>>79324708A sense of decency?
They do have systems in place for verification though. The only one you can really game is the calorie counter one, since that's based entirely on you synching your tracker app.
The gym one needs to be GPS verified. Essentially you'll go to your gym, and turn on wifi and GPS. Select your gym from a list of gyms that show up for that location, and start a workout. I believe a workout has to be thirty minutes minimum for it to count.
Because it involves GPS, you can't just fool it and say you're at the gym when you're in bed. You need to actually be in the vicinity. Though if you're lucky and your gym is beside a cinema, you could make it work.
Eating x amount of fruit/vegetables requires verification by the community. You have to take a photo of the fruit/vegetable as you're eating it, and then other users vote on whether or not it's a real piece of fruit/vegetable, and whether it's being eaten or not. So, if you upload a picture of an apple with a bite taken out of it, that'd count. If you take a photo of say, an unpeeled orange, you'd probably get told it's not going to count towards your goal.