Ben Goldacre, who does a lot for public understanding of health and science, among other things including being a GP for the NHS, is often asked for some positive health advice after he warns about the worthless-at-best value of most health advice. If I recall correctly, his response is always "Try to increase the amount of fresh fruit and veg in your diet, try to reduce alcohol and cigarettes, do some exercise.".
Also, this comedy sketch from Fry & Laurie is relevant, especially the "too much is bad for you" rant at 2m00s.
> especially the "too much is bad for you" rant at 2m00s.
It's also pretty futile. The point is not that a theoretical excessive quantity of something does you significant damage, the point is whether or not you are exposing yourself to that amount now, and/or enough people are for it to be a public health problem. You could make the same rant about being obese, or about hardly moving throughout the day.
That is especially relevant when you have food companies engineering their products to be as pleasurable as possible, without reference to the health consequences - see the enormous amount of sugar in ready meals, or the introduction of trans fats previously.
Of course, that doesn't mean we actually can tell what is good and what is bad for you, or what doesn't matter either way, which is the point of Goldacre's statement.
Fruit might be good for it's vitamins, but in moderation. Increasing fructose consumption after a certain threshold - which could be easily crossed when increasing it's consumption - would not necessarily be a good thing.
That's not really a concern as long as it's just fruit, not juice or processed fruit. There's so much fiber and water in fresh fruit, it's difficult to consume enough at a fast enough rate for the sugar intake to be problematic.
Do you have a reputable source for that? Fruit is definitely good for more than its vitamins.
Also, we are not monkeys anymore, but monkeys eat a lot of fresh raw fruit. Arguably they climb trees while doing so but eating like a monkey seems like a relatively safe thing to do to me.
Elephants and manatees are closely related, as well, but I would not recommend that they look to one another for dietary recommendations.
Speciation can occur when different populations fill different niches. Human physiology (along with still extant hunter-gatherer cultures) indicates that we are opportunistically omnivorous cursorial hunters. The species closest to us genetically are opportunistically omnivorous frugivores. Chimps and bonobos eat fruits and nuts most of the time, and eat monkeys maybe once a month. If you want to consult the animal kingdom for dietary advice, look to wolves for the meat and bears for everything else.
Eat like a bear until you see a potential prey animal, then run it down and eat it like a wolf. When you finish, switch back to bear mode. That seems like a relatively safe diet to me.
This is just one source, of course, but is not the only one in that direction. Carbohydrates in excess - specially sugars like fructose - are being linked to increase of fat accumulation on the body and much of the modern day metabolic diseases - Google scholar should give you a bunch of results in this one too.
Also, this comedy sketch from Fry & Laurie is relevant, especially the "too much is bad for you" rant at 2m00s.
https://youtu.be/XV4yK-26smM