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Diagnosing Vegetable Trouble

The full article on vegetables hinted at some of the ways that not all vegetables are good choices for everyone. If you’re still reacting to something on Paleo but you’re not quite sure what it is, it’s very likely to have a vegetable cause – so here’s a handy symptom-checker to help you troubleshoot.

A word of caution right at the start: this article should not make you afraid of vegetables. All the foods featured here are perfectly nutritious and safe to eat for the vast majority of people. If you don’t have a sensitivity to them, there’s absolutely no need to feel uneasy.

The point of this article is to be a resource for that small group of people who do benefit from eliminating additional food groups. Often, these people have very little accurate information available to them; they might not even know their symptoms are caused by diet. If you aren’t having any vegetable trouble, eliminating more and more food groups will do nothing but make your life more difficult.

With that in mind, scroll down to read through the full list of potential vegetable issues, or click on the group of symptoms that sounds most like you:


Old hands at Paleo will recognize FODMAPs right away, but if you’re new to the lifestyle, you may never have heard of them. FODMAPs are a group of carbohydrates found in vegetables like crucifers (broccoli, cabbage, cauliflower, and kale), alliums (leeks, onions, and garlic), and a few other culprits. They can cause gas, bloating, constipation, and general digestive upset (including a common feeling of food “sitting like a brick in your stomach”). Check out the full article on FODMAPs for the whole list of culprits, and what you can do about them.


Thyroid problems usually stem from a kalevariety of sources, and vegetables aren’t among the top contenders. It’s more common for hypothyroid symptoms to result from overtraining, undereating, iodine deficiency, or simply genetics. But a specific group of vegetables can sometimes add fuel to the fire: they’re called goitrogens, and they interfere with iodine uptake.

It’s important to stress that goitrogens don’t have any negative effect on thyroid function in healthy people, as part of a varied and balanced diet. They’re not “bad;” they’re just not quite right for some individuals. But if you’re one of those individuals, you might consider avoiding goitrogenic foods:

Cooking can partly inactivate the goitrogens, especially boiling (if you discard the water afterwards).


Autoimmune diseases (especially osteoarthritis and other forms of autoimmune joint pain) can sometimes be triggered by a group of vegetables called nightshades. This only happens in people who already have autoimmune diseases. They won’t give you an autoimmune disease out of nowhere, and they’re very nutritious otherwise, so there’s no need to avoid them “just because.”

Common nightshade vegetables include tomatoes, potatoes, eggplant, all varieties of peppers, and a few other less-common species. To read up on them, check out the full article on nightshades.

Improperly Prepared Vegetables

Sometimes, it’s not really about the food; it’s about how you prepare it. Take a look at some of the foods that can cause stomach upset or even vomiting if they’re not prepared correctly:


If the plant is under stress, parsnips produce a group of natural toxins called furocoumarins. Furocoumarins can cause stomachaches and other unpleasant symptoms in human consumers – they aren’t very dangerous, but they’re certainly unpleasant. To prevent this, avoid parsnips that have visible damage and peel them before cooking. Heat destroys a lot of the furocoumarins, so after cooking (and discarding the cooking water), your parsnips should be good to go.


Potatoes naturally contain a toxin called solanine – most potatoes don’t have nearly enough of it to make us sick, but green potatoes or potatoes that have already sprouted can contain potentially dangerous levels. So if you’ve ever eaten potatoes and immediately felt like you were “poisoned” (common symptoms include nausea, diarrhea, vomiting, stomach cramps, and a burning feeling in your mouth), you probably were! To avoid this, it’s not necessary to avoid potatoes. Just avoid green and sprouted potatoes. If it tastes bitter, spit it out.


Zucchini are almost always fine. Rarely, you’ll find a zucchini that has an abnormally high level of cucurbitacins (another group of natural toxins). This is common in wild zucchinis, but quite infrequent in the cultivated breeds found in the grocery store. It does sometimes happen, though. The solution: if your zucchini tastes bitter or smells strongly of anything, don’t eat it. If the zucchini does contain high levels of cucurbitacins, it will taste and smell noticeably “off.”

