Humanity :)

As Shaun says, there is a big difference between philosophy and the practice of science. As with any system the moment we involve actual, emotional, self-interested, messy Humans it goes to pieces.

That having been said, science, as other free endeavors, tends to be self-correcting in the long run. Of course this goes out the windows when the state gets involved and these days it is the state that funds science. When I think about it I am surprised that it is not even more messed up.

If our science and tools cannot find something, then it must not exist

Feynman's take (I can't find the source right now) was that science had nothing useful to say about things it could not measure.

The principle of falsification is a useful one. It is more useful to say "God does not exist" because that can be proven false. All God has to do it show up and presto, the statement is shown to be false. Saying "God does exist" is not useful because it can never be disproved.

Likewise the scientific method is a very useful tool. Where I have a serious problem with many skeptics (Sagan and Gardener for example) is that they refuse to apply the method to things they dismiss. Double blind studies of acupuncture have shown it to be very effective in some cases. Yet they ignore these. And of course, they simply refuse to carry out experiments in certain areas. Rupert Sheldrake is a great example of someone who has conventional training and wants to investigate out-of-the-ordinary phenomena, using the standard approach, but can't get any funding.

Overall, I'd say that where it has been relatively free of state interference the short history of modern science is a pretty good one. However, this is probably the case because of the 'paradigm shifts' that Shaun referred to.

Diet is an interesting area. Having lived in Asia for many years, I know that the claims that an "Asian" diet is good for you are false. Some Asians live long lives, and diet is undoubtedly a contributing factor. But there are many Asian foods, a lot of which are not contributors to longevity (shellfish & noodles fried in pork lard comes to mind).

We do know a few things, such as if you are over weight your heart will have to work harder, also if you have too much of some chemicals in your body you are at higher risk. So if your family history also gives you higher risk you may want to consider reducing your intake of some foods.

Overall, diet, while important, is only one of many factors.