I have been working out nearly every day for the past 6 months. Recently noticed that I can barely fit into my jeans anymore, like the waist size is too small. I looked it up and some people say its because of water retention/muscle gain under fat and its a "bulking before slimming down" situation. Others say its because of poor diet, but I've been eating a lot better recently. So which is it? Its really bumming me out.
It‘s hard to say which of those factors is the reason for your increased waist size. It’s not as if we have a scan of your body before and after your six months of exercise. So, I have a few questions that may help you figure it out:
Did you do a lot of ab exercises in the past months? If so, muscle growth could play a roll in the increased waist size.
Where does your body store fat? All our bodies are different. As a result, when you gain fat-weight, your body might store it in different places than someone else’s body does. If your body primarily stores fat in the waist area, it’s an indication that you a) gained fat-weight, or b) gained more muscles in the waist area than you lost fat there.
If your body primarily stores fat in different areas (e.g. thighs), then it’s a slight indication that the size of your waist is not due to additional body fat.
Do you take supplements that lead to water retention in the muscles? That could play a (small) role too.
Did you over-exert or injure yourself in the waist area recently? Both might lead to swelling. Rest might help.
Did you train a lot of strength in general? Heavy strength training and weight reduction are very hard to do at the same time, because the body needs a lot of energy to build muscle. So much so, that a many people prefer to build muscle while eating more calories than their bodies need (I hear it’s called a bulk phase). Weight reduction and an increase in muscle mass can be achieved at the same time, but it’s even harder than doing one at a time.
There are a lot of stories/”workout advice“ on in the internet about how training the abs supposedly reduces waist size. That is not correct. You cannot spot reduce body fat (where you loose/gain body fat first is determined by your genes). You can, however, increase the circumference of specific parts of your body by training the muscles there.
All of that aside: Congratulations on the huge lifestyle changes you introduced these last few months!

That’s a big accomplishment! Please don’t focus too much on the size of your waist if that size happens to be within the realm of what can reasonably considered healthy. If you’re working out and eating healthy (or at least healthier than before), you’re doing yourself a big favour. Don’t be discouraged by something as trivial as a pair of jeans. If you feel stronger and more energetic than you used to, there’s probably not reason to worry
Edit: You stopped smoking? That’s an excellent explanation for gaining some weight. It seems to happen to everyone. But it also means that even more congratulations are in order! You’ve done so much for yourself! Ignore that potential weight gain and keep doing what you’re doing. You’re on the right path here
