There have been studies showing that consuming large amounts of fructose or sugar are bad for you. I don't recall seeing any studies showing that eating a peice of fruit has any harmful effects at all. Most studies show a neutral or positive correlation between fruit consumption and improved health outcomes.

If you eat too much protein you will poison yourself. Does this mean you should remove all protein from your diet? Most things are not poisonous at any quantity. The dose makes the poison. Even water can kill you if you drink enough of it.

There is no evidence of harm from the amounts of fructose in whole fruit but there are many benefits from other components of the fruit including vitamins, soluable fiber and phytochemicals. This probably does not apply to fruit juices that mostly just sugar so avoid drinking your fruit. If you have metabolic problems and cannot handle any fruit in your diet or need to restrict fruit to lose weight those are individual issuse, not the fault of the fruit. Of course not all fruits are equal but this applies to all foods. Fruit is not magic, simply the fructose content is to low to be problem, but it tastes good and at moderate consumption it has benefits.

A couple of sciency bits I found online:

http://endo.endojournals.org/cgi/content/full/139/3/827 You have a transporter protein in your gut thats only job is enable you to absorb fructose. Why would you have this if you were not meant to eat any fructose?

http://www.nutritionandmetabolism.com/content/7/1/42 Fruit intake is independantly asscociated with lower levels of inflammation, which most people would consider a good thing.

Acceptable doesn't mean good. There's a lot to be said for certain components of fruit and the possibility they carry of compensating for other deleterious lifestyle choices (anti-oxidants, anyone?). For those of us avoiding the negative sides of contemporary living (though it's all-but impossible to live perfectly cleanly these days) there may be some small benefit from eating fruit.

Personally, I don't eat any fruit because it raises my blood sugar, and I try to minimise all inflammation in my body, especially while I try to burn excess fat.

Fruit is, at least, meant to be eaten and therefore not full of the 'don't kill me' chemicals of veggies, but given our digestive system and the impact sugars have had on most of us throughout our lives, fructose may well still be a poison in its unrefined state.

Like all things, I think it's best to find out how your body responds before you rely on theories and grok-logic to make your nutrition decisions for you.

Just because something is toxic doesn't mean our metabolic system can't deal with it. Humans have been ingesting fructose, in relatively small quantities, since before they were humans; this is basically proven by comparative anatomy (grinding teeth are for veggies, etc). Sugar and fructose critic Robert Lustig has quipped that the sweet taste of fructose is like a lure that gets us to eat fiber and other useful micronutrients. Very much something that Michael Pollan might say (e.g. botany of desire).

Fructose toxicity is more of a long term, chronic concern than a short term concern; unlike alcohol, a single overdose of fructose will not kill you immediately. Long term chronic overexposure can kill you, but periodic exposure to limited quantities, so long as the total carbohydrate load of the diet is low, will not really hurt you. Our ancestors had periodic, seasonal fluctuations in the amount of fructose they ingested. If your fructose ingestion follows the same pattern, you should be fine.

Nevertheless, modern science would suggest that carbohydrate sources that are higher in starch or glucose are less toxic and should be preferred if you for some reason need to load carbohydrates. In that sense, at least, a white potato might be better than a sweet potato!

There's a simple way to check if fruits are good for you or not. Buy a blood glucose monitor at your local drug store with some test strips. Take your fasting blood sugar in the morning. Then, have a meal with some fruit. Test your blood sugar one and two hours after. If it's above 120 two hours after the meal, fruit is causing dangerous elevations in blood glucose and you'll need to moderate it. If it's below 120 the amount of fruit you're eating is probably fine.

Obviously how you feel eating it should also determine the choices you make.

according to Cordain's original Paleo Diet book, fruit has a different effect on blood sugar than refined sugars do. takes longer to process or something, doesn't cause a spike, but rather, a more gradual release into the blood sugar.

Don't forget that the fruit (and vegetables) of today barely resemble their wild cousins that our paleo ancestors evolved eating. They have, for the most part, been bred to be larger, sweeter and juicier than nature intended.

