If you're hired to promote a topic considered as sensitive by Facebook advertising policies, such as health / diet services, you should take extra care in the way you'll craft your ads, especially when it comes to personal attributes.
In this very good piece, Sean Flanagan compares Facebook to an online cafe where everyone should feel at ease (Facebook's #1 objective is to keep people in their agora). You would not come across strangers in a public space and immediately tell them they should care about their weight, their financial situation or their mental health. This would sound rude and would be totally counterproductive. They would usually leave rather offended. Similarly, Facebook doesn't want you to reference or allude to personal attributes or characteristics of the group or individual you're targeting.
You can't say in your copy: "Are you overweight?" or "Do you want to lose weight?" but you could say "Here's the weight loss programme everyone's talking about!" Your message will then resonate with the right people without offending those who would not be prepared to digest your message.
Be aware though that your ad creative might be rejected even if you comply with this simple rule, especially if your visual is slightly too provocative. Again, think about how random people would react to your publication. If it could scare them away from Facebook, there's a chance your ad will be rejected. An image featuring a curly measuring tape, a (unhappy) fat person or a bathroom scale will usually be rejected since they allude a bit too closely to weight-related issues.You probably won't see these images in Facebook ads
See how Weight Watchers (now called WW) is approaching ad copy & visual creation via the very useful Facebook Ad Library (where you can search for any FB page's active ads). You'll notice that most creatives are either generic (No matter what your goals are, WW is for you.) or diluting the tricky topic into another one (With WW, you can still enjoy your favorite foods and reach your weight loss goals.).
Facebook Advertising Policies section provides you with a few examples of Do's and Don'ts for a variety of use cases.
For instance you could promote "Atlantis Gay Cruises" but you can't ask potential travelers "Are you gay?" to sell them a gay-friendly package. You can't tell someone "Questioning your gender identity?" but you can invite anyone to "Come meet transsexual singles." You can't market debt-consolidation by asking "Broke ? Bankrupt ?" but you can say "We have financial services to cover every need."
There's also a bonus comment re: the use of "other". You can't allude to the group someone is part of by using the "other" word. For instance you can't say "Meet other Buddhists." but you can say "Looking for Buddhists near you?". Subtle difference.Avoid the "Other" word.
Basically anything which mentions a detail related to the targeted user's identity is strictly forbidden: race, religion/philosophical belief, age, sexual orientation/behaviour, gender identity, disability or medical condition, financial status/information, criminal record, name.
Be creative to find the right balance between commercial efficiency and social acceptability.