DIY soylent for seniors


I have recently gotten my dad into soylent. So far he seems to like it and is willing to keep drinking it for his breakfast and lunch. He is 5’9"ish, 191lbs, 67 years old, sedentary, and is trying to lose weight. He has the expected joint issues and as far as we know is otherwise healthy. I have created a DIY recipe just for him and today will be the first day he will be drinking it. What I am interested in is if there are any supplements I could add to make it even better for him. The obvious will be joint support supplements of course. For the most part bioavailability and effectiveness are more important than price so if a supplement is a little on the pricy side that is ok just so long as its not crazy expensive.