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MyFitnessPal Community

Is There A Body Fat Percent "Trap" During Weight Loss?

AnnPT77

Here's what I think: It's surprisingly common to see posts here about body fat or muscle-mass percent changes that don't really hold together, because many people don't understand the arithmetic.

My basic point, because this is going to be long (again): If you care about body composition, convert body fat or muscle-mass percent into actual pounds/kilos of body fat and not-body-fat, or muscle pounds/kilos and not-muscle pounds/kilos, before reacting to results.

Looking at the percent can lead to misinterpretations in two directions. To talk about it, I'm going to pretend these percents are exact, even though we all know there's an error rate in the picture, too, especially if the numbers come from a home BIA scale.

A recent post, specific details changed so as not to (bleep) on someone's happiness, celebrated a thing like going from 250 pounds to 200 pounds, while also increasing muscle mass from 55% to 65%. Increasing muscle in a deficit, yay!

But no. Look at pounds: 55% of 250 is 137.5 pounds of muscle mass. 65% of 200 pounds is 130 pounds, so a net loss of 7.5 pounds of muscle. Not quite so yay - not bad in this fake example (I'll explain why later), but a decrease, not an increase in muscle mass.

The real case was actually more extreme than my fake example. The person had lost well over 100 pounds - genuine, sincere yay - but when considered in pounds, the person's lost weight was nearly 40% muscle, 60% fat (or maybe other tissue, too, but probably mostly fat). That's startling, and IMO way less yay.

We all lose some lean tissue when losing fat, some of which we objectively don't need anymore. A common rough rule of thumb is that reasonable weight loss will be around 75% fat, 25% lean mass. (Noting that lean mass is a larger category that includes muscle mass, so is not the same thing as muscle mass.) Those proportions vary in individuals, for a lot of reasons, so that's a very, very rough approximation.

The weight loss rate in the actual case was very rapid, like over 4 pounds weight loss per week on average . . . high risk of losing muscle mass. The result was losing 40% of the weight in muscle mass, higher than that rough 25/75 estimate by a good bit, and still not considering whether additional lean mass was lost that wasn't muscle. Y'know how we often tell people not to lose weight too fast because it can cause unnecessarily high loss of lean mass? Yeah.

OK, I mentioned misinterpretations in two directions. Here's the other direction:

Another thing we see sometimes is people saying something like "I've lost 20 pounds, but my body fat is still 30%. Why didn't I lose fat?" Well, if they used to weigh 220 pounds, and now weigh 200 pounds, 30% of 220 is 66 pounds of fat, and 30% of 200 is 60 pounds of body fat. (Yeah, that's still not a great fat to lean tissue loss ratio, but I totally made up the numbers in this example. Any given percent of a big number is more than the same percent of a smaller number. The main point holds: If weight changed, but body fat percent didn't, the pounds of body fat have changed.)

Again, my main point: Don't just look at the percents. Look at the pounds or kilos, too. Looking at both will provide better insight.

P.S. I was gonna post this in Health and Weight Loss, but decided someone would probably want to debate it. 😉

Replies

nossmf

I admit, I opened the thread thinking you were going to debate whether people get too focused upon reaching a specific body fat % rather than objectively looking at their body itself, but instead simply nodded along with your discussion.

AnnPT77

https://community.myfitnesspal.com/en/discussion/comment/48531899#Comment_48531899

That - shooting for a specific "ideal" percent - is also a potential trap, in some cases. That's doubly problematic if the percent is coming from a BIA scale, maybe.

What really freaked me out, though was the "I gained muscle mass in a deficit" belief in a case where the facts were IMO completely in the other direction, a person believing results were unusually great when they were maybe atypically worrisome.

If health is OK, and the person is happy, all is well. I'm not mostly interested in telling people what their goals should be. But the perception of the facts in a case like that is . . . counterfactual. 😬

I've noticed in other parts of life that a lot of people aren't very good at interpreting scenarios where percents are used. Another one that routinely makes exclamation points stand out all around my head is the kind of thing where people get excited about some article says "reduces risk of XYZ cancer by 25%" when what that really means is the incidence went from 4 in 10000 people to 3 in 10000 people or some such thing.

