Much of the fruit that humans consume today is not the same fruit that humans evolved to eat.
Take the peach, for example. The peach probably originated in China (1) and has been cultivated as far back as 4000 BC. The natural peach was 25 mm in diameter, consisted of 64% edible flesh and 36% seed, and tasted "earthy, sweet, sour, and slightly salty" (2). In 2016, the average peach is 100 mm in diameter, consists of 90% edible flesh and only 10% seed, and tastes "sweet, refreshing, and juicy" (2). After only a few thousand years, which is an inconsequential blip in evolutionary time, the peach has become 16 times larger not to mention juicier and sweeter than its wild cousin. Clearly, it's not the same peach it once was.
Consider the watermelon. The watermelon originated in southern Africa (3) and has been cultivated since 3000 BC, yet back then it would not have even been recognized as the watermelon of today. In 3000 BC the natural watermelon was only 50 mm in diameter (that's not a typo), consisted of only 1.9% sugar, and tasted "extremely bitter or bitter-sweet" (4). Today, the watermelon has been cultivated to a massive 660 mm in diameter, consists of 6.2% sugar, and tastes "deliciously sweet and so juicy that it sometimes explodes when ripe" (4). Wow! So again, after only a few thousand years, the marvels of human cultivation have produced a watermelon that is 1,680 times larger not to mention juicier and sweeter than its wild cousin. Just like the peach, it's not the same watermelon it once was (in fact, the watermelon may be the least natural fruit in existence).
Now I'm not here to pick on peaches and watermelons. In fact as far as fruits go, peaches and watermelons are nowhere near the worst offenders with regards to what I am going to talk about. They're not big-time, they're small-time. The big-time offenders, the Al Capones of the fruit world, well they would have to be dried fruit, the apple, the mango, the grape, the pear...umm, I'd better stop there.
The problem with fruit is fructose, a sugar that masquerades as a good guy when in fact it is a bad guy.
Table sugar, or sucrose, can be found among plants such as the sugarcane whereupon it is harvested for human consumption. Too much sucrose in the diet leads to obesity, type II diabetes, and many other health problems. But why? To answer this, we must realize that sucrose is actually composed of two simple sugars - it is 50% glucose and 50% fructose.
The first component of sucrose, glucose, is found in certain plants in the form of sucrose, and it also circulates in the blood of animals as blood sugar. The effect of a food on blood sugar can be measured using a scale called the glycemic index, which gives glucose a value of 100 and measures all other foods against it (5). The higher a food's glycemic index, the more it spikes the blood sugar, and spikes in blood sugar crank up the body's release of a hormone called insulin which is public enemy number one when it comes to producing insulin resistance, the prelude to obesity and type II diabetes (5). Some of the foods with the highest glycemic index include white rice with an index of 72-89, white bread with an index of 70-75, and coca cola with an index of 63 (6). If spikes in blood sugar resulting in high blood insulin levels are bad for health, then white rice and white bread are truly evil.