I'm not a fan of these questions - but the trend seems to be that as long as they're clearly-focused, they get accepted.
I would suggest that you at least skim these questions and try to get feel for the language. Several members of the community (including myself) did feel that those questions were off-topic - more along the lines of "health & diet" which is an explicit off-topic subject.
However, in my opinion this is about more than just a black-and-white off-topic/on-topic distinction, it's about what kind of questions will actually get good answers. Just because a question doesn't get closed doesn't mean that it will actually end up being helpful. My suggestions to you are:
Try to ask specific questions. A super-generic question about removing fat from a recipe doesn't tend to get a lot of useful answers. On the other hand, a question about cooking onions without oil or lowering the fat/sugar content of a peanut butter treat do much better. As well, these are clearly identifiable as culinary questions as opposed to diet questions.
If you can't be specific about a recipe, try to frame it as an ingredient substitution. For example, butter has plenty of sodium and vitamin A, so if you (or your friend) needs to cut out butter from the diet, try asking for ingredients low in fat that will also provide those other nutrients or perform the same culinary function. In other words, don't just tell us what you don't want; tell us what you do want.
Also make sure to describe the specific restrictions; "low fat" means a lot of different things to different people, and although you've already mentioned the specifics here on meta, members on the main Q&A site aren't necessarily going to know that.
Please, please, avoid using words or phases like "ideas", "suggestions", "recommendations", etc. Putting aside the issue of scope, questions should still have definitive answers and not solicit opinions.
Personally, I would much rather see two dozen specific questions about issues specific to low-fat cooking than one supersized "tips and tricks" question. We had one like that on gluten-free cooking; it didn't do very well. If you're interested in that subject, you're much better off looking at the entire gluten-free tag. Our low-fat tag is pretty small, but that's mainly because it hasn't been used properly; a search for "low fat" turns up a surprisingly high number of relevant results.
So it is essentially up to you; you can try tiptoeing along the health/diet off-topic border and probably end up with an OK, but not great, result. Or you can do a tiny bit of digging on your own - for example, talking to the parents to find out how they'd cook without the restriction - and then ask a series of more targeted questions about fat reduction, and probably receive much better answers over the long haul.