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An Introduction to the Psychology and Physiology of Dieting

Over the next series of articles, I want to look at both physiological and psychological reasons that diets can fail.

But before doing that I need to make something very clear: the distinction I’m making between psychology and physiology is simply for convenience, it’s not one that really truly exists.

That is to say, psychology impacts on physiology and physiology impacts on psychology and the days of pretending the body and mind are separate non-interacting entities are long, long gone. Again, I’ll make the separation primarily for reasons of convenience, it will save me some needless complexity in the upcoming discussion. Just keep in mind that it’s an artificial and non-existent separation in reality.

Modern science, for example the field of psychoneuroimmunology, recognizes that the brain and body are in a constant state of interaction and involvement with one another. This is sort of the basis for the idea that you can think yourself sick, or for the idea that people with a more positive attitude are more likely to survive certain diseases (such as cancer). Your thought processes can impact on such workings of your body as immune function.

Put more simply, how you think affects how your body works and how your body works can affect how you think or feel.

Incidentally, for anybody who is interested in this topic, I would highly, highly, highly recommend almost any of the books by science writer Robert Sapolsky, especially his book Why Zebras Don’t Get Ulcers where this topic is discussed in some detail (primarily wrt: cortisol and stress). This is literally one of my top-5 books ever and I cannot recommend it too highly.

Anyhow, while you’re sitting there reading this, I want you to start thinking about something that really makes you angry. Taxes, gas prices, my inability to blog consistently, take your pick. Really get a good anger going. Now stop for a second and pay attention to your body: odds are that your heart rate is up, if we measured blood pressure it would be increased too, you might be breathing a little bit harder, you get the idea. The mere act of thinking about something that upset you had a strong physiological effect throughout your body.

Here’s another example in the reverse direction: everybody knows how they get really lethargic and lazy when they are sick with something like the flu or a bad cold or what have you. It’s as if when you are sick your body is deliberately trying to get you to lay around all day and rest. This turns out to basically be the case.

When you are sick, your body releases short-lived chemicals called cytokines, some of which are inflammatory. Inflammatory cytokines, in addition to making you feel like warmed over crap when you have the flu or something, they also directly impact on the brain and your motivation to move around.

I’d note that a similar mechanism has been suggested as a primary cause of overtraining; called the cytokine hypothesis of overtraining I think it ties together a lot of conflicting and contradictory data on the topic. It explains changes in performance along with behavior and ties together the previous held (but wrong idea) of local versus central overtraining. It turns out that they are the same thing and local effects (tissue damage) is causing central effects (behavior and motivation changes).

Essentially constant/chronic/excessive inflammation locally (in the muscles you’re training) causes an increase in inflammatory cytokines and this is responsible for the lack of motivation to train and lethargy that often sets in. Essentially, your body (your muscles) are trying to ‘tell’ your brain to give it a rest and take some down-time. Of course, humans, being the stubborn folks that we are, often choose to ignore or over-ride these signals.

This has a lot of relevance to the issue of dieting failure which is what I’ll be talking about next.

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