As brief background: years ago I was obsessed with getting a 6-pack. I was possibly the worst body type: skinny but with a flabby midsection. After years of P90X, I didn't quite achieve a 6-pack, but I did get a nice 4-ish pack; I still had to flex a little to see it on my skinny frame, though.

Now: I feel like I'd like to gain some muscle mass. I've read from various sites, including this StackExchange, that when adding calories to fuel muscle growth (along with exercise, of course), it is inevitable that you will add some fat, i.e. your gained weight cannot be 100% muscle.

Question: I plan on ramping up my caloric intake, perhaps in 100 calorie increments, while doing a muscle growth-themed workout (Body Beast). How can I know whether I'm getting sufficient calories to fuel muscle growth? Although I cannot avoid some gain in fat, I would like to minimize it, which is why I am trying increasing my calories in 100 calorie increments.

Also, what would be the long-term (weeks/months) effect of performing a muscle growth-themed workout without ingesting sufficient calories?

(Btw, I know gaining muscle mass is a years-long endeavor; i.e. though I'm doing Body Beast, I know to not expect drastic changes in 90 days)

  • I can’t speak to the quality of the “Body Beast” program, but it’s promise of 10 lbs of muscle in 90 Days is completely impossible. Commented Nov 16, 2018 at 0:26
  • @JustSnilloc - no argument: I'm aware of that. I know exercise/diet is a lifestyle, not a once-and-done effort. I just like working out along with a program, and don't plan to stop after 90 days (though I may switch programs if BB isn't right for me). Any thoughts on the question at hand, though: how to know if I'm eating enough to sustain muscle growth?
    – StoneThrow
    Commented Nov 16, 2018 at 0:32
  • Gaining 10 lbs of muscle in 90 days is certainly possible - I gained 16 lbs in the first 3 months of Starting Strength, probably 12-14 lbs of which was muscle, and that's as someone who doesn't gain muscle easily for a male. However the fact that Body Beast apparently doesn't involve the big three barbell movements and is an infomercial program doesn't inspire me with confidence in it. Commented Nov 16, 2018 at 0:58
  • @DavidScarlett - interesting, I will look into that program. I'm always looking to improve; I only went with Body Beast because I was familiar with Beach Body, having done P90X, and liking the program, so I went back to them for a new program out of associative cognition. Anyhow, I'm still curious for an answer to the actual question :) how can one know if one is taking in enough calories to feed proper muscle growth? I'd like to correct my progress as quickly as possible if I'm not doing something right.
    – StoneThrow
    Commented Nov 16, 2018 at 1:10
  • @DavidScarlett - While I'm sure you gained some muscle, perhaps even several pounds, I'm doubtful that 12 lbs of that was muscle. For you to have gained 12 lbs of muscle in three months, your bodyfat percentage would have only increased by 1% at worst and 0% at best. What I'm saying is that you would have noticed little to no difference at all in visible fat, but a huge difference in musculature. Here is a chart looking at the possibilities - i.imgur.com/746j8V5.png Commented Nov 16, 2018 at 2:11

1 Answer 1


By knowing what to expect.

Gaining 1 lb (.45kg) of muscle each month is a quick rate, while 2 lbs (.90kg) of muscle each month tends to be the upper limit. Fat is much quicker with 6 lbs (2.72kg) per month being fairly easy to gain with a sufficient caloric surplus (~50%). What determines if the weight you gain is fat or muscle? Your activities and nutrition have an intertwined relationship with your resulting size and shape. I like to say it like this; your nutrition will determine your size while your activities determine your shape.

Without any physical activity, your body has no reason to add any muscle to your frame while in a caloric surplus, therefore 100% of your increased weight should be fat. With the "ideal" maximum amount of physical activity stimulating muscle growth (along with proper rest and nutrition) your body will add the maximum amount of muscle that it can, but it's limited in capacity (2 lbs tends to be the upper limit). The conclusion here is that while in a caloric surplus it is possible to gain both fat and muscle, but the latter is only possible by providing a stimulus. To minimize fat gain, you'll want to keep your caloric surplus from growing beyond what you need for muscle growth.

In general, this boils down to watching the scale. If you are gaining between 1 lb and 2 lbs (.45-.90kg) of weight per month while providing your body with sufficient exercise and rest, then you can assume that most of that is muscle. At worst with this kind of lean bulk, you might expect to gain 1 lb of fat with every 1 lb of muscle.

If you're really at 17-20% bodyfat though, you're a prime candidate for a body recomposition. For that, you simply want to maintain your bodyweight. What happens during a recomposition is that your body uses its own fat as calories to fuel muscle growth. So you lose fat while building muscle. My advice would be to do the recomp if appearance matters to you, do the lean bulk if it doesn't. You can always do a bulk later after your bodyfat percentage gets low enough.


  • "I plan on ramping up my caloric intake, perhaps in 100 calorie increments" - This is probably the best route, perhaps not the quickest, but probably best. Continue doing this until you reach the desired monthly change on the scale.
  • "What would be the long-term (weeks/months) effect of performing a muscle growth-themed workout without ingesting sufficient calories?" - If you have enough fat, you'll start burning the fat. If your caloric deficit is too large however or your bodyfat percentage is too low, you'll start losing muscle too. You'll also notice a dip in energy.
  • "I know gaining muscle mass is a years-long endeavor." - Yep, and knowing about how much growth to expect at a time is key in optimizing both motivation and results.
  • If you don't mind a follow-up question: if you need to pause your workout for a short while (e.g. one week), would you keep your caloric intake the same as when you're working out, or would you reduce? I've gained a lot of strength in just three weeks of lifting heavy, but need to go on a business trip: I'm afraid of two possibilities: (1) if I keep my calories up without exercising, it seems that excess will become fat, but (2) if I reduce my calories - without exercising - I'm afraid of my body cannibalizing my gained muscle for energy. Appreciate any insight you may have.
    – StoneThrow
    Commented Nov 29, 2018 at 19:39
  • 1
    @StoneThrow - The first thing I would recommend is to do your best in continuing some form of exercise that week. A lot of hotels have gyms, and short of that resistance bands/tubing is easy to travel with. There are also plenty of challenging bodyweight exercises out there, but if you simply cannot manage to squeeze in time for exercise I would offer a simple solution. Eat at TDEE maintenance (neither gaining or losing weight) for that week and get enough rest. Commented Nov 30, 2018 at 0:02

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