DomorVerbeuk

It connects with an issue I have with the fatpercentage as a pure guideline instead of the lbs of fat compared to the expected lbs of fat at a moderate weight.

Although BMI isn't a perfect guideline at all, the average (caucasian*) person at 165cm (5ft5in) with an 'ideal' bmi (which was the bmi where the least likelihood of death was at, looking at 20 years from that moment) of 20.5 is 56kg (123lbs). For females 24% fat seems to be around ideal healthwise (but that is from my part an educated guess, I'm absolutely interested in scientific articles confirming or correcting this number). Which is around 13.5kg (30lbs) of fat.

For a woman with her 'ideal' bmi fat percentage under 17.0-17.5% seems to have some connections with a lower health status because the body needs fat, especially for the reproductive system, but the lower you get, the more systems are affected, while over 28% seems also connected to higher health risks.

Now: how would you rank the following list of women based on likely to be more healthy (1 being the most healthy), still going with the 165cm woman:
1. an 80kg woman (bmi 29.4) with 20% fat, having 16kg fat.
2. an 80kg woman (29.4) with 16.8% fat, having 13.5kg fat (the 'perfect' amount at 20.5bmi)
3. a 70kg woman (25.7) with 22.8% fat, having 16kg fat.
4. a 56kg woman (20.5) with 28.5% fat, having 16kg fat.
5. a 56kg woman (20.5) with 24% fat, having 13.5kg fat
6. a 56kg woman (20.5) with 16.8% fat, having 9.4kg fat.

To be honest, I'm not really sure. And I haven't managed to find research that looks into this data. But I do find it fascinating.

*caucasian because the ideal bmi of other backgrounds seems to shift -0.5 to +1.0 depending on from where exactly. It's also not taking extremely long or short people into account).

claireychn074

https://community.myfitnesspal.com/en/discussion/comment/48532620#Comment_48532620

I don’t have the answer to the questions but I’ll just throw yet another variable in here: medically “ideal” fat percentages in women are sometimes shown according to age. I haven’t looked for pubmed verification, but the consensus appears to be that lower body fat is more harmful post-menopause (partly because of the role some fat plays in oestrogen production and therefore linked to bone density). Some of the “ideal fat” tables online suggest women over 50 should carry c24% body fat as a minimum, whereas younger women can be c18% body fat without causing issues (varies per person obviously - at 15% I started experiencing issues but I appeared okay at 18% ie no period interruptions).

I have a BMI of nearly 22 and I’m probably about 24-25% fat based on visual eatimate - but I have a lot of muscle for my size (aged 50, 5’3 and c56kg)

TrekkieLianne

Body fat measurement is so inaccurate that people shouldn't get carried away with this. I should know because I've been one since last October when I was close to 33% and decided to go below 30% as a winter fitness goal. What a chore!

The BIA scales vary wildly, tape/caliper measurements are too subjective and even DXA's accuracy depends on muscle glycogen and hydration on the day you get measured. In the course of this rather arduous project, I've had a realization. I'm 69 years old, and at my age its actually better to have a bit more body fat than when I was younger, as long as it isn't visceral fat. The scale is hovering between 29 and 30 these days, so I've given myself until the end of the month and then I'm done no matter where I end up. The variability in monitoring progress to have a handle on what your actual fat percent is on a daily basis is super frustrating. I believe I should just be satisfied that I'm healthy, athletic and pretty fit for someone pushing 70. Two more weeks of small daily deficits with progressive resistance lifting and moderate cardio, and I'm done chasing that number. Maintenance of lost weight is hard enough without getting bogged down with a statistic whose reliability is questionable in the first place.

AnnPT77

This thread is taking a direction I didn't anticipate, but there's good stuff about body fat coming up, so as the OP of the thread, I'm going to say that the discussion is still on topic. 😉

AnnPT77

https://community.myfitnesspal.com/en/discussion/comment/48532620#Comment_48532620

I'm not even going to take a stab at that list, because I think there are missing variables that are very, very important, things like health history, current health markers, some body type issues, family history, fitness level, nutrition, and even personal preferences. "Ideal weight", even "ideal body fat" is not generic, it's individual and multi-factorial. Not incorporating that kind of thing is also a limitation of BMI, right? Some "fat" people are healthier than some "ideal weight" people; and some "skinny" people may be, too.

