The above is a common thought/statement made by a number of clients as well as a number of fitness professionals. The question is; Is it true? There are a couple of parts to the statement, but overall the above statement is NOT true! Read on to find out why.

It is amazing how many times I have heard “muscle weighs more than fat”, from both my clients and other fitness professionals. The statement, as it is usually stated, is really nonsensical without a specific VOLUME qualifier. Here is an example; if I would to say that “lead weighs more than feathers” then I would be making another illogical statement; does 5lbs of lead weigh more than 5lbs of feathers? I hope you said no! Obviously 5lbs is 5lbs. However, if I would to say that lead has a very high-density of weight and for the same amount of space (density) lead would be much heavier, then I would be making a logical and likely obvious statement. The weight density is greater for lead than feathers, think a feather pillow versus a lead block of the same size. This is what I think people really mean when they say “muscle weighs more than fat”. They mean 5lbs of muscle is smaller than 5lbs or fat. So muscle does not weigh more than fat, again 5lbs of muscle is the same as 5lbs of fat, but rather muscle has a higher weight density. Therefore, the correct statement should be “a given amount of muscle tissue will take up less space than fat tissue”. That leads me to the next important aspect; how big of difference is there in size?

Is the weight density of skeletal muscle and fat similar to the lead versus feathers example? Hardly! It seems that the weight density difference between muscle and fat is a whopping, wait for it….18% (wiki). This is much less than what is typically said about the difference between these two tissue, which is usually in the range of 50 to 100%. However, this approximately 20% difference in volume could potentially make a difference in girth measurements, i.e., the size of your waist, hips, thighs, etc. This difference in waist size, etc. could occur even if you did not lose any weight. If you would to replace (more on that in a minute) say 5lbs of fat with 5lbs of muscle your measurements could get smaller but your weight on the scale would not change. Would you be 20% smaller? Probably not. It is likely not that simple as there are other tissues (bones in the arms and legs and organs, along with the bones from the spine for a waist measurement) that also account for the size of a specific area. The point being that the circumference of an area is not solely determined by the amount of fat and muscle. At this point I am not sure how to figure out how to determine exactly how much of a specific area’s measurement is determined by the amount of muscle and fat, so I am unable to give any concrete answers on what would happen if you lost 5lbs of fat around your waist and gained 5lbs of muscle in that same exact area. This scenario is not likely (see next section) but it would be cool to know what would happen. Anyway, for today (hopefully someone can give me some specifics) I am going to assume it is 50% (half of the tissue in a certain area), therefore an equal exchange of fat for muscle tissue could cause a 9% (half of the 18%) change in the size of an area if you lost ALL of the fat in that area and gained an equal amount of muscle in that area (anybody confused yet, my head hurts a bit). To illustrate this point, if you had a thigh measurement of 25 inches and you lost all of the fat in that area, we will say it is 5lbs, and replaced it with 5 lbs of muscle, then it would be possible to change the size of your thigh circumference by 2.25 inches (9% of 25) resulting in a thigh circumference measurement of 22.75 inches (25 minus 2.25). There is certainly a difference and the exchange of muscle for fat can make a difference in your measurements but will that likely happen?

The previous paragraph was mostly a thought experiment because gaining large amounts of skeletal muscle (5lbs is a large amount) while you are trying to lose fat is not likely to happen. This aspect of the discussion really deserves a separate post (a related post here, also read the exercise chapter in the book), but I will highlight a few aspects now to make my point.

During weight loss it is generally not easy to gain ANY muscle (Hansen et al; Stiegler et al). There are a number of variables, such as total calorie intake, amount of protein intake, exercise or not, type of exercise, age, and gender, that will determine the change (Hansen et al; Stiegler et al). Here are the results from some of the research to drive home this point.

Schmitz, KH et al (2003). Strength training for obesity prevention in midlife women. Inter J Obesity; 27

  • 60 women, aged 30-50 years old
  • strength training 2 times a week, 50 minutes each, doing 8-10 repetitions per exercise
  • followed closely for 15 weeks
  • not following a hypocaloric diet (the aim of the study was not weight loss)


  • at the end of 15 weeks: an average gain of about 2 lbs of muscle (fat-free mass)
  • An important aspect; the women where NOT following a hypocaloric diet, meaning they were not trying to lose weight

Meckling, K & Sherfey, R. (2007). A randomized trial of a hypocaloric high-protein diet, with and without exercise, on weight loss, fitness, and markers of the Metabolic Syndrome in overweight and obese women. Appl Physiol Nutr Metab; 32

  • 60 overweight or obese women, average age of 41
  • 4 hypocaloric treatment groups, all of which reduced total daily calorie intake by 500
  1. control diet
  2. control diet with exercise (3 days a week of a 36 minute circuit training program)
  3. high-protein diet (1.5 g/kg of protein/day)
  4. high protein diet with exercise (same as above)
  • Followed for 12 weeks


  • after 12 weeks: all interventions produced weight loss, ranged from 4.6 to 15.4 lbs, there was no loss of muscle mass in any of the interventions, and a few of the groups gained some muscle, with the maximum average of 2.6 lbs

