This is a really good question! I'm glad you like my depictions of different body types, i worked really hard to get better at that so im happy folks enjoy em!! I didn't actually learn from a book or tutorial, it was mostly looking at fat bodies IRL and learning to incorporate those features onto what I already drew. As it turns out, we're all human, so if you understand the anatomy enough to draw a skinny person, you have the tools to understand the anatomy of a fat person.
So, like, here, this is my sketch of someone with a very average build. If I were to draw a fat body, I would still use all the basic principles I use here. One mistake I think folks run into is "isolating" parts, which can lead to things like this
which isn't necessarily bad, but if its not what you're going for, the issue is pretty apparent. Weight affects ALL of the body, not just the stomach or the face or the limbs. If you think about how that weight affects everything in tandem then you can start drawing fat bodies that work more in your style.
for this, this is the same quick sketch using the same pose and principles as the first one. but! I allowed the weight to be distributed across the body. Notice how the legs, belly, arms, etc all got thicker? The key to drawing fat bodies and making them look like they fit is allowing that weight to affect everything. without it, it just looks like you're adding on features to someone rather than considering everything at once.
my other tip is: don't be scared! things like fat arms or chins or bellies or stretch lines are not something that's bad to depict. if you want to draw fat bodies, you gotta not be scared to draw things the way they are. someone having a fat body is not bad, and you drawing that fat body is not bad either. Experiment! To me, art is about representing ideas, and the only way to get better is to experiment with how you represent those ideas. I'm by no means an expert, and I think you can also get a ton done by looking for resources aside from me, but I hope this helps, and have fun!!
