Is there a caffeinated, very-low-oxalate tea?
You can check the answer of the people under the question at Quora “is coffee high in oxalates“
Is there a caffeinated, very-low-oxalate tea?
You can check the answer of the people under the question at Quora “is coffee high in oxalates“
It might help to decouple the need for caffeine from the other requirements.
Caffeine is readily available (at least in the US) in tablet form. That allows for more precise control over caffeine level than you can get from teas, which vary pretty wildly in how much caffeine they contain.
For example, with a separate source of caffeine you might consider Rooibos or Honeybush tea. These contain antioxidants, but no caffeine.
Your brother might be able to precipitate and filter out calcium oxalate. That would probably be a lot of trouble though.
Some tea vendors might be able to provide you with information about oxalate content if you contact them.
A2A White tea, Green tea, and Oolong tea have lower oxalic acid than black tea, but still contain some caffeine. Herbal teas are very low in oxalates, but are also caffeine free. African Red Bush Tea (Rooibos) is caffeine free as well, but has a more robust flavor than standard herbals if you want a heartier flavor and are willing to forgo the caffeine. If you are looking for caffeine stick to White, Green, and/or Oolong tea in moderation, for even lower levels of oxalic acids will add up.
Green tea in general has less oxalate content than black tea which makes it less harmful to people. You can refer to this article about oxalate content and green tea: Green Tea Prevents Kidney Stones
Green tea in general contains lower caffeine than black tea and coffee, but still contains caffeine. I would suggest quality green tea such as Premium Japanese Green Tea – Loose Leaf 3.5 oz Covered Tea – Nozomi or Japanese Pu-Erh tea: Japanese Diet Pu-Erh Tea – Saryu Soso (Tea Bag) which both products have less in oxalate and high in Vitamine C, E.
Also Nozomi contains high Polyphenol and Gallic Acid which reduces absorpion activity in stomach with 0 cholesterol and 0 sodium. Zero sodium is good for kidney stone as you are not supposed to be taking much of salt when you have kidney stone and should be drinking lots of water which by consuming green tea allows more hydration than drinks such as coffee which dehydrates body.
Hojicha is a roasted green tea made from twigs and older leaves, which have been shown to have lower oxalate content than young tea leaves. As well, oxalic acid sublimes (like caffeine), so it’s possible much of the oxalate content of the tea that goes into hojicha could be destroyed by the roasting process.
However, hojicha is also fairly low-caffeine for the same reason.
Here is an article (in German) which was the only evidence I could find to support my surmises above, though. It doesn’t appear widely-studied.