There’s a lot of talk about sugar these days, and broadly, there are three competing schools of thought:

  1. Sugars naturally occurring in foods like fruit and honey are okay to eat, but added sugars (sugars that are removed from their original source and added to foods) often found in processed foods are unhealthy and should be avoided.
  2. All sugars are unhealthy and should be avoided.
  3. Sugars of any kind aren’t unhealthy and shouldn’t be avoided or even restricted.

Each of these philosophies are wrong. 

Once eaten, all forms of carbohydrate, including all sugars, are either metabolized into glucose (a simple sugar) or are left undigested, serving as dietary fiber. This is equally true of the monosaccharides (“simple sugars”) in a candy bar as it is of the polysaccharides (“complex sugars”) in vegetables.

Why, then, does research show that regularly eating large amounts of added sugars like sucrose and high-fructose corn syrup is associated with an increased risk of heart disease, type 2 diabetes, and being overweight, whereas regularly eating large amounts of vegetables is associated with improved health and longevity?

Some people say it’s mostly the speed with which the body breaks sugars down into glucose—simple sugars are processed quickly and spike blood glucose levels whereas complex ones take longer to digest and produce smaller elevations in blood sugar levels—but such an explanation can’t explain the magnitude of the health effects.

That is, while repeatedly mushrooming blood glucose levels isn’t “healthy” per se, this mechanism alone couldn’t produce the disastrous health outcomes so often seen among people whose diets are rich in added sugars.

The actual culprit is twofold:

  1. Many foods with added sugars don’t have much in the way of essential nutrients, and studies show that eating a lot of these foods can lead to nutritional deficiencies that in turn can lead to disease and dysfunction.
  2. Diets rich in added sugars generally provide more calories than low-sugar ones and thus are associated with increased body fatness and its concomitant health risks.

Therefore, to formulate a sensible answer to the question of how much sugar we should eat, we must first distinguish between micronutrient-rich sources of sugar like fruit and unwholesome sources like donuts. 

Practically speaking, nobody gets fat and sick by eating too many apples, so go ahead and enjoy a couple of servings of fruit every day. 

Now, as for the type of sugar in donuts—added sugar—the “dose makes the poison” principle applies. Up to a point, added sugar is harmless—especially if you have a healthy body composition and exercise regularly—but exceed that limit too often, and you’ll likely damage your health and body composition.

That threshold will vary from person to person, but the World Health Organization has providable reasonable universal guidance. They recommend that added sugars comprise no more than 10% of daily calories (roughly 50 grams or 12 teaspoons for a 2,000-calorie diet) to preserve health and no more than 5% of daily calories to further enhance health.