I think all diet guides include the advice to “never go grocery shopping when you are hungry”—and when I had young children, I added “and never with young children”—because either of these factors seem to lead to less wise food choices. Tal and Wansink offer scientific support for this common sense advice in their study of grocery store purchases after short-term fasts.
Redberg RF. Snack (Healthily) Before ShoppingComment on “Fattening Fasting”. JAMA Intern Med. 2013;173(12):1148. doi:10.1001/jamainternmed.2013.749