I'm going to illustrate what I mean by personalizing this, talking about myself and how I think about it FOR ME.

By coincidence, I actually am 5'5"/165 cm, and female. For full transparency, I weighed 133.2 pounds/60.5 kilos this morning, which is a little bit above my personally-defined best weight around 125lb/56.8kg. My current BMI is 22.2, so above the speculated ideal in the quoted post.

As you say, body fat estimates are approximate, but I figure when multiple poor estimates converge in the same general area, that's probably close enough. In my case, there's a convergence among my BIA scale, the so-called "Navy Fat Calculator" online, and comparison to those photos of "here's what X% body fat looks like on women". The totality suggests my current body fat percent is kind of somewhere midway between 25 and 30 percent, which is also a little higher than I'd prefer.

For convenience not accuracy, I'm going to pretend that today's BIA scale estimate of 27.3% is accurate. That would imply that I have about 36 pounds of fat (16.3 kg), so somewhat above the ideal mentioned in your quoted post; and 97 pounds of lean mass (44.2 kg), which would include muscle, water, bones, and several pounds of gut microbes that aren't even genetically me.

I'm also 69 years old, reasonably athletically active, and yeah, caucasian, mostly Scandinavian/European ancestry.

Am I healthy? I think I'm doing OK, way better than 10 years ago for sure, but not perfect. I'm going to run down the categories I said I thought mattered in a spoiler at the end if anyone cares, using myself as a case study, not with the intention of either criticizing myself or bragging, but to just as a specific, concrete example of what I think matters and why.

In general, I think the questions about a good personal body fat percent or body weight are something we need to determine ourselves, for our own unique selves. If anyone needs to be involved in that assessment, I think it's a personal primary care physician, and maybe specialist doctors too if relevant to an individual. I don't think there's any generic or theoretical right answer that applies to an individual. I think friends and relatives - let alone internet "influencers" and the like - are truly terrible sources of advice about this sort of thing.

I also don't think there's much point in worrying about ideal weight or ideal body fat percent until close to it, when it's easier to figure things out. If we're doing the right things to head to a goal like less fat or more muscle, working at optimizing that strategy to the extent practical, then having a precise numeric goal really doesn't change anything about what needs to be done - doesn't change the process. When getting close, it's a lot easier to decide questions like "Am I healthy (enough)?", "How fit am I?", "Do I like my appearance or do I want something different that's achievable?", etc.

Like I said, personal details in the spoiler as an example/case study, feel free to ignore, but also feel free to criticize or question the assessment, because I have a thick skin. 😉😆

Health history: Past breast cancer, which was estrogen fed, matters because fat tissue does manufacture estrogen even after menopause. (Chemo put me in menopause almost instantly at age 45.) Hypothyroid (medicated, monitored every 6 months). Osteoporosis (currently medicated, and probably partly caused by cancer treatment). Osteoarthritis in various spots, including knees and hips. At least one torn meniscus. History of overweight/obesity. History of borderline to high blood pressure. History of very high cholesterol and triglycerides. When my gallbladder was removed because of adenomyomatosis (not stones or sludge) it was an ugly cholesterolized thing with actual holes in it - yikes.

Current health markers (most recent readings, all within last few months): Blood pressure 114/72. HDL cholesterol 72.4 (high), LDL cholesterol 122.3, triglycerides 71.3. These are fairly typical values for the years since weight loss, though obviously there are some minor ups and downs. No meds for any of these things. Blood glucose was 101 at last test, still in the normal range, but I was in the hospital at the time and some things were weird. It's usually 80s/90s, and was never above the normal range even when I was obese so A1C has never been tested.

Body type: Maybe more like a 14 year old boy than a li'l ol' lady, because I have a fairly narrow pelvis, not much booty, and literally no breasts (post bilateral mastectomies with no reconstruction). More muscular than typical for my demographic.

