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.

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!

Hunter-gatherers didn't just eat meat. It is likely that fruit made up a very large portion of calories. It's easy for people living in cities as many of us do to forget that food exists outside in the wild, whether in animal or plant form.

Most vegetables do not have much in the way of calories. The botanical definition of fruit also includes nuts. Fruit and nuts both have a fair amount of calories.

That was the concern. Getting more calories with more nutrition. They didn't have a culture of processed food, nor did they have a diet book culture. Humans in the wild devote their lives to food. Food is primal, and few things are more primal than fruit.

I read about wolves ravaging watermelon farms. Yep, they were eating the watermelons. Some people think humans are carnivores, but not even carnivores like the wolf can resist sweet fructose temptation.

Recently there has been reports of a study done where tumors were fed glucose and then fructose and from this they concluded that tumors "thrive" on fructose. Well, the vast majority of fruits are far from having 100% fructose like in those studies. Did they also feed these cancer cells protein or fat? They had a hypothesis (fructose makes tumors fat) and sought to replicate that. And maybe they didn't care whether it made sense or was logical or not. It fed into the current talk of fructose.

The fructose scare is doing nothing to make America healthy. All it will make people do is avoid HFCS, which is laughably small way to make a change unless one consumes sugary drinks regularly. Diet drinks have made a huge success in the market already. I think you have to consider the food that's being eaten, in what quantities, and the person's activity level. And because they think fructose is bad they are going to avoid healthy fruit.

Remember the low-fat craze, then there was a low-carb craze. And between all this we got lots of mini crazes based on avoiding this or that ingredient. HFCS (and all fructose by association) becomes a scapegoat for America's gluttony and sloth.

I would like everyone to consider the Kitava who consume lots of carbs including fruit and consider whether they are unhealthy, they're not. And obesity is rare. Most other hunter-gatherers also consume fruit. Only when humans ventured into cold climates (or perhaps also very hot desert climates) did we have to adopt very low carb diets simply because there wasn't much fruit to be found. Would it be close to the diet of much of our evolution? No. Would it get us through the harsh winter? Yes. Humans find ways to survive.

I just don't see how early apes would go from eating lots of fruit as they most likely did (our evolutionary heritage is arboreal, just look at all the other primates) to getting to a point where consuming it would be bad for our health. It seems contrary to evolution for such a nutritious and energy dense food source to become bad for the human species.

Recently I read a post on a low-carb blog extolling gluconeogenesis as proof that humans actually don't need any carbs. Our livers produce glucose anyway. Why would our bodies produce something we don't need in the first place for use in our body's systems? If sugar is so scary, why is glucose, abundant in our blood, a form of 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.

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)

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.

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.

Good in small doses, bad in large doses.

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.

In the area where I hunt, there are a number of wild apple trees. It's mostly old farmsteads that have been abandoned long enough to reforest, and the apple trees, or their wild descendants, have hung on. The deer love them.

Their fruit is small, plum-sized at most, and tart; tarter even than Granny Smith apples. Modern apples are much larger and much sweeter. And when you consider that these wild apples are at most a couple of generations removed from strains that are at most a couple of centuries old?

Grok probably ate a lot of fruit. The fruit we get in the supermarkets is so engineered that one piece contains vastly more sugar than several of its paleolithic ancestors.

Ned Kock is correct when he tells us that fructose consumption is relatively benign (and even positive) when the liver is in a state of glycogen depletion. But let's remember, that's only after hard exercise and fasting. The rest of the time there is nothing positive that comes about from consuming fructose. However, when do most of us consume fructose? Generally, it is not when the glycogen stores are empty.

A careful look at the literature will convince the unbiased that fructose is a very problematic foodstuff. And it doesn't matter how you get that fructose. A poison is a poison--even if taken in small amounts and even if it is bound up with 'fiber' and 'micro-nutrients'.

Sandra, if you eat a bunch of fruit all at once when you are not accustomed to it, it can cause the trots. Also, if you eat a bunch of fat, all at once when you are not accustomed to it, this also can cause constipation or the trots. In both cases, the dose makes the poison. If you eat a load of something you are not adapted for, you may suffer a bit at first. This does not necesarily mean the food is toxic. I bet you our ancestors in climes where fruit existed, would sometimes gorge on fruit as well. Maybe they had stronger gut health than we do.

Also, there are sweet fruits like the date and the sapote, that exist in nature. Fruits were probably more accessable in tropical climes when access to fruit is not entirely seasonal and where humans probably evolved in the first place. Our ancestors very likely knew how to dry fruit and store it for months. Dried fruit is very shelf stable. Our ancestors probably also obtained honey from time to time.

WHile it is true that ancient paleos probably did not have the same kind of access to sugars as we do now, it is very likely that they had some access and very likely utilized it as much as they could. Fruit are relatively easy to safely catch and store. Sugars also help replenish glycogen and our bodies have a specific metabolic pathway to process fructose. If fructose is so bad for us in any quantity, why did our bodies create this pathway to utilize it? If sugar is so bad for us, why do we have a taste bud specifically designed for us to enjoy it and cause us to seek more? I think clearly, the problem is not sugar itself, but over consumption of sugar, that causes problems. Such levels of sugar that we now have did not exist during the majority of our evolution. But some levels of sugar did exist and our bodies are designed to both enjoy it and utilize it efficiently, so I think there is a good case for moderate sugar intake as being healthy and natural, especially for those whose metabolic pathways are not already damaged by decades of unhealthy eating.

I was always taught that fructose is a better sugar source than glucose and polysaccharides of glucose because of the time it took for fructose to be converted into glucose. I see elements of this in diabetic products ( they sell pure fructose in the diabetic section). I personally feel great eating fruits and veggies. And I know there are a bunch of other substances in fruit that will benefit me. This war over fructose, which started with the infamous High Fructose Corn Syrup, is about rediculous.

I'll hear people talking all about HFCS and how its in everything, and is the reason for this and that. They sound so dumb, like its a conspiracy or something.

I eat fruits, nuts, vegetables, and low fat protein. There is no HFCS in any of that. If you're stupid and just learned to read the label on everything and suddenly find everything you eat has HFCS, you haven't been eating a well balanced diet.

Dr. Barry Sears really laid out what people should be eating, he says to stay around the perimeter of the grocery store,and mostly avoid the aisles.

High sugar is bad for you. High fat is bad for you. High protein is bad for you. Some recommend %60-%70 percent of calories come from carbs. I stick with Dr. Barry Sears', %40.

So, based on that I would have to say fructose isn't bad for you when eating part of a balanced diet. Case closed. New fad, step right up.