#234 Should You Eliminate Nightshades from Your Diet?

Should You Eliminate Nightshades from Your Diet?

The Internet and popular health books would have you believe peppers, tomatoes, eggplant, and other nightshades cause inflammation, autoimmune diseases, and gastrointestinal diseases.  As I am often asked about nightshades, this article explores the research behind the misinformation and myths about nightshades.  And when it comes to health books, it is important to remember the following quote from Mark Twain:

Be careful about reading health books.  You may die of a misprint.

What are nightshades?

Nightshades are the edible parts of the flowering plants in the Solanaceae family (pronounced sō-lə-ˈnā-sē-ē).  In fact, there are thousands of plants in the Solanaceae family.  While many are inedible, humans have eaten the edible nightshades like peppers, tomatoes, eggplant and potatoes for thousands of years without any problems.

Why are nightshades called nightshades?

It is unclear why nightshades are called nightshades.  While there are many theories, my best guess is that it is because many of these plants prefer to grow in shady areas or they flower at night.

What Are You Giving Up by Avoiding Nightshades?

If you are going to follow the popular Internet and “health” book advice and avoid nightshades, you need to know what you are giving up.  If you do choose to give up these foods, you will have to work hard to make sure you pick up these key nutrients and disease fighting abilities from other foods.

1. Tomatoes

Tomatoes are one of the best sources of the powerful anti-oxidant, lycopene.  Tomatoes are also high in vitamins A, C, and fiber.

Tomatoes have been shown in medical studies to help prevent heart disease and cancer.  These two conditions alone account for approximately 80% of all deaths in the US.

2. Peppers

Peppers are another nutritional powerhouse food.  If you give up peppers you will need to make up for the lost vitamins A, C and B6 as well as folate and fiber from other food sources.

In addition to giving up these key nutrients, studies show you will also lose the weight loss benefits, metabolism boost, pain reduction, and heart disease protective effects of peppers.

3. Eggplant

While eggplant may not be as flashy as tomatoes and peppers when it comes to nutritional qualities, they can still hold their own.  Eggplant is a high fiber food which is also high in anthocyanin.

Anthocyanin is that same purple color that is in blueberries.  Many studies show that anthocyanin improves brain function and protects you from many brain diseases including dementia.

4. Potatoes

Potatoes have a bad reputation.  This is probably because more than 90% of potatoes are eaten as french fries or potato chips in the US.  However, if you bake a real potato, and eat it with the skin, you will get a heathy dose of vitamins B6 and C, potassium, and fiber.

For those with diabetes or blood sugar issues, potatoes can be eaten as a resistant starch.  Merely the process of baking a potato, putting it in the fridge overnight, and then reheating it the next day changes it into a resistant starch with no significant blood sugar spike for most people.  To learn more about resistant starches, please read blog number 164, How to Eat Pasta Without Gaining Weight.

Do Nightshades Cause Autoimmune Diseases

One widely propagated belief on the Internet and in “health” books is that nightshades causes autoimmune diseases.  This belief arises from the alkaloids which are in nightshades.

Anecdotally, many people claim that eliminating nightshades helped their autoimmune diseases.  And for those people who report an improvement in their autoimmune disease by cutting out nightshades, they should continue to avoid these foods  However, despite these anecdotal reports, there are no credible studies in humans linking nightshades to autoimmune diseases.

Personally, I used to suffer from the autoimmune disease ankylosing spondylitis.  In my quest to find relief, avoiding nightshades had no impact on my condition.

However, I did find that by following the healthy lifestyle of the people living in China’s Longevity Village, my autoimmune disease went into remission.  If you want to learn more, it is all described in our new book, The Longevity Plan.

Do Nightshades Cause Leaky Gut?

A leaky gut is what medically we refer to as intestinal permeability.  With intestinal permeability, the tight barrier between your gut and your blood stream is broken.

As a result, things in the gut can get in the blood stream without proper digestion.  When this happens, autoimmune diseases may be triggered.

To support the claims made by Internet sites and popular “health” books, I could find one study suggesting that feeding processed potatoes to mice may lead to intestinal permeability.  However, before you give up nightshades based on one obscure study, please remember that this study used processed potatoes not real whole baked potatoes.  Also, please remember that this effect has never been shown to occur in humans.

Do Nightshades Cause Irritable Bowel or Inflammatory Bowel Disease?

As with autoimmune diseases and leaky gut, the Internet and popular “health” books would once again have you believe that nightshades are the cause of your gastrointestinal symptoms.  As with the other claims, there are no scientific data to support these beliefs.  The only study I could find on this topic was that same obscure study in mice demonstrating that processed potatoes may trigger inflammatory bowel disease that we already discussed.

Do Nightshades Cause Arthritis?

Some people believe nightshades cause arthritis.  This belief arises from the theory that calcitriol in nightshades causes calcium to be deposited in joints.

While it is true that people with rheumatoid arthritis may have higher levels of calcium in their blood, there is no scientific proof that eating nightshades causes your blood calcium levels to go up.  As with the other conditions discussed in this article, if you find that cutting out nightshades helps your arthritis then please avoid these foods.  However, if you are like most people, you will probably find that nightshades have no impact on your arthritis.

Practical Tips

Humans have thrived on nightshades, like peppers, tomatoes, eggplant, and real potatoes (not french fries or potato chips) for millennia.  Indeed, some of the healthiest and longest lived people on this plant, like the Mediterranean people eating tomatoes or the Japanese eating peppers, are proof that most people thrive on nightshades.  It is also interesting to note that some of the lowest rates of autoimmune diseases and arthritis occur in people following either the traditional Mediterranean or Asian diet.

While the vast majority of people thrive on nightshades, we are not all created equally.  Some of us may react differently to different foods.

For this reason, if you don’t do well with nightshades then you will need to work hard to make up for this nutritional and disease fighting deficiency from other foods.  This means you will have to significantly increase your intake of a wide array of colorful fruits and vegetables.

How do you do with nightshades?  Please leave your thoughts and questions below.  As always, I’ll do my best to answer every question.

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Disclaimer Policy: This website is intended to give general information and does not provide medical advice. This website does not create a doctor-patient relationship between you and Dr. John Day. If you have a medical problem, immediately contact your healthcare provider. Information on this website is not intended to diagnose or treat any condition. Dr. John Day is not responsible for any losses, damages or claims that may result from your medical decisions.

  1. Thank you for your comments although at the end your “practical tips” still leave this topic not clear. I wish you meet with Dr. Grundy and get into a “real practical tips” regarding lycopene. I am a psychiatrist (former Hopkins faculty) and several of my patients take statins and deal with the side effects of such medications in addition of their anxiety and pains. I help my patients first with the natural way (exercise, diet, social life, psychotherapy, etc) that is why I am super interested in diet. Thank you very much again and hope I can hear from you soon.

    • Hi Elizabeth,

      Thanks for reading and commenting. So glad to hear that you also use lifestyle medicine when treating patients.

      I agree, there is still so much that we don’t understand about diet and nutrition. It always takes time for the science to catch up…



  2. Really appreciate your scientific and honest approach. You supply references if appropriate and state if you’re not sure. Thanks

  3. Great review Dr Day, as usual! Glad we don’t have to give up our garden, which consists only of tomatoes, eggplant and peppers.

  4. I love tomatoes. What are your feelings about tomato juice? I drink the low-sodium variety every morning

    • Hi Carol,

      Of all the fruit juices, tomato juice is probably the best as the sugar content is low. I agree with the low sodium versions as tomato juice can be sky high in sodium.