The next time you peel a kiwi or trim a head of broccoli, you might want to think twice before tossing the scraps. Some of the parts we routinely throw away contain surprising amounts of dietary fiber.
Researchers at King's College London examined 12 common fruits and vegetables and found that the parts typically discarded contained more fiber than the portions we usually eat in 10 of the 12 cases. Published in the International Journal of Food Sciences and Nutrition, the study suggests we may be overlooking an easy way to get more fiber from the foods we already buy.
Some of the differences were striking. Kiwi skin contained nearly three times as much fiber per 100 grams as the flesh, while the skin, seeds and stringy insides of butternut squash contained more than four times as much as the portion we usually eat.
Pineapple skin and core, measured together, contained more than five times as much fiber as the flesh. However, that doesn't mean you should start eating pineapple skin. Some discarded plant parts may contain compounds or residues that raise food safety concerns, and the researchers say more work is needed to understand how to use them safely.
Not everything followed the same pattern. Broccoli florets actually contained more fiber than the stalks, but that doesn't make the stalks worthless. They're still a source of fiber and can be chopped into stir-fries, soups or other dishes instead of being thrown away.
The findings are especially relevant because most Americans don't get enough fiber. It's important for healthy digestion, and diets rich in fiber are associated with a lower risk of heart disease, type 2 diabetes and certain other chronic conditions.
Getting more fiber doesn't always require buying different foods, either. Leaving the washed skin on a kiwi, cooking broccoli stalks or roasting properly prepared squash seeds are simple ways to use more of the produce you already have.
Of course, just because something is nutritious doesn't mean everyone wants to eat it. When the researchers spoke with 40 university staff members and students, some expressed concerns about the taste, texture or digestibility of produce scraps. But many said knowing the nutritional benefits would make them more willing to give these overlooked parts a try.
The study does have limitations. Researchers tested only 12 types of produce, examining one specimen of each, and measured fiber in raw samples. They also didn't test whether eating more of these parts would actually improve people's health or increase their daily fiber intake.
And not every peel, seed or stalk belongs on your plate. Some require particular preparation, while others may be better left uneaten.
Still, the research offers a different way to think about food waste. That pile of scraps on your cutting board might contain more nutritional value than you'd expect.
The study was supported by the One King's Impact Fund at King's College London.