The deal behind the pregnancy hormone is that it triggers the body that it is "OK" for it to release its precious fat stores for consumption to save the "baby" in time of "famine".
If there isn't some training on a permenant new eating style and easing them back into a regular calorie lifestyle, that poor person will just put the weight back on as soon as the injections stop and they aren't "pregnant" anymore.
"My days of not taking you seriously have come to a middle."
~ Captain Malcolm Reynolds