Most of us routinely discard the peels, skins, stalks, and seeds of fruits and vegetables at mealtime. But new research from King's College London suggests these scraps could be a valuable – and overlooked – source of dietary fibre, offering potential benefits for both public health and the environment.
The study, published today in the peer-reviewed International Journal of Food Sciences and Nutrition , analysed 12 common types of fresh produce in the UK.
It found that 'root-to-tip' components – the parts typically thrown away, such as peels, skins, and stalks – contained significantly higher levels of dietary fibre than the portions we normally eat in 10 out of 12 cases.
Health and waste, a double crisis
Globally, dietary fibre intake falls short of recommendations in most developed nations, whilst food waste has reached crisis proportions. The United Nations has set ambitious Sustainable Development Goals to address both issues .
In the UK alone, only 4% of British adults meet the recommended minimum daily intake of 30g of dietary fibre, consuming an average of just 16.4g per day. At the same time, approximately 10 million tonnes of food is wasted annually, with fresh fruits and vegetables representing 36% of this.
Dietary fibre is particularly important. It plays a crucial role in digestive health, helps reduce the risk of type two diabetes and heart disease, and promotes feelings of fullness. It can reduce the risk of cardiovascular disease, certain cancers, and premature mortality.
Up to five times more fibre in the waste
The study, which was carried out by an extensive team of experts from across King's College London's Department of Nutritional Sciences and King's Food, examined produce commonly used in foodservice settings. This included butternut squash, bell peppers, broccoli, kiwi fruit, pineapple, and watermelon. In the laboratory analysis, the team measured the total dietary fibre content of both the 'root-to-tip' components (peels, skins, seeds, stalks) and the parts typically consumed.
The key findings showed that in 10 of the 12 produce types analysed, 'root-to-tip' components contained more fibre than commonly consumed parts.
For example:
- The watermelon rind contained 2.10g of fibre per 100g – roughly equivalent to the fibre in a slice of wholemeal bread.
- Butternut squash skin and seeds contained 9.25g per 100g – nearly as much fibre as a bowl of bran flakes. To put this in perspective, just 100g of butternut squash skin and seeds (about the size of a small apple) could provide nearly one-third of your daily recommended fibre intake.
- Pineapple skin and core contained 453.7% (five times) more fibre than the flesh. Eating just the skin and core from a pineapple could provide as much fibre as eating five portions of the flesh alone.
- However, broccoli stalks contained 28.4% less fibre than the florets we typically eat—so in this case, most people are already eating the more fibre-rich part.
"The variation in fibre content between the parts of the food we consume and that most throw away was striking," says project lead, Dr Rachel Gibson, a Reader in Nutrition & Dietetics, from the Department of Nutritional Sciences at King's College London.
"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.
"This isn't just a nutritional loss, it's also a financial one; you're effectively throwing away a substantial portion of what you've paid for."
Dr Balazs Bajka, Senior Lecturer in Nutritional Sciences, who lead the laboratory fibre testing in the study adds: "Importantly, this is not about encouraging people to eat '100g of butternut squash skin and seeds' to increase fibre intake.
"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. Emerging research also suggests that consuming a wider variety of fibre sources may help maximise the health benefits associated with dietary fibre."
The proof is in the (fibrous) pudding
To understand how people might begin to start incorporating these foods into their diet and gain a better understanding of people's attitudes towards them, the researchers introduced a 'root-to-tip' menu at King's College London .
Before it was launched, they tested the concept on a focus group of 40 university staff and students.
Feedback from participants revealed important barriers to root-to-tip eating:
- A "mental discomfort" about eating these items.
- Concerns about digestibility.
- A lack of nutritional information online, particularly on social media, where trends rapidly change and credibility is unclear.
"Interestingly, participants viewed nutritional benefits – particularly fibre content – as a stronger motivator than environmental sustainability when considering whether to adopt 'root-to-tip' eating," lead author Georgia Browne (Research Assistant, King's College London) adds.
Caterers and manufacturers could make an impact
Whilst the researchers emphasise that 'root-to-tip' eating doesn't require dramatic dietary changes, just simple modifications to food preparation, they state that changes are required at the food manufacturing stage or at the places we go to eat out for tangible results on health at a population level.
"At home we can do things such as leaving skins on kiwi fruit, using broccoli stalks in stir-fries, or incorporating bell pepper seeds into dishes. However, for real change to reduce food waste and improve fibre intake at scale, it would be great to see caterers and food manufacturers exploring what fruit and vegetable waste is generated and looking at ways to use it to enhance the healthiness of meals," adds Dr Gibson, who specialises in both workplace, diet and health; as well as dietary patterns and health.
The future of sustainable eating
Whilst the research provides valuable insights, several limitations should be noted. For example, studying only 12 types of produce – each measured for fibre content when raw (so cooking methods could alter fibre content and digestibility).
The researchers hope that future studies will look to better understand how 'root-to-tip' eating can be practically and safely implemented across diverse populations and settings.
Concluding, Dr Gibson says: "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, which is exactly why we trialled the root-to-tip menu at King's.
"Even small steps towards using more of the plant can have cumulative benefits for health and the environment."
