If you’re new to Keto, it can be challenging to figure out which vegetables are Keto-friendly and which aren’t.
With some veggies, it all comes down to serving size. Tomatoes are one such veggie. And we can’t imagine a world without salsa, marinara, or Keto-friendly BLT’s, so in this post we’ll share everything you need to know about including tomatoes in your Keto diet.
We’ll also review some other nightshades and whether or not they’re Keto friendly.
What Is Keto?
Before we dive into tomatoes and nightshades, let’s do a brief refresher on Keto.
There are several potential advantages to being in ketosis. First, it may help you lose weight by more efficiently burning stored body fat. It also improves insulin resistance and blood sugar management in people with type 2 diabetes. Additionally, many people report that going on a Keto diet drastically reduces their appetite.[*]
However, in order to reap all the potential benefits of Keto, you need to drastically limit your net carb intake to about 5% of your daily calorie intake or less. (Net carbs, by the way, are total carbs with indigestible fiber and certain sugar alcohols (e.g., isomalt, maltitol, polyglycitol, sorbitol and xylitol) removed).
For this reason, a vegetable that contains just 5 grams of net carbs per serving, although it may seem very low carb, can actually use up a great deal of your daily carb allowance on a Keto diet.
What Are Nightshade Vegetables?
Tomatoes belong to a family of vegetables called nightshades. The nightshade family of plants is known by the Latin name Solanaceae. There are thousands of varieties of nightshade plants, but the vast majority of them aren’t used as food. In fact, some are extremely poisonous - like belladonna (or “deadly nightshade”), which has powerful sedative effects and can be fatal to consume.[*][*]
What all nightshades have in common are the class of compounds they contain called alkaloids. Because of these compounds, some people may not be able to tolerate nightshades in their diet very well.[*]
The alkaloids in nightshades serve as the plants’ natural defense system against pests. They’re extremely bitter in taste, and have some insecticidal properties.[*]
In fact alkaloids from belladonna are even used to make some sedative medications.[*]
But there are also some nightshades that we really love to eat. Don’t worry, these veggies don’t contain enough alkaloids to be toxic. Most people are able to tolerate these particular nightshade veggies in their diet just fine.
Nightshades commonly used as food include:
- Tomatoes: Tomatoes are featured heavily in many cuisines around the world, like Mexican, Italian, French, Spanish, and Greek. They’re also used in sandwiches, and to make various dips, sauces, soups, and casseroles.
- Tomatillos: Tomatillos are small, green cousins of tomatoes. They have a tangy flavor, that makes them an excellent key ingredient in salsa verde (green salsa).
- Potatoes: Potatoes are starchy tuber veggies that can be boiled, fried, baked, or mashed as a side dish for nearly any food. Interestingly enough, sweet potatoes are not nightshades.
- Peppers: All peppers - including bell peppers and all varieties of chili peppers - are nightshades. Milder peppers like bell peppers can be eaten raw or cooked as a vegetable, while hotter peppers can be used to add flavor to dishes. Hot peppers are also used to make hot sauce. Note: black pepper and peppercorns are not nightshades.
- Goji berry: Goji berries, or wolfberries, are tangy, antioxidant-rich fruits that are often added to smoothies.
- Eggplant: Eggplant is a purple-skinned veggie that is used regularly in Mediterranean and Asian cuisine. Thinly-sliced, it fries up nicely for dishes like eggplant parmesan, but it’s also great in stir-fries because it absorbs so much flavor.
Additionally, the adaptogenic supplement ashwagandha is a nightshade, as is tobacco. Also, because peppers are nightshades, seasonings made from peppers - like red chili flakes, paprika, cayenne, and chili powder - are also nightshades.
Fun fact about nightshades: we don’t really know where the term nightshade originated. Some people believe that the term nightshade was originally applied to some of the more toxic members of the Solanaceae family (like belladonna) thanks to their unpleasant side effects, and that the name just stuck. It may also refer to the fact that the flowers of many nightshade plants only bloom at night.
Are Tomatoes Keto Friendly?
So, are tomatoes Keto? They can be perfectly Keto-friendly if you eat the correct serving size.
For instance, a ½ inch thick slice on a sandwich provides just 1 gram of net carbs, but an entire large tomato provides 5 grams of net carbs - a significant chunk.
The carbs in canned tomatoes can also add up pretty fast, so be mindful of this if you use canned tomatoes to make soups or casseroles. A ½ cup serving of canned diced tomatoes contains 4 grams of net carbs.
You’ll also want to be careful with tomato products like ketchup or premade spaghetti sauces. These products often contain added sugars (and many more grams of net carbs than you’d expect), so you’ll want to look for no-sugar-added or Keto-friendly versions. And even then, you’ll still want to check the label.
Are Other Nightshades Keto Friendly?
As you may be able to tell just from looking at the list of edible nightshades, nightshades can be low or high in net carbs. Some nightshades are Keto-friendly, while others should probably be avoided on Keto because they’re too high in net carbs.
Peppers - including bell peppers and hot peppers - are ideal for Keto. A medium bell pepper contains just 4 grams of net carbs, and a 2-inch long jalapeno pepper provides just 1 gram of net carbs.
Eggplants are also Keto-friendly, as long as you’re careful with your portion size. A full-sized medium eggplant clocks in at 16 grams of net carbs, so you may want to split the eggplant across multiple servings to keep the carbs at a reasonable amount for Keto.
Potatoes are, unfortunately, a no-go on Keto - unless you want to use most of your daily net carbs on a small portion. A cup of potato provides 29 grams of net carbs, and a whole medium potato provides 26 grams of net carbs.
In addition, Goji berries should be avoided on a Keto diet. A ½ cup serving of Goji berries contains a whopping 14 grams of net carbs, so they can also quickly use up most of your daily carbs.
Tomatillos, however, are Keto-friendly. A whole tomatillo contains just 1 gram of net carbs.
Who Should Avoid Nightshades?
People with autoimmune disorders, in which the immune system attacks healthy cells, may be particularly sensitive to nightshades. They can have a reaction to nightshades that mirrors an allergic reaction, including skin rash, digestive problems, itching, and congestion.[*][*][*]
Many people with autoimmune diseases have reported improvements in their symptoms after removing these veggies from their diet. However, there hasn’t been a great deal of research on the subject - so most of the evidence for nightshade avoidance to improve autoimmune symptoms comes from anecdotal reports.
Many people without autoimmune diseases also report sensitivities to tomatoes, in particular. They can be a common trigger for heartburn.[*] Most of the evidence for nightshade avoidance to improve autoimmune symptoms comes from anecdotal reports, or from research on the Autoimmune Protocol (AIP) diet, which includes temporarily eliminating nightshades from the diet. [*][*]
If you notice allergy-like symptoms or heartburn after eating tomatoes or other nightshade veggies, you may want to try eliminating them from your diet for a while. You can do this by eliminating the potential trigger food or foods for two weeks, then reintroducing a small serving and monitoring your symptoms. If you have a reaction, then it was likely caused by that food. Try doubling the amount 2-3 days later and see if you have the same reaction. If you don’t have a reaction, you may be able to reintroduce it to your diet.
The nightshade family is a huge family of plants, and it includes some common veggies like tomatoes, potatoes, peppers, and eggplant. Potatoes are too high in carbs for Keto, but tomatoes, peppers, and eggplant can be included on a Keto diet as long as you’re careful with portion sizes.
You can use tomatoes on Keto for pizzas, pasta, salsas, sandwiches, casseroles, soups, salads, and more — and using fresh tomatoes is a great way to avoid added sugars in things like spaghetti sauce and pizza sauce, too. Just remember - serving size is key!