Avoiding or at least minimizing (eating only a little and only once or twice a week) gluten and/or dairy will make a pleasant breath and heal even severe bad breath.
For some people gluten is the main issue, while for others, milk and milk products are the main issue. In the beginning milk or gluten (after testing by elimination which is the main issue) should be more carefully restricted (even in the beginning one can make occasional exceptions), after which, minimizing one or both will be sufficient.
At times other foods or food groups may be contributing to the problem. One should test by eliminating the particular food or food group for a few days or more. One may be amazed how quickly the breath becomes sweet, when the food that the person's body can't tolerate is avoided.