Fitness: Rowing or cycling most days of most weeks, half an hour to an hour, occasionally other things; over the last year averaged 72 minutes of moderate exercise and 103 minutes of vigorous exercise weekly (according to Garmin Connect as tracked by my Vivoactive IV). Resting heart rate averaged 52 bpm over the past year. Garmin says my estimated VO2max is in the top 5% for my age ("Superior") and my estimated walking fitness age is a startling and truly unrealistic 28. I have enough endurance to do longer sessions of activity or intense activity sometimes, such as a workout last week that included 24 minutes of the hour in HR zone of a 5-zone scheme, average HR for the hour 135bpm, peak 162. (Yes, it was fatiguing, but not ridiculously so - very achievable.)

Nutrition: Long-term ovo-lacto vegetarian - since 1974. Targeting 100g minimum protein daily, usually exceeding it, and getting most of the protein from essential amino acid complete and bioavailable sources. Targeting 50g minimum fats daily, usually hitting it, though that takes more attention. Shooting for mono- and polyunsaturated fats in the mix daily, now averaging around 12-15g poly and 7g mono, around 16g saturated fats; supplementing Omega-3s but also eating less bioavailable plant sources of Omega-3s; shooting for at least 400g varied/colorful veggies/fruits daily, usually exceeding, often double that. I get blood tests for nutritional issues I'm concerned about roughly once a year, and supplement certain things if I think I'm not getting enough, or when my medical team has recommended I supplement something.

Am I healthy?

Assessment: I think I'm doing OK. I should be doing more strength exercise, but hedonist that I am, I don't enjoy it so tend to back-burner it, to my detriment. I'd prefer to weigh a bit less, but am not trying to lose right now because I'm still healing bone from a skull fracture in early November, so eating at/near maintenance calories is IMO more healthful for a few more months, and my current weight isn't causing any negative health consequences. I prefer to be a little lighter because of the estrogen issue, and because my osteoarthritis and torn meniscus hurt less when lighter. Fitness could always be better, but I think it's adequate.

My primary care doctor and I talk about this regularly, and she thinks I'm in a good zone, better than most of her patients. She's on board with regular blood test for the things I want to track, generally. I'm curious about A1C and some other things but my insurance wouldn't cover them, and I'm not concerned enough to self pay.

age_is_just_a_number

MFP article on this topic.

https://blog.myfitnesspal.com/stages-of-weight-loss/?4a934b73fd678698ea3c05a172f2107d=true

Alatariel75

This is so interesting and I have never done the math. I just did.

According to my Withings scale (so grain of salt), I went from 123.2kg at 45% muscle (being 55.5kg) to 85.6kg at 57.5% muscle (being 49.2kg), so of my 37.6kg loss so far, around 17% of it was muscle.

ninerbuff

This is why I don't get into too much discussion with muscle/fat ratio with clients because it can get confusing.

Mirrors and a pinch test usually gives me analysis that's pretty accurate for clients.

A.C.E. Certified Personal and Group Fitness Trainer

IDEA Fitness member

Kickboxing Certified instructor

Been in fitness for 40+ years and have studied kinesiology and nutrition

PAV8888

around 17% of it was muscle.

Around 17% of it was non-fat mass.

Not quite the exact same thing as muscle

AnnPT77

https://community.myfitnesspal.com/en/discussion/comment/48575978#Comment_48575978

She seems to be using her scale's estimate of muscle mass, not LBM?

My new BIA bluetooth IOT idiot scale, in its VeSync app, gives me the following estimates:

In pounds, weight, fat-free weight, visceral fat, muscle mass, bone mass.

In percents, body fat, sub-Q fat, body water, skeletal muscle, protein.

Plus BMI, BMR and metabolic age.

All kinds of graphs over time and evaluations, too. (Various different eval scales for different things, just to keep it more puzzling, I guess).

It doesn't cross-foot in any sane way and some of those estimates seem to me to be complete and utter nonsense. I admit, I haven't spent much time trying to figure it out, because I think a more productive time investment would be to - say - count the leftover recycled rubber bands in my junk drawer. But on the surface the numbers don't seem to make much sense in my case. But it's not a Withings, it's an Etekcity.

