Why is calorie surplus prescribed for muscle growth? Is eating at maintenance enough?

You'll often see people who preach building muscle at maintenance calories. They also claim surplus is not needed at all!

When Calorie Intake equals Maintenance Calories, no body weight change takes place.

Let's say you are 80 kg and you eat 2700 kcal each day, and your weight registers no change after 3–4 weeks. We can safely say your maintenance calories are 2700 kcal, let's assume you don't lift weights nor you consume optimal amount of protein when this maintenance calories was calculated for you based on 3-4 weeks of observation period.

The energy needed for Muscle Protein Synthesis (MPS) is already part of the maintenance calories.

Does it mean eating 2700 kcal and lifting weights is going to grow muscles?

Here’s a key detail people miss: when you start eating more protein, especially if you used to eat less protein before, MPS will go up. It’s not an energy efficient process; energy has to come from somewhere. This boosts your maintenance calories, so your maintenance calories will no longer be 2700. Maybe it becomes 2800 or 2900 kcal now. Don't worry about the exact magnitude of increase yet.

In theory, the moment you start gaining muscle, your maintenance will rise because of multiple factors: a) increased TEF from higher protein intake (muscle building diet plan often have higher protein perscriptions than average person's diet) b) increased muscle maintenance cost (13 kcal per kg of muscle) c) energy required for higher MPS

The process of muscle gain alone is sufficient to maintenance calories (TDEE)

But if you believed your maintenance is still 2700 kcal, technically now you'll find yourself in a deficit as your maintenance has increased to 2800–2900 kcal.

But here’s something that appears contradictory:

a) if eating at maintenance does not increase bodyweight b) muscle gain can happen at maintenance

How is it possible that the addition of muscle may result in no change in bodyweight? This is possible if, let’s say, you lost 1 kg of fat but gained 1 kg of muscle, so your bodyweight is still 80 kg.

But what if the body has very little fat? Let’s say you are already very lean, around 9–12% body fat as a male.

MPS will begin to decline as it registers low fat storage. Your rate of muscle gain at maintenance will slow down because there isn’t enough fat in the body to burn for the energy needed for muscle growth.

Now let’s look at this lean bulking guide section:

To gain the least fat while gaining muscle, lean bulking is what you need. The key is to focus on your rate of weight gain, not a specific calorie number or surplus percentage. Weekly Weight Gain Rate: Beginners: 0.25–0.5% of body weight Intermediates: 0.25–0.4% Advanced Lifters: 0.1–0.25% Usually, a calorie surplus of +5–10% of TDEE (roughly 100–300 kcal/day) may get you there, but if it doesn’t, adjust your calories up or down to reach the desired weekly weight gain rate.

Why is surplus in lean bulk applied with rate of weight gain calculated using the 1 kg = 7700 kcal equation, which is for fat-to-calorie conversion, when what we want to add is muscle?

They don’t, they use the Rate of Weight Gain (0.25–0.5%) as the target, and they use 7700 kcal backwards to estimate how much to adjust if the scale isn’t moving fast enough.

1 kg of fat store equals 7700 kcal. But if our goal is to gain muscle, why don’t we use 1 kg muscle store = 1500–1600 kcal to calculate required surplus?

The answer is cost of acquisition, as muscle gain is metabolically inefficient and expensive compared to fat gain, which is often 2.5x the stored energy = 4500 kcal.

Total cost of acquisition + storage = 4500 + 1500 = 6000 kcal.

Storing fat only costs around 15–20% additional energy (DNL pathway), so 7700 kcal + 23–25% or 2–3% (depending on whether fat gain is from carbs, fats, or proteins, as fats are most efficiently stored as fat compared to carbs or proteins).

But then why don’t we use 1 kg muscle = 6000 kcal for calculating surplus in lean bulk which factors in both acquisition and muscle’s stored energy?

That brings us to our initial point: the cost of acquiring muscle is already part of maintenance calories. When we lean bulk, we are ensuring we gain fat by using a slight surplus, so that there is always some amount of fat available to be burned and available as a buffer to keep feeding MPS.

Note again:

Weekly Weight Gain Rate:

Beginners: 0.25–0.5% of body weight

Intermediates: 0.25–0.4%

Advanced Lifters: 0.1–0.25%

And we keep this fat gain as small as possible, we keep this fat gain larger in beginners because beginners can gain muscle at higher rate deleting fat reserves faster compared to intermediate lifters.

As you move from beginner -> intermediate -> advanced, rate of weight muscle gain drops.

But don’t think of this as "eating less food", as you move from beginner -> intermediate -> advanced, your maintenance calorie will go up as your body now has more mass, more muscle, while the surplus applied during lean bulk will drop but you are still eating more than you used to!