Claude reads the sentence into items and amounts. Every gram comes from Open Food Facts or USDA FoodData Central — the model is not given anywhere to put a nutrient, so it cannot supply one. Where a database has no value the field stays empty rather than being estimated.
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Totals roll into the daily record at the end of each entry. Added sugar is only totalled when every entry that day has a value for it — a partial sum would read as a whole day and be silently low.