Peels, stalks and seeds pack more fiber than what people usually eat

Clinical takeaway: For budget and health conscious patients looking to improve their diet, remind them that cauliflower cores and leaves, broccoli stalks, and bell pepper stalks can go into stir-fries and soups instead of the trash. 

More than 90% of US women and 97% of men fall short of recommended fiber intakes, leaving most patients with a fiber deficit. Peels, stalks, and seeds seem like an obvious place to find more, as these often fiber-rich plant parts are frequently discarded.

Public food composition databases leave out most of the parts cooks cut away, and the fiber values that do exist often come from manufacturing studies reported on a dry-weight basis, offering little insight into what ends up on a plate. This laboratory analysis puts numbers on the discarded parts of common produce and compares them with the portions people typically eat, extending the evidence from the factory to the kitchen.

In 10 of 12 produce types, the parts cooks typically discard contained more fiber than the parts people eat. Pineapple skin and core contained more than five times as much fiber as the flesh, while butternut squash skin and seeds had the highest fiber content overall. Broccoli stalks were an exception, containing less fiber than florets, and fennel cores and outer layers also lagged behind.

Bell pepper stalks and seeds, kiwi skin, and cauliflower cores and leaves each contained at least twice as much fiber as the parts people typically eat. The discarded portions accounted for roughly one-quarter to nearly one-half of each item’s weight, meaning a substantial share is routinely cut away.

Participants in the focus groups viewed nutritional benefits, particularly fiber, as a stronger motivator than sustainability for eating these parts. Some expressed discomfort with eating skins and stalks, while others raised concerns about digestibility.

Researchers measured fiber in the discarded parts of 12 raw fruits and vegetables, testing one specimen of each in duplicate, and compared the results with database values for the parts people typically eat. No foods were tested after cooking. Six focus groups involving 40 university staff and students explored attitudes toward consuming the discarded parts.

The next step is testing cooked produce, since this analysis measured only raw parts and cooking can alter how fiber behaves in the gut. Exposure is a second challenge: retained peels may carry higher pesticide residues, and pineapple skin contains cyanogenic compounds. Washing, cooking, and blanching can reduce exposure, but the extent depends on the preparation method and plant part, and the investigators say that remains to be determined.

“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,” said Balazs Bajka, a nutritional sciences lecturer at King’s College London who led the laboratory fiber testing. “Emerging research also suggests that consuming a wider variety of fiber sources may help maximize the health benefits associated with dietary fiber.” 

Source: Browne G, et al. (2026 Oct 30) Int J Food Sci Nutr. The dietary fibre content of fruit and vegetable kitchen preparation waste and UK consumers’ dietary fibre-related attitudes regarding its consumption