I don't eat gluten because it makes me physically stomach sick.
Gluten is a gliadin (a type of protein found in certain grains) so the major issue is going to be with baked goods, pastas and cereals -- although anything that contains grain products can be a problem, and they turn up in odd places...like the flour in some brands of ice cream, for example. If you want to avoid gluten completely, it's mosty a matter of reading labels carefully and asking about ingredients if you eat away from home (flour is sometimes used as a thickener in things like soups and sauces, for example).
Here's a list of gluten-containing grains:
Wheat (note: "durum semolina" is wheat)
Triticale
Spelt
Kamut
Rye
Oats (usually -- there are apparently gluten-free varieties)
Barley
Here is a list of gluten-free grains:
Millet
Rice
Sorghum
Teff
Amaranth
Buckwheat (not related to wheat despite its name -- it's related to plants in the same family as rhubarb, I think)
Corn
Oats (sometimes...I've never chanced it, myself)
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