The rate of potential muscle hypertrophy is individual specific with gender, age, training history & current body composition having an effect. This post is not attempting to cover all of these potential factors, and instead, focus on total calories eaten and its effect on muscle hypertrophy.
What is generally accepted across the literature is that a calorie surplus is required for muscle growth. However, it's unclear exactly how much of an increase is required per kg of muscle mass gained, because of individual differences. Slater et al. (2019) generally advocate a surplus of between 350 & 475 calories per day, although the size of the individual should be considered here, as the effect of an extra 350 calories for a 60kg female will differ from a 95kg male.
The mechanisms behind muscle hypertrophy still aren't entirely understood, however to the best of my knowledge in the presence of the following 3 components, it has a high chance of happening.
1) Increases in muscle protein synthesis.
2) A regular and progressive mechanical strain on the muscles and associated tendons & ligaments.
3) Regular metabolic damage to the muscle tissue.
Components 2 & 3 are unable to be stimulated by dietary factors, however, increased muscle protein synthesis is a common simultaneous occurrence when measuring muscular growth (1).
Being in a calorie deficit causes a reduction in the enzymes and hormones responsible for muscle protein synthesis (3,4), a less than ideal situation for growth. Although interestingly muscle hypertrophy is possible in a calorie deficit by increasing protein intake above 2.4g/kg of body weight. But, this seems to mainly be reported in overweight or very untrained populations (2).
So it's clear that total caloric intake is important for muscle growth, but what about rest days?
"You don't grow while your training, you grow while you're recovering" Unknown
Muscle protein synthesis is elevated for upwards of 48 hours after resistance training (5) so there is scope that keeping the calories high even on rest days is important.
Also when in a calorie surplus, eating smaller meals more often could be beneficial, mainly due to the feeling of fullness being a limiting factor. When in a calorie deficit, eating more frequent meals can help maintain muscle mass, however, it doesn't appear to matter when in a surplus, so organise your eating day how you like (6)
What about Carbohydrates & Protein?
Loose guidance of 4-7 g/kg body weight for carbohydrate has been suggested to sustain the exercise performance that is required to drive muscular adaptation (7) (you need to train hard to grow your muscles). Ideally, most of this carbohydrate should be eaten around the exercise window (2-3 hours before and after training) but it doesn't seem to be essential.
Finally, protein, the magical food of bro science.
It is commonly thought that there is a dose-response relationship with eating protein and gaining muscle. The more protein you eat, the more muscle you grow. Yet, as long as calories are sufficient, the research suggests a modest 1.6 g/kg body weight of protein is sufficient to grow muscle (meta-analysis of 49 studies across 1,863 males and females).
- If you want to build muscle you need to be in a calorie surplus and being in a eucaloric state doesn't seem to be sufficient.
- Eat 350 to 475 calories OVER what your exercise and daily needs are.
- Eat 4-7 grams per kg of bodyweight in carbohydrate daily (choose the lower end for moderate to lower volume training and 7 for longer high-intensity training days).
- Eat 1.6 grams per kg of body weight of protein daily.
- Have the remaining calories come from healthy fats like olive oil, nuts, and avocados.