Dani, eating mostly fruit when when you're diabetic is going to f**k you over.
Lentils are also cheap, while I personally don't eat legumes or lentils etc, they're not a bad option.
Honestly, I notice the difference in how I feel when I'm eating right and being active, I used to be a fat merkin, and I can tell you I'm much happier now, I also realised that my bi-polar ius most under control when I eat well. I am eating what I want when I'm eating meat, veggies, eggs nuts and fruit, so I don't feel deprived.
I look at these things from my own experience, epidemiological research and a biochemistry, physiology, psychology, anatomy perspective and that's what I genuinely believe. If someone doesn't value health and fitness etc, or would rather indulge in junk food etc and they believe it makes them happy, that's not my business, humans have free will and that's a wonderful thing. Also, if someone enjoys being fat, that's their choice. I see my job as a trainer to put science based research into a package someone can apply to their training, I give very basic nutrition advice, my qualifications are in exercise prescription nothing more yet.
It's true there's a lot of bullshit in personal training and there's a lot of shit trainers, but if I didn't believe in the service I wouldn't have invested in my own trainer.