At the extreme both are essential. That said, most people get at least a semi-acceptable sleep schedule so supplying a diet that supports growth is probably a more common problem. The bottom line is that if you don't supply an excess of calories and decent nutrient balance (nothing crazy is required for growth - just basic blocking and tackling) you will not grow. Obviously if you have some healthy BF levels, you might already have an excess built into your diet but for someone who is already fairly lean that's usually an indicator that their consumption will need to increase to support more muscle.
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