JTSR71 wrote: "In my opinion, science has really failed when it comes to dietary advice."
Oldbooks1 wrote: " My "hunch" is that the problems are just too complex to make it possible to sort out implications in a specific case."
My two cents: Probably the most important cause of medical science's flip-flopping and inability to provide us with sufficient knowledge about diet, cholesterol, triglycerides, and other important health information, is the result of poor science or poor scientific studies, which, in turn, is the result of the large amounts of money and long spans of time that are needed for proper studies. We know how to do rigorous studies but lack the funds and the patience to accomplish them.
Over the years much of the advice concerning medical issues has been educated guesses from leaders in the various medical fields and not from properly designed scientific studies: in other words, educated assumptions were taken as fact. A recent example was the ADA, who said it knew that dental flossing was absolutely necessary,according to dental science, for good dental health. But there was never a study done that actually verified said practice. Also,there were recent guidelines put in place in the US for who should take statins. Some mathematicians from Oxford using the same study and methodology that these guidelines were derived from discovered that taking a handful of nuts everyday or eating an apple everyday instead of taking statins would produce the same medical benefits, though this activity would cost more but would not have as many adverse side effects.Thus why have X number of people taking stains when we already knew that a handful of nuts per day would bring about the same results. Poor science?
A proper study--- a few years ago the VA began a long term supposedly rigorous volunteer study of the DNA of 1 million military veterans, which I happened to volunteer for. To date they have about 500,000 DNA samples with 500,000 to go. This study will take decades but will probably yield new and important information that could not be obtained without access to so many people for so many years. In medical science, large studies of this kind are rare, but are a must if we want to stop the guessing about what is or is not healthy. Hopefully it will not get the budget ax.
One other thought. To me, the biological sciences are immature, or perhaps even different in kind, compared to the "hard" sciences, and are unable, for various reasons, to achieve the same levels of reproducible and "certain" knowledge as a hard science such as electrical engineering, for example. So it could well be that medical science has innate limitations that we must live with.