Then it was low cholesterol. Then it was low fat. Then we were touting whole grains. Then is was low carbs, but as much fat of any kind. Then it was Paleo.
It was carbs in the morning. Then it's no carbs at all. Now it's carbs after your workout.
It was eat every 2-3 hours. Now it's intermittent fasting.
Why do we keep being duped? Who are we supposed to listen to?
The thing with science isn't so much that it's changing. The science is always the same. It's that we are learning more and have methods now to delve deeper into the biochemistry of how we work and how nutrients affect us.
Think of it like a game of hang-man or Wheel of Fortune. At first, only part of the solution shows and you find phrases or words that fit what you know. As more letters are revealed, you have to change your mind as to what the answer is.
Nutritional science is like this. Things keep changing not because the science was wrong, but because the conclusions to the data were simply a best fit for what they knew at the time.
Unfortunately, a lot of "experts" and those in the health and fitness industries will take the theory of the moment, something that maybe works or has worked for them in the past, and hold onto it despite what new research says. Then you end up with people holding desperately to the whole wheat and low fat paradigm and ignoring or scoffing at the tidal wave of new research that says otherwise. It's not so much because they are TRYING to dupe you, it was the best fit for the data we had at one time. It's no longer the best fit anymore, though.
The best thing to do is keep on top of the research. That's a tall order, though. Other than that, find someone that you can track how their opinions have changed with the emergence of new science and try to follow their lead. And take it easy on people who still follow a long refuted dietary method, this stuff is HARD to keep up with!