Use an absolute difference when the comparison baseline is zero

Relative percentage change divides by the baseline amount. If that baseline is zero, the usual formula is undefined. A food comparison should say so and report a meaningful absolute difference instead of forcing a percentage into the result.

Follow a simple hypothetical example

Imagine two records for the same nutrient and the same food quantity. Record A says 0 g and record B says 2 g. Subtracting the displayed amounts gives a difference of 2 g. Calculating an increase relative to A would require 2 ÷ 0 × 100, which has no defined result.

Calling that a 100% increase is incorrect. A 100% increase means doubling the baseline, and doubling zero remains zero. Describing the result as “infinitely more” is also unhelpful for a shopping comparison because it suggests a quantitative conclusion the calculation does not supply.

Check whether the zero is exact

Nutrition zeros can involve rounding. The FDA trans-fat guidance gives a specific example in which a declared zero can represent an amount below a threshold. Do not assume the same threshold applies to every nutrient.

Consequently, even a reversed calculation such as “A is 100% lower than B” can overstate what is known about the underlying food when A's zero is only a printed declaration. A narrower description is “the displayed values differ by 2 g on this basis.”

Choose an output that preserves the uncertainty

• Display the two original values and their units.
• Show the absolute difference based on those values.
• Mark relative change as unavailable because the baseline is zero.
• Retain any rounding or less-than wording from the original source.

Do not replace zero with a tiny invented number merely to make a spreadsheet formula return a percentage. That technique can generate an enormous figure determined mostly by your invented denominator.

Keep missing values separate

A blank field is not the same as a zero declaration. If a nutrient is absent from the available record, mark it unavailable and postpone that comparison. The appropriate remedy is better source information, not a default zero.

This approach produces a useful, reviewable result even when a relative percentage is impossible. It also prevents an ordinary data limitation from being turned into a dramatic nutritional claim.