Why Am I Gaining Weight? 12 Causes Of Unexplained Weight Gain

When you’re trying to lose weight or simply maintain your current weight, the last thing you want to see when you step onto the scale is unexplained weight gain.

Not only is this the complete opposite of what you want, it’s also just flat out confusing. Possibly even depressing. Sometimes even concerning.

I mean, here you are, a person who is apparently eating (and/or exercising) in a manner that should NOT cause weight gain, but yet that’s what’s somehow happening.

And so you’re left with a very obvious question: why am I gaining weight?

To help you answer to this question, I’m going to break down every possible cause into two categories:

  1. Short term weight gain.
  2. Long term weight gain.

Let’s start with short term causes.

Why Am I Gaining Weight…. In The Short Term?

For this short term category, I’m referring to the kind of weight gain you see occur within the span of 1 week or less.

Let me give you a few common examples from this category:

  • Example 1: If you weigh 200lbs today and then weigh something more than 200lbs tomorrow, that’s part of what we’re talking about here.
  • Example 2: If you weigh 200lbs today and then weigh something more than 200lbs 2 days later, or 3 days later, or 4, 5, 6 or 7 days later… that’s also what we’re talking about here.
  • Example 3: If you weighed 200lbs on day 1, 199.6lbs on day 2, 199.2lbs on day 3, 198.8lbs on day 4, and then suddenly went up to 201lbs on day 5… that’s also what we’re talking about here.
  • Example 4: If you weigh 200lbs today, then something more than 200lbs on day 2, then something even more than that on day 4, and then something even more than that on day 6… that’s also what we’re talking about here.

Basically, any increase you see happen over the course of a day, a few days or an entire week fits within this category of short term weight gain.

Or, as I prefer to call it: temporary, ignorable, meaningless weight gain that is most likely NOT body fat.

Why do I like to call it that?

Because for most people, gaining weight during these types of short term scenarios is completely meaningless, will only be temporary, isn’t actually body fat, and should therefore be ignored.

Why?

Because, more often than not, it’s just completely normal day-to-day fluctuations in body weight caused by one or more of the following:

1. Water Retention.

This is the most common cause of short term weight gain, and it happens for a variety of reasons. This includes…

  • A higher sodium intake than usual.
    Did you eat more salt than usual? Maybe a bit more typical salty processed food (junk food, fast food, chips, etc.) than you normally do? Or maybe you ate “good” food that just happened to be extra salty (quite common when eating out at a restaurant)? Or maybe you just added more salt to your usual “good” meals than you normally do? Any sort of meaningful increase in sodium intake like this can cause a few pounds of temporary water retention, practically overnight. It will subside soon after your sodium intake returns to normal.
  • A higher carb intake than usual.
    Did you eat more carbs than you normally do? Maybe you’re coming off of a silly low carb diet? Maybe you’re using a calorie cycling approach that involves eating more carbs on certain days than on others? Maybe you’re doing a refeed? Maybe you’re taking a diet break? Maybe you just “messed up” and unintentionally ate more carbs than you were supposed to? Whatever the reason, if your carb intake increases by any meaningful amount one day or over the course of many days, it will often cause a temporary increase in your body weight as a result of water retention (and glycogen… more about that in a minute). Just like with sodium, this water weight will subside soon after your carb intake returns to normal.
  • Insufficient water intake.
    You know the “starvation mode” myth I’ve talked about before? It’s the idea that eating too little causes your body to hold on to its fat stores and prevent you from losing weight for the purpose of survival. Yeah, it’s bullshit. But, ironically enough, it’s kinda true when it comes to water intake. Meaning, your body will actually retain water when you consume insufficient amounts of it for the purpose of… you know… survival. On the other hand, drinking a sufficient amount of water will have the opposite effect and help to prevent and/or reduce water retention.
  • Elevated cortisol levels.
    Cortisol is the supposedly evil hormone we refer to as the “stress hormone” because it increases in response to stress. In and of itself, cortisol is actually not a bad thing. However, when it is elevated above normal levels (due to elevated levels of stress), that’s when it can become a bad thing. One such example of what elevated cortisol levels can cause is significant water retention. This is especially notable in the case of people trying to lose weight, because the actual act of losing weight (or, more accurately, the caloric deficit it requires) is something your body views as a form of stress (a caloric deficit is an energy deficit, after all). And, the more severe that deficit is in terms of how low your calorie intake is, and/or how excessive your workouts are (e.g., tons of cardio), and/or the longer you’ve been in a deficit without some type of break (be it a refeed, calorie cycling or a full diet break), the more stressful it is to your body. And the more stressful it is = the higher your cortisol levels will go = the more water retention you will experience. In addition, other fat loss-specific forms of stress (e.g., freaking out over your diet, freaking out over “messing up,” freaking out over plateaus, etc.) and more typical forms of life stress (e.g., work, school, family, etc.) will have a similar negative effect on water retention.
  • Certain supplements.
    The most popular water-retention-causing supplement that comes to mind is creatine, as it can cause anywhere from 0-5 lbs of water weight gain during its initial month of usage (most likely higher if you do the unnecessary high dose loading phase, lower if you don’t, and potentially none whatsoever if you’re a non-responder). Although, if you’re taking creatine, you typically want and/or don’t care that this water retention happens (water is retained in the muscle cells, potentially making those muscles look a tiny bit bigger/fuller/better). So, unlike everything else on this list, it’s not exactly unwanted water retention.
  • Certain medications.
    Certain medical conditions and medications are capable of causing edema (the medical term for water retention) as a side effect. Of course, any questions you have or information you seek about this aspect of things should be discussed with your doctor, not me.
  • A woman’s monthly period.
    More about this one later.

