I feed guests at 9am, 1pm and 6-7pm with maybe an ice cream or slice of cake around 4pm, but not always. Surely 2 (by the time you finish eating) till 6 or 7 is a normal interval between meals?
Well... without the 4pm snack it's still a 4-5 hour interval, which is a long gap for many people. I prefer to eat very lightly at mealtimes and snack in between. This is personal preference, I've always been very slim and seem to use up calories quickly... if I went 4-5 hours without eating I'd start feeling queasy and faint.
I find it odd and inhospitable when hosts insist on 'feeding' guests at set times, with no snacks or nibbles offered in between. You are basically imposing your family's eating pattern on guests rather than accommodating different eating patterns. How difficult is it to provide a tray of nutritious non-filling snacks that guests can graze on at leisure (e.g. vegetable sticks, cheese and biscuits, nuts, individually-wrapped cereal/granola bars, rice-cakes, a dish of crisps with some yogurt for dipping, an attractive bowl of fruit?)
If guests complain of hunger an hour before food is served, wouldn't it be polite to provide an appetiser like bread and olives or a small salad with crutons? I think it's mean to make them wait. I feel irritated when hosts insist everyone goes hungry 'to work up a good appetite'... it's as if appreciation of their cooking is more important than guests feeling relaxed. When I have guests, it's about company and fun, not showing off my cooking skills.
There is no evidence to suggest 3 substantial meals is better for you than 6 very small meals or 3 light meals with 3 snacks. Remember some guests don't like eating big meals or may not like your cooking, so they need other options. No-one's suggesting a 24-hour buffet... but it's not difficult to provide a variety of accessible snacks. If you don't want your DC snacking, why not tell them the snacks are for guests only, or put a basket of non-perishable snacks in guestroom? If guests want to graze constantly instead of eating big meals, that's their choice. They are adults and can choose how to eat. Unless you've specifically invited them for a weekend of culinary experiences, it's not rude to eat between meals. IMO part of being a good host is being generous with food, flexible over eating patterns, and accommodating different needs.
Rookie I'd be mortified if a guest felt faint and had to ask me for some nuts! What a horrible experience for you. Guests' comfort is more important than sticking rigidly to a routine or imposing your beliefs on them.
If I was invited to stay with friends who had a '3 meals a day no snacks' rule I'd be tempted to take along fruit, nuts, biscuits and a big box chocolates, open everything and share them round between meals!