Histamine and/or Salicylates

The symptoms of these two sensitivities are very difficult to distinguish – and many people are sensitive to both. Both cause a group of symptoms typically associated with allergies: itchy rashes or hives, swollen or red skin, coughing or sneezing, breathing trouble (wheezing, etc.), and headaches. Neither are truly allergies in the technical sense of the term, but they often seem that way to the sufferer. More rarely, they can also be responsible for a variety of other, apparently unrelated, symptoms.

Histamines: For more on histamines, including a list of vegetables high in histamine, take a look at the full article on histamines.

Salicylates: A clue that you might be reacting to salicylates specifically is an intolerance to aspirin, BenGay, and Pepto Bismol: all three of these drugs are made from purified and extracted salicylates. For more on salicylates, this page lists some vegetables very high in salicylate as: canned olives, capsicum, chili peppers, hot peppers, peppers, radishes, tomatoes, tomato products, and zucchini (courgette).


If you have kidney stones or other kidney issues, you may have heard about restricting oxalates. (A few other rare health conditions also require very strict oxalate avoidance: if you have one of these issues, you’ll know because you’ll have a doctor’s diagnosis). The rationale for this is that most kidney stones are calcium oxalate stones, so restriction of dietary oxalate may reduce the raw materials of the stones, thus preventing their formation.

The actual evidence for restricting oxalates is very conflicting – for one thing, the oxalate in diet makes up only a small fraction of the oxalate in urine, so it’s not clear how much changing your diet can really help. Still many doctors advise kidney stone patients to avoid oxalates as much as possible. So if you’re trying to eat a low-oxalate diet, consider avoiding the following foods:

Oxalates, unfortunately, can’t be destroyed by cooking (regardless of what method you choose).

Vegetable allergy

Yes, there’s such a thing as a vegetable allergy. If this is your problem, you’ll notice distinctive allergy-like symptoms in your mouth (swollen lips and tongue, itching, and/or tingling) starting right after you eat the vegetable. Unlike histamine/salicylate sensitivity reactions, which are spread out over the whole body, the reaction of a vegetable allergy is specific to the mouth.

This is more common in people who are also allergic to pollen (hayfever) – allergists think that the structure of the allergens in the vegetables might be similar to the allergens in the pollen. But here’s the good news: it’s not equally bad with all vegetables. According to Allergy UK, the vegetables most likely to set off a reaction are:

In many people, these vegetables are completely fine when cooked; the symptoms only occur when the food is raw.


Purines are organic compounds that naturally occur in food. The purines themselves aren’t the problem; it’s when you break them down into uric acid. Uric acid isn’t a problem in healthy people (in fact, it’s a necessary antioxidant!), but some people have trouble keeping levels of uric acid stable. If too much of it accumulates, it concentrates as crystals around your joints, causing a painful condition called gout.

Because dietary purine has a relatively strong effect on the production of uric acid, eliminating purines is often recommended for gout sufferers. The foods highest in purines are all animal products, but vegetables relatively high in purines include asparagus, cauliflower, and mushrooms.


If reading through all these potential sensitivities is making you feel a little paranoid (or if you have 5 different tabs open right now and all of them are diagnosing you with sensitivities to everything), step back and take a deep breath. Sensitivity to even one of these compounds is quite rare. Don’t rush out on a low-everything diet all at once (for one thing, it’s not useful since it doesn’t allow you to identify specific sensitivities).

If you do suspect you have one of the conditions above, it might be helpful to try a 30-day elimination of just that food group. This doesn’t mean that you need to give up those foods forever; it’s just a test to see whether or not they’re really to blame. If they aren’t, there’s no reason to keep them out of your diet, and if they are, now you have your answer!