I've read of several diet plans and books now that claim that naturals sugars are good to eat - while supposedly unnatural / added sugars are not good for you. Can this possibly be true?
First, let's look into the basics of this discussion. There are four main sources of energy that the human body can use - fats, carbohydrates, proteins, and alcohol. Of these, carbohydrates include sugars and starches. Just looking at sugars, there are many types of sugars. To generalize, fructose comes from fruits. Lactose comes from milks. Sucrose comes from places like cane sugar. Sucrose - refined - then gets added to all sorts of products like peanut butter, ketchup, salad dressing, because our modern world has created us all to crave sugar in every thing food item we eat.
So are there really differences in whether you ingest your sugar in the form of fructose, lactose, or sucrose? The answer seems to be NO!! All of these very basic forms of sugar are still sugar. They are still handled by your body as sugar, at the rate of about 50 calories for every tablespoon worth of sugar you ingest. This doesn't somehow miraculously vanish if you happen to be eating fructose sugar that's part of an apple.
My guess is that these various diet plans don't want to scare away their members. They are focusing on the "worst sugars". If you eat a pile of raw sugar in the form of a candy bar, that has no benefit at all. If you eat an apple and take in 13g of fructose sugar, sure you're ingesting 61 calories, but at least you got some apple nutrients into you. So the diet is "cutting its losses" and encouraging you to eat apples and pears and other fruits in the hope you will move on to more healthy items.
While this approach is understandable, it also leads to unhealthy practices. I know someone who ate apples with peanut butter (laden with sugar) all day long because he figured it was "healthy". When his doctor realized he was doing that, the doctor told him to cut it out. The sugar he was taking in was causing him a lot of harm. Yes certainly it was better than eating candy bars - but at some point in life we need to have higher "bars to surpass" than that of eating candy bars all day long.
So the bottom line here is that ALL sugar counts. ALL sugar damages your body and your teeth. Yes of course if you currently are in a state where all you eat is candy bars all day long, you need to move up the scale and move over to real food. But that should be a temporary transition, and once you get off that candy bar habit you should be moving towards HEALTHY foods that support your long term goals.