IDIOMS

pack on the pounds

(idiomatic) To gain weight, especially as a result of vigorous or excessive eating.

Example: 1936, "Today, these healthy Dionne Quins had Quaker Oats" (advertisement), Windsor Daily Star (Canada), 3 Dec., p. 27 (retrieved 13 Nov 2010):
  For growing youngsters, this marvelous nourishment helps pack on the pounds, adds inches to height.
1969, Dr. George C. Thosteson, "Methods of Controlling Cholesterol," Milwaukee Sentinel, 10 Dec., p. 17 (retrieved 13 Nov 2010):
  One can stick to low cholesterol foods, yet eat such quantities as to pack on the pounds.
2009, Bonnie Rochman, "First Comes Love, Then Comes Obesity?," Time, 6 July:
  Not only are married people more likely to become obese than those who are just dating, but young people who move in with a boyfriend or girlfriend tend to pack on the pounds too.