Reducing Body Fat Percentage by Gaining Muscle – Q&A

Question: I want to reduce my body fat percentage but I also want to gain muscle and would rather not diet.  A guy at my gym told me that if I gain muscle, this will have the effect of reducing body fat percentage, is this true?

Answer: Yes and no.  Strictly speaking, yes, if you can gain muscle without any accompanying fat gain, you will reduce your body fat percentage. However, the reality is that when you work the math, the impact of gaining muscle mass is minuscule approaching irrelevant, especially compared to the impact of actually losing fat through diet/activity.

To illustrate this, let’s consider an average lifter who is 170 pounds with 15% body fat.  As I showed in Body Composition Calculations, we can determine the total amount of body fat (in pounds) that this person is carrying by multiplying their weight by 15% (or 0.15).  So our lifter has

170 pounds * 0.15 = 25 pounds of body fat and 145 pounds of lean body mass.  We don’t actually need the lean body mass number for any of the calculations I’m going to do.

Let’s look at how much of an impact gaining pure muscle mass has in terms of changing body fat percentage.  For these calculations, I’ll assume that the lifter is gaining 100% muscle and no fat; please note that this is not usually a good assumption.  But it makes the math easier.

The table below demonstrates how various increases in muscle mass affect body fat percentage; note that his fat mass will stay static at 25 pounds throughout the calculations.  So all I’m doing is dividing total fat mass (25 pounds) by the new body weight after adding the muscle that was gained.  For the unadulterated hell of it, in addition to more reasonable numbers, I’ve done the calculation assuming this lifter can gain a whopping 40 pounds of true muscle mass with zero fat gain.

Impact of Muscle Gain on Body Fat Percentage

Muscle Gain Fat Mass Total Weight Body Fat Percentage
5 pounds 25 pounds 175 pounds 14.2%
10 pounds 25 pounds 180 pounds 13.8%
15 pounds 25 pounds 185 pounds 13.5%
20 pounds 25 pounds 190 pounds 13.1%
40 pounds 25 pounds 210 pounds 11.9%


As you can see, adding muscle mass doesn’t really have the impact on body fat percentage that you might hope.  Every 5 pounds of true muscle gained reduces body fat percentage slightly (by about 0.4%).  Sure, if our lifter can gain a tremendous 40 pounds of muscle mass with no fat gain, he will reduce his body fat percentage by nearly 4% but we need to consider the time frame involved here.

As discussed in What’s My Genetic Muscular Potential, with realistic rates of muscle gain, it might take this lifter 3-4 years to gain that 40 pounds of muscle mass.  That’s if he gains it at all (i.e. it may be beyond his personal genetic potential).

As well, it would be staggeringly unlikely for this lifter to gain that much muscle without gaining some fat; and by ‘staggeringly unlikely’, I mean basically impossible.

Now, for comparison, let’s look at the impact of fat loss on body fat percentage.  The calculations here are a little more complex because both fat mass and total weight are changing.  The table below demonstrates how losing fat impacts on body fat percentage, using values similar to the above.  For what should be obvious reasons, I can’t do the calculation for a 40 pound fat loss since our lifter only has 25 pounds to start with.  If he lost 40 pounds of fat, he’d be long dead.

Impact of Fat Loss on Body Fat Percentage

Fat Loss Fat Mass Total Weight Body Fat Percentage
5 pounds 20 pounds 165 pounds 12%
10 pounds 15 pounds 160 pounds 9.3%
15 pounds 10 pounds 155 pounds 6.4%
20 pounds 5 pounds 150 pounds 3.3%


See the difference?  Whereas a 5 pound gain in muscle only lowered body fat percentage by less than 1%, the same 5 pound fat loss lowers it a full 3%.  By the time the lifter has lost 10 pounds of fat, he’s dropped from 15% to 9.3% body fat; the same 10 pound muscle gain only lowered body fat percentage by 1.2%.  And where a 20 pound gain in muscle only lowered body fat percentage from 15% to 11%, the same 20 pound fat loss took him from 15% to full contest leanness.