Demling, R. & DeSanti, L. (2000). Effect of a hypocaloric diet, increased protein intake and resistance training on lean mass gains and fat mass loss in overweight police officers. Ann Nutr Metab; 44

  • 12 week study
  • males, aged 28 to 40
  • 3 treatment groups
  1. hypocaloric (HC) diet only (80% of predicted need)
  2. HC diet with a high protein intake (1.5g/kg/day) using a casein protein supplement, plus 4 days a week of weight training lasting 30-35 minutes, doing a variety of exercises for 8 to 10 repetitions each
  3. HC diet with a high protein intake (1.5g/kg/day) using a whey protein supplement


  • Group 1: (average) lost 5.5 pounds of fat and no change in muscle mass
  • Group 2: (average) lost 6.2 pounds of fat and gained 8.8 lbs of muscle mass
  • Group 3: (average) lost 5 pounds of fat and gained 4.4 lbs of muscle mass

A couple of interesting aspects to this study. First, the diet only group lost no muscle mass. This is not typical in diet only weight loss interventions (Hansen et al; Stiegler et al). Second, Group 2 and 3 both gained a substantial amount of muscle mass in 12 weeks. The authors of the study were also a bit surprised by this results and stated;

“We consider the large gains in lean [muscle] mass in the police officers to be in large part restoration of lost lean mass rather than gaining new muscle, a process similar to lean mass gains in the post-injury period or in the deconditioned elderly” (p.28).

Continuing with the last point made by the authors of the Demling et al study, I think it is important to realize that many of the studies that show an increase in muscle mass during weight loss used participants that are initially sedentary so there is a potential for a greater initial change due to their beginning physical condition. This also means that after an initial increase in muscle tissue there will likely be no change or little change in the amount of muscle tissue over the long-term.  A final thing to point out is the likely difference between males and females with respect to muscle gain. As the above studies show, as well as the review papers by Hansen et al and Stiegler et al, women will generally gain less muscle, if any at all, during weight loss, compared to males.

A recap of the studies mentioned above. There are many more studies pertinent to the question of muscle gain or loss during weight loss. I pick these to show that it is possible to gain some muscle during weight loss. However, there are many studies that have found only a maintenance of muscle or a loss of muscle during weight loss. If I wanted to cherry-pick the data, I could have just presented that information, but that would not be an honest representation of the facts. The first study does show that older women can gain some muscle mass from doing resistance training when not following a hypocaloric diet. The second and third studies demonstrate that some muscle can be gained during a reduced calorie diet. However, when the sum of studies are evaluated the general trend during weight loss, if resistance training or possibly cardiovascular exercise is done, is the amount of muscle tissue a person has will stay about the same, plus or minus a couple of pounds (Hansen et al; Stiegler et al).

The use of the “muscle weighs more than fat” and “I haven’t lost weight but I have probably gained some muscle” are usually used to make us (trainers, nutritionist, doctors, etc and clients) feel better when they don’t lose weight. While there is a small kernel of truth in the second statement (see above for why it is likely small) the use of “I must of gained some muscle” is really a diversion tactic. It is a way to avoid the hard truth that you are likely eating too many calories and not moving enough. I am not saying that it is easy to lose weight (see this post on that aspect), but avoiding the reality of the situation will not help the situation.

IF you are 30 years or older, trying to lose 20 or more pounds of fat, eating a reduced calorie diet with ample protein, and you exercise on a regular basis (5 x week with at least 2 x week of intense weight training) your are still NOT likely to gain more than 5lbs of muscle tissue. In fact, it is common for people to NOT gain any lean tissue and sometimes actually lose muscle tissue during weight loss (Hansen et al; Stiegler et al). Here is an example/common scenario that should help to illustrate my point;

  • goal is to lose 30lbs
  • lose an average of 2 lbs a week
  • will take 15 weeks to reach goal
  • will gain 5lbs of muscle during the 15 weeks, would average out to an increase of .3lbs/wk
  • if we minus the .3lbs of muscle tissue per week, that still leaves about 1.7 lbs of fat that you will still need to lose per week.

The example above is a bit simplistic and very linear but it is still a good example of the fact that you should still be seeing a decrease in the scale most weeks, even if you gain a good amount (2 to 5lbs) of muscle tissue. Therefore, if the scale is not going down, then you need to re-evaluate your diet and activity levels.

Muscle has a bit higher weight density than fat does so it is possible to change the size of your body a bit by replacing some of your fat with muscle tissue. However, for most people, particularly women, the amount of muscle tissue that will be gained is usually not enough to make any significant changes in the size of their body. For those of you who’s goal is to lose fat, then the scale should be moving down on a regular basis and saying “I must be gaining muscle” is not likely true and will not help you reach your goal as it will likely divert your attention away from what  is likely happening; you are eating more than you body needs in order to lose weight.


Hansen, D. et al (2007). The effects of exercise training on fat-mass loss in obese patients during energy intake restriction. Sports Med; 37(1)

Stiegler, P. & Cunliffe, A. (2006). The role of diet and exercise for the maintenance of fat-free mass and resting metabolic rate during weight loss. Sports Med; 36(3)

"I haven't lost any weight but I think I have gained some muscle. Since muscle weighs more than fat I have probably lost a good amount of fat even though the scale has not changed"
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