Is a Promise the Best Headline for Launching a Program?

I am going to launch my new program for weight loss (which has not yet been tested) and I am searching for a remarkable headline.

I am thinking about something very specific and compelling enough such a strong promise like: “Lose 5 kg in 60 days” or “Your last 3 kg forever in 60 days”. Honestly, I am quite sure that almost everybody can achieve that (as long as they stuck with my program) but, I can’t guarantee that they are going to lose 5kg in 60days because this doesn’t depends totally on me: it depends also on how committed is the person or maybe they have other medical conditions – illnesses, take some medications that interacts on it.

Somehow, I feel that with this headline, I promise something that I can’t assure by itself. Should I change the headline?

C – Searching a headline for my program
T – Maybe this promise is not achievable for everyone
F – Doubtful
A – Rumination about the headline, questioning my program, head spinning, procrastination, delaying my launch…
R – I don’t launch my program (so, I confirm my thought: This promise is not for everybody…by the moment, is for nobody)

I am a little bit stuck here…Is definitively a promise the best headline?