PAV8888

Ha: we use the same app/scale Ms Ann! You should check how *kittened* up their "month" to "month" comparisons are. They take the LAST entry of the month. Not the average. Not the low, high, or median. Just the last entry. And that's what their month to month is.

My point to the 17% was that regardless of how the estimates are presented to us users, basic bio-impedance analysis only knows fat mass and non fat mass.

The rest is based on assumptions put forth by the apps, scaled by gender, weight, and age.

On the off chance that I might have been relying on older info, I warmed up the planet a bit to double check. But, yes, it sounds to me that the state of the art is still the same (bolding is mine). Which means that regardless of what the scale says it only knows fat mass and not fat mass without knowing the actual breakdown of not fat.

AND, last but not least. ANYTHING beating the simplified 75% Fat mass to 25% Fat free mass lost "rule" would actually be on the good side of the ledger. If Ann wants to play with math I don't understand she can check out Forbes, Thomas, and Hall :)

Now back to our scales:

Fat vs. non-fat differentiation:
- Bioimpedance distinguishes fat from fat-free mass (FFM) based on electrical conductivity. Fat-free tissues (muscle, organs, blood) conduct electricity better due to higher water and electrolyte content, while fat acts as an insulator1 5 7.
- The method assumes FFM has a constant hydration of 73%, allowing total body water (TBW) measurements to estimate FFM2 4.
Limitations in tissue specificity:
- Scales cannot directly differentiate muscle from other non-fat components like water, organs, or connective tissue2 4 6.
- Muscle mass is inferred statistically using population-based equations that incorporate age, gender, and height5 6.
Bone estimation:
- Basic models estimate bone mass using height and gender due to the relative consistency of skeletal mass in healthy populations3 8.
- Advanced bioimpedance systems now claim direct bone mineral density (BMD) measurement capabilities, though accuracy varies (±10% error compared to DXA)3 8.

Key assumptions and errors

Component	Assumption	Potential Error Sources
Fat-free mass	Constant 73% hydration	Dehydration, edema, ascites4 6
Body geometry	Uniform cylindrical conductor	Amputations, obesity, atypical body shapes4 5
Tissue resistivity	Standard values for muscle/fat conductivity	Pathological tissue changes2 4
Bone mass	Derived from height/gender or proprietary algorithms	Osteoporosis, ethnic variations

Alatariel75

@PAV8888 and @annPT77 haha yeah, the grain of salt comment was definitely to indicate I really don't trust it for anything but my actual weight, the rest is just interesting trivia. If anything, it saying that I've only lost 17% muscle mass considering my rate of loss etc indicates that its measurements are full of bullhockey, I have lost fast and not in the healthiest way (not intentional, but lots of stress and un-ideal conditions) and there's no way I've maintained a lot of muscle.

But I am still pretty strong and have great hiking stamina so meh, maybe.

PAV8888

@Alatariel75 my personal experience was (and has corroboration in literature) that "available" fat does play a major role.

I had the opportunity to get some DEXA scans done while losing. Sadly not from the very beginning, but I did the first one in the series while I was still obese. The fat/non-fat loss ratio changed from over 8:1 (that would be better than 88% fat to 12.5% non fat) while I was obese, to as little as 1.5:1 (66.6% to 33.3%) when I was closer to "normal" weight.

And I was doing a lot more to preserve lean mass by that point than I had ever done in the beginning!

In any case, and to perhaps return a bit more to Ann's theme, I found zero correspondence between the number that were getting thrown out by the Aria scale I was using at the time and the changes shown by DEXA. Sure. Fat levels were going down for both. And so was weight. But the percentage changes never had a relationship that MY math skills could figure out *

they actually are pretty basic and I'm sure that someone with SKILZ could probably figure out some sort of equation to describe something. Just not one * I * could see with pen, paper, excel and google sheets! If I had the data in front of me and I was doing this today I might TRY to throw it into an AI and ask it to come up with something.

AnnPT77

@PAV8888, yes - great post about how BIA estimates. Love it.

I'm going to mini-quote you a couple of times, too, to comment:

ANYTHING beating the simplified 75% Fat mass to 25% Fat free mass lost "rule" would actually be on the good side of the ledger.

