If you want to be technical, any habitual pattern of eating is a diet.

But technicalities don't define words, usage and context do, and, for the vast majority of people, including people here, diet means a change in your habitual pattern of eating designed to induce weight loss. That's how it's universally understood in this context.

Being more technical does not mean being more correct.

"Universally understood" shouldn't be true for this. I've known a number of people who were on diets to gain weight for medical or self image reasons, and it's known still known as a diet.

Yes, but we already knew in which context btilly was writing, so I'm not sure being pedantic is justified.