In the gym, the debate is as old as bodybuilding itself: should you eat a lot to gain a lot, even if it means gaining fat and then cutting later, or eat a little more, gain slowly and stay lean? Each camp has its anecdotes. Since 2023, there's also a randomized trial.
Twenty-one trained practitioners, eight weeks, three sessions per week, and three groups: maintenance, 5% surplus, 15% surplus. This article reports what the trial measured, what its authors acknowledge as limitations, what a leading review admits it doesn't know, and what we can deduce from it to achieve clean muscle gain without deprivation.
The trial. 5% surplus versus 15% over eight weeks in trained practitioners: same muscle thickness in the biceps, triceps, and quadriceps, same squat, slightly better bench press with the larger surplus, and more skin folds. The regression concludes that faster weight gain primarily increases the rate of fat gain. The limitations. 17 people at the end, eight weeks, weak signal for the biceps.
What we don't know. The optimal surplus has never been validated, says a review from the Australian Institute of Sport. What we can deduce. Slow gain, 0.25 to 0.5% of body weight per week, protein around 1.6 g per kilogram, and scale-based monitoring. Dirty bulking has no data in its favor; lean bulking has the only trial that exists.
The two strategies
Lean bulking , or lean bulk, aims for a moderate surplus, around 5 to 10% above maintenance, with controlled nutrition, to limit fat gain and extend the phase. Dirty bulking, or dirty bulk, accepts a large surplus, 15% or more, often with little dietary control, betting that excess energy accelerates muscle building and you'll cut later. The question isn't which is more virtuous: it's whether the large surplus bet is justified. The randomized trial, result by resultMaintenance, 5%, 15%. Eight weeks. What changed and what didn't.
Parallel-group randomized trial, Sports Medicine - Open 2023
DOI: 10.1186/s40798-023-00651-y
Measurement 5% surplus
| 15% surplus | Reading | Biceps, triceps, quadriceps thickness | Progression |
|---|---|---|---|
| Identical progression | Tripling the surplus didn't build more muscle | Maximal squat | Progression |
| Identical progression | No strength gains linked to surplus | Maximal bench press | Progression |
| Développé couché maximal | Progression | Superior Progression | The only advantage of the large surplus, on a movement |
| Skinfold Thickness | Weak Increase | Clear Increase | The large surplus adds fat |
| Weight and Skinfold Regression | Strong Evidence, R² of 0.49 | The faster weight increases, the more fat increases | |
Three things to remember. The large surplus produced neither more muscle nor more strength on the squat. It gave a slightly better bench press, which is a real result, but only one. And it produced more fat, which the regression confirms robustly: half of the variation in skinfold thickness is explained by the rate of weight gain.
What the trial does not say
The pandemic reduced the sample to 17 people at the end, which prompted the authors to supplement the group analysis with a regression on the whole. Eight weeks is short for measuring hypertrophy. Participants had varied training experience and moderate volume, three sessions per week. The only signal in favor of the large surplus, on the biceps, the most solicited muscle in the program, is weak. The authors themselves write that their results are limited to the conditions of the study and that other contexts must be tested.
What the trial therefore does not prove: that a large surplus can never help, anyone, over a longer duration or with higher training volume. What it shows: in the only randomized test we have, it produced no more muscle and produced more fat. The dirty bulk camp has no comparable data point to counter it.
What we still don't know
A review published in Frontiers in Nutrition by researchers from the Australian Institute of Sport, including Eric Helms himself, poses the question in the title and answers straightforwardly: there is clear evidence of an anabolic stimulus linked to a surplus, but the precise surplus needed has never been validated in a trained population. Current recommendations are based on energy theoretically stored in tissue, and ignore other costs of muscle synthesis and the body's metabolic adjustments in response to excess. The "sweet spot" between muscle and fat has never been measured.
This means that neither the "5%" nor the "300 kcal" are truths: they are starting points. What is established is the direction, faster intake adds more fat, and the protein ceiling, approximately 1.6 g per kilogram according to Morton's meta-analysis of 49 trials, beyond which there is no further lean mass gain. Between the two, everyone finds their surplus on the scale.