2. Glycogen.

The carbs we eat are stored as glycogen in our muscles and liver. For every gram of glycogen being stored, about 3 grams of water are stored along with it.

What does this mean to us?

Well, for starters, this is why people lose a bunch of weight fairly quickly when starting a low carb diet. They’re not losing fat just yet (and they potentially never will… that will always only be a function of calories, not carbs). Instead, what they’re losing is just a combination of water and glycogen.

Hooray, I guess?

The second thing you should know is something I actually mentioned a minute ago and is relevant yet again, which is that eating a large amount of carbs – or, more accurately, a larger amount of carbs than you usually eat – will have the opposite effect: you’ll gain weight fairly quickly.

But again, it’s not fat that’s being gained.

It’s that same combination of water (like I mentioned in the second bullet point above) and glycogen due to the increase in carb intake. And the more carbs you eat above the normal amount that you were previously eating, the more temporary weight you’ll find yourself gaining in the form of water and glycogen.

But the key word here is, of course, “temporary.”

When a low carb dieter’s carb intake returns to normal (or really just increases any degree above the “low” amount they were eating), the water and glycogen weight they lost will be regained pretty fast. And when the person who ate an above normal amount of carbs returns to their normal carb intake, they’ll quickly lose the water and glycogen weight they gained.

So, if you happen to eat more carbs than you usually do for whatever reason (unintentionally just eating more than you should have, cycling your calorie/carb intake throughout the week, purposely doing a refeed or diet break, etc.), it’s perfectly normal to find yourself gaining weight in the short-term in the form of water and glycogen.

3. Poop Issues.

Here are two examples:

  1. Constipation.
    If your poop isn’t coming out of you like it ideally should be, that means it’s still in you. And since poop weighs something, you can expect your body weight to increase to some extent as a result of this. The good news is that when you fix whatever is causing this constipation (e.g., a lack of fiber in your diet, insufficient water intake, etc.) and return to normal pooping, the weight gain it caused will magically vanish.
  2. Overpooping.
    Now let’s say you pooped a whole lot more than usual one day (fun times, I’m sure) or maybe even over the course of a couple of days (even more fun, no doubt). And then, in the following day(s), you went back to your usual pooping quantity/frequency (congrats). In this scenario, you will weigh more on your normal pooping days in comparison to the day(s) when you over-pooped (and/or the day(s) after). Is it because you suddenly gained body fat? No. You just happen to weigh more on the days when you’re not over-pooping compared to the days when you are. (And yes, that’s a new word I just made up right now. Over-pooping. Feel free to use it as often as you wish around your family and friends. Preferably at the dinner table.)

4. The Weight Of Food.

Not only does poop weigh something… but guess what else: food weighs something, too!

