The Part You Always Peel and Throw Away Turns Out to Be Rich in Nutrients

Nutrients Related to Muscle Health Found in Onion and Apple Skins
Be Sure to Wash Thoroughly When Eating with the Skin

Generally, most people peel vegetables or fruits before eating them, but it has drawn attention that eating them with their skins can provide additional nutrients. In particular, it has been found that the skins or the areas near the outer surface of certain vegetables and fruits contain components related to muscle health.

For onions, it is easy to remove not only the dry outer skin but also several layers of the fleshy part just inside. However, the outer fleshy layer is rich in quercetin, a type of flavonoid. A study published in the Journal of Agricultural and Food Chemistry in 2011 found that the flavonoid content in the first fleshy layer of an onion was significantly higher than that in either the dry outer skin, the second fleshy layer, or the inner fleshy layers.

There are also human studies investigating the relationship between quercetin and muscle strength. In a randomized, double-blind, controlled trial published in the European Journal of Nutrition in 2025, 26 healthy older adults performed resistance exercises for six weeks while taking 200 mg of quercetin glycoside or a placebo daily. As a result, maximum knee extension strength increased in both groups, but the increase was greater in the quercetin group compared to the placebo group. It has also been found that apple skin contains more ursolic acid, which is related to increased knee strength, than the flesh of the apple.

It is known that eating vegetables or fruits with their skins can provide some additional nutrients. Pixabay

Carrots, cucumbers, eggplants, potatoes, sweet potatoes, and pumpkins can be eaten with their skins if they are thoroughly washed. The skin contains dietary fiber, vitamins, minerals, and antioxidants, so eating it provides extra nutrients and helps reduce food waste. The skin of cucumbers contains dietary fiber and vitamin K, so it is recommended to eat it after washing thoroughly. Eggplant skin contains the antioxidant nasunin. However, the skins of large or old eggplants may be tough, so it is fine to peel them for better texture.

Potatoes and sweet potatoes can also be cooked and eaten with the skin. However, caution is needed if potatoes have turned green or have many sprouts. Potatoes exposed to sunlight may develop increased levels of glycoalkaloids in their skins, green parts, and sprouts. Consuming large amounts of these can cause gastrointestinal or nervous system symptoms, so it is safest to avoid eating potatoes with extensive green areas or a lot of sprouts.

Pumpkins like chestnut pumpkins become soft-skinned when cooked, so after washing they can be steamed or roasted and eaten with the skin. In contrast, pumpkins with thick and tough skins, such as mature pumpkins, are usually peeled. Likewise, tough and hard-to-digest parts such as the dry outer skins of onions and garlic or the husk of corn do not need to be eaten.

Experts emphasize the importance of washing when eating skins. Rubbing the surface well under running water is fundamental, and even vegetables that will be peeled should be washed first. Cutting unwashed vegetables with a knife can transfer soil or microorganisms from the surface to the inside.

This content was produced with the assistance of AI translation services.