Researchers at King’s College London found that commonly discarded portions of 10 out of 12 fruits and vegetables contained more dietary fiber than the parts usually consumed, suggesting simple food preparation changes could improve nutrition while reducing waste.
By yourNEWS Media Newsroom
LONDON — Fruit and vegetable scraps routinely discarded during meal preparation may contain substantially more dietary fiber than the portions people typically eat, according to new research from King’s College London that identifies potential nutritional benefits in everything from pineapple skins to squash seeds.
The study, published Oct. 29 in the peer-reviewed International Journal of Food Sciences and Nutrition, examined 12 types of fresh produce and found that peels, skins, stalks, seeds and other commonly discarded portions contained more fiber per 100 grams than conventionally consumed portions in 10 of the 12 cases.
Researchers identified particularly large differences in pineapple, butternut squash and bell peppers, suggesting that consumers may be throwing away valuable sources of dietary fiber while struggling to meet recommended daily intake levels.
Pineapple skin and core contained 453.7% more fiber than the fruit’s flesh, equivalent to approximately 5.5 times the concentration. Butternut squash skin and seeds provided 9.25 grams of fiber per 100 grams, approaching one-third of the United Kingdom’s recommended daily intake of 30 grams.
Watermelon rind contained 2.10 grams of fiber per 100 grams, approximately equivalent to the amount found in a slice of whole-grain bread.
Bell pepper seeds and membranes also contained substantially higher concentrations of fiber than the flesh typically used in cooking.
Broccoli was among the exceptions, with its stalks containing 28.4% less fiber than the florets.
The researchers said the findings challenge common food preparation practices that remove potentially nutritious portions of produce before cooking.
In an Oct. 30 announcement from King’s College London, project leader Dr. Rachel Gibson, a reader in nutrition and dietetics, described the differences as substantial.
“The variation in fibre content between the parts of the food we consume and that most throw away was striking,” Gibson said.
“The ‘root-to-tip’ components in our study represented between 25% and 48% of the total weight of the produce. That means people are discarding a significant portion of the produce we buy. And these are parts of the plant that could help address our dietary fibre deficit.”
The study examined beetroot, bell peppers, broccoli, butternut squash, cauliflower, celeriac, curly kale, fennel, kiwi fruit, leeks, pineapple and watermelon.
Researchers measured the fiber content of raw produce components using laboratory analysis and compared concentrations between parts normally eaten and those usually discarded.
The team also examined consumers’ willingness to incorporate overlooked ingredients into meals, an approach known as root-to-tip eating.
The findings are significant because dietary fiber plays an important role in digestive health, blood sugar regulation and cardiovascular function.
Fiber supports normal bowel movements and helps nourish beneficial intestinal bacteria. Higher dietary fiber consumption is also associated with reduced risks of cardiovascular disease, type 2 diabetes and certain cancers.
Despite those benefits, many adults consume substantially less fiber than recommended.
In the United Kingdom, average adult fiber intake is approximately 16.4 grams daily, and only 4% of adults meet the recommended minimum of 30 grams.
American dietary patterns reflect a similar shortfall, with average intake around 16 grams daily, compared with commonly recommended amounts of approximately 25 to 38 grams depending on age, sex and other factors.
Researchers suggested that making greater use of produce already purchased could help consumers increase fiber intake without substantially changing their diets or spending more money on specialized products.
Dr. Balazs Bajka, senior lecturer in nutritional sciences at King’s College London, led the laboratory testing.
“Importantly, this is not about encouraging people to eat ‘100g of butternut squash skin and seeds’ to increase fibre intake,” Bajka said.
“Rather, by making better use of the often-overlooked parts of fruits and vegetables as part of everyday meals, we have an opportunity to increase dietary fibre intake in a simple and sustainable way.”
The project also examined whether consumers would accept dishes incorporating ingredients they normally discard.
Before introducing a root-to-tip menu at university dining facilities, researchers conducted focus groups involving 40 staff members and students.
Participants identified several obstacles, including discomfort with eating unfamiliar produce parts, concerns about digestibility and uncertainty about nutritional information.
Some participants also expressed difficulty distinguishing credible dietary guidance from information circulating on social media.
However, researchers found that participants were more motivated by potential nutritional benefits than by environmental concerns.
Georgia Browne, a research assistant at King’s College London and lead author of the study, said the response provided insight into how dietary changes might be encouraged.
“Interestingly, participants viewed nutritional benefits – particularly fibre content – as a stronger motivator than environmental sustainability when considering whether to adopt ‘root-to-tip’ eating,” Browne said.
The university subsequently introduced dishes using more complete portions of fruits and vegetables through its dining facilities.
The project explored how professional kitchens could incorporate ingredients such as vegetable stalks, peels and seeds into meals without requiring consumers to make substantial changes to their eating habits.
Researchers suggested that households could adopt similar practices by leaving kiwi skins intact, using broccoli stalks in stir-fries or incorporating bell pepper seeds into prepared dishes.
Squash seeds can also be roasted, while certain vegetable stalks can be added to soups, stews and other cooked meals.
Pineapple skins require additional preparation because their tough, spiky surfaces can be unpleasant to eat and may cause irritation. They are better suited to appropriately prepared or cooked applications rather than being consumed raw.
Not every discarded plant component is safe or suitable for consumption, and researchers emphasized the importance of appropriate food handling and preparation.
The study did not establish that all peels, rinds or seeds should be eaten.
Its measurements involved raw produce, meaning cooking, processing and other preparation methods could influence fiber concentrations, texture and digestibility.
The analysis was also limited to 12 produce types, and the laboratory work involved a small number of specimens. The findings therefore require further research before they can be generalized across all fruits and vegetables.
Researchers did not conduct a long-term clinical trial demonstrating that people who consume additional produce scraps experience measurable improvements in health outcomes.
Instead, the study established that many commonly discarded components are potentially valuable sources of dietary fiber.
The nutritional findings also have implications for food waste.
According to King’s College London, approximately 10 million metric tons of food are wasted annually in the United Kingdom, with fresh fruits and vegetables accounting for 36% of that total.
In the United States, estimates from food waste organizations indicate that tens of millions of tons of food are discarded annually, including substantial quantities of produce.
Because consumers frequently purchase fruits and vegetables by weight, discarded peels, stalks and seeds also represent food that has already been paid for.
The researchers suggested that restaurants, food manufacturers and institutional kitchens could achieve larger reductions in waste by reconsidering how these ingredients are handled.
Such changes could reduce the volume of edible food discarded during commercial preparation while creating opportunities to increase the fiber content of meals.
However, broader adoption would require attention to food safety, consumer preferences, preparation techniques and the practical costs of processing less familiar ingredients.
Gibson emphasized that the approach is intended to encourage manageable changes rather than impose rigid dietary requirements.
“This isn’t about perfection and this isn’t about forcing people to eat unpalatable food – it’s about recognising the nutritional value in components we’ve been conditioned to discard,” she said.
The research team plans to continue studying how root-to-tip eating can be introduced safely and effectively across different populations and food service settings.
For consumers, the findings suggest that increasing dietary fiber may not always require purchasing additional foods or supplements.
In some cases, a meaningful portion of the fiber already purchased with fresh produce may be found in parts that would otherwise end up in the trash.
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