The fruit and vegetable skins and cores typically thrown away are packed with dietary fiber, according to new research from King’s College London.
Researchers put 12 of the most common fruits and vegetables to the test: pineapple, watermelon, butternut squash, broccoli, and bell peppers. What they found was “striking.” Skins, peels, seeds, and stalks contained more fiber than the actual fruit.
Their findings suggest that adding more of these commonly discarded parts to meals could increase fiber intake while reducing waste.
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 tons of food is wasted annually, with fresh fruits and vegetables representing 36% of this.
5x times more fiber in skin
Pineapple skin and core had the densest fiber content, at 453.7% more fiber than flesh. It would take about five portions of the fruit to match that figure.
Butternut squash skin and seeds contained 9.25 grams of fiber per 100 grams, nearly one-third of the UK’s recommended daily intake of 30 grams.
Watermelon rind contained 2.10 grams of fiber per 100 grams, approximately the equivalent of a slice of wholemeal bread.
Researchers found that the refuse accounted for 25% and 48% of the produce’s total weight.
Researchers examined whether “root-to-tip” eating, which incorporates discarded edible plant components into meals, could increase fiber intake and reduce food waste.
“Importantly, this is not about encouraging people to eat ‘100g of butternut squash skin and seeds’ to increase fiber 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 fiber intake in a simple and sustainable way.”
Dietary fiber plays an important role in digestive health and reduces the risk of cardiovascular disease, type 2 diabetes, and certain cancers, according to the release.
Consumers prioritize nutrition over sustainability
The researchers acknowledged several limitations: the small selection of produce types that they tested, the methods used, and the need to consider risks associated with consuming skins.
“Future research should also address any unintended consequences which may arise from increased consumption of ‘root-to-tip’ components, including managing exposure to anti-nutritional plant residues which can have adverse health effects if ingested above safe limits,” the authors wrote.
They identified pesticide residues, heavy metals and naturally occurring toxic compounds as potential concerns requiring further investigation. And they didn’t establish whether incorporating skins, seeds, and cores would improve health outcomes.
Researchers stated that they’d had to conduct further research to quantify any increase in dietary fiber intake through ‘root-to-tip’ eating and to investigate associated health outcomes,” the researchers concluded.
According to Gibson, the approach wouldn’t require dramatically changing one’s diet, but rather figuring out how to integrate these skins, seeds, and cores into the food we normally consume.
“This isn’t about perfection,” Gibson said. “And this isn’t about forcing people to eat unpalatable food – it’s about recognizing the nutritional value in components we’ve been conditioned to discard, which is exactly why we trialed the root-to-tip menu at King’s.”
Even small steps, the press release concluded, can have cumulative benefits for the health and the environment.