I’m still experimenting, and will comment more as I eventually address many of these foods in more detail. But here are a few ideas for substitutes of the most common nightshades. Note: I explain the adverse effects of nightshades in more detail here.
Sweet Potatoes for White Potatoes – While sweet potatoes belong to the same plant order as nightshades (Polemoniales), they are not part of the Solanaceae family – and most significantly, they don’t contain alkaloids. So they make a great substitute for potatoes in all occasions. For example, mashed sweet potatoes.
Plums, Peaches and Beets for Tomatoes - Tomatoes are actually a fruit. So perhaps a good substitute would be a fruit? I’ve tried plums and peaches before in various salsas and sauces. Fresh peaches (or nectarines), which often ripen at the same time as tomatoes, are surprisingly fantastic grilled, and drizzled with olive oil, your favorite herbs (e.g. basil or thyme) and a little salt and lemon pepper. If you’re wanting that red coloring, try beets. I’ve made a fantastic herbed ragout sauce with a combination of mung beans and beets – it has the same consistency as your typical tomato sauce, and tastes uniquely wonderful!
Cauliflower, Zucchini or Okra for Eggplant - Like eggplant, cauliflower and zucchini both have a relatively neutral taste so they absorbs the flavoring of its companion herbs and spices, and it has a similarly soft and creamy consistency when cooked. Other options would be okra, which as a similar unctuous, or slimy, texture and a somewhat peppery taste.
Radishes or Black Pepper for Capsicums (red pepper, sweet peppers, cayenne, paprika, etc) – Daikon or red radishes can add that kick to replace sweet peppers. They’re great in stir fries. And we can all be grateful that black pepper, which belongs to the Piperaceae family, is not a member of the nightshade foods.
So there it is. Just try substituting some of the above 1 for 1 in your favorite nightshade recipes. I think you may be surprised at how little we actually need so much of these foods that we are seemingly so attached to.