Additionally, since fat can be lost much faster than muscle can be gained, it should be clear that losing fat is a far more effective method of lowering body fat percentage.  On a hard diet such as the Rapid Fat Loss Handbook, our lifter could achieve a true 5 pound fat loss in 2 weeks, compare that to the roughly 10 weeks it might take him to gain the same amount of muscle.

Even on a more traditional diet, a 5 pound fat loss should be easily achievable within 5 weeks; twice as quickly as the same gain in muscle mass and with a much greater impact on body fat percentage.  And where the 20 pound fat loss might take 20-24 weeks (taking the lifter from 15% to shredded), compare that to the 1-2 years it would take to gain the same amount of muscle mass.

Which is why I said yes and no originally.

Yes, gaining muscle mass can have an impact on body fat percentage but the effects are generally very small and I think it’s an inefficient way of approaching the goal.  Losing the same amount of body fat can not only be done much more quickly compared to gaining muscle, the equivalent fat loss has a much larger effect on body fat percentage compared to gaining muscle.

Of course, as you might imagine, gaining muscle while losing fat has the largest impact on body fat percentage (noting that the major effect occurs from the fat loss).  But achieving that is generally even more difficult although it can be achieved with complex cyclical diets such as my Ultimate Diet 2.0.



21 thoughts on “Reducing Body Fat Percentage by Gaining Muscle – Q&A

  1. Good post! Nice clean math.

    NW, yeah having more muscle does burn more fat, but not a significant amount really. I think it’s about 5 calores/day/#.

    Is that right, Lyle?

  2. Hey Lyle,do you think that being on either a high protein or moderate protein/fat diet(by percentage) that is low in carbs would cause glycogen depletion enough to allow a ‘refeed’ similar to your Ultimate Diet EVEN on above maintence calories???

  3. Deb/dimitris: The most recent value I’ve seen for caloric expenditure at rest for skeletal muscle is about 13 kcal/kg. 6 kcal/lb. Whoopee. If you gained 40 lbs of muscle, you’d burn 240 calories more per day. Which does add up but will take years to achieve. And of course, a female will never gain that. The major calorie burn will come from the weight training itself and the energy required to synthesize the muscle.

    Jared: Refeeds are needed irrespective of glycogen depletion.

  4. I’ve been mostly losing fat, half-assedly building muscle. I’ve lost a bunch, and have hit my lowest weight as an adult. The last time I was here (at this weight), I was a size 6-8, and now I’m size 10. I’m not fond of weights, but that’s a significant difference, so I’ll try a bit harder to build up some muscle.

  5. While the tables are great…there are much more complex interdependencies that are not being discussed here. Your tables assume muscle gain = weight gain and fat loss = weight loss. In reality we all know that is not generally the case. Your last comment is the most valuable. Muscle gain and fat loss in combination are the ultimate and can be achieved with the correct combination of diet, strength training (as opposed to weight lifting…they are different) and cardio

  6. Work the math, the impact of muscle gain is still negligible on body fat percentage, the majority of the effect is due to fat loss just as the simplified equations show.

    And losing fat while gaining muscle is exceedingly difficult under most conditions. It can be done but not easily.


  7. Hi Lyle. While doing biosignature modulation with Charles Poliquin, there was a place he has written that 1 pound of muscle = 50 kcal. I had read that article already with your comment being only 6kcl for one pound. Since i’m a nobody and cannot argue with him, I didn’t speak. But could you point the study where those value come from so that if i’m having a chance I can point that out to him.

    Big thanks.


  8. The value of 6 cal/lb at rest for muscle (~13 kcal/kg) comes from a chart in this paper

    Curr Opin Clin Nutr Metab Care. 2001 Mar;4(2):143-7.Click here to read Links
    Dissecting the energy needs of the body.
    McClave SA, Snider HL.

    The 50 cal/lb value is decades old and completely incorrect.