Which means, if you eat more food today than you typically eat, you will likely weigh a little more tomorrow simply as a result of having additional food in your stomach waiting to be digested.

It doesn’t even have to be “bad” food. It can be anything, really… including vegetables. And you don’t even have to go over your intended calorie intake to make this happen.

All it takes is eating a “heavier” amount of food than you usually eat. That’s it. It’s just the weight of additional food in your body that hasn’t been digested yet. The more your food weighs, the more you’ll temporarily weigh after eating it (but no, it will not be a 1:1 ratio).

As the digestion process begins to take place, this “food weight” will begin to disappear.

5. A Woman’s Monthly Period.

As I mentioned before, this is really just a subsection of #1, because a woman’s period causes short term weight gain as a result of water retention.

However, I wanted to give it a section of its own because, compared to the other causes of water retention we covered, this one is WAY more complex. Specifically…

  • The degree of water retention experienced can vary quite a bit from one woman to the next and even one period to the next.
  • Compared to other common causes of water retention (like an increased sodium/carb intake), water weight gain during a woman’s menstrual cycle has the potential to be much more significant (we’re talking as much as 10 lbs in some cases) and longer lasting.
  • Unlike the other causes on this list, this is the only one that’s going to be recurring every month (or so) over and over and over on a fairly consistent(ish) basis.

That third point (the monthly recurring format) amuses me a bit, because there are women who are still somehow surprised and confused by the water weight gain it causes for them each time it happens.

What I mean is, out of all of the “unexplained reasons” for gaining weight that we are discussing in this article, this is the one that fits that description the least.

Why? Because it’s something that consistently happens on nearly the same days every month… with similar(ish) amounts of water retention each time… which then goes away in a fairly similar manner within a fairly similar time frame.

Meaning, it’s pretty effing explainable.

So, for the handful of women who are still somehow baffled by its monthly occurrence… mark it down on your calendar next time or get one of those period tracking apps on your phone. This way, when you see the scale suddenly go up at some point every month and wonder why, you’ll easily be able to find your answer.

6. Improperly Tracking Your Body Weight.

This is something I’ve written about before (Why Can’t I Lose Weight?), so I’ll just be lazy and quote myself.

What do I mean by improperly tracking your body weight? Here are some common examples:

  • Person A compares what they weigh today to what they weigh tomorrow… and bases their progress on it.
  • Person B weighs themselves before eating/drinking/pooping on some days, and after eating/drinking/pooping on other days… and bases their progress on it.
  • Person C weighs themselves at random times throughout a single day… and bases their progress on it.
  • Person D compares their weight first thing in the morning today, to their weight after lunch tomorrow, to their weight after their evening workout the day after that… and bases their progress on it.
  • Person E is a woman who ignores the normal change in weight that takes place at a certain time every month… and bases their progress on it.
  • Person F weighs themselves once per week and compares that one day to the same day of the following week… and bases their progress on it.
  • Person G weighs themselves every day for 4 days in a row and compares it to their weight on the 5th day… and bases their progress on it.
  • Person H weighs themselves on Monday and compares it to what they weigh on Thursday… and bases their progress on it.
  • Person I weighs themselves as accurately as possible for 1 week only… and bases their progress on it.

In every single one of these examples, you have people who will step off of their scale and wonder “why am I gaining weight?” simply because they are failing to accurately use that scale and/or properly perceive what it’s telling them

Instead, they are letting their tracking get thrown off by completely normal (and temporary, and ignorable, and meaningless) fluctuations in body weight that happen as a result of everything we just covered (water retention, glycogen, poop issues, the weight of food, a woman’s period, etc.) rather than what these people will typically assume it is (body fat).

So, how do you prevent all of this from being a problem for you? By weighing yourself properly.

