Kiwi skins and squash seeds deliver 30-150% more fiber than flesh across tested produce

New Scientist coverage of fiber measurements in produce waste streams rests on compositional analyses performed at multiple food labs. Researchers weighed and extracted fiber from matched samples of skin, seeds, and flesh using AOAC enzymatic-gravimetric methods on 12 common items. The design compared within-plant fractions rather than across diets, isolating the contribution of the usually discarded tissues.

These data align with earlier work in Food Chemistry (2019) on apple and pear peels and a 2022 Journal of Agricultural and Food Chemistry study on cucurbit seeds, both reporting elevated total and insoluble fiber in outer layers. The pattern reflects plant anatomy: structural polysaccharides concentrate in epidermal and seed-coat tissues to deter herbivores and resist desiccation. Public-health modeling suggests that routine inclusion of well-washed skins could close 10-15% of the average adult fiber gap without added cost or volume.

Limitations include the absence of human feeding trials measuring actual absorption or gut-microbiome shifts after chronic skin consumption. Larger RCTs that randomize participants to skin-inclusive versus peeled diets for 12 weeks, tracking fecal fiber output and cardiometabolic markers, would strengthen causal claims. Regulatory guidance on safe washing protocols for pesticide residues would also be required before broad recommendations.