According to About.com, apples have 10.4 grams of sugar per 100 grams of fruit, oranges have 9.3 grams of sugar per 100 grams of fruit and tomatoes have 2.6 grams of sugar per 100 grams of fruit. Of the three, tomatoes have by far the lowest amount of sugar.
Apples, tomatoes and oranges are naturally low in calories and are healthy food choices. All are very low in fat, cholesterol-free and excellent sources of dietary fiber. All are very low in sodium and are sources of iron and vitamin C. In addition, tomatoes provide vitamins A and B6 and are high in potassium, manganese and phosphorous.