On top of that, they are all available in greater quantities and for longer periods of time than we would typically expect to find in nature.

Combine those two points and you've got nature's candy bar on a tree (shrub or bush) staring you in the face.

Good in small doses, bad in large doses.

I used to avoid fruit, then I added it back in to see what would happen, never more than one serving a day mind you and nearly always accompanied by a fat, such as a chopped kiwi with natural yoghurt on top. I lost weight faster, go figure, I think it satisfied a need in me and actually helped keep me on track. Mind you I never go above the one serving a day otherwise I mess too much with my blood sugar.

Something that is not discussed very often is that a kind of food can be good and bad at the same time. It can be good for your (Darwinian) fitness: more reproduction of genes. But it can be bad for long term health.

I think fruit could be considered to be like this. Fruit could cause beneficial nutrients (energy, phytochemicals, ...) that put our organism in a 'go-and-reproduce-now-is-the-time' modus.

This could (partially) explain why most of us like fruits: ancestors who liked fruits reproduced more offspring, even at a cost. Darwinian medicine talks about these trade-offs quite a lot.

(edit: just adding something to the discussion here, not saying all of the before mentioned answers are wrong, quite the contrary. My two cents on fructose: the poison is in the dose)

Personally I eat very little fruit. Mostly berries, although on rare occasions a bite or two of another fruit. I've never been a huge fan of fruits, so it's fairly easy for me to go without.

Fruits are, for the most part, all sugar....for macro-nutrients. But there are all kinds of vitamins and minerals in fruits, so most people find them at least acceptable. Most fruits also actually contain fairly small amounts of fructose as far as their total sugar content.

I love berries, but I tend to lose self control and eat a bunch. I am considering keeping them out of the house and eating them once a week, on grocery day. It would be like our ancestors randomly, stumbling across a huge batch and gorging, then not finding any for the rest of the week. I currently do that with extreme dark chocolate and its very satisfying.

This is a summary answer based on the following post:

http://healthcorrelator.blogspot.com/2010/06/fructose-in-fruits-is-good-for-you.html

Fruits are among the very few natural plant foods that have been evolved to be eaten by animals, to facilitate the dispersion of the plants’ seeds. Thus, from an evolutionary standpoint, the idea that fruits can be unhealthy is somewhat counterintuitive. Given that fruits are made to be eaten, and that dead animals do not eat, it is reasonable to expect that fruits must be good for something in animals, at least in one important health-related process. If yes, what is it?

Well, it turns out that fructose is a better fuel for glycogen replenishment than glucose, in the liver and possibly in muscle, at least according to a study by Parniak and Kalant reviewed in the post above. The study also suggests that glycogen synthesis based on fructose takes precedence over triglyceride formation. Glycogen synthesis occurs when glycogen reserves are depleted. The liver of an adult human stores about 100 g of glycogen, and muscles store about 500 g. An intense 30-minute weight training session may use up about 63 g of glycogen, not much but enough to cause some of the responses associated with glycogen depletion, such as an acute increase in adrenaline and growth hormone secretion.

If one’s liver glycogen tank is close to empty, eating a couple of apples will have little to no effect on body fat formation. This will be so even though two apples have close to 30 g of carbohydrates, more than 20 g of which being from sugars. The liver will grab everything for itself, to replenish its 100 g glycogen tank.

In the Parniak and Kalant study, when glucose and fructose were administered simultaneously, glycogen synthesis based on glucose was increased by more than 200 percent. Glycogen synthesis based on fructose was increased by about 50 percent. In fruits, fructose and glucose come together.

What leads to glycogen depletion in humans? Exercise does, both aerobic and anaerobic. So does intermittent fasting.

What happens when we consume excessive fructose from sodas, juices, and table sugar? The extra fructose, not used for glycogen replenishment, is converted into fat by the liver. That fat is packaged in the form of triglycerides, which are then quickly secreted by the liver as small VLDL particles. The VLDL particles deliver their content to muscle and body fat tissue, contributing to body fat accumulation. After delivering their cargo, small VLDL particles eventually become small-dense LDL particles; the ones that can potentially cause atherosclerosis.