Strangely, none of these things is likely to be helpful to most folks, and yet, many folks do all of these things on the thought that "There must be a reason why so many people tell me to do this. They have a PHD, they must know what's best, its magic to me but they must know."
It's the presumption that someone out there knows the answer which drives this kind of behavior. It's what led me to go "low fat" for a few years, which also led to a monster fat gain, which led to me finally deciding I had to figure the food and fat thing out.
In the past, it was not unreasonable to assume that other people would "know" the important things. It probably made sense to do what your doctor told you to do. Doctors back in the day had access to much information that you didn't have access to, and a vast depth of training and experience. They also had many fewer tools to work with than they have now, so they likely knew the ones they had very well and had seen the results of using that or those tools many times.
That's all different now. You can know as much as your doctor about your individual situation, in many cases. You can take responsibility for your own circumstance. You no longer need believe that the voice of authority is right, at least not for your situation. You don't have to treat health and diet recommendations as if they are the magic elixir, distributed by those who know the dark secrets.
Let's take the case of salt/sodium for an example. If you have a blood pressure problem, and you reduce your salt intake, you may notice a reduction in blood pressure. There's quite a bit of evidence that reduction of blood pressure results in better health. So if you reduce sodium intake and your blood pressure numbers improve, voila, you've just proven that sodium reduction is a worthy pursuit. Of course, about 80% of those who have high blood pressure can control this problem by carb restriction, and in that case, can eat all the salt they want to. Either way, you choose your intervention and you get the results based on your own judgment of cost/benefit.
What if, on the other hand, you don't have a blood pressure issue? Strangely, the authorities will still tell you to reduce your salt intake. This is not because they can prove that reducing sodium intake will make your life better, this is because much of the information we hear about salt and such is "public health science." That is, it is intended to address the needs of and health outcomes of populations. From the public health perspective, if you tell 1000 people to reduce sodium intake and 500 comply, and of that group 100 get a benefit, that's a win. In other words, they don't really care if you or your family or anyone you know will benefit from the recommendation, because they are on a mission from god to change health statistics for a population, so they make recommendations that may or may not help you. These recommendations are promulgated because the "scientists" entered their assumptions about the recommendation in question along with estimation of compliance and estimates of the theoretical benefit of the recommendation. If their computer model calculates (based on their assumptions) that the recommendation in question will "save" thousands of life if implemented in our population of 300+ million - Yahoo! Another public victory!
Isn't that great!?!
Vaccinations are a variance on this theme. If you give enough kids a vaccine, one or more will die as a result of a reaction to the injection. If you are the parent of the dead child, it will be cold comfort to know that in theory thousands of lives, or hours of suffering, were "saved" by the vaccination of the masses.
In short, "public health" and the science that this discipline draws on is not focused on you, your circumstances or your individual interest. Knowing that, I'm stunned at how many people labor under the misinformation that this field so skillfully distributes.
The point is "don't trust the experts." If they say it is true, try it and measure the result.
If there is no change, don't assume this is some magic that should guide your life based on your faith that the government scientists must know more than you know, and must be faithfully interpreting the results of the science they work with.
Test it! If eating whole grains makes your blood sugar skyrocket, don't believe it when they tell you that whole grains "break down more slowly in the gut and therefore have a lower glycemic load." If you don't have a blood pressure problem, don't worry about salt intake. If you try carb restriction and your gout, your blood pressure, and your lipid profile improves, tell them they can go suck it when they say you need to eat 11 servings of grain each day. If you are eating a mountain of fat every day (as I do) and your blood lipids look good, you feel good, you perform well, you sleep well, your hunger is minimal to non-existent (most days I eat by habit and routine, and almost never for hunger), your waist is small (or getting smaller), then have a good laugh when they tell you to cut the red meat and animal fats and graze on vegetables 24/7; and pray for their eventual enlightenment (hopefully before I die so I can say "I told you so").
By the same token, if you can suck down bread like there's no tomorrow, and you look feel and perform just like you want to, more power to you! There's no one on the planet who's smart enough to question something that works for you - assuming it does.
And that's where this narrative gets tricky, because we often accept compromises based on our belief that they are "normal." I see people daily who think their aches and pains are normal. They think "well everyone else is taking statins and BP meds, that doesn't mean anything, it's just part of aging and boy aren't we lucky that these great meds are available and my insurance company will pay for them." They wrestle with heart burn daily but "so does everyone else in their family." I see people who think their expanding waistline is just part of getting older. I see people getting dental work who just think it's great that the dentist can remove and replace teeth with minimal pain. I see people who think osteopenia is just "aging bones" and don't question the recommendation to eat calcium. I have come to believe that all of these issues are not normal, and when I confront one I will fool around with diet until I can find a solution. This has been successful in eliminating several chronic conditions that I thought were just "normal" or part of my own genetic defects - IBS, having my nasal passages close each night (how well do you sleep when you nose is stopped up from a cold? How would you like to feel that way every night?), or having such high levels of knee pain that I was taking 800mg of ibuprophen three times daily. I have fixed all of this and more, so yes, I'm a believer.
In other words, if you don't think something is wrong, how likely will you be to change? You will just bravely suffer on, hoping the meds don't ever stop working. And of course, this is another reason why the public health authorities make recommendations as they do - they don't think you are smart enough to figure out what's wrong or what to do about it.
I would hope that most of those who are reading this "won't be that guy/girl" who's too ignorant to know what's wrong and what to do about it. Find a solution, take action, be persistent. Magicians are fun but I don't recommend that you take their advice about diet and health.