A lean bulk means gaining on a small calorie surplus, so that more of the gain comes from muscle and less from fat. In practice that works out to a surplus of roughly 10 to 20 percent above maintenance. Bigger than that mostly delivers fat faster, not muscle faster.
Muscle growth has a speed limit. Fat storage does not. That is the whole case against the dirty bulk in two sentences.
What is a lean bulk?
A lean bulk, sometimes called a clean bulk, is a building phase where you deliberately hold a small surplus rather than a large one. The goal is muscle growth with as little fat gain as possible. Its counterpart is the dirty bulk, where you eat what you want and accept the fat gain.
I am not a fan of the dirty bulk, and not for aesthetic reasons. It makes the cut that follows longer, and it puts your blood values under pressure along the way.
The maths for your maintenance and your surplus is in how many calories to gain weight. This article is about what happens in your blood meanwhile.
How large a surplus do you need?
Smaller than most people run. A surplus of roughly 200 to 400 kcal a day is enough to support muscle growth for many advanced lifters. Beginners can still build a fair amount of muscle on a larger surplus, while advanced lifters mostly convert that extra into fat.
| Surplus per day | Weight gain per week | What you usually see |
|---|---|---|
| 100 to 200 kcal | Roughly 100 to 200 grams | Slow, little fat gain |
| 200 to 400 kcal | Roughly 200 to 400 grams | Workable for most advanced lifters |
| 500 kcal and above | 500 grams or more | A larger share of the gain is fat |
Research on strength training under an energy deficit shows that energy is the main driver of gains in fat-free mass (Murphy and Koehler, 2022). That means you need to eat enough to grow, not that more is always better.
Protein still matters during a bulk. Sports nutrition reviews describe intakes for strength athletes well above the Dutch Voedingscentrum's general guidelines (Helms et al., 2014). The detail is in how much protein per day.
How much fat do you gain during a bulk?
Almost always some, and that is part of it. On a small surplus you often see a split where part of the gain is fat and part is fat-free mass. The larger the surplus and the further along you are in your training career, the more that split shifts towards fat.
For a beginner gaining 12 kilos in a year, that can work out well. For someone with eight years of training, that same 12 kilos is largely fat.
Where that fat ends up is not neutral. Increases in abdominal fat are associated in research with shifts in blood lipids and insulin sensitivity (Despres, 2012). What that type of fat actually is can be found in visceral fat.
What does a dirty bulk do to your blood values?
A large and prolonged surplus can push several values the wrong way. Triglycerides respond fairly quickly to a high energy intake. Fasting glucose and insulin can move along with it. Liver values such as ALT can rise as fat storage in the liver increases.
This is exactly where a bulk quietly gets expensive. You do not see it in the mirror, because you are getting bigger and stronger at the same time.
Concretely: a lifter going from 82 to 95 kilos in five months on an 800 kcal surplus sees his bench climb and his trousers tighten. His triglycerides and fasting glucose are a more honest report card than his training log.
The values most often looked at here are triglycerides, fasting glucose and ALT. A lipid profile brings the blood lipid side into view.
How long should a bulk last?
Long enough to build something, short enough not to derail. In practice, blocks of three to six months work comfortably for many people, followed by a period at maintenance or a short cut. The exact length depends on where you start and how you respond.
Starting at a high body fat percentage is rarely smart. You end up bulking further away from your goal, and the cut afterwards runs longer than the block itself.
What that cut involves is in cutting. The nutrition side of growth is covered in nutrition for muscle growth.
When do you stop bulking?
When fat gain starts overshadowing muscle gain. Usable signals are a waist growing faster than your upper body, weight climbing faster than planned, and blood lipids or fasting glucose that have clearly shifted. One of those three is a hint, two or three is a pattern.
Waist circumference is your cheapest alarm here, because you can repeat it every two weeks. How to take it without error is in measuring your waist.
If you also want to know what you can track in your blood during a building block, that is in reducing visceral fat and, more broadly, in measuring metabolic health.
From next Monday, measure your waist and your weight on the same morning, and repeat every two weeks. If your waist grows faster than your lifts, you know enough.
References
- Murphy C, Koehler K. Energy deficiency impairs resistance training gains in lean mass but not strength: a meta-analysis and meta-regression. Scand J Med Sci Sports, 2022. PMID 34623696
- Helms ER et al. Evidence-based recommendations for natural bodybuilding contest preparation: nutrition and supplementation. J Int Soc Sports Nutr, 2014. PMID 24864135
- Despres JP. Body fat distribution and risk of cardiovascular disease: an update. Circulation, 2012. PMID 22949540
- Voedingscentrum, guidelines on protein and energy intake for the general population.
Every blood test result includes a professional assessment from a BIG-registered doctor. For treatment decisions, discuss your results with your GP.
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