Absolutely! Even as a very rough estimate based on BIA and approximation algorithms, @alaterial75's results were excellent. I don't know how I did - didn't even have a BIA scale to call my own back in the day - but was simply happy to maintain athletic performance in objective (pace) terms.

The not-identified person I mentioned in my OP here, who lost something like 40% of weight as lean mass but was happy that he'd "gained muscle mass" based on the percents . . . honestly, that made me feel sad. I don't want to rain directly on someone's parade so didn't comment on his thread . . . but I also don't want to feed the mostly-myth that lots of muscle mass is likely/possible to be gained in a very steep calorie deficit. IMO, spreading that idea can hurt others, which is also sad.

If Ann wants to play with math I don't understand she can check out Forbes, Thomas, and Hall :)

Touché 😆🤣.

PAV knows, as others may not, that arithmetic often fails me (or I fail it), but I kinda like math, and am not terrible at that, mostly. Give me a spreadsheet, and I can apply formulas to a moderate degree of complexity. Ask me to carry the one, or multiply 6x7 in my head or on paper . . . well, results may vary. 😉

PAV8888

The math-sies are a bit over my head-sies though I could have sworn I may have pretended to use similar looking notations at some point during my trouble making youth… yet now I have no idea what they mean!!!

The below article should include enough references to get one started down the rabbit hole if one is interested enough.

https://pmc.ncbi.nlm.nih.gov/articles/PMC3970209/

Suffice it to say… our general discussions and findings seem to be in agreement with the equations. Or the other way around. OR…. KITTENS: just eat less, move more and strength train, and call it a day! ;-)

PAV8888

Ask me to carry the one, or multiply 6x7 in my head or on paper . . . well, results may vary. 😉

A while back I dimly recall someone wondering whether @AnnPT77 was an AI! Be careful Ann…. varying results when processing 6x7 MAY give credence to your AI credentials! I can attest that ChatGPT once had me violently uprooting my hair given her ever changing answers to my simple arithmetic problem!

AnnPT77

https://community.myfitnesspal.com/en/discussion/comment/48577510#Comment_48577510

🤣🤣🤣

An Ai. Ann, AI.

🤣🤣🤣

Yeah, no. 🤣

AnnPT77

https://community.myfitnesspal.com/en/discussion/comment/48577247#Comment_48577247

Good article you linked there. It does seem to be a well-justified, fancied-up way of mostly saying that the 75/25 fat to lean mass loss idea varies lots in individuals, and that severely under-eating, sub-ideal nutrition, or lack of exercise will maybe/probably will make things worse.

I'm bookmarking it. 😉

AmunahSki

I was curious enough to plug in my own numbers… I have a Healthkeep BIA scale (accuracy highly doubtful but hopefully useful for trend/comparison over time) providing these numbers:

From: 164.6lb 33.6% body fat, 109.2lb fat-free, 102.8lb muscle mass

As at today: 142.8lb 28.2% body fat, 102.6lb fat-free, 96.4lb muscle mass

Check my arithmetic, but I think that’s a loss of 5.4% (15lb) of fat and 6.4lb muscle mass, which is 70% and 30% (and close to the 75/25 figure if these scales can be trusted)😢.

If I calculate my muscle mass as a % of my total body weight, it went from 62.4% to 67.5%, which then gives me back my sense of achievement! 😉

AnnPT77

https://community.myfitnesspal.com/en/discussion/comment/48588185#Comment_48588185

Honestly, I think that's a good result looked at in any of those ways . . . anything within spitting distance of the 75/25 seems pretty great IMO. As discussion above illustrates, there's quite a bit of individual variation around that very generic 75/25. Context matters.

BTW, I'd share my numbers if I had any. I didn't have a BIA scale until after I'd lost weight, and don't have all the tape measurements I'd need to fill in the so-called "Navy fat calculator" for my pre-loss self. Somewhere around here, I think I have body fat percent numbers from an handheld BIA device used when I was part of a study (using the term loosely) of exercise for breast cancer survivors, but I haven't been able to put my hands on it in the chaos of my paper filing system. It's probably even less reliable than the BIA scales anyway.