There are different strategies I've taken with different groups of people.

When I first got started, I only let in my closest friends and colleagues on what I was doing, so they would understand in advance why I wouldn't be able to have certain meals with them anymore, like a pizza or curry. These were people I was in regular contact with already, so this was a major potential avenue of pressure that I was able to ward off from the start.

For people I don't see as regularly, I would still let them make the offer before explaining why I couldn't take it. I often didn't have to go into any more detail than simply "I'm trying something with my diet at the moment". For people in this group who have known me for some time - extended family, for example - they will know my history with weight and most will realise that the best thing they can do to enable the changes I was seeking, was to not jeopardise my efforts in any way. Sure there are some know-it-alls in this group, but at all times my food choices remain mine to make, and if they are offended by that, well that's their choice too.

Then there are the one-offs, like restaurant staff for example. Generally these sorts are quite accommodating of my particular requests for certain things. For anyone who tries to push anything in particular, "oh, wouldn't you rather have this or that," I can simply say "sorry, I can't eat that, I have an intolerance." And technically that is true. I think when most people hear the word "intolerance" they assume something specific like lactose or gluten as opposed to an entire macronutrient. In any case, they typically won't ask for specifics though for fear of offending their customer, which is fine by me, as long as I get what's appropriate for me in the end.