Should I bulk or cut first?
Cut first if you are above roughly 20% body fat (men) or 30% (women); otherwise start building.
The main reason to start lean is practical: a gaining phase always adds some fat, so starting at 20% body fat means a longer cut afterwards. A larger surplus mostly adds fat, not extra muscle, so a gaining phase should be modest whatever your starting point.
The common claim that leaner people turn more of a surplus into muscle is poorly supported. This is a judgement call based on indirect evidence, not a settled question.
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Sources
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- Iraki, J. et al. (2019). Nutrition Recommendations for Bodybuilders in the Off-Season: A Narrative Review. Sports (Basel) 7(7). Recommends starting a gaining phase from a relatively lean baseline.
- Garthe, I. et al. (2013). Effect of nutritional intervention on body composition and performance in elite athletes. Eur J Sport Sci 13(3). Elite athletes on a larger surplus gained more fat but no more lean mass than those eating freely.