ate 1.6g/kg body weight) were shown to have lower body fat.
To be clear, a correlation study shows the association between two points of interest, in this case eating high levels of protein and having lower levels of body fat. However, these studies do not provide a CAUSE to the association, and there is no control for other conflicting influences like cardio or the rest of their diet (which could place a proportion of the subjects in a calorie deficit instead of a surplus regardless of how much protein they ate). This study also only interviewed 19 bodybuilders (9 of which ate high protein and 10 did not) so, unfortunately this study is basically a scientific version of me going to a local gym, asking the 9 biggest bodybuilders what they eat and coming to the conclusion that this is the reason they are the biggest.
You may remember a previous post called “Muscle Growth & Calories” that went into detail about how the most effective way to grow muscle was to be in 350-475 calories surplus. This was to ensure that your body has enough “fuel” to grow as a response to exercise.
If you keep a regular eye on your body fat, body weight, and track your calories intelligently, you could tread the fine line of gaining muscle mass without gaining very much body fat. This is what people have called a “lean bulk”, which when you think about it, is just growing muscle. The term “lean bulk” (in my opinion) puts emphasis on the “lean” rather than on the desired outcome of growing muscle.
Like gaining body fat for a short period of time while you make your body more physically resilient, strong, and robust is a bad thing.
Let's compare this idea with another industry.
Money – Increases in money are deemed good, decreases are deemed bad.
Body fat – Increases are deemed bad, decreases are deemed good.
Money – If I invest money (spend it on education) and in 6 months to 1 year later I have gained more earning power as a result (gained a qualification for a new job), this is deemed good. Even through the process, most people will be supportive of this process.
Body fat – If I am in a calorie surplus for 6 -12 months to ensure that I can effectively grow muscle mass. Which will make my body stronger more resilient, more useful and healthier as I age, this should be deemed good. However we are conditioned to see people who are lean as the ones who have their lives together, and the ones that have gained a little weight over the past 6 months as “letting themselves go”.
To summarise, gaining body fat for a short period to make sure you gain muscle is a beneficial trade-off. Staying lean because you care what other people think about how you look, and as a consequence blunting your potential for muscle growth and potentially impacting your long term health is not “healthy”.