Recently my gym bought a fat analyzer (InBody scanner). I have used it twice now. I'm a bit perplexed and disappointed by the results.

A little back story:

I'm 39. I've been maintaining the same workout for about 3 years. Hit cardio, 4 to 5 times a week. During the summer I usually run on the weekends as well. My typical diet for quite some time now is moderate to high protein, reduced carbs, especially grains containing large amounts of gluten. I steer clear of most heavily processed foods (the only thing I grab out of the center isles of the grocery store is coffee). I eat a lot of fish and a lot of vegetables. Some fruit, usually for breakfast. I cook a lot of Mediterranean food which has a lot of fried foods, bit nothing deep-fried or breaded. I do drink a decent amount as well.

4 weeks ago I used the body fat analysis machine for the first time, and after that, I decided I would try to put on some muscle mass and shed some of this winter fat. Below are results for week 0 and week 4

Week 0: Body fat: 19.0%
Skeletal Muscle Mass: 85.8lbs Weight: 185.5lbs Metabolic Rate: 2210.4

Week 4: Body fat: 18.3%
Skeletal Muscle Mass: 84.7lbs Weight: 182.3lbs Metabolic Rate: 2194.8

I didn't change my workout regiment or main diet. The only things I changed were:

  • I cut back on drinking, especially beer.
  • I started supplementing a protein shake after every workout.
  • I started adding L-arginine to my water bottle, which does seem to help with recovery.
  • I don't really count calories, but I made sure I was eating enough to hit my metabolic rate. On days I worked out I targeted around 2700 to 3000.

I didn't expect much of a change, but I was really concerned about retaining muscle mass. What did I do wrong? Do I just need more calories in general? More protein? or am I missing something completely?

  • 2
    It would be interesting to know what type of "analyzer" your gym is using. Some are more accurate than others. And, the experience level of the person doing the analysis is also important.
    – rrirower
    Feb 17, 2020 at 15:08
  • Well, that would be me, since I'm just following instructions on the analyzer. But I should also point out that conditions such as time, fasting prior to weighing, posture during the process were controlled. I'm not sure if the Body mass calibration is linear, but if it is, and as long as it didn't didn't slip in 4 weeks, I would results would be proportional. BTW, it's an InBody scanner. I don't know the model.
    – mreff555
    Feb 17, 2020 at 15:16
  • Regardless of the "analyzer", it's important to know the technology that is used to perform the calculations. For example, Hydrostatic Weighing is reputed to be the most accurate for measuring body composition. Bioelectrical impedance is also common. I'm not familiar with the device you've indicated, so, I'd urge you to research any studies relating to the accuracy of the methodology it uses.
    – rrirower
    Feb 17, 2020 at 17:44
  • It’s bioelectrical
    – mreff555
    Feb 17, 2020 at 19:54
  • 1
    Well your muscle to fat ratio went up, so I wouldn't be so harsh on yourself :) It's quite hard to lose weight and gain muscle at the same time. That's why body builders go through bulking and cutting phases.
    – ericcurtin
    Feb 18, 2020 at 10:26

3 Answers 3


Don't worry about it.

My gym has had an InBody scanner for a few years now, so I've had a bit of experience with them. Assuming it's the same model as the one I'm used to, it uses bio-electrical impedance to measure your fat / muscle percentages.

The problem with these is that, although you believe you're keeping all other variables the same, it's just not possible, so minor variations are going to occur. Differences in hydration levels lead to different results, and from that you've got differences in excretion / elimination levels as well.

I believe there's also small, but noticeable, difference with foot position, hand position, etc. You can see this for yourself by doing several tests back to back, you'll probably notice variations in muscle and fat percentage.

As you'll also learn over time, the numbers don't always make sense. The machine has registered a drop of 1.5 kg in bodyweight for me before, 0.3 kg of which is muscle, and 0.6 kg of which is fat. I'm not great at math, but even I know those numbers don't add up.

Instead of measuring twice, four weeks apart, you're much better served by measuring once a week / once every two weeks for a few months, then look at the overall direction things are going in.

Your body does not change lineally, measuring day on day, and panicking about daily variations, is how people develop complexes and unhealthy behaviours around their bodies.

If, after a few months, you're still losing muscle mass and gaining fat mass, then I'd say come back, post your full routine and ask the question again.

  • 1
    "The machine has registered a drop of 1.5 kg in bodyweight for me before, 0.3 kg of which is muscle, and 0.6 kg of which is fat. I'm not great at math, but even I know those numbers don't add up." Full bowel vs empty bowel?
    – nick012000
    Feb 18, 2020 at 7:26
  • 2
    @nick012000 hydration level could also be a factor.
    – Haem
    Feb 18, 2020 at 8:15
  • @nick012000 Honestly don't know. I train after work, so jump on it then, which means there's a whole day's worth of variables to take into account. I'll likely never figure it out, just always makes me chuckle
    – Dark Hippo
    Feb 18, 2020 at 10:01
  • I've noticed that full bladder vs empty bladder makes a huge difference
    – J_rite
    Feb 18, 2020 at 10:36
  • 1
    "hydration level" has been mentioned already but to put a fine point on it, the 0.6kg missing from the equation could easily be water weight. 600g of water is, of course, 600ml of water, or for Americans like me, about 2.5 cups. The manual for the scale probably mentions that computed water weight isn't displayed by the scale. Feb 18, 2020 at 16:36

Bioelectrical impedance analysis of body composition can give quite variable results, and in particular is known to be affected by water and food intake independent of body composition. So I wouldn't trust the numbers it's given you.

If you're aiming to maintain or increase muscle mass though, you'll need to be resistance training. (You said your current training is "Hit cardio, 4 to 5 times a week" - did you mean HIIT?) Merely adding protein to your diet is unlikely to cause significant muscle gain.

  • What would you suggest? I primarily added the protein because when I tried counting calories, I realized I was most likely not consuming enough calories to meet my metabolic rate on a daily basis.
    – mreff555
    Feb 19, 2020 at 2:47
  • @mreff555 for resistance training, you mean? It depends what you have access to, but assuming a full gym, I'd suggest finding a beginner-specific free weights program focussing on compound lifts such as squats, bench press, deadlifts, overhead press, etc. It may be beneficial to initially hire a coach or trainer to help familiarise you with these movements. Feb 19, 2020 at 3:05
  • The majority of the movements I do involve weights. As I said, it is HIIT cardio. It’s also a fairly standardized program, (Orangetheory).
    – mreff555
    Feb 19, 2020 at 3:16
  • Ah, that's trickier then, as you're limited to the class content. HIIT classes are not particularly effective for gaining muscle - they're more cardio focussed. Sure you use weights, but there's a big difference between the low-load, high-rep, short-rest structure of HIIT and the high-load, lower-rep, longer-rest structure of most strength training programs. You'll be able to gain some muscle doing HIIT, but nowhere near as much as on a dedicated strength program. (This is why most countries' physical activity guidelines recommend separate strength and cardio exercise sessions.) Feb 19, 2020 at 3:55

Bear in mind that cardio is not great for building muscle mass anyway. In fact depending on the type of cardio you're doing it may reduce your muscle mass slowly anyway, especially as you get older.

If you really want to increase muscle mass you'll need to get more weights involved and do a bit less cardio. Try switching some of your cardio sessions to more weight intensive work outs.

  • It is HIIT cardio, so a good portion involves weights.
    – mreff555
    Feb 19, 2020 at 2:49

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