Are Green Tomatoes Poisonous?

It’s that time of year again. Nights are getting cold, too cold for your tomatoes to mature on the vine, so you bring them in and put them in a warm spot. Some do continue to ripen, soon turning red, but others remain resolutely green. Can you still eat them?

That’s when you start to hear two different stories. 

“Yes, go ahead and cook them up,” says one side. After all, recipes for green tomatoes abound: chutneys, ketchups, jams, even green tomato bread. And remember the film Fried Green Tomatoes?

“No, don’t!” says another, “They’re poisonous!”

So, what gives? Are they toxic or edible? 

The answer to both is … yes! 

Green tomatoes: Toxic, But Not Deadly

Most plants contain toxins and that includes your ordinary, everyday vegetables and herbs. People have gotten ill by overeating spinach and carrots, for example. Plants use toxins to protect themselves from predation. But, as omnivores, we humans are pretty good at digesting plant poisons: we can absorb and break down most toxins as long as they’re not too concentrated. So, we can consume a lot of plants and plant-derived foods that other animals (including our dogs, cats and other pets) can’t: onions, coffee, chocolate, walnuts, garlic, etc.

The Toxicity of Tomatoes

As for tomatoes (Solanum lycopersicum), they’re in the Solanaceae family, renowned for its poisonous plants: deadly nightshade, mandrake, henbane, datura and more. 

All Solanaceae all contain various toxic alkaloids, of which solanine, atropine and nicotine are the best known. Tomatoes, although they contain a considerable amount of solanine and some atropine, are richest in a less toxic alkaloid called tomatine. 

More Mature, Less Toxic

However, the level of toxic alkaloids is lowest in mature fruits. After all, the plant wants to protect its immature green fruits from predation so they can mature safely and produce viable seeds, so it makes sense green fruits should be toxic, yet mature fruits were designed to be eaten by animals. That’s how fruiting plants reproduce. As the fruit is consumed by a bird, reptile or mammal, its seeds are either dropped on the ground in a new spot or pass intact through the digestive system unharmed, so the animal partner disseminates the seeds far and wide it its feces. 

If tomatoes and other fruits turn bright colors at maturity, it’s an invitation to frugivorous animals: “come and eat me!” the fruit is saying.

As a result, the toxicity of many fruits in the Solanaceae group (tomatoes, eggplants, peppers, ground cherries, etc.) drops to nearly zero as they reach maturity. And that’s why most people can eat ripe tomatoes with impunity.

But what about green ones? 

The Green Tomato Situation

The closer tomatoes are to ripeness, the less toxic they will be. And the tastier. (Alkaloids are very bitter.) That’s why cooks who know what they’re doing use fairly mature green tomatoes in their recipes: not the hard, dark green balls that are young tomatoes, but full-size fruits starting to turn a paler green, a sign they’re ripening. They’re not as concerned about toxicity (I suspect most cooks don’t even know they are somewhat toxic) as about flavor. Those rock hard, very immature tomatoes have a nasty taste and hiding their bitterness takes a lot of inventive food preparation. Also, many recipes that include very immature green tomatoes seriously dilute them with other ingredients. There’s more flour than green tomato in green tomato bread, for example!

Do note that cooking does not destroy alkaloids (it does destroy other toxic compounds), although they do dissolve in water to a certain degree, so if you boil green tomatoes and drain away the cooking water, that would reduce their toxicity. Even so, most recipes involve them being “cooked in their own juices”: nothing is drained away. Under that circumstance, a cooked green tomato will be just as rich in alkaloids as a raw one.

Whatever Doesn’t Kill You, Gives You Gas?

Still, even hard-as-nails green tomatoes won’t kill you. Their toxicity is quite limited. At worst, if you eat a few, depending on your sensitivity to tomatine and solanine, you may experience a bit of gastrointestinal distress. And indeed, some people seem so highly sensitive to tomato alkaloids, they may not even be able to eat mature tomatoes even though their alkaloid level is very low. So, if green tomatoes make you feel queasy, don’t eat them! 

And don’t eat bowlfuls of green tomatoes, either. That could send you to the hospital. One estimate suggests an average-sized man would have to eat around 300 green tomatoes to reach a lethal dose. But discomfort will set in at much less than that. Moderation in all things is best!

A Few Don’ts

• Don’t feed green tomatoes to your pets. Cats and especially dogs are much more sensitive to solanine and tomatine than humans.
• Don’t eat potato fruits. Potatoes are related to tomatoes and indeed, their fruits look like small green tomatoes, but are much more toxic.
• Don’t eat green tomatoes in large quantities or if you have a hard time digesting tomatoes.
• If a green tomato recipe tastes bitter to you, the cook probably used very immature tomatoes that may be fairly rich in toxins, so don’t eat a lot of it.

So, are green tomatoes poisonous? Yes, but only a slightly, not enough to do any harm in most cases.