Lean Mass Gain, in Practice
22.9 g of protein for 117 kcal per 30 g serving, 1.8 g carbohydrates, 2 g fat. Reaching 1.6 g protein per kilogram without inflating the surplus is exactly what lean bulking demands: precise protein within a tight caloric budget. One serving post-workout or as a snack, counted in your total.
View the Whey IsolateIf weight isn't increasing despite adequate intake, a gainer is the tool, not whey.
Frequently asked questions
What is a lean bulk and a dirty bulk?
Two strategies for the same objective, building muscle, which differ in the size of the caloric surplus. The lean bulk aims for a moderate surplus, around 5 to 10% above maintenance, to limit fat gain and extend the phase. The dirty bulk accepts a large surplus, 15% or more, often with less controlled eating, betting that excess energy accelerates muscle building. The question is whether this bet is justified.
Does a large surplus build more muscle?
Not according to the only randomized trial on the question. Twenty-one trained practitioners followed eight weeks of weight training three times per week, divided between maintenance, 5% surplus, and 15% surplus. Group analysis showed no difference in bicep, tricep, and quadriceps thickness, nor in maximum squat. The 15% group progressed more on bench press, but also increased their skin folds more. Regression analysis concludes that faster weight gain increases primarily the rate of fat gain, not strength or muscle thickness.
What are the limitations of this trial?
Its authors state them themselves: a sample reduced to 17 people by the pandemic, eight weeks only, practitioners of varied experience, moderate training volume. The only signal favoring the large surplus concerns the bicep, the most targeted muscle in the program, and it is weak. The trial does not prove that a large surplus can never help; it shows that in eight weeks, in trained practitioners, it produced no more muscle and produced more fat. It is the only randomized data point we have, and it points in only one direction.
What caloric surplus should you aim for when bulking?
No one knows the optimal figure, and it's a review from the Australian Institute of Sport that says so: the precise surplus necessary for hypertrophy has never been validated in a trained population. What the Helms trial allows us to say is that a moderate surplus produces the same muscle as a large surplus with less fat. The practical benchmark that follows is slow weight gain, around 0.25 to 0.5% of body weight per week, adjusted by the scale rather than calculated.
Should you eat anything during a bulk?
No, and for a reason that has nothing to do with dietary morality. Protein has a useful ceiling of around 1.6 g per kilogram according to a meta-analysis of 49 trials; below it you lose potential muscle, above it you gain no more. The rest of the surplus can come from carbohydrates and lipids without the source changing hypertrophy, but highly processed food makes the surplus difficult to control, and it is precisely this control that separates a lean bulk from a dirty bulk. Eating clean is not a virtue, it is a precision tool.
How long does a lean bulk last?
Longer than a dirty bulk, and that's its advantage. With a gain of 0.25 to 0.5% of body weight per week, a 75 kg person gains 200 to 375 g per week, or 3 to 6 kg in four months, of which a proportionally higher share is muscle than with a 15% surplus. The phase can last as long as skin folds remain acceptable, which delays or shortens the cut period that follows. A dirty bulk gains faster but requires a longer cut, during which some of the acquired muscle may be lost.
What to remember about lean bulk versus dirty bulk?
That the only randomized trial produces the same muscle with a 5% surplus as with 15%, and more fat with 15%. That the optimal surplus is unknown, but faster is not better. That protein caps out around 1.6 g per kilogram. That a lean bulk is controlled by the scale, with slow gains, and allows for a longer phase and shorter cut. And that the dirty bulk has no data supporting it.
Sources
The studies cited below were identified via PubMed.
- Helms ER, Spence AJ, Sousa C, et al. Effect of small and large energy surpluses on strength, muscle, and skinfolds in resistance-trained individuals: a parallel groups trial. Sports Medicine - Open, 2023;9(1):102. DOI
- Slater GJ, Dieter BP, Marsh DJ, Helms ER, Shaw G, Iraki J. Is an energy surplus required to maximize muscle hypertrophy associated with resistance training? Frontiers in Nutrition, 2019;6:131. DOI
- Morton RW, Murphy KT, McKellar SR, et al. Systematic review, meta-analysis, and meta-regression of the effect of protein supplementation on muscle mass and strength gains induced by resistance training in healthy adults. British Journal of Sports Medicine, 2018;52(6):376-384. DOI
