One serving against a day's fiber
The Dietary Reference Intakes set an Adequate Intake for total fiber of 25 g a day for women aged 19 to 50 and 38 g for men of the same ages. Measured against those, the 2.3 g in a 1 large piece/slice serving of cake or cupcake, chocolate, no icing is 9% of the first and 6% of the second. US food labels use a single Daily Value of 28 g instead, which puts this serving at 8%.
Calorie for calorie, the figure is 0.8 g of fiber per 100 kcal (this serving is 303 kcal). Among the 110 packaged with USDA energy data here that is 58th, and 820th across all 957. The intakes above were derived from 14 g of fiber per 1,000 kcal, or 1.4 g per 100 kcal, so this food sits below the ratio a whole day of eating is meant to reach.
Getting all 25 g from cake or cupcake, chocolate, no icing alone would take 11 servings, and 38 g would take 17. Most days reach the target through several different sources.
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