Everyone reacts differently to learning that they have prostate cancer. A Gleason score 6 means a low-grade cancer that is likely confined to his prostate and, therefore, is curable. Some people do lose weight during this stage when they change their diet. I would encourage him to read Dr Patrick Walsh's book, Guide to Surviving Prostate Cancer, and look at the online material at PCF.org and PCRI.org for Gleason 6 prostate cancer. You will find that exercising and a healthy diet are recommended both to help with stress reduction (along with other stress reduction techniques) and to prepare for any future treatments that he may choose. Lastly, he is very fortunate to have you as a partner that is helping him through this journey.