My answer (please read my health disclaimer):
As you probably know, I recently went gluten-free, and also greatly reduced soy, refined sugar, and oils. And it's not as tough as it seems, I just have to be creative and appreciate food in it's natural form. I had a great conversation with someone today about how spoiled our palettes are, so much so that we don't like "plain" food and instead prefer it with a ton of salt, oil, and sugar. However, when we remove those additives from our diet we begin to develop a taste for fruits, vegetables, nuts, and seeds in their pure forms.
In the mean time, there are a lot of great transition products available, especially for gluten-free eating. At first, GF pasta (rice, corn, quinoa) with Daiya cheese was my staple, and now that's more of an occasional treat because I'm avoiding oil. Now, I eat a lot of rice, quinoa, beans, and potatoes since they are filling and can easily be made without a lot of oil or salt; I have them with fresh veggies and herbs, and they are delicious. Raw nuts and seeds are also satisfying, but should be had in moderation. I like to keep fruit around so I have something sweet without consuming refined sugar, but if your friend is avoiding sugar all together then those should be avoided (I've noticed that since I stopped eating refined sugar, I don't even want fruit that often). I also suggest drinking herbal teas for flavor (high quality, organic, and fair-trade if possible) - now is a great time to make iced tea (though some sites say all but green tea should be avoided on a yeast-free diet).
As for avoiding yeast, since I've been eating mostly whole foods, I don't usually encounter too much of that. It's usually found in sugar and wheat, so avoiding those foods should make a big difference. I read that alcohol, vinegar, fermented products, and starches like potato and corn may need to be cut out as well.
You mentioned that your friend is avoiding oats, but I think she can still have them as long as they are labeled gluten-free (easily found in natural markets). There are also gluten-free breads, english muffins, and pizza crusts available: check out Food for Life and Energ-G.
I've found that the macrobiotic diet is quite in line with the way I've been eating recently, except for the soy content. I highly recommend checking out macro cookbooks (like The Kind Diet and The Self-Healing Cookbook), websites, and restaurants.
That's about as far as my knowledge goes on the subjects, so I encourage you to do some further research. Remember that every body is different, so it's important to consult professionals. I recommend seeing a few different doctors to get varied perspectives, and to see some with holistic knowledge if possible. Depending on where your friend is located, I can recommend some great specialists.
Do you have further advice? If so, please add it in the comment section below.
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