This can be a tough and lengthy one to get rid of, and it will depend on how bad it is and how much he takes care of it with rest/stretches/ice, etc… Going too long without taking care of it can lead to bone spurs and arthritis. For sure the fact the he is overweight doesn’t help, but there are things that he can do… Has he been to a doctor or physical therapist? That would be the first place to start.
In addition, I would have him avoid high impact activities, ice it after a workout, have him do the recommended stretches for it, and make sure his footwear and make sure it has proper arch supports or orthotics. (he should probably avoid going barefoot in the house as well. I’ve also heard great things from clients about wearing Birkenstocks for this).
Here is one good article from ACE that addresses this, as well the connection to other areas of the body such as the calf muscles and the hip flexors. Hope you can use it…