Hi Sudhira,
Afternoon nap does promote weight gain, in my opinion. Earlier, out of boredom I used to doze off while reading something -- so evening times I used to feel irritable/ guilty and night also won't get sleep before 11 pm. Some rest after lunch, about 30mins. is fine I guess but not more because then full routine gets upset. Body becomes sluggish,

metabolism is reduced and one does tend to get lazy.
There is a saying in tamil : "Pagalil thookkam, panni pol oruvam " which means sleeping in day time gives body shape of pig !! But this doesn't suit my co-sister at all ------ she has a compulsory nap of 45mins. before lunch and at least 2 1/2 hrs.

after lunch .
Still she has 'beedi body' .

....guess body constitution also matters a lot .....
Cheers..