It's best to assume all nutritional claims are bogus, because the vast majority of them probably are, and there is no way for us to tell which at this point.
Cholesterol is ultimately used (and therefore made) by the body in an attempt to heal conditions that cause heart disease (The main use is for making vitamin D, whose other ingredient -- sunlight -- is in short supply for most people in the western civilization).
Thus, cholesterol is a good marker for pending problems, but is not itself the problem.
Analogy: People who take an advil are likely to report a headache 1 minute after taking it. Therefore, seeing someone take an advil is a good indication for a headache. But it is not the cause of the headache - and in fact, banishing all advil will not make anything better. But somehow, people think that banishing cholesterol will -- despite evidence to the contrary.
(Yes, statins do decrease heart disease, but they increase all cause mortality. And there have so far been many cholesterol-decreasing drugs developed - but none other than statins have decreased heart disease)
"I don't know anything about ____. Therefore all these claims the so-called experts are making about ____ are clearly bogus!" This kind of dismissive line of thought (there are some variations on the theme - many people don't like to admit that they don't know something) pops up in a lot of areas and it is pretty embarrassing.
In the real world when I meet people with attitudes like this, it invariably says a lot more about the person than the supposed inscrutability of the topic under discussion. The narcissism to dismiss entire lines of study and the lack of curiousness of someone who hasn't bothered to form an opinion on which ideas are better than the others... even when you hang out with a community of avowed skeptics, these attitudes really help separate the wheat from the chaff.
He doesn't advocate that we give up, crawl into the fetal position, and stop trying to understand the world any more than any of the other popular statistics skeptics do.
I maintain that there's a meaningful difference between "often wrong" and "almost all" wrong and "assume all claims are bogus" and "view claims skeptically." One approach is a license to intellectual laziness (defeatist) and the other requires effort but can reap benefits.
I agree with you that a lot of our diets (especially fad diets) are based on little to no science. At best, they're based on incomplete science. But what dietary guidelines would you recommend to someone?
Personally, I try to follow Michael Pollen's advice (Eat food. Not too much. Mostly plants.), whether or not it's based in complete science. Because with diet, one can't simply wait for science to settle things out.
Cutting too much on salt is indeed harmful http://en.wikipedia.org/wiki/Hyponatremia - up until 30 years ago or so, hyponatremia because of too little salt intake was virtually unheard of in the west, and now it is rare but not unheard of, because some people take the "cut back on salt" recommendations seriously.
What's the harm in eating only bland food? No harm. Also no harm in cutting back on listening to your favorite music. But why on earth would you do that? It's no different than avoiding alcohol or pork for religious reasons, or not driving on a saturday for the same religious reasons. If you like it, no one is stopping you. But it is based on blind faith, rather than science.
> But what dietary guidelines would you recommend to someone?
I was going to quote Pollen, but you beat me to it :) I think another recommendation from Pollen is helpful: "Do not eat anything that your grand-grandmother wouldn't have recognized as food".
Personally, given that I've found so much evidence that the "common knowledge" is wrong, I look at the fringes hoping to find something more useful. To that end, I recommend following the blogs (and mostly, but not exactly, the advice) of Dave Asprey (Bulletproof Executive) Tim Ferris (4 Hour Body) Paul Jaminet, Gary Taubes, Stephan Guyonet, Mark Sisson ... start browsing any of them and you'll find the others.
Is salt bad for you? (hint: unless you have a very specific hypertension condition, all the bad things you heard about salt are not relevant to you)
How much is too many eggs per day? (hint: no known limit. Cholesterol from eggs was never shown to be a problem)
Well, how about butter and fat? (hint: right kind of butter is good for you, as is the right kind of fat)
But surely, saturated fat is bad for you! (hint: no proof of that)
But at least bacteria and dirt are bad for you, I'm sure of that! (hint: life span is correlated with eating lots of fermented - i.e. bacteria laden foods. Also, people who work in sewage have higher life span and less illness overall)
You are taking tens or even thousands of bets based on bogus research without even knowing that. It is not unreasonable to assume that washing your hands all the time and keeping your house clean significantly raises the probability of autoimmune disease.
And really, if you go through nutrition literature and try to trace the knowledge to repeatable and demonstrable experiments, you'd agree with "very little". e.g., the calorie marking system used on foods is based on bomb calorimeter experiments (which you can debunk at home) and atwater factors (which have been shown to be grossly inaccurate, as in tens to hundreds of percents).