How come sometimes one's clothes size is reduced without losing any weight?

Because you can lose inches without losing a noticeable amount of weight.

Are you shopping for the same brands? Different brands size their clothes differently. I know I'm a 10 in some brands and an 8 in others. It depends. Also, if you lose fat but gain muscle, you might not change your weight on the scale, but you'll lose inches. Not to mention water weight... There are lots of possible explanations.

muscle weighs more than fat, but is more compact and dense. If you have been eating right and exercising lately, you probably lost body fat and gained muscle creating a trimmer body for you.

If you are simply getting older, you probably lost muscle and gained fat and fat is squishier and has less density than muscle, therefore your clothes may feel looser.

One other reason may be that you are just wearing clothes that are sized differently. My Levi's fit me great in a size 10L, but if I wear my Gap size 10L, they hang off my a$$ because they are sized like the Levi's 12.

Designer clothes are notorious for being on the small side of the sizing because they are largely based on European sizing system. Most people's (especially womens) sizes can range by 2 or 3 sizes. I am an 8,10, or a 12 depending on what brand I'm wearing. Look at your smallest size and look at your largest size in your closet. I bet there's at least 2 or 3 in there.

just go and lose some weight not eat alot