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

AnnPT77
AnnPT77 Posts: 35,704 Member
edited March 17 in Debate Club

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
    nossmf Posts: 13,291 Member

    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
    AnnPT77 Posts: 35,704 Member
    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
    DomorVerbeuk Posts: 23 Member
    edited March 18

    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
    claireychn074 Posts: 1,781 Member
    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
    TrekkieLianne Posts: 12 Member

    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
    AnnPT77 Posts: 35,704 Member

    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
    AnnPT77 Posts: 35,704 Member
    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.

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