Fluctuations in BF% on Scale

jeffininer

So I'm no stranger to the fact that body fat % on a digital scale isn't the most accurate tool. I get that. I use it for a trend, not for accuracy. But, when I step on in the morning and it shows 35%, then if I step on in the evening it shows 28%. What's up with that? I only weigh and log in the mornings, so the evening weigh is just curiosity. But, why the huge fluctuation in BF%? Now I'm wondering if my morning weigh ins show a much higher BF% then is actually true.

Anyone have any experience with these digital scales and BF%? What would you suggest as a tool to check without going somewhere?

SezxyStef

could be a difference in hydration...hence the reason these scales aren't even good for tracking trends.

Mischievous_Rascal

could be a difference in hydration...hence the reason these scales aren't even good for tracking trends.

This, except you have to use them correctly to get a good trend. My scale is within 0.5% of my bod pod test, and my readings are pretty steady from week to week with it. (Mine has separate regular and athletic functions, though, which makes it closer to your true BF%.)

The instructions say you should use the BF function just before your main evening meal, so I weigh in just before diinner. It states something about most of your water weight pooling in your torso during sleep, so it throws off the number in the morning. It doesn't hurt that my smallest weight for the day is after work, too, so that's the time I use to get my baseline each week.

SezxyStef

based on my understanding bod pod can be less accurate due to hydration as well so not sure that is a good comparison either.

dexa scans are (based on what I have read) the most accurate way to get a BF% reading...anything else has room for error based on hydration, human error etc.

My choice outside of a dexa scan is having people who know what they are doing look at photos flexed/unflexed and give me an estimation that way.

jeffininer

I have a routine, which is why the trend works (all my graphs are definitely going down and muscle mass is going up). I weigh as soon as I get up, no clothes, after the restroom.

The instructions say you should use the BF function just before your main evening meal, so I weigh in just before diinner. It states something about most of your water weight pooling in your torso during sleep, so it throws off the number in the morning. It doesn't hurt that my smallest weight for the day is after work, too, so that's the time I use to get my baseline each week.

That's nuts, I had no clue. Thanks for that info! Makes since about the water weight in the morning.

jeffininer

based on my understanding bod pod can be less accurate due to hydration as well so not sure that is a good comparison either.

dexa scans are (based on what I have read) the most accurate way to get a BF% reading...anything else has room for error based on hydration, human error etc.

My choice outside of a dexa scan is having people who know what they are doing look at photos flexed/unflexed and give me an estimation that way.

Thanks. I just have no clue where I am. I started off in the Overweight/obese category. I have a feeling I"m now in the normal category, but I just don't even know. Now that I'm not so much worrying about the number on the scale, I'm curious where I stand.

CariS001

I have been wondering that myself! I always weigh in at the same time, same circumstances. I went away on vacation and dropped from 17% body fat, to 10% when I returned (which shouldn't even be possible, as a woman!), I did NOT change my eating habits much at all, kept up the same water intake. I thought... give it a week, it will settle in. So far, I'm up a bit, but still lower than before (at 14%). My routine is totally back to normal, and yet the % is holding firm. My husband found it went down, but then came back up within a few days (and went a little higher, but he indulged a bit on vacay!).

Seems so strange! It's making me want to get a set of calipers just to compare.

jeffininer

I have been wondering that myself! I always weigh in at the same time, same circumstances. I went away on vacation and dropped from 17% body fat, to 10% when I returned (which shouldn't even be possible, as a woman!), I did NOT change my eating habits much at all, kept up the same water intake. I thought... give it a week, it will settle in. So far, I'm up a bit, but still lower than before (at 14%). My routine is totally back to normal, and yet the % is holding firm. My husband found it went down, but then came back up within a few days (and went a little higher, but he indulged a bit on vacay!).

Seems so strange! It's making me want to get a set of calipers just to compare.

I thought the same thing. With such a big difference, I just would like to know.

sijomial

My scales will tell me I'm 18 or 19% in the morning and 14 or 15% in the afternoon.

They work by sending a tiny current through your body and so differences in hydration cause big variations. You could track same time of day every day to get a trend or just take progress pictures.

