Tuesday, January 15, 2013

An Evolutionary Approach to Chronic Disease

Most people don’t know what causes chronic disease.  In their eyes it ‘just happens’ and is due to genetics, for example: ‘I have breast cancer because my mother did’.  When you’re surrounded by so many who are overweight, diabetic, have had a heart attack, are aging poorly, etc, it can seem that chronic disease is normal.  When you combine normality with a lack of understanding, chronic disease seems inevitable and that there’s little you can do. 

Population-Wide Freedom of Chronic Disease 

However, many of the chronic diseases we suffer from are very rare among modern day hunter-gatherers (HGs) and the traditional cultures (TCs) visited by Weston A. Price. 

When HGs or TCs adopt a western diet they succumb to the same diseases as we do.  This suggests their diet, rather than their genes, protects against chronic disease, and that it’s possible to have near population-wide freedom from chronic disease. 

A counter argument is that those people didn’t live long enough to show signs of chronic disease.  But this counter argument lacks merit:

  • Average life expectancy at birth was quite low for HGs, which is due to high infant and childhood mortality.  Most who make it to 15 live to 45 and 45 year old HGs can expect to live another ~20-25 years [1]
  • Biomarkers of disease risk such as elevated fasting glucose, blood pressure, atherosclerosis are rare among HGs and common in age matched western populations [2]
  • Chronic disease can occur in early age: certain autoimmune diseases are more likely to begin in younger people, childhood obesity and diabetes is climbing and early signs of atherosclerosis can be seen in young people
  • Most of the increase in coronary heart disease in the early 20th century can’t be explained by changes in average lifespan [3] 

Where’s the Selection Pressure? 

There’s some further supporting evidence for low chronic disease among HGs and TCs. 

In Chris Masterjohn’s presentation for the Real Food Summit he makes an excellent point (in Part 1 at ~24:00) that among populations free of chronic disease the most vulnerable and the least vulnerable members are protected from chronic disease.  He described that and other details as a strength of Price’s work.  For this post I’ll take it in a different direction. 

Most people agree that chronic disease reduces fitness (evolutionary/natural selection fitness that is)*.  If a person’s genetics were such that they spontaneously developed obesity (ob-/ob-) for example, those genes would have strong selective pressures against them and go quickly out of the gene pool. 

Some genetic mutations, such as familial hypercholesterolemia (FH), and some polymorphisms, such as the GG phenotype of myeloperoxidase (MPO), are associated with a higher risk of disease (in both cases CVD).  (Other genetic mutations and polymorphisms would be associated with lower risk of disease.)  These are the kinds of things that are meant by genetic risk/vulnerability and is how family history can be predictive. 

But you’ve got to wonder how these and other ‘bad genes’ are around, seeing as they are seemingly so harmful now. 

If one were genetically susceptible to disease and in an environment that promoted disease, then those genes would have strong selection pressures against them.  Perhaps they would pass those genes to the next generation, but on a large scale those genes would become rarer over time. 

In an environment that doesn’t promote disease, there’s no selection pressure against ‘bad genes’ and so the ‘bad genes’ stay around.  This is important because it provides support for both chronic disease being previously rare and ‘bad genes’ not being a death sentence. 

Except for some pretty extreme gene mutations such as homozygous FH, chronic disease doesn’t have to run in the family and we should not become fatalistic. 

* Some theories are based on the idea that a vulnerability to chronic disease has been and can be adaptive.  These theories will be the focus of a future post. 

Paleo and WAPF 

The diet of HGs and TCs seems to be the main protective element against chronic disease and is a main starting point for the Paleo and WAPF approach to eating 

Without understanding the causes of chronic disease we can have reasonable guess that switching to a Paleo/WAPF approach to eating is probably to going to improve someone’s health and may even reverse their chronic disease.  We can make this guess and somewhat generalise to them based on:

But understanding the causes of chronic disease is important because simply recommending that one should eat Paleo/WAPF may not be as convincing or as helpful as the advice could be.  Valid questions that we could be asked include:

  • How does Paleo/WAPF help?
  • Are there any new foods that are helpful and any old foods that are harmful?
  • What about supplementation?
  • What about other lifestyle factors? 

Without much understanding we can’t properly answer those questions.

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