How is muscle repair affected by a caloric deficit?

Question

Background

Weightlifting creates micro-tears in the muscle. Protein and other nutrients repair the tears so the muscle grows back stronger and larger.

Question

How is muscle repair affected by a caloric deficit during a weight training program? I can think of these three scenarios:

1. Muscle still has the potential to grow back stronger and bigger, but at a much slower rate. It patiently waits for what little nutrients come in day after day.
2. Muscle remains the same - there is equilibrium.
3. Muscle senses it does not have proper nutrients and gives up. It does not completely repair and becomes smaller and weaker.

Which one is correct? Or is there a different scenario that happens?

Application

I'm trying to lose fat by eating less (including protein). I still exercise every day. I enjoy weightlifting, but hate cardio. Will my muscularity be compromised because of this combination of weightlifting and eating less?

Answer 1

You can gain muscle while losing weight, but really only in specific circumstances, which you most likely don't fall into. You need to be fairly obese to start with, and eating the correct nutrients to support the lifting that you are doing. However, you are most likely not in that category, since you have been training regularly already.

If you are in a caloric deficit, then you aren't going to be gaining muscle size, with one possible exception that I will detail below. What you will be doing is preserving lean body mass, and using fat stores to maintain the muscle that you currently have.

This study suggests that adding weights to dietary restriction results in maintenance of lean body weight, but it's a little oddly worded in the abstract, as it suggests that diet + exercise and exercise only both increased mass and strength in obese women, but I don't know if the "diet" is just a change in what they are eating normally.

A study using bodybuilders showed that energy restriction reduced muscle size, and theorizes that it impacts the anabolic pathways in spite of high protein intake. This makes sense intuitively, as many bodybuilders are relatively much heavier during training, even while maintaining relatively little bodyfat, and they lose quite a bit of weight while dropping down into the single digit ranges for bodyfat when prepping for a contest.

Finally, another article discussing cellular biology (Which is mostly way way over my head) suggests that caloric deficits impact the pathways by which cells get the signal to grow. This article is very heavy on the cellular biology.

I did find one article that suggests that people go through catabolic and anabolic phases during each day, so if you are (as they say) "fanatical" about the planning and timing, it is possible to gain while dieting. This was about the only reference I found that said it's possible to run a caloric deficit and still gain, and I don't think you can run much of a deficit or for very long.

However, for the rank and file crowd, I do believe that if you are anywhere past the relative beginner stage (Who will see gains in the initial adaptation period), you cannot be in a caloric deficit and still gaining muscle. Rather, you are maintaining muscle and losing fat. For your situation, I believe that you will fall into the same area as the bodybuilders in that you might lose some size while losing the weight.

Answer 2

I do a full-body, two-hour workout twice a week. I progress at a normal rate.

With that said, I can lose about two to three pounds of fat a month (roughly 240 to 360 calories loss a day).

It's not much, I know, but it's better than nothing.

All you need is 1 gram of protein per lean body weight, and just enough carbs for workout days to get you through.

Eating tons of protein and carbs is a stupid myth!