  9. So, one thing not addressed here and probably what the person originally asking the question was after is a change in appearance. While certainly losing body fat is going to change appearance, adding 10, 15, or 20 pounds of muscle with even a bit of fat gain is certainly going to alter appearance significantly. Probably in the direction the person wants.

  10. I gained muscle (about 30% strength gain and visible development in the showy muscles) while also losing 3#/week. Did not do anything fancy. Ran a basic diet (NutriSystem, but I think any other would work fine) and lifted at the YMCA. I think the key was just being diligent with both the lifting and the dieting. Too many people worry that their lifts are not “helping” because the gains are not sudden. Sometimes, you get the same issue with dieting as well although here losses are faster. I think the average person can easily maintain muscle and actually get stronger, if they just stick to a program. And it does not need t be something fancy. Just something stuck to!

  11. Just as you can lose weight way faster than gaining muscle, ALSO it is a much faster way to better appearance. All these fatsos thinking that they will be stick figures or that they look good because of muscles are like fat women who think guys like their tits. If you have some big serious fat deposits, diet them off! Don’t eff around. It is so fricking easy. Just put down the beer, put down the donut. Pick up the salad.

  12. What is the avg of Body fat % loss in a month… if you are working out 6x a wk and eating a healthy diet… eating every 2-3 hrs, little carbs, no sugars, or whites (breads/sugars)???
    I am 5’2″ and 105lbs with 25% and my GF is 155lb and 28%… I don’t know what would be a considered a “good” loss after each month…

  13. Hi Lyle 8 weeks ago i started the workout from hell it consists of 30 reps 3 sets 8 different exercise aday mon tues back and chest tues bis and tris off wednesdaythen same thurs fri off 2 days with filling in cardio and legs.also some cardio everyday then the next 4 weeks is 15 reps with as much as u can do as im finished the 8 weeks my next 4 weeks is 5 reps piling on as much as i can do 3 sets still on all. .my strength increased dramtically but what i dont understand is i went from 165 to 175 in 8 weeks.ive lost 40 lbs in the last year getting down to 163 at my clothes pants are still the same shirts fitting better is it possible tat this is muscle if so how mch is muscle versus eating more cause im flat out 50 yrs old never lifted much until this past year so am i gaining muscle at a faster clip then someone who weightlifts for years .thanks…

  14. i forgot im on hase three nowwhich is 5 reps of each 3 sets .phase 2 was 15 reps 3 sets again though with as much weight u can do on the first sets

  15. I really like your charts that you use in your posts. Their are a lot of people out their that think that you can lose body fat without any strength training .

    This post really breaks it down to where you can understand. I love to do plenty of cardio, but I notice that it breaks down your strength levels over time, so I cut back on it considerably. It all depends on the look you are trying to achieve.

  16. this is the first time i’ve visited this website lyle and it seems interesting but what you say kinda confuses me. im currently doin the new rules of lifting for women workouts and the diet section seems to contradict everything you say here. they advise eating at maintenance level and eating enough protein so your body can build (or atleast maintain) muscle while losing some fat. also , take a look at this blogpost which is super interesting:

    the gist of it is that this girl was about 117 pounds with 27% BF and yet she lifted really heavily and ate about 3000-5000 cals (mostly clean) a day and she totally lowered her BF and gained muscle. one line that really sticks out in the post is “If you strength train while eating a normal amount of calories, you will lose the fat on top of your muscle, and leave behind the muscle you already have – giving you that toned look. Make the mistake of just eating less and running more, you’ll burn through both fat and any muscle you have as you lose weight.” i really want the toned look, im female , 137 pounds and about 25% BF. i dont want to diet like you suggest because i like my legs , booty , etc and i dont wanna get thin allover , which is what happens when you diet. eating maintence while strength training seems like the perfect solution , but should i be dieting and strength training? is that the only way the BF% will go? wont that make my muscle tissue go as well? the last thing i want to do is to be “skinny fat” with no strength at all.

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