Sudden weight gain: What's going on?

Roger Rodriguez said:I’m not sure what caused the sudden weight gain Carol Wilson5 mentioned, but I have to disagree with the points made above.
When I broke my leg two years ago, I gained six pounds in a single week. I couldn't believe it when I stepped on the scale. Sure, I wasn't moving much because of the cast, but trying to get around on crutches is exhausting work...
So, the theory that gaining three or four pounds in a week is impossible just isn't true.
But, like I said, I really don't know how someone's weight can spike so quickly without any changes to their diet or activity levels.

First off, she gained four pounds over several days.

Second, you put on three pounds in a week, but two of those were just the weight of the cast—maybe even more considering how big that thing was on your leg. That last pound was probably just inflammation in the tissue where the bone snapped.😁

Douglas Cook2 said:I’m with stormyheron4 on all four points here—it's been a while since I actually agreed with someone 😁, but they nailed it!

I’ll just add a few more numbers to help with that whole thin vs. overweight dilemma.

Look, at 120 lbs and 5'7", you're right on the edge of being classified as anorexic.

Your BMI is already sitting slightly under 19 with that weight (and 19 is basically the floor for BMI standards established back in the day), whereas for your age, it really ought to be somewhere between 20 and 25.

Bottom line? You're underweight right now.

(For context, I'm 5'4" and used to be 120 lbs before I had kids, and I was considered super slim.)

Of course you'd agree with me since you actually know what we're talking about. 😁

stormyheron4 said:First off, there is zero chance that 110 pounds is your ideal weight.

Second, you didn't just magically gain four pounds overnight. It doesn't work like that. If you're seeing extra weight specifically around your stomach, you might actually be pregnant.

Third, take a second to actually process what I just said. Accept the facts, because they're true. Period.

And as for your sister? There is no way she put on twenty pounds in a few days unless she was lugging around a heavy bag of Quikrete on her back.

I completely agree with that, just like I mentioned earlier. It’s actually pretty alarming that I got a calculation like that from some "smart" American website—honestly, I feel like that kind of math should be illegal.

Believe it or not, this all happened in less than a week. And no, I am definitely not pregnant!

BMI isn't everything. Your body frame matters so much, which you can tell just by looking at wrist circumference, and I've been naturally tiny since birth. There's a massive difference depending on your bone structure. Being thin and being small are two totally different things. As far as being thin goes, the fact that I wore a 30C bra while weighing only 110 lbs speaks for itself; everyone I knew was shocked I had any curves at all at that weight. My former doctor actually sent me for blood work because he was worried about my "thinness," but the results were absolutely perfect—everything was totally normal. He told me then that he wasn't going to worry about the numbers anymore.

Honestly, that's the kind of response I expected. If something doesn't affect someone personally, they tend to think it couldn't possibly happen to anyone else.

Carol Wilson5 said:I completely agree with that, just like I mentioned earlier. It’s actually pretty alarming that I got a calculation like that from some "smart" American website—honestly, I feel like that kind of math should be illegal.

Believe it or not, this all happened in less than a week. And no, I am definitely not pregnant!

BMI isn't everything. Your body frame matters so much, which you can tell just by looking at wrist circumference, and I've been naturally tiny since birth. There's a massive difference depending on your bone structure. Being thin and being small are two totally different things. As far as being thin goes, the fact that I wore a 30C bra while weighing only 110 lbs speaks for itself; everyone I knew was shocked I had any curves at all at that weight. My former doctor actually sent me for blood work because he was worried about my "thinness," but the results were absolutely perfect—everything was totally normal. He told me then that he wasn't going to worry about the numbers anymore.

Honestly, that's the kind of response I expected. If something doesn't affect someone personally, they tend to think it couldn't possibly happen to anyone else.

Look, if you actually gained 4 pounds in just a few days, you'd have to eat way more than 4 pounds of food. Your metabolism burns energy and you lose stuff when you hit the bathroom, so you're constantly losing a chunk of whatever you consume.

Basically, over those few days, you would've had to shove at least 13 or 15 pounds of food down your throat, assuming your body absorbed every single bite, which is basically impossible.

Two things are likely here: either you didn't actually gain fat and you're just dealing with massive water retention (thanks to PMS, salty snacks, a full moon, or starting a new workout routine, etc.), or your scale is just lying to you. Personally, I'm leaning toward the scale being busted.

stormyheron4 said:First off, she gained four pounds over several days.

