> [citation needed]

I don't have a citation either, but google search reveals the following points:

1) One serving, or one medium apple, provides about 95 calories, 0 gram fat, 1 gram protein, 25 grams carbohydrate, 19 grams sugar (naturally occurring), and 3 grams fiber. 2) Recommended amount of consumed sugar for an adult is 30 grams per day. 3) You can also find a lot of citations how increased sugar consumption increases chances of diabetes.

So two apples already gets you above the recommended amount. An apple is basically 80% sugar in terms of calories: 19 * 4 / 95 = ~80%