I know stress, bitterness, depression, etc. can have a profound effect on your body and what happens to it.
Do you think most illnesses are caused psychologically?
I'd argue that depression and most general negativity are physical inflammatory conditions. I think most conditions start in the diet, although stress and psychological factors can certainly exacerbate them from there and turn them into full on life-altering diseases.
In regard to the state of depression:
I believe that we, as humans, in our natural happy-brained state (that is to say, proper DHA levels and stable neurochemical levels from nurturing one's hormonal responses/levels) are fully equipped to cope with a certain level of stress. That level may vary by the individual, but nonetheless, there is a threshold, over which, one may succumb to depression, feelings of being over-whelmed; general non- or reduced- functionality.
If we induce chronic, general stress responses by eating unnatural foods, we may be close to (or even OVER) our natural threshold just on the level it takes to maintain daily functionality. Throw in an unprecedented event such as the death of someone close to us, and there is just no hope of coping in a healthy way.
By that, I fully intend to imply that we are equipped, as human beings, to cope with devastating events around us - I think the determining factor here (as I said: diet) is the amount of chronic stress that we go into said event with.
In regard to the relationship between body and mind:
I feel that one can develop a weakness either in body or mind (the above explanation expounds on the possibility of breaking down mentally, I believe), and either one will leave the other susceptible due to their interconnectedness. I've been eating paleo for a year now, and I've reached several unparalleled high points, but due to my physical injury, have also gone through phases of extreme depression - even though my diet did not change, I continued nurturing my insulin sensitvity and proper DHA levels, but my body was damaged in such a way that I couldn't avoid lamenting it.
However, I feel that in regard to society's general state: most folks are eating poorly overall, and "surviving, rather than thriving." This leaves them frail and exposed in the event that something should happen.
Honestly, I intended to expand on my original conclusion, but ended up providing a bit of a murky answer that may support or negate the premise... I apologize for that. I've rewritten this three times in an attempt to NOT begin with "it's physical" and end with "both are important", but I can't seem to do it. Perhaps one can say that it is easier and more common for one to weaken themselves through poor diet and succumb via that route; although other methods of detriment are possible.
I think, at the very least, we as paleo followers have an inherent advantage that we are not stressing our bodies on a physical level from day to day. We are more equipped than your average citizen to deal with whatever may come our way. And be it physical or mental, stress is stress, and it has its consequences.
There is alternative evidence that suggests that depression can be caused by altered intestinal flora.
I would be more ready to believe that most illnesses start in the gut.
Illnesses caused psychologically sounds like vitalism to me.
My view is that it's a mistake to separate mind from body, or even diseases to just one organ vs the whole. We're not cars, you can't just fix one thing and you're off on the road again - that does work in a somewhat limited way, but whenever you have a change in one organ it will have effects in others.
As an example, even when you take it to a the skeletal muscles, say you hurt your knee, you're now walking with a limp, so it places extra stress on your ankle or hip, which in turn may affect your posture, which in turn may affect your lung capacity because you're now hunched over and the lungs don't have the ability to have the same volume to move in, etc.
Sure, it may start in one place, but the effects are likely to be systemic, and you'll find multiple problems.
While I sort of believe (on faith, really) that stress can lead to all sorts of bad things, the idea always made me wonder how that could possibly be so. By what mechanism can this magical thing stress (or other handwavey psychological things) possibly cause IBS-type symptoms, depression, anxiety, etc.
Once I got a handle on my depressive episodes, I realized that it was like a mask occasionally applied to me, and not something from within my mind. It's not like my mental state causes the depression, it's that something goes wrong somewhere, and changes my mental state. I like the gut health hypothesis for this, because there's more of a mechanistic explanation there. It makes a lot more sense to me than just blaming it on stress with a big black box of an explanation.
As an aside, one of my main research interests is causality: given multiple time series, when and how can we assert that one set of time series causes another. There's little known in this field, but one thing clear to me is that it's really easy to get the direction of causality wrong, given the other inputs, and you can often say with much better certainty that two things are causally related than which direction the causal relation goes.
So, to answer your question, no, I don't think any illnesses are caused psychologically. I think our psychological states happen in response to the illnesses that are caused by something more tangible.