> I really do not like these articles that say "science says not to worry, you must be a very stupid and uneducated person to be worried about this." Any honest scientist will tell you that science does not know exactly how the human body processes food and there is no model which will exactly predict the effects of the human body ingesting a certain food.

It's true that we have a very limited understanding of the human body.

But this is the whole point. Unless there's some science to back something (or you have some personal experiences) then it's irrational to change your behaviour. [Note that I'm certainly not discounting personal experience here. Because the body is complicated, I think that's worth more than science. But you've got to be careful about your biases.]

The example of trans fats is an interesting one. AFAIK, the science (early 90s?) predated anyone seriously changing behaviour or policy. Although people suggested a connection earlier, it would not have been reasonable to start altering the entire food industry around some unsubstantiated claims. There are random connections suggested all the time. Unfortunately, they are only insightful in retrospect and no one remembers the ones that didn't turn out to be true.

> So I am very very suspicious of any food additives. The only rational decision for a human being is to eat the type of foods humans have eaten for tens of thousands of years before and for which our bodies have evolved.

While it's sane to be suspicious of food additives, I don't think it's rational to go back ten of thousands of years. Modern humans live much longer and are healthier than humans ten thousand years ago. There are plenty of modern additives about which there is little to no debate:
* Iodine added to salt.
* Vitamins A and D added to milk in Northern countries (incl. USA and Canada).
* Fluoride added to tap water.
I'm sure there are many other additives that are generally accepted as good, but I'm not aware of. And aside from additives, I certainly wouldn't want my food to stop being pasteurized...

> MSG is especially worrying because there are some studies that show negative effects of MSG and the fact that other studies show no effects does not quite negate these.

IIRC, the studies that showed negative effects were done by injecting MSG directly into rats. I believe the consensus is that the ingestion of glutamate is much different than direct injection. You consume glutamate every day in your food (I'm sure there are plenty of things you eat which would do very bad things if injected directly into your blood). I don't think anyone has the view that studies are negated because they are contradicted by others, but they are frequently negated due to poor protocols or new information.

I actually don't find MSG very worrying because it seems to be a cultural phenomenon, more than a scientific one. (There are many: third-hand smoking, resveratrol, anti-oxidants, etc. Not to say there's no science there, just that the cultural view is only tangentially related to the science. It's like our fan death.)

I went through my own little discovery: A few years ago, I was shocked to discover that a girl I was dating frequently cooked with an MSG sauce (she was from Mexico). Stunned, I researched the whole MSG thing. Turns out it's quite popular all over the world, except in english-speaking countries. The popular demonization stemmed from a few poorly-done studies that very quickly become part of the zeitgeist (it's suggested that this was partly due to racism/xenophobia since it was seen as an asian thing). And despite its widespread use for decades, there's no real evidence that suggests what people fear about it. And because of the fear, it's actually one of the most-tested of all food ingredients and yet it remains legal to sell and use as an additive everywhere.

> Furthermore, I myself feel negative effects when eating certain foods that I suspect of containing MSG.

One last quick point --
I don't think you should treat your own experience as the addendum. As you suggested, the human body is a complex system so I think the best thing that you can do is listen to your instincts. [Of course, you should also try to keep in mind the psychology at play. You feel bad, so you suspect the food has MSG; or you suspect the food has MSG, so you feel bad.]