Did you know that onions contain sugar?
According to Wikipedia, "Most onion cultivars are about 89% water, 4% sugar, 1% protein, 2% fibre and 0.1% fat." The USDA reports that a serving of onions contains 4.7 grams of sugar. The following infographic by ZocDoc reports that a cup of onions contains 7 grams.
Google has added a search option where you can now select a vegetable to learn how much sugar is in a serving.