Based on what I know about the words "professor" and "emeritus" and "cornell", I assume this is written by an authority in the field of nutrition.

The value of being an authority in a field is that you can accurately convey the consensus within that field. Whenever consensus within a field does not exist, the ancient injunction against "argument from authority" remains true. The "authority" derives not from the authoritative individuals themselves, but the collective wisdom of the field to which they've been exposed.

1. Science is crap. Don't believe expert predictions about the natural world.

Science isn't crap - it's just that when science is weird and inconsistent and wrong it's obvious and everyone notices because science has better epistemic hygiene practices than non-science methods of discovering things. You're just overestimating the degree of accuracy and agreement science aught to have.

I might have the specifics of this story wrong, but once upon a time, scientists (correctly) showed that blood cholesterol is correlated with bad things. So people stopped eating more than 1-2 eggs a day. Now we know dietary cholesterol doesn't directly control blood cholesterol and you can eat lots of eggs and your LDL won't rise in a meaningful way. That doesn't make the original findings wrong, it just means the resulting interpretation was wrong. The original scientists weren't being dumb, it was perfectly reasonable interpretation to make.

The China study found some probably correct things assuming they followed protocol and did statistics well, and now they're interpreting it to mean "go vegan". As a consumer of primary research, you should ask yourself if the findings -> practical interpretation link is reasonable.

nutrition science is crap

It's really not significantly different from "we thought there was Aether, and now we don't", but in fields like economics and psychology and nutrition people notice more when you mess up, because laymen understand enough to know what it means to make a mistake - Everybody votes, deals with minds, and eats, but most people don't understand the implications of their not being an aether. .

But, yeah - scientists are people, and some fields tend get more contaminated with personal biases that the researchers might have acquired entirely outside the laboratory. This can inform the types of questions they study, confirmation bias, bias in the interpretation of the data, and so on. Also, whenever an issue of public policy is at stake, I imagine special interests groups get involved.

Why isn't this good enough to inform your dietary choices?

The evidence certainly does inform my hypothesis, but that's not the same thing as agreeing with the author's interpretation. (I don't say "choices", because my interest is mostly academic and I'm not particularly diet conscious in my personal life, and I do factor in moral concerns with respect to meat, which makes my actual diet not particularly in line with what I think is nutritionally optimal.)

The important thing is to inform ones views based on the evidence gathered, rather than trusting the researcher to interpret their own evidence.

I accept that chinese diets are likely superior to Western diet. Leafs, shoots, roots, fruits, nuts, and the like are all extremely, extremely important. When meat replaces or otherwise funges against those foods (as you'd expect it to given limited calories per day) meat is bad. The average American lives on meat and grains, skipping the fruits and veggies, and that's no good. The average American vegetarian will probably be healthier than the average American omnivore for this reason, even controlling for caloric intake. The average American would probably benefit from going vegetarian, not to mention the various moral horrors and environmental damage meat entails. It's not surprising that we see the same trend in China.

But, well - none of that means that vegan is nutritionally optimal. Hunter gatherers, lacking grains and dairy to provide calories, would have probably "maxed out" the benefits leafs, shoots, roots, fruits, nuts, and other plants despite also eating lots of meat. The Inuit pretty much just eat meat and do fine. (Don't try it at home - the Inuit can only do this through judicious consumption of organ meats, which are glycogen rich and nutrient dense. They actually often discard the lean muscle meat, probably because they've intuitively grasped the macro-nutrient ratio problem it would pose.)

When you look at the evidence provided from the China study - not the interpretations, just the evidence - there's very little room for suggesting that hunter-gatherer diets are suboptimal.

Assuming you don't plan to become an expert in the field of nutrition yourself, what's a better way to inform your dietary choices?

There's no way out. I can say "Eat a balanced diet, with natural real foods" or whatever but the true meaning of "balanced" and "natural" is a lot more controversial than it seems at first. If you don't do your research you are down to guesswork, and after you do your research you are still mostly down to guesswork due to how little we really know.

FWIW, having a totally optimal diet is probably not extremely important in the grand scheme of things. For all practical purposes you'll be just fine so long as (1) your calories are okay, (2) your macronutrient ratios are not horribly awful, (3) you have no obvious symptoms of micronutrient deficiency, and (4) you exercise. Everyone agrees on those four and that you should eat fruits and veggies. Beyond that, it's all controversial and I doubt the additional worrying will really buy you that many extra years of quality health when one factors in the likelihood of choosing the correct arguments among the controversy. (Outside view. Inside view, I totally think I'm right in choosing the "take cues from hunter gatherers" thing.)