Second, you put on three pounds in a week, but two of those were just the weight of the cast—maybe even more considering how big that thing was on your leg. That last pound was probably just inflammation in the tissue where the bone snapped.😁

Of course you'd agree with me since you actually know what we're talking about. 😁

So you're saying that this time, you actually get what's going on.😁

The scale's definitely busted, I'm telling you 😁

Plus, if it’s one of those smart scales, I wouldn't even be surprised. 😁

I thought about water retention too, but it feels weird that both scales are showing such a massive jump at once. 😕

Carol Wilson5 said:I completely agree with that, just like I mentioned earlier. It’s actually pretty alarming that I got a calculation like that from some "smart" American website—honestly, I feel like that kind of math should be illegal.

Believe it or not, this all happened in less than a week. And no, I am definitely not pregnant!

BMI isn't everything. Your body frame matters so much, which you can tell just by looking at wrist circumference, and I've been naturally tiny since birth. There's a massive difference depending on your bone structure. Being thin and being small are two totally different things. As far as being thin goes, the fact that I wore a 30C bra while weighing only 110 lbs speaks for itself; everyone I knew was shocked I had any curves at all at that weight. My former doctor actually sent me for blood work because he was worried about my "thinness," but the results were absolutely perfect—everything was totally normal. He told me then that he wasn't going to worry about the numbers anymore.

Honestly, that's the kind of response I expected. If something doesn't affect someone personally, they tend to think it couldn't possibly happen to anyone else.

Exactly. Small, petite, but packs a punch. 😁🤣

Carol Wilson5 said:I completely agree with that, just like I mentioned earlier. It’s actually pretty alarming that I got a calculation like that from some "smart" American website—honestly, I feel like that kind of math should be illegal.

Believe it or not, this all happened in less than a week. And no, I am definitely not pregnant!

BMI isn't everything. Your body frame matters so much, which you can tell just by looking at wrist circumference, and I've been naturally tiny since birth. There's a massive difference depending on your bone structure. Being thin and being small are two totally different things. As far as being thin goes, the fact that I wore a 30C bra while weighing only 110 lbs speaks for itself; everyone I knew was shocked I had any curves at all at that weight. My former doctor actually sent me for blood work because he was worried about my "thinness," but the results were absolutely perfect—everything was totally normal. He told me then that he wasn't going to worry about the numbers anymore.

Honestly, that's the kind of response I expected. If something doesn't affect someone personally, they tend to think it couldn't possibly happen to anyone else.

I don't get why people act surprised. It's not that deep. I'm even smaller than you and I wear a slightly larger cup size myself😁😉

now that I'm pregnant, don't even get me started😍

Carol Wilson5 said:I completely agree with that, just like I mentioned earlier. It’s actually pretty alarming that I got a calculation like that from some "smart" American website—honestly, I feel like that kind of math should be illegal.

Believe it or not, this all happened in less than a week. And no, I am definitely not pregnant!

BMI isn't everything. Your body frame matters so much, which you can tell just by looking at wrist circumference, and I've been naturally tiny since birth. There's a massive difference depending on your bone structure. Being thin and being small are two totally different things. As far as being thin goes, the fact that I wore a 30C bra while weighing only 110 lbs speaks for itself; everyone I knew was shocked I had any curves at all at that weight. My former doctor actually sent me for blood work because he was worried about my "thinness," but the results were absolutely perfect—everything was totally normal. He told me then that he wasn't going to worry about the numbers anymore.

Honestly, that's the kind of response I expected. If something doesn't affect someone personally, they tend to think it couldn't possibly happen to anyone else.

That's awesome👍

especially if those tests were recent.

I haven't been browsing here for a little while because I’ve been stuck with this new doctor who is just impossible to deal with, though everything was always totally fine before her. My doctor actually told me he was bracing himself for a disaster based on my height and weight ratio, but once he saw the actual lab results? He told me to eat whatever I want, whenever I want, because apparently, everything is functioning perfectly.

The issue is that I've gained 9 pounds in about a week without changing anything at all about my lifestyle—no changes to my diet or exercise routine. It isn't just the scale talking, either, because I can't even zip up any of my pants, and they were already a bit loose on me until recently. At first, I figured it was just PMS, but that passed and nothing changed. And I am definitely not pregnant.

A thyroid shield?

fadedmarlin402 said:A thyroid shield?

