I have come to realize that many people are complaining about having back aches and all. They do it when it's convenient, to the point that I don't even know if I should believe them. Honestly, I don't. I highly doubt about it.
It's not so much about having back aches, but more like, it's their weight that has been influencing it. See, it's totally fine that you are on a heavier side and exercise. It's really not okay if you don't exercise, regardless of your weight. That person does not. Complaining about back pain every other time. People get bored with it.
You may be the thinnest person, but you can be the ones with the most percentage of body fats. So, don't question someone when you see a thin person working out. It's not about losing weight, it's about living a healthier life. You can be on a heavier side, and that does not mean that you are the unhealthiest of the lot. It's not always the case. There are so many factors, like the bone factor, the lifestyle and etc.
It's actually more dangerous for a thinner person to go binge eating because there are no changes on your body, you feel there is nothing to worry about. In fact, you should worry more because there's no changes despite you eating too much. Don't be too cocky just because you don't gain weight. You never know what's happening inside. It's them that take things for granted, you feel you can eat whatever you want because you don't gain weight? You're so wrong. It's the same, whether you're bigger or smaller, you need to watch what you eat.
I see a lady who eats McD every single day, and she's so damn freaking thin. That does not really mean that she has no weight issue. Who knows all the fats are hidden somewhere, that it does not interpret visually. It's really hazardous.