It is not strictly necessary to be in a caloric surplus to build muscle, but a moderate surplus can optimize growth compared to a deficit, whereas an excessive surplus primarily promotes fat gain.

noli's read

The creator relies on solid evidence to nuance the strategy for muscle gain. The idea that body recomposition (building muscle while losing fat) is possible, especially among beginners or those returning to training, is well supported by systematic reviews such as the one published in 'Nutrients' (PMID: 31482093). The claim that a significant caloric deficit hinders muscle protein synthesis is also corroborated by scientific literature (PMID: 34623696, PMID: 20300017). Regarding the surplus, research indeed confirms that aggressive bulking ('dirty bulking') does not offer a significant advantage for muscle gain and primarily increases fat mass (PMID: 37914977). The statement is very balanced and accurately reflects the current consensus in sports nutrition. It avoids generalizations by emphasizing that individual context (training level, body composition) modifies optimal energy requirements.

the sources

No named source held this one up — that absence is part of the verdict.