I was actually thinking the exact same thing.
To be honest, I suddenly found myself gaining weight at an absolutely frantic pace—just ballooning up almost every single day. At the time, my job kept me so busy that I barely had any chance to sit down for a meal, so there was no way this was coming from overeating. For most of my life, I’ve maintained a pretty steady weight, usually hovering around 110–115 lbs at 5'4", and I could eat whatever I wanted without a second thought.
Once the scale started acting erratic, the only logical conclusion in my mind was a thyroid issue, so I went to get my hormone levels checked. As it turned out, it was hypothyroidism (Hashimoto's), which I've been managing for two years now—a period during which I ended up packing on about 35 pounds.😱
At first, they wouldn't even put me on medication; then, they gave me a dose only to cut it in half just as I was finally starting to feel better and thought the swelling might subside, which only triggered a downward spiral and some dangerous weight gain.
Eventually, I sought a second opinion from another doctor who finally stabilized my dosage, which gradually halted the weight gain. But now, I'm stuck with an extra 35 pounds on my frame and I have absolutely no clue how to shed it.😠 🙂

The weight gain happened so rapidly on a near-daily basis that I was literally outgrowing my clothes right before my eyes.😲

If you're asking for my advice, you should head to a clinic immediately to get your T3, T4, and TSH checked; if those results come back looking suspicious, then you'll need to go deeper with FT4, antibodies, and the rest of the panel.

I’ve hit a plateau for now—holding steady at about 120 lbs in the morning and maybe 120.5 lbs by evening. Things haven't taken a turn for the worse just yet, but I can't help feeling a bit uneasy about how fast this all happened. What's next? Who knows. To make matters worse, everyone keeps jumping down my throat telling me I'm already way too thin. It makes me nervous to think about what my doctor—who tends to be a bit of a hypochondriac herself—is going to say when I bring this up.
Are you still dealing with any other thyroid symptoms?

PS Thanks for the heads-up!

stormyheron4 said:First off, she gained four pounds over several days.

Second, you put on three pounds in a week, but two of those were just the weight of the cast—maybe even more considering how big that thing was on your leg. That last pound was probably just inflammation in the tissue where the bone snapped.😁

Of course you'd agree with me since you actually know what we're talking about. 😁

Hey, I'm not crazy! 😁 I wasn't weighing myself while wearing the cast; honestly, I think I could have easily confused the cast's weight with an extra three pounds over these last two years.🤣
After a week, I took the brace off and stepped on the scale to see where I stood. I'm just saying, it's perfectly possible to see the scale jump in such a short window.
The part that really trips me up is her claim that she was eating and moving around just like usual.
Carol Wilson5, first check if your pants just shrank in the wash. 😁
And definitely get that thyroid checked; I'm honestly stumped on what else it could be.

Roger Rodriguez said:Hey, I'm not crazy! 😁 I wasn't weighing myself while wearing the cast; honestly, I think I could have easily confused the cast's weight with an extra three pounds over these last two years.🤣
After a week, I took the brace off and stepped on the scale to see where I stood. I'm just saying, it's perfectly possible to see the scale jump in such a short window.
The part that really trips me up is her claim that she was eating and moving around just like usual.
Carol Wilson5, first check if your pants just shrank in the wash. 😁
And definitely get that thyroid checked; I'm honestly stumped on what else it could be.

👍 Sadly, they didn't. 😁

When you're dealing with hormonal imbalances, absolutely anything can happen.😉

I’m starting to get a little worried now, though I guess I did go looking for this myself. Thanks for all the input, everyone. It sounds like it could be my thyroid or maybe just some water retention. Has anyone else dealt with similar symptoms? Please share if you have!
Another thing—I’ve noticed that after walking just a single mile, I feel like I’ve been hit by a truck. My legs start aching like crazy, even though I used to walk several miles without a second thought. Could there be a connection there? Who knows?

Carol Wilson5 said:I’m starting to get a little worried now, though I guess I did go looking for this myself. Thanks for all the input, everyone. It sounds like it could be my thyroid or maybe just some water retention. Has anyone else dealt with similar symptoms? Please share if you have!
Another thing—I’ve noticed that after walking just a single mile, I feel like I’ve been hit by a truck. My legs start aching like crazy, even though I used to walk several miles without a second thought. Could there be a connection there? Who knows?

