Give him a break
It's not easy to suddenly change habits after 30+ years. I know even at my age it took me a few months to get eating habits down.
Karma, just make sure that whenever you go out and buy tomatoes again, be conscious of what you're going to eat them with.
Whenever i buy tuna, I know that that isn't enough(too clean), so I make sure to buy the right amount of cottage cheese at the same time. Then whenever I eat tuna, I coat it with cottage cheese. protein + fat OR protein + carbs should constitute all of your meals. Carbs + fat is a surefire way to gain bodyfat. Protein by itself gets used by the body as a fuel source, and thus doesn't get pumped into the muscles.
When u eat pro. + carbs, the body can more easily break down carbs, so it uses them for energy and the protein gets stored. Same thing with dietary fats.
Remember, make sure whenever you put any food into ur piehole, it always contains protein+carb or protein+fat.
cheers!