Even though the images used for training already contain an overweight character, I find the best way to get consistant body weight is to use chubby woman in the prompt.

Here is an example of a prompt:
l34n0r, chubby woman, lying on a bed, wearing red silk pyjamas

First try on an overweight character LoRA created with z-image-turbo generated inputs.
I find it hard to generate consistent body weight with z-image-turbo, and I wanted to see if with a LoRA trained on a dataset with an already chubby figure it would be easier (it kind of is).

The dataset creation process:
I first generated a prompt that would define the character exhaustively, locked the seed and generated about 200 images with various actions / lighting / clothes.
I then do a pass of face recognition on the generated images to keep as much consistency as possible for the input images and select about 20 that are used for training.