The idea that tomatoes cooked with potatoes are poisonous is a misconception. This belief likely stems from the fact that tomatoes and potatoes both belong to the Solanaceae family, sometimes referred to as the "nightshade" family, and this has led to some confusion.

Here’s the truth:

1. Tomatoes and Potatoes Are Not Poisonous Together

• Tomatoes and potatoes are commonly used together in many recipes (e.g., stews, casseroles, and roasts), and when prepared correctly, they are safe to eat. There is no scientific evidence to suggest that combining these two foods creates any harmful or toxic substances.

2. Nightshade Family and Solanine

• While it is true that both tomatoes and potatoes belong to the nightshade family, only certain parts of the plant (such as potato sprouts or green potatoes) contain high levels of solanine, a natural toxin. Solanine is most concentrated in the skin, sprouts, and green areas of potatoes, and can be toxic in large amounts, but it is not an issue when the potato is properly prepared (peeled, sprout-free, and cooked).

• Tomatoes, on the other hand, contain a small amount of solanine as well, but the levels are very low and not harmful in normal consumption. The green parts of tomato plants (like leaves and stems) are where solanine is concentrated, so it's important not to consume those.

3. Cooking Process

• Cooking both potatoes and tomatoes eliminates much of the potential for toxins (such as solanine) to be harmful, especially when potatoes are peeled and prepared properly. The concern about tomatoes and potatoes being poisonous is more related to consuming raw or improperly prepared potatoes, rather than the combination of the two foods.

Conclusion:

Tomatoes cooked with potatoes are not poisonous. The key to safe consumption lies in properly preparing the potatoes (removing sprouts and green parts) and cooking both ingredients thoroughly. This combination is common in many dishes worldwide and is completely safe when prepared correctly.