Accuracy of Body Scales and Loss of Muscle mass

Pinback78

I have a question about the accuracy of body scales. I bought a Garmin scale and monitor my body fat and muscle mass during my weight loss journey.
So far I lost about 40lbs. It seem like 30lbs of it was body fat, 6lbs muscle mass and I guess the rest is water. My question is: how accurate are those scales? Why did I lost muscle mass at all? I have quite a good amount of protein, I workout regularly (cardio 3 days, strength 3 Days) I feel my overall fitness goes up, energy goes up, and my arms feel pumped. But every time I scale myself there is a slight loss of muscle mass.

Lietchi

Accuracy isn't something you should expect from these scales, it just sends an electrical current through your body (and often only through your legs, if it's a classic scale) and measures the resistance. Results can vary wildly depending on your hydration level alone.

Also, you're doing a lot of things to minimize muscle loss, but one thing that is missing is: how aggressive is your calorie deficit? Losing weight quickly is a risk factor for losing muscle mass.

Pinback78

It varies. I am a big guy, 6.7” and I can’t be consistent during individual days, but within 7 day average my deficit is 500-800 kcal / day.

rightoncommander

I second Lietchi's comment about accuracy, for precisely the reason stated - the scales are extrapolating from three data points - height, weight and electrical impedance. There's a lot of assumptions and guesswork involved.

Having said that, if the scales are accurate, 30:6 is an excellent fat:muscle loss ratio, especially for someone like you who is losing weight relatively quickly. Don't worry about some silly number on a screen, you're doing great! You are bound to lose some muscle mass when losing weight. You are using your muscles 24 hours per day, even in your sleep, so three hours per week in the gym won't fully counteract the reduced strain caused by the 34lb loss of fat and water. Don't try to maintain muscle mass, just do what you are doing now in order to minimise the loss of muscle and keep that ratio as high as possible.

cwolfman13

They aren't accurate at all in the sense of giving you a true number...maybe, possibly there is something useful in terms of long term trends, but even then...given the numbers aren't true, I don't know what the benefit would be. Consumer Reports actually stopped reviewing them because none of them can really do what they claim.

That said, some muscle loss while dieting is inevitable. Sufficient protein, reasonable calorie deficit, and resistance training can mitigate this to a large extent, but ultimately in a calorie deficit, you are in a catabolic state for which you will lose both fat and and some muscle.

autobahn66

Just chiming in as this piqued my interest in my own data and fully agree with all the posters above.

I am 180cm with a start weight of 123.9kg on July 22nd (but the graphs here start at c.118kg and August 5th as the numbers are not easily interpretable before this date due) and was 104.4kg this morning, making my weight loss over this time similar to yours. I have been working with a similar(ish) deficit, and have been doing cardio (running and rowing - between 500 and 750 kcal on average) 4 times per week without strength training.

I got a Huawei scale 3 which measures BF% by BIA, and gives an absolute muscle mass value as one of 11 different metrics it provides.

I got quite anxious about 1 month into losing weight that I was losing muscle mass very quickly (according to the scale), but after reading about their accuracy issues I decided to essentially ignore the numbers other than the absolute change in weight.

Now a few months later:

The x-axis is days and the y is weight change in kg.

What I think this shows:

1. The day-to-day result of the muscle mass/fat mass/BF% is not useful. You can see that there is a reciprocal relationship in the upper graph - on a day where I weighed more I tended to have a spike in "muscle mass" which likely represented an decrease in impedance related to retained water from inflammation or diet (I suspect salty food - which has a direct effect on increasing total body water to maintain the sodium content in the blood)
2. The longer term trends in the lines (smoothed by a 7 day moving average) are more useful to track trends, were more consistent than I expected and provided me with some reassurance (deserved or not) - the rate of decline in muscle mass was most rapid in the first few weeks and slowed such that over the past few months, although my muscle mass has apparently fallen, it has done so at a much slower rate. I am guessing that there has been some process of physiological adaption in the muscles (perhaps in neuromuscular recruitment or overall composition) or change in my behaviour (particularly exercise behaviour) that has changed this.
3. None of this means anything in an absolute sense. I have no idea what my true muscle mass/BF% is. There are several methods of measuring this, including DEXA scans and densiometry etc. I am not willing to pay to find out a true number which has no specific bearing on my activity (i.e. I cannot imagine that I don't have an elevated body fat % and I know that this distribution of this fat is mainly abdominal. I know that in the longer term, strength exercises will be a useful way to support muscle strength - but I will be using strength and endurance as metrics of improvement, not absolute mass in both strength training and cardio - I could not run for 5 mins previously, but ran 10k in an hour in the gym last week)
4. I don't think it is possible (for me at least) to lose weight without losing both fat and muscle. Doing proper recomposition seems to be really difficult as there are directly contradictory goals of anabolism of muscle and catabolism of fat. I am happy if I weigh less over time and find a stable state of diet and exercise to maintain that weight. It is a bonus to see an increase in fitness and endurance in the gym, but one which reflects that my possibly lower muscle mass is less important than my ability to use those muscles.

livendive

I decided Garmin's muscle mass calcs are mostly nonsense when I saw mine perfectly matching my BMI change, even though the latter has precisely nothing to do with body composition. Also, I think it's highly unlikely that I've lost a pound (10%) of my bone mass this year. I have calipers being delivered today...I'll see how those trend against the Garmin values.

coryhart4389

Just yesterday I got an InBody scale after my Omron scale, also new, stopped working because my body fat% was below its range. I realize these scales have an error. However, I’m already very happy with the InBody, while it was expensive, $349, I like it. The InBody does not use a formula to calculate body fat %, it uses 10 impedance measurements at 2 different frequencies. The Omrom uses 1 impedance measurement at 1 frequency while using assumptions based on height, weight, and age. Both scales use hand and foot sensors and both gave me the exact same weight.

AnnPT77

Agree with others that the accuracy is marginal, not very useful except perhaps to establish a long term trend.

One question is what is included in their definition of "muscle"? (Rhetorical question, you don't need to answer, but maybe need to know in order to interpret the results (however imperfect).) For example, sometimes muscle is used as shorthand for lean mass, but lean mass includes some things that we really would probably prefer to lose, because a smaller body simply doesn't need it.

Though it's not the only thing, one possible example is blood volume. I think I'd look pretty odd if my blood volume were the same as when I was much bigger in inches, and almost 50% heavier than I am now.

MercuryForce

https://community.myfitnesspal.com/en/discussion/comment/46420541#Comment_46420541

I was amazed at the difference that can make! Over the last 2 years I've lost about 40 lbs. 30 of those I was losing very slowly, like it took me a over a year to lose them. During that time, according to the scale at my dietitian's my muscle level trend was very steady, sometimes even going up a little. Then, I lost the last 10 lbs in about 3 weeks due to a break-up and medication change and about half of that was muscle. It definitely proved slow and steady was the way to go for my goals!

marius_paps

These scales are fun but I don't think they can be accurate.
They're just a gimmick but they aren't a scientific instrument.

Don't look at the absolute numbers and observe the trends over a week or so.

For me:
Weight: down, and therefore BMI down
Body fat is going up again: well no, it's definitely disappearing. I can see, feel and measure the difference!
Muscle mass: down: that's a possibility, unfortunately, but there also I have my doubts
Alt least my scales are pretty consistent regarding bone mass. 😁
While losing weight, my scales think my body water % has increased. What does that mean? More muscle? That contradicts the muscle mass measurement. It's even possible that if I weigh myself after the shower and my hair is still wet, it'll measure that as increased body water %.

That said, I like these scales as long as the weight goes into the right direction and the graphs are fun.