"Elsewhere" is a paywalled study so I can't get details.
NOTE this does NOT mean apples bananas etc. are unhealthy, just that they are higher calorie (per study relevant nutrients) than the stuff on this quiz. If you are trying to minimize your calories intake, you are indeed better off eating leaves & stems than the parts of the plant designed for storing energy.
Some other comments point out that this study is looking at a variety of nutrients, whereas bluberries are known for being high in just a few specific nutrients. I can't speak to the accuracy of that comment but it might explain why blueberries didn't make the list.
My dad is on a low carb diet, so for breakfast he chops up a large bunch of parsley and fries it with eggs. He buys parsley by the pound. But he is weird :P
I looked some more, apparently we have koolraap en kohlrabi... very confusing (ánd knolraap..which is turnip, which is the word often used in england scotland and northern ireland and Newfoundland for rutabanga.) all the names in that family seems a bit of a mess, and different ones are used in different countries for a variety of these products.
It is like they said, ok we ve got a few of these vegetables which are related and /or lookalike and we ve got these bunch of names... help yourself! Take a pick
Like i recently learned the american robin and european robin are two completely different birds, not the same with a slight twist (that would have after separation). Not even in the same family. As similar as a pigeon and a seagull... only thing in common is the red chest. But I have only ever heard them being called robin, on both sides of the pond. So initially you assume it is the same bird.
"apples, bananas, corn, and potatoes" are specifically described as "low nutrient density" in the study (though their source for this is behind a paywall). Note that this does NOT mean these four are unhealthy, just that you need to eat a larger/higher calories serving of (say) apples than (say) watercress to get the same amount of disease-preventing vitamins and nutrients. This is obvious to anyone who has eaten both apples and watercress, but its nice to have a study explicitly measuring the differences I guess.
Of 47 foods studied, all but 6 (raspberry, tangerine, cranberry, garlic, onion, and blueberry) satisfied the powerhouse criterion (Table 2). Nutrient density scores ranged from 10.47 to 122.68 (median score = 32.23) and were moderately correlated with powerhouse group (ρ = 0.49, P = .001). The classification scheme was robust with respect to nutrients protective against chronic disease (97% of foods classified as PFV were separately classified as such on the basis of 8 nutrients protective against cancer and heart disease).
Blueberries are probably still great for you to eat but they don't help prevent disease which was the point of the study.
Also I'm pretty sure the study did not test avocados at all.
Isn't an apple a day supposed to keep the doctor away? :P
Also, beans are much more calorie-dense (lots of good starch and protein as you mention) so that would also rank them lower than all the leafy stuff on this quiz.
Note that this does not mean that blueberries are "unhealthy" (depending on what your health/diet goals are). Just that if you want to get the nutrients this study is looking at, you can do so more efficiently with the foods on this quiz.
That said adding watercress to your diet probably won't hurt! And it's not bad as stringy, leafy foods go. :P
Bananas are ranked lower because they are very starchy & sweet, so have lower nutrient content *PER CALORIE* than the quiz answers.
secondly the study is rather shaky, they choose a limited amount of items they considered to be powerhouse food and nearly all met the 10%requirement. They picked 46 items and 41 made the cut (all of which (onion, garlic and several berries) besides tangerine were decided to be added to the list alongside the suspected powerhouse foods based on being associated with benefits of the cardiovascular system, )