Serve food restaurant style rather than family style.
If the person is an all-day snacker, make the available snacks low-calories and fill.
Provide the person with plenty of activities to engage in to distract them between meals.
Store snacks out of sight and out of reach so that the person has to ask for them rather than help himself.
Don’t deny the person food that you are eating yourself.
Reassess any of your own habits that might be encouraging the person with dementia to overreact.