Nicola,
I think what you are asking is why, if some specific food, say raw meat, is the proper thing for us to eat, then why do we (and so many others) have different experiences with it - sometimes good, sometimes not so good.
I've thought about this a good bit myself and have come to what I believe is a reasonable explanation. Just a theory of course, but the idea seems to hold true in other areas of the natural world.
I've always loved plants and came very close (but not quite
) ) to getting a degree in Ornamental Horticulture. I love the natural form that plants take. It is fascinating to watch the form of a tree develop from seedling through maturity. Stick with me here, there is a point, albeit a long one.
When we plant a tree seed in its natural environment, the seed sprouts when conditions are right, and depending on the type of tree, a tap root is sent down in search of water. If things go well, the tap root will reach the underground water source before a cycle of drought sets in and the tree survives - often for hundreds of years.
Now take the same tree seed and plant it in a commercial nursery setting. First the seed is planted in a tray until it spouts. It is then transferred over time to larger and larger containers, until, at some point, it is sold. The proud owner takes it home, often to an area and/or climate that is not natural for that tree species. He plants it in his garden and cares for it by watering it 3 times a week with sprinklers as he waters is lawn. The tree appears to be doing fine.
Then drought strikes. The water company rations water and now the garden must fend for itself. We expect the grass and flowers to die because they have such shallow roots, but what about that big tree in the corner? Well there is a good chance it will die as well. You see it never developed a tap root to reach the water table. The original seedling tap root was destroyed by growing the tree in a container. Then by watering it constantly through out its life there was no need to develop a new tap root as there was plenty of water on the surface. In sort, the tree was not allowed to develop naturally. This is why, when a fruit orchard is abandoned and irrigation stopped, most of the trees die. They never developed their natural tap root system to reach subterranean water.
Now it is possible to condition a tree like this to survive during drought. You must alternate shallow and deep irrigation cycles, withholding water after the deep cycles to encourage the tree to sink its roots deeper. This process can take several years, and it causes a lot of stress to the tree, but it can be done.
What does all this have to do with us and diet? Well, my thinking is that we are often fed incorrect foods from the time we are born, (just like the tree in the nursery). Our bodies do their best to adapt to the unnatural environment. Enzymes appropriate to the foods we are eating become dominant. Bacteria in our digestive tracts develop to feast on the large carb load we consume. The large mass of waste products created (fiber anyone) distends and weakens our colons. Our muscles and other body systems become used to large amounts of blood glucose always being present. In other words, like the tree in the corner of the yard, we've created a totally unnatural environment for our bodies for most of our lives.
Then we suddenly decide that what we are doing is not right, and embark on a new path that is completely opposite from what we were doing before. No longer are we going to eat cooked starches, we're now going to eat nothing but meat and we're going to eat it raw! To our bodies this is creates an environment similar to our corner tree suddenly experiencing drought. The enzymes our bodies are making are suddenly inappropriate for the new food we are eating. The large amount of bacteria in our digestive tracts that are dependant on carbs and fiber to survive start to die off, creating toxins in the process. The massive fiber load disappears from the digestive tract as the meat and fat leave little waste so there is nothing to push the dying bacteria through. First we become constipated and then the toxin load causes diarrhea. We are stressed just like we stressed the tree to cause it to extend its root system, and this causes us to worry that our new diet is not the correct one after all because we're having all these horrible problems.
Well, like adapting the tree to again be able to survive in normal water/drought cycles (which is its true natural state), it will take time for our bodies to adapt to the new foods, even though they are actually our proper foods. Our bodies must shut down production of enzymes for digesting carbs and create new enzymes for digesting fat and protein. Our intestinal flora must change from fermentive bacteria to putrefactive bacteria. Our colons must shrink and adapt as best they can to the much smaller load of waste products. Our muscles and other body systems must adapt to using fat and ketones instead of glucose for fuel. Like forcing the tree to deepen it's root structure after its tap root was destroyed, this may take a considerable amount of time and involve a lot of stress. I've been at it for 5 or 6 years now (3 of them meat only), and I'm still seeing changes. Also, like the tree, we'll never have a proper "tap root" as we weren't allowed to develop properly from the beginning. We can get much better, but probably never reach true 'normal'. For instance, once we've stretched our colons from years of consuming a heavy fiber and carb load, they will never shrink back to the size they should be. Better? - yes. Best? - no.
Anyway, this has been my experience and there are many examples of initially raising something outside its natural environment and then requiring much attention and time to readapt it to survive on its own in natural conditions. Our bodies are no different.
Thoughts?
Lex