Dissection is the most accurate measure but has unfortunate side effects.

tycho_mx

I have been wondering that myself! I always weigh in at the same time, same circumstances. I went away on vacation and dropped from 17% body fat, to 10% when I returned (which shouldn't even be possible, as a woman!), I did NOT change my eating habits much at all, kept up the same water intake. I thought... give it a week, it will settle in. So far, I'm up a bit, but still lower than before (at 14%). My routine is totally back to normal, and yet the % is holding firm. My husband found it went down, but then came back up within a few days (and went a little higher, but he indulged a bit on vacay!).

Seems so strange! It's making me want to get a set of calipers just to compare.

I thought the same thing. With such a big difference, I just would like to know.

It is normal, well understood, and people should not freak about it. In this case, it is completely related to hydration levels.

Scales with BF% are based on body impedance - basically, they measure how well your body conducts electricity. Fat = insulation; water + electrolytes = conductor. A way to improve accuracy and repeatability is getting your body fat measured in a more reliable way (DEXA, immersion, even calipers by an expert) and correlate it.

Then, measure consistently. At least it'll give you a trend. Matt Fitzgerald's Method from "Racing Weight":

1. Always measure body fat at the same time of day, preferably at least 2 h after eating
2. Make sure you are well hydrated
3. Use the bathroom before stepping on the scale
4. Moisten a towel and step on it with bare feet before stepping on the scale (enhance conductivity)
5. Make sure the scale is on a flat, hard surface.
6. If you have a good reason to believe your body fat percentage is low (e.g. visible abdominal musculature) purchase a scale with an "athletic" mode.

(My notes)

4 - (a bit gross) - big calluses on feet from running and riding a lot impede conductivity, too!
6.- based on a DEXA test, my body fat % correlated better with non-athletic setting even with visible abdominal musculature in my case.

jeffininer

My scales will tell me I'm 18 or 19% in the morning and 14 or 15% in the afternoon.

They work by sending a tiny current through your body and so differences in hydration cause big variations. You could track same time of day every day to get a trend or just take progress pictures.

Dissection is the most accurate measure but has unfortunate side effects.

Yeah, at least I'm being consistent and watching the trend, not the number. But just curious about the number

Yeah, dissection doesn't sound that great to me

It is normal, well understood, and people should not freak about it. In this case, it is completely related to hydration levels.

Scales with BF% are based on body impedance - basically, they measure how well your body conducts electricity. Fat = insulation; water + electrolytes = conductor. A way to improve accuracy and repeatability is getting your body fat measured in a more reliable way (DEXA, immersion, even calipers by an expert) and correlate it.

Then, measure consistently. At least it'll give you a trend. Matt Fitzgerald's Method from "Racing Weight":

1. Always measure body fat at the same time of day, preferably at least 2 h after eating
2. Make sure you are well hydrated
3. Use the bathroom before stepping on the scale
4. Moisten a towel and step on it with bare feet before stepping on the scale (enhance conductivity)
5. Make sure the scale is on a flat, hard surface.
6. If you have a good reason to believe your body fat percentage is low (e.g. visible abdominal musculature) purchase a scale with an "athletic" mode.

(My notes)

4 - (a bit gross) - big calluses on feet from running and riding a lot impede conductivity, too!
6.- based on a DEXA test, my body fat % correlated better with non-athletic setting even with visible abdominal musculature in my case.

Great information! Thanks for taking the time to write that out. I'll give it a go.

jstout365

Here is a little bit about the scales "Body fat scales use Bioelectrical Impedance Analysis (BIA). A very small, harmless electrical current passes through your body tissues, slower through fat and quicker through muscle. Resistance is what is being measured. So, actually it is not analyzing your body fat percentage so much as your body density. The scale then takes this reading and uses a formula to give you a body fat percentage reading."

So, if it isn't fat, it is being put into the lean mass category. So....you have a higher BF% reading in the morning than you do in the afternoon, well, yeah, because you have more food and fluid in you that will go into the lean mass category, dropping your BF%.

Consistency is key for trend analysis. Keep it to the morning since that will be the time when conditions will be more consistent from weigh in to weigh in.

The other thing I do is break it down into lbs of fat and lean mass. That way I can see the amount of fat in relation to the fluctuations in lean mass, most often due to water weight.