Chapala, I'm speaking specifically of natural foods in an animal's natural habitat.
For humans, this means nothing cooked, nothing dehydrated, nothing messed with. Definitely true of birds too. If that's the case, great apes (humans), most parrots, and many other animals are very drawn to whole fruit. Most birds wouldn't find dried fruit, sunflower seeds, sprouted grains or legumes, or junk food in their natural habitat. (They're not native to the same areas or not found naturally at all.) You can't argue they don't eat the most proper diet in the wild, and they do eat fruit. What would my birds find in the rainforest that is like legumes or grains? (I would really like to know if anyone has insights. BESIDES the birds that eat CULTIVATED grains, because they are not native to where the birds evolved and therefore NOT part of their natural diet.) Much less meat (specifically cooked) besides insects, or potatoes (they don't dig--not my species), or etc, etc....
Fruits are one of the least changed foods from the wild-- you will find most of them in the wild! Even when sizes, shapes, flavors [cannot be changed drastically] and colors have changed, nutrients (macro and micro) haven't much at all. The sweetness of fruits depends on how ripe they are. They do eat unripe fruits often, which are less sweet but also toxic. (This is the reason, they say, my species spend so much time eating cliffs--to undo the effects of eating unripe fruit.) Depleted soil does not affect fruit trees nearly as much as other crops whose nutritional value actually is compromised.
Also, who is to say your birds would become obese if they were fed high fat but were also allowed to fly as much as they should according to their physiology? Particularly Macaws. As for malnutrition, anti-nutrients are just as bad as lack-of-nutrients. For instance, because of the sulfur/protein in milk, it takes more calcium to digest it than the milk contains. Milk actually CAUSES osteoporosis. Things like this happen with many foods people eat! Since the effects of anti-nutrients have not been studied in parrots (because different animals thrive on different diets), I can only do the best I can. My conjecture is that if a food is not whole, raw, local (to where the animal evolved), and still attractive, it is not a proper food for that animal.
Dehydrating a fruit doesn't increase the sugar content PER CALORIE. It does PER GRAM simply because there are significantly less grams of water left. This is bad, agreed, because the water in foods is the best, cleanest source of water there is. Just sayin', it's not really higher in sugar if it's dehydrated, it's just lower in water. The ratios of sugar per calorie stay the same. It's easier to overeat on dehydrated foods, though. And if a food is packaged (by nature) with water, it should be eaten with that water.
