[gayprogrammer]

Insulin goes bad about 30 days after first use. Pretty much all diabetics need to buy a vial or two every month, no matter if you've used it all or not.

Think of it like keeping milk stocked in your fridge. Even if you spread it out to last more than a month, the remaining half will go bad before you got to it.

So although changing diet and increasing physical activity may reduce insulin requirements in both type 2 and type 1 (as several people have anecdotally shared here), you can see how it doesn't avoid buying insulin every month.