Arthritis is inflammation. Sugar is inflammatory. There are several ways in which sugar provokes inflammation.
My diet is as much protein as I want, plenty of cheese ( 40% fat ) and a small amount of butter. Unsweetened yoghurt.
My carbohydrate intake is limited to low carb vegetables - broccoli, lettuce, cabbage, green beans, cauliflower and bamboo.
On that diet, my weight went from 93 kg to 78 kg. I have since backslid to 81 kg, as I allow myself half a small bar of chocolate a day. I don't drink alcohol.
If the body is deprived of sugar, it has to start burning fat instead, for energy. IMO it's that simple.