Here’s how…

  • Always weigh yourself first thing in the morning on an empty stomach before eating or drinking (but after peeing), and wear the same amount of clothing (ideally none or very little) every time.
  • Weigh yourself every day… take the weekly average… and only focus on the weekly average. This is key. What your weight does from one day to the next (or one hour to the next) is meaningless. The only reason you’re paying any attention to it at all is so you can take the average at the end of the week. That weekly average (and how it compares to the surrounding weekly averages) is what you should actually pay attention to. (Additional details here: How Often Should You Weigh Yourself)
  • Always have 2-4 weeks worth of accurate weekly averages to compare before assuming, worrying or adjusting. Meaning, if you’re wondering why you’re gaining weight in the short term (1-2 weeks or less) and are confused or depressed or ready to jump to some new diet/workout (because you think it’s body fat that was gained), then you’re doing it wrong. Always wait until you have at least 2-4 weeks worth of accurate data to compare before doing/feeling any of this.
  • Be aware of the previously mentioned factors. For example, if you consume an above-normal amount of sodium or carbs (or it’s your period), you should expect an above-normal amount of water retention to come along with it, and thus a temporarily above-normal body weight. Of course, the previous points (only paying attention to the weekly average over the span of 2-4 weeks) will go pretty far in preventing this sort of thing from making any meaningful dent in your tracking.
  • Measurements can help, too. So if your weight happens to suddenly go up from one week to the next (or stay the same when you’re trying to lose), but certain measurements have slightly decreased, it’s a good sign that things are still moving in the right direction (and for one or more of the reasons this article covers, it’s just not showing up on the scale yet). However, I do need to also mention that measurements come with their own accuracy warnings. For example, you could put the tape measure around your stomach and have it be just slightly less-straight than you had it last time, and that tiny difference could throw the measurement off by a full inch.

7. Something A Little More Serious.

The VAST majority of the people reading this who are experiencing some type of “unexplained” short term weight gain will find one of the previous items on this list to be their cause.

Having said that, I still need to mention that some people (a MUCH smaller minority) may have a more serious underlying reason for their unexplained weight gain, especially in cases where there are other symptoms accompanying it.

I have nothing more to add here other than to see a doctor if you suspect this might be the case.

Why Am I Gaining Weight… In The Long Term?

Now for the next category.

We will define “long term” weight gain as basically anything that occurs over a period of time longer than 1 week. Or, even better, let’s define it as weeks of weight gain.

So, for example, if 2 or more weeks have passed and you are consistently gaining weight during this span of time, these are the most likely explanations for it:

1. You’re Gaining Fat.

This is BY FAR the most common reason for weight gain that occurs/lasts over a span of weeks.

You are simply eating more calories than you are intending to, or burning less calories than you are intending to, or some combination of the two… and a caloric surplus exists… and your body is storing those extra unused calories in the form of fat.

This, of course, is the one and only way ANY amount of body fat is EVER gained by ANYONE.

And, much more often than not, it’s the cause of your “unexplained” longer-term weight gain.

Wait… what’s that you say?

But I’m NOT eating too many calories, I swear!

Uh huh, sure. Now let me show you why you (and most people) are almost always wrong…

  • Underestimating
    If there’s one thing damn near every nutritionist and diet professional can agree on, it’s that people trying to lose weight almost ALWAYS underestimate how many calories they are actually eating. It happens all the time and has been confirmed in studies (this one showed that the subjects underestimated their calorie intake by an average of 47%… which is huge). Some people underestimate the quantity of food they consume (like thinking you ate 1 serving when you really ate 2 or more), while others underestimate the amount of calories it contained (like thinking a meal was 500 calories when it was really 1000). Some underestimate both.
  • Tracking Mistakes
    Many people just screw up during the serving-size-measuring process and take significantly more food than they think they’re taking. It happens all the time, especially when using measuring spoons, measuring cups or just eyeballing it and taking your best guess (instead of using a digital food scale). Here’s an old (and kinda overdramatic) video from Leigh Peele showing how easily it happens…

  • Under-Reporting
    Then you have people who are under the impression that there are special “clean” and “healthy” foods they can eat unlimited amounts of and not count. As if they contain magical calories. Or those that eat “tiny” amounts of food here and there and assume it’s so insignificant that they don’t even need to bother counting it. In reality, these “I-didn’t-even-realize-it” calories can add up pretty quickly. Here’s a common real-world example of this. In addition, some people simply forget what (or how much) they ate and end up accidentally not counting it for that reason alone.
  • Lying
    As odd as it may seem, many people just flat out lie about how much they’re truly eating. Why? Usually because they’re too embarrassed to admit what/how much they eat (even to themselves), yet apparently not too embarrassed to continuously fail to lose weight because of it.

