It is true that fruit is good for you and that your body can handle a certain amount of fructose without any harmful effects.
However, research shows that fructose, the natural sugar found in fruit, is severely detrimental to health if taken in large quantities.
Fructose is something our body has not been evolved to deal with in the quantities it is in our diet these days. An apple a day would not be a problem even to those who are somewhat Fructose intolerant, but added to fructose from the ketchup, the sweetening agent in yogurt and can of soup and so on, it can easily become excessive.
Health researchers at the University of Southern California have discovered that the fructose that occurs naturally in fruit, increases triglycerides levels, effects uric acid levels, results in ‘fatty liver’ and also abdominal fat. It can also lead to insulin resistance. It also leaves people hungrier, and hence more gluttonous, than glucose, and is an important contributor to the growing prevalence of obesity. Of course glucose in excess is itself a cause of obesity.
In addition to contributing to many metabolic abnormalities, fructose has been reported to affect homeostasis of numerous trace elements. It increases iron absorption, decreases the activity of the copper enzyme superoxide dismutase (SOD) and reduces the concentration of serum and hepatatic copper. Fructose also increases albumin which binds to testosterone and renders it inert.
Fructose is chemically similar to glucose but it tastes significantly sweeter and is processed differently by the body. While cells throughout the body regulate the amount of glucose they use to make energy, fructose is generally metabolized in the liver. It also does not drive the body to produce insulin, a hormone that plays an important role in curbing appetite. All this is to be expected as fruit was not a major part of the diet of our ancestors, and whatever little fruit they found would generally have had more seed and little pulp, while the fruit we consume today are bred to be the other way.
Within limits the natural fructose in fruits isn’t thought to be a health concern because the fruit’s fibre and cellular structure slows the rate at which it hits the liver. However, as the adage goes, sugar (which is mainly glucose) feeds cancer and cancer cells find fructose even more metabolisable than glucose thus encouraging their proliferation even more.