See me once, See me twice #15

Question

See me once, greetings to my brother in town
See me twice, my effect is weighing you down

I'm prepared to give a hint in a day, if needed. Usually my riddles are solved very quickly though :) Good luck and have fun.

_{If you are not familiar with my See me once riddles, I recommend you first have a look at the latest riddles in this series and their solutions:
#10, #11, #12, #13, #14}

Answer 1

See me once, greetings to my brother in town

yo - an informal greeting

See me twice, my effect is weighing you down

yo-yo effect - the cyclical loss and gain of weight