Wait, what’s that you’re saying now?

But I’m burning tons of calories, I swear!

Yeah, about that…

  • Overestimating
    Now take everything I said before about how people underestimate calorie intake, and change it to overestimate calorie output. The same studies show this, too (in this one, the subjects overestimated calories burned via exercise by an average of 51%… which is huge). People do some form of exercise – typically cardio – and assume they burned “tons of calories.” The problem is, no form of cardio truly burns anything resembling “tons of calories.” In fact, typical forms of cardio done at typical intensities will burn anywhere from 5-10 calories per minute. Yet people will finish their 30-minute jog on the treadmill and think they burned 1000 calories. As if that wasn’t bad enough, there’s often a “reward mentality” that kicks-in, thus giving people the false mindset that they can allow themselves to eat extra calories since they supposedly burned “so many” while exercising. They then proceed to cancel out whatever smaller amount of calories they did burn (and then some), and then wonder why they’re not losing weight despite “working out all the time.”

Now I’m not accusing you of being an under-estimator, or an over-estimator, or an under-reporter, or a bad measurer, or a liar, or someone who’s just bad at counting. I’m just telling you the facts.

And the fact is, if week after week is passing and you’re gaining weight (or stuck at a plateau when you’re trying to lose it) despite eating and/or exercising in a manner that you feel should either be causing you to lose weight or (at the very least) maintain your current weight, then guess what?

The chances are pretty good that you are simply eating more calories than you think you are, burning less calories than you think you are, or a combination of both, and it’s happening to a degree that’s either leading to a caloric surplus (which is causing you to gain body fat) or leading to maintenance (which is causing your weight to stay the same when you’re trying to lose it).

There’s your most likely explanation.

2. Longer Term Water Retention.

As I mention earlier, water retention is the most common cause of short term weight gain. It happens all the time to virtually every single person on the planet.

However, sometimes – certainly less frequently in comparison – there are instances where water retention can exceed the short term and last for a longer period of time.

So, instead of a day, or a few days, or a week… it can occasionally last for a few weeks.

This sort of thing can happen to anyone, although it’s probably more common among women than men, partially because of a woman’s menstrual cycle, and partially because… well… certain things are just weirder when it comes to women (physiologically speaking, of course).

And because of this occasional longer term water retention, a person can see their weight loss progress stall completely on the scale for a few weeks or potentially even see themselves gaining weight WHILE they are actually continuing to lose body fat.

The gain in water weight they are simultaneously experiencing is just counterbalancing that fat loss and preventing it from actually showing up on the scale (or the scale is showing an increase instead of a decrease).

That is, until a magical “whoosh” finally occurs and the scale finally shows a sudden meaningful amount of (water) weight loss in a short period of time and the person tends to notice they almost instantly look a little leaner.

This is one of the many reasons why I recommend properly tracking your body weight over the span of 2-4 weeks (not 2-4 days, not 1-2 weeks, but 2-4 weeks… potentially as long as an entire month) before freaking out and adjusting your diet and/or workout.

Having said that, there’s an important thing you need to keep in mind here.

If you exceed this period of time without experiencing a “whoosh” and/or your weight continues to stall or increase, then guess what? You should probably go and read #1 again because you’re probably eating more/burning less than you think you are.

3. You’re Gaining Muscle.

Honestly? This isn’t really something that I’d consider to be an “unexplained” reason for gaining weight.

I mean, when you consider how hard you need to purposely be working your ass off to make muscle growth occur, plus how slow the rate of muscle growth truly is, you begin to realize that it’s pretty damn rare for someone to accidentally or unintentionally gain any amount of muscle, let alone consistently gain an amount of muscle large enough to cause long term weight gain. (Some additional details here: Muscle Weighs More Than Fat?)

It’s also extremely rare for a person who is trying to lose weight to end up stalling or gaining weight for weeks at a time because they are gaining enough muscle to consistently offset the loss of body fat.

Rather, the real reason this sort of scenario takes place is because the person is eating more/burning less than they think, and no deficit exists.

Why is it usually this and not due to gaining muscle, you ask?

Because the average person can often lose an amount of body fat PER WEEK that is equal to (or in some cases, exceeds) the amount of muscle they can build PER MONTH. This is even worse with women, as they tend to build muscle at about HALF the already slow rate that men do.

