I'm still a bit confused about the original topic - is the OP asking if he/she can refuse the First Class meal service - in advance, no less? Last time I checked, on most First Classes, even the lowly ones offered by U.S. carriers, you can pretty much do whatever you like regarding the meal. Eat - don't eat, it don't much matter. If the passengers don't eat it, the crew happily will.
Per chance, is the OP from a harshly autocratic country where the flight crew might force him/her to eat whatever's served? I can only imagine...
"What would you like for dinner tonight?"
"Oh nothing, thanks. I think I'll just try to get some sleep."
"I'm sorry, but regulations stipulate that you must eat. Now what'll it be?"
"Well, maybe just a salad, then..."
"I'm sorry, but you are required to eat a minimum of 1200 calories at each meal."
"B-but, I don't sleep well on a full stomach!"
"You really should try our Turkey Medallions with Valerian Root Sauce. They're loaded with tryptophan."
"Well, I..."
"And we'll start you out with a big tumbler of 18 year old Scotch, as well. You'll sleep like a baby!"