I'll get back to you on this later, but yes, there are lots of contradictory studies in nutrition, and in every scientific discipline as well. The easiest way to resolve these conflicts a priori is to apply the sort of "central dogma" of each discipline. Geology has plate tectonics. Chemistry has atomic theory. Physics has quantum theory (though this is constantly being revised), mechanics has relativity, etc. In the life sciences, the central dogma is evolution. If two studies contradict one another, then the one which makes evolutionary sense is the one which should probably be subscribed to more readily. Of course, this doesn't always lead to the correct conclusion, but usually if you're wrong, it's because your evolutionary reasoning was wrong or because the particular aspect of evolutionary theory you used to draw your conclusion is wrong.
Because evolution is a fact and it is the guiding principle of the development of human physiology and, by extension, nutritional requirements, interpreting nutritional studies in light of evolution should be common practice. In the biology labs I've worked in, evolution has always been a factor in the discussion of our results. My wife worked in nutrition science during undergrad, and evolution was never spoken of. That is the key flaw in the study of nutrition. As it is now, there's a lot of epidemiological studies going on in nutrition to find vague associations and correlations which tend not to be very trustworthy because the data generated relies so heavily on the study design and human memory and classifying the whole of foods available to humans into just a few study categories. A lot of nutritional studies set themselves up for failure in this way. Some don't.
So the tl;dr is this quote which showed up in basically every biology class I've ever taken (and then stopped showing up in my medical classes... hmmmm...): "Nothing in biology makes sense except in the light of evolution" - Theodosius Dobzhansky
edit: So how do you interpret nutritional studies in light of human evolution? This isn't always entirely accurate, but basically, if a caveman had access to it, you should eat it, and you should do so in a quantity which made sense for cavemen to eat it in. Studies of modern-day hunter-gatherers can be useful, too, to learn about how "natural" populations eat. Trying to replicate that in a reasonable way has been extremely successful for a lot of people, myself included. But this is a really loaded concept, and it's not always as simple as comparing yourself to a caveman, because a caveman you ain't. There's a lot of genetic variation across the human population, so your nutritional needs and foods you tolerate best may be a little different than the next guy's. To find the palette of foods best suited for your palate and your health, it takes a lot of self-experimentation. Here's a pretty decent primer which outlines some of the concepts I'm talking about, but don't take it all for absolute truth.