Have you tried the weight loss icecream? Sims are dropping weight like mad and get a happy mood buff from it. I completely forgot about this, easy mode for my lazy sims who don't want to work out.
Ah jeez, and here I was forcing my sim to eat fish and chips everyday because it has zero cal and jogging so there's no weight gain. Now she can eat whatever she wants and just eat the Taste of Diet and a 30 sim-minute jog!