Dr. Greger consistently provides the most interesting science-based health videos on the net. Where else would you get the idea to test your urine pH with purple cabbage juice? This is home chemistry at its best!
I actually blended some water and purple cabbage right away, and got a nice turquoise color as a result! I knew that plant-based diets are alkaline-forming, but I was still positively surprised.
As Dr. Greger mentions, those on modern Western diets tend to get more acidic and lose muscle mass - not to speak of gout, kidney stones, and so on - the list of risks is a long one. Uric acid is very bad stuff indeed.
The main take-away point from this is that to preserve/gain muscle as you age, you need to eat more alkaline-forming foods like fruits and vegetables and avoid acidic "protein sources" such as meat, fish, dairy and eggs.
I really do recommend you subscribe to NutritionFacts.org youtube channel, it's always fun, informative and helpful.