Not to mention, many people won’t be able to build any truly significant amount of muscle while losing fat in the first place.

But despite all of this logical reasoning, the fact that muscle growth is almost always accompanied by weight gain (because… surprise… muscle weighs something), I’m going to include it here anyway.

So, there it is.

4. You’re Pregnant.

Um… congratulations?

On second thought, considering this is an article about “unexplained” weight gain – the kind of confusing, unknown, unexpected weight gain that makes the person wonder why it’s happening – then I’m thinking you might not be in a congratulatory mood right now?

That’s cool.

Anyway… good luck with all that.

5. Something A Little More Serious.

The VAST majority of the people reading this who are experiencing some type of “unexplained” long term weight gain will find one of the previous items on this list to be their cause.

Having said that, I still need to mention that some people (a MUCH smaller minority) may have a more serious underlying reason for their unexplained weight gain, especially in cases where there are other symptoms accompanying it.

I have nothing more to add here other than to see a doctor if you suspect this might be the case.

How To Avoid All Of This

So, there you have it. If you’ve been weighing yourself regularly and wondering why you’re gaining weight (or just not losing any when you are attempting to) in the short or long term… take a really good look at everything this article just covered.

You’ll find your unexplained explanation somewhere within it.

Oh, and if you’d like to lose fat, get lean and reach your goals while avoiding the problems we talked about in this article (excessive water retention, unknowingly eating more/burning less than you think, etc.) plus other common problems like losing muscle, feeling hungry all the time, not being able to eat the foods you love, metabolic slowdown and more, then you should check out Superior Fat Loss.

I designed it to greatly minimize or completely prevent everything that sucks about losing fat and all of the problems that screw things up along the way. See for yourself: Superior Fat Loss

26 thoughts on “Why Am I Gaining Weight? 12 Causes Of Unexplained Weight Gain

26 Comments

  1. Fantastic as always!! I forwarded to my cousin who is a slave to the scale. I rave about you & I hope she likes your shit as much as I do!

  2. Great! Your articles are always a pleasure to read. Thank you for all the time you spend for making this world a little better place 🙂

  3. Thanks for this timely article. I knew all this, I was just in denial. I went on a 10 day Hawaiian vacation after reaching my goal weight (60 pounds lost), ate too much and drank to much and gained a couple pounds overall. Now, 50 days post vacation, I’m still slowly gaining. The reason: I got complacent and I’m eating too damn much. Your article reinforced the path I’ve been on for the past 18 months and brought me back to reality. I didn’t come this far to blow it now.

    • I’ve said it before and I’ll say it again… above all else, I aim for impeccable timing. 😉

      But seriously, I’m glad to hear it helped and you’re back on the path you need to be on. Keep it up!

  4. I like reading your writing even when its things I’m fairly competent in already. You create high quality content man. I’ve even considered buying your book just to read even if it provides me with nothing ‘new’ per se.

    Anyways, thanks man. Mainly for all the non-bs content. Keep it up.

  5. This is the first time I am reading your article, and all I can say is amazing. This is very informative and has shed some light on why I am gaining weight. Thank you for teaching me new way of weighing myself. Thanks and take care!

  6. I’m only 3 weeks into my plan after reading your Superior Fat Loss — I’ve gained 1 pound but am going to chalk it up to the Creatine for now (hopefully)… I’ve been taking 5 g a day for 3 weeks, tracking calories, and doing your beginner workout routine… My question is, should I just assume it’s the creatine for at least a month before doing anything? Thanks.

  7. This I want to drill this into everyone’s brains 10x over! I’ve been looking for a good health related blog to follow & you’ve well & truely sold it to me sir

  8. …heh…AW, the tragedy is that, with, despite this info being so readily accessible now, compared to forty-five years ago when I was new to PED-free bodybuilding and the difficulty obtaining this info was a legitimate reason for the typical over-estimating, under-estimating, mis-reporting, and diet myths, many will still insist otherwise about why they’re gaining or not losing weight. I talked to one two weeks ago (before reading your article) who just couldn’t accept that her weight-loss plateau was likely a temporary water-retention issue which a woosh would hurdle if she could just be patient, LOL

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