@Elliandre, you have to eat healthy with a sim for a few days for every meal and after enough days and healthy meals they will get the lifestyle. It only took me a few sim days, maybe 3 or 4, of eating nothing but healthy food, but eating "junk food" at the same time would slow it down.
The non-special recipes that count as healthy include all salads (even fruit and watermelon salads), spinach fritatas, steamed fish, fish tacos, whole wheat bread, and grilled fruit. Pretty much everything I 'thought' should be healthy that I tried so far has been. Once the sim has the lifestyle it unlocks a new pie menu option on the refrigerator to "cook healthy meal" and there's somewhere around a dozen+ new things to cook there. Stuff like "Scrambled egg whites and turkey bacon" in addition to the chickpea items I mentioned already.