Are you experiencing any shortness of breath, a racing heart or lungs for no apparent reason, skin discoloration, dizziness, excessive sweating, chronic fatigue, constipation, or anything along those lines?

So, I was wondering... are you maybe on birth control pills?

Carol Wilson5 said:I’ve been feeling pretty desperate lately, so I figured I’d just put this out there and ask.

I’m 26 years old, 5'7", and weigh about 120 lbs. I know that’s not a massive amount for my height (even though I saw some site online claiming my "ideal" weight was 110 lbs!!!!). The thing is, for the last few years, I was consistently sitting right at 110 lbs. Personally, I felt like that was actually too low, so my goal was really more like 115 lbs. But even though I haven't changed what I eat or how much I move, my weight suddenly jumped up to 120 lbs. I noticed a huge difference in my stomach area—I never had a totally flat stomach, but now it feels massive. I just chalked it up to bloating or PMS, you know? But even after those days pass, neither the bloat nor the weight has budged an inch. I eventually convinced myself I’d just subconsciously eaten a bit more, and honestly, I didn't think it was a big deal since I could probably drop a couple of pounds in a week or two. I did cut back on food slightly (not drastically, since I don't eat much to begin with) and moved around more, but it hasn't done anything to my weight. I wasn't expecting a miracle, but I thought I might at least lose half a pound or a pound in a week. To make matters weirder, the exact same thing happened to my sister when she was my age. She gained 22 lbs in just a few days. I thought she was exaggerating or just eating more without realizing it, but now the same thing is happening to me—though on a much smaller scale, even though I’ve always been significantly lighter than her.

So, let me emphasize: the issue isn't that I'm 120 lbs. The real issue is that I gained 9 lbs in just a few days, despite not eating extra calories and keeping my activity levels exactly the same. Another weird part? Cutting calories and moving more hasn't had any effect on my weight at all (and yeah, this happened to my sister, too). Even though it's only 9 lbs, I can literally feel it.

I’m honestly scared of what comes next. I’d go see a doctor, but my primary care physician is impossible to talk to; even if you're in a crisis, she brushes everything off as "nothing," so there's no way she'd listen to something like this.

So, if anyone has any smart suggestions, please share them with me.

Thanks to everyone for sticking through this long-winded update! 🙏

So, what ended up being the cause for your sister?

Carol Wilson5 said:I haven't been browsing here for a little while because I’ve been stuck with this new doctor who is just impossible to deal with, though everything was always totally fine before her. My doctor actually told me he was bracing himself for a disaster based on my height and weight ratio, but once he saw the actual lab results? He told me to eat whatever I want, whenever I want, because apparently, everything is functioning perfectly.

The issue is that I've gained 9 pounds in about a week without changing anything at all about my lifestyle—no changes to my diet or exercise routine. It isn't just the scale talking, either, because I can't even zip up any of my pants, and they were already a bit loose on me until recently. At first, I figured it was just PMS, but that passed and nothing changed. And I am definitely not pregnant.

Hmm, I don't know. My aunt has hypothyroidism and my sister-in-law has hyperthyroidism, and from what I understand, thyroid issues don't usually cause weight gain specifically in the gut area—especially not a sudden jump in just 4 days. But hey, anything can happen, 🤷 every patient is unique in the end.

Are your bathroom habits regular?

Here is what Mayo Clinic says about different types of thyroid disorders and their symptoms:

hypothyroidism

hyperthyroidism

I’m not taking any pills at all. I don't deal with any of that stuff like shortness of breath or dizziness. The only thing is maybe my heart rate jumps up a bit faster when I'm out for a walk. My digestion is perfectly fine—regular every single morning, pretty much on schedule. And my cycles are totally normal too.
My sister, my mom, and my grandma all claimed they just started gaining weight out of nowhere without changing what they ate. But honestly? They just decided that was the reason and used it as an excuse to start overeating. I think my mom and grandma were about 5'1" and probably weighed around 200 lbs. Then there's my sister. Three years ago, she insisted she was too busy with work to eat anything more than a single sandwich a day, yet she kept putting on weight. And she actually shot up from maybe 125 lbs to 150 lbs in a really short window (which takes a lot of calories!). I used to think she was exaggerating and eating way more than she let on, but now I'm starting to believe her. She's sitting at about 140 lbs now, but she swears she can't get below that no matter what she tries. Plus, she'd rather die than actually go see a doctor.