It’s a little ambiguous. One regular meal for one person could be very different than for another. I think they should make this more specific. Normally breakfast and lunch are smaller meals anyway, so how is it different except about not snacking, which I rarely do?
True fasting implies that you will be hungry.
Well, you think about things a bit. ‘Regular’ doesn’t necessarily mean what YOU’RE accustomed to eating, rather what a regular person would eat.
So if a normal meal for you is three huge courses, then you might want to rethink the dessert or the portion size on a fast day, for example, because it’s highly IRregular for most people (except in the US and other lardo nations like mine, Australia) to eat three huge courses for a meal.
And then you remember that your TWO other meals TOGETHER have to be LESS than the main meal, not equal to it. Now that’s not normal for most people - they tend not to have such small breakfast AND lunch, for example, that together they’d be less than their dinner.
So you’d have a less-than-appetiser-sized meal for one of them (which is less than most people eat for any mea and will leave them hungry for the most partl) and a less-than-entree-sized meal for the other. Most people would be hungry on this unless they’re restaurant sized portions.
If you normally eat in a restrained way such that the fasting guideline is no hardship, then you’re in the same position as someone who is vegetarian would be on a day of abstinence.
You have the option of obeying the letter of the law and eating as per normal, or entering into its spirit and imposing other restrictions on your eating, or performing some other penance, in order to get into the spirit of the day.