First, let me say, "$300 a month for a family of 5". You must be a great shopper.
To be honest, it will probably increase the grocery expenditures a bit. My overall expenses however, have decreased once my prescription medicine bill is considered. I have cut my medication expenses over $200 per month due to the weight loss and blood sugar control that is a result of my new Way of eating. Replacing soft drinks with water and cutting out Little Debbies and Three Musketeers has also helped cut back expenses, although with $300 grocery bill you probably weren't spending much on those items.
Overall, though, I would consider the added expense as if I were paying premiums on an insurance policy. If we can increase our health by our style of eating, it is worth a little extra expense.

Lots of luck,
Johnie