Parts of fruits and vegetables that are usually discarded may contain more fiber than those that reach the plate. A study from King’s College London concludes that taking advantage of peels, seeds and stems can simultaneously help improve diet and reduce food waste.
The peels, seeds, stems, and other parts of fruits and vegetables that are habitually thrown away can be an important source of dietary fiber. This is the conclusion of a study conducted by researchers at King’s College London in the United Kingdom, which analyzed 12 types of fruit and vegetable products and identified higher fiber concentrations in the parts normally discarded in 10 of the 12 cases.
Published in the International Journal of Food Sciences and Nutrition, the work advocates a dietary approach called “root-to-tip” (from root to tip), which involves making a greater proportion of plants available in meal preparation. The proposal aims to address two problems: the insufficiency of dietary fiber intake and food waste, especially of fruits and vegetables.
In the United Kingdom, only 4% of adults meet the recommended minimum daily intake of 30 grams of fiber, with an average consumption of 16.4 grams. At the same time, about 10 million tonnes of food are wasted annually, of which 36% are fresh fruits and vegetables.
Dietary fiber plays an important role in digestive health and satiety, and is also associated with reduced risk of type 2 diabetes, cardiovascular diseases, and some types of cancer.
Up to five times more fiber in discarded parts
Among the examples identified by the researchers is the watermelon rind, which contains 2.10 grams of fiber per 100 grams, an amount similar to that found in a slice of wholemeal bread.
In the case of baby pumpkin, the rind and seeds present 9.25 grams of fiber per 100 grams. Meanwhile the rind and core of the pineapple contain 453.7% more fiber than the flesh, equivalent to almost five times more. Not all results point in the same direction, however: broccoli stems contain 28.4% less fiber than the florets typically consumed.
The parts normally discarded represent between 25% and 48% of the total weight of the products analyzed. For Rachel Gibson, the project’s lead investigator and a specialist in Nutrition and Dietetics, this difference represents an opportunity that is being wasted.
“The variation in fiber content between the parts of the foods we eat and those that most people throw away was surprising,” says the researcher. And she adds: “This is not only a nutritional loss, it is also a financial loss: we are, in effect, throwing away a substantial part of what we paid for.”
Balazs Bajka, a senior Professor of Nutrition Science and head of the fiber analyses in the laboratory, notes that the aim is not to encourage the isolated consumption of large quantities of peels or seeds, but to integrate them more regularly into meals.
“By making better use of the parts of fruits and vegetables that are often forgotten in day-to-day meals, we have the opportunity to increase dietary fiber intake in a simple and sustainable way,” he explains.
Changing habits also requires changes in the food industry
To understand how this approach could be applied, the team developed a “root-to-tip” menu at King’s College London, after testing the concept with a group of 40 staff and university students.
The experience helped identify some obstacles to adopting these habits, namely the discomfort in consuming parts of foods that are usually rejected, doubts about digestibility, and the lack of credible nutritional information available on the internet and on social networks.
Georgia Browne, the study’s first author and a research assistant at King’s College London, also highlights a finding from the experience: “Interestingly, participants regarded the nutritional benefits, especially the fiber content, as a stronger incentive than environmental sustainability when considering adopting a diet that uses all parts of foods.”
At home, some changes may include consuming kiwifruit with the skin, using broccoli stems in stir-fries, or incorporating bell pepper seeds into meals. However, the researchers believe that catering and the food industry could play a decisive role in expanding the impact of this practice.
“At home, we can do things like leaving the skin on kiwifruit, using broccoli stems in stir-fries, or incorporating bell pepper seeds into dishes. However, to achieve an effective change in reducing food waste and improving fiber intake at the population level, it would be important for catering services and food manufacturers to analyze the fruit and vegetable waste they generate and seek ways to use it to make meals healthier,” argues Rachel Gibson.
The researchers acknowledge, however, some limitations of the work. The study covered only 12 types of fruits and vegetables, and the analyses were conducted on raw foods, so cooking methods may alter fiber content and digestibility.
The team hopes that future investigations will assess how this approach can be practically and safely applied in different populations and contexts.
“This is not about seeking perfection or forcing people to eat unappetizing foods. It is about recognizing the nutritional value of components we have become accustomed to discarding, and that is precisely why we tested the ‘root-to-tip’ menu at King’s,” concludes Rachel Gibson. “Even small steps toward leveraging a larger part of the plant can bring cumulative benefits for health and for the environment.”
