fatten up

Verb

 * 1)  To cause to gain weight by means of feeding.
 * My cat looks underweight, so I'll fatten him up with higher-calorie cat food.
 * I visited my mother for a month, and she managed to fatten me up 20 pounds.
 * 1)  To become fat or fatter by gaining weight.
 * 2)  To make bigger; to expand.
 * 1)  To make bigger; to expand.