Monday, August 12, 2013

Applying Mismatch Theory to Diet

  • In 2007, 67.4% of Australian adults were overweight.  In 2005, 20% of Australian adults were obese, which was projected to rise to roughly 29% in 2010 [1]
  • Cardiovascular disease is the leading cause of death in Australia, causing 31% of all deaths in 2011 [2]
  • Cancer is the second leading cause of death in Australia, causing ~30% of all deaths in 2010 [3]
  • In 2007, 45% of Australians (aged 16-75) had suffered from a mental illness at some point in their life and about 20% were/are suffering from a mental illness in the last 12 months [4]*

These statistics are pretty grim, worse still when you consider that this doesn’t include all the other diseases, disability adjusted life years (DALYs) and the CV events and cancers that don’t kill people.  I think it’s a fair call that we aren’t well adapted to the modern world. 

Let’s apply mismatch theory: what are humans better adapted to? 

The earliest evidence for anatomically modern humans is from some incomplete fossils which date to ~200,000 years ago.  For most of human history we lived as hunter-gatherers, up until about 10,000-13,000 years ago (11,000-8,000 BC) when people living in the Fertile Crescent developed agriculture.  We have been hunter-gatherers for ~95% of our evolutionary history as humans**. 

Hunter-gatherers seem to be mostly free of the chronic, non-communicable diseases that are so common in the modern world.  Biomarkers of disease such as obesity, IR and high BP are rare among modern day hunter-gatherers*** [5] 

Given the history and rates of chronic disease, I think it’s a fair call that we are well adapted to a hunter-gatherer diet and lifestyle.  One could say our genes may ‘anticipate’ these things from us. 

Diet has perhaps the most important effect on health and disease, which is why I’ll focus on it, but we shouldn’t ignore the potential consequences of mismatches related to lifestyle (exercise, sleep, sun exposure, stress, etc) and the environment. 

There’s a lot of debate as to what paleolithic hunter-gatherers actually ate because modern hunter-gatherers aren’t a perfect analogy to paleolithic hunter-gatherers and the diet of hunter-gatherers would vary a fair bit by location, season, etc.  That being said, I don’t think a perfect accounting is necessary for the following reasons: 

  • Modern hunter-gatherers are good enough.  We can use a bit common sense, for example: if modern HGs have refined sugar, refined grains and alcohol they would have gotten it from an industrialised society
  • The commonalities between HGs tribes are probably more important than the differences
  • The diet of HGs is only a starting point and re-enactment is not the end goal.  Let’s use the information to generate some hypotheses, conduct some studies (clinical trials that compare diets or foods, and looking at what’s contributing to the mismatch) and use what’s effective.

Cordain, et al found the following****: 

  • On average modern HGs get 45-65% of their calories from animal foods and 35-55% from plant foods.  And 19-35% of their calories from protein, 29-48% from fat and 22-40% from carbohydrates [6]
  • Modern HGs got most of their calories from meats, fish/shellfish, fruits, roots, tubers, nuts and seeds [6]
  • Modern HGs had low amounts of or no: dairy foods, cereal grains, refined sugars, refined vegetable oils, alcohol, salt, fatty domestic meats [7]
  • Modern HGs on average had a lower GL diet, a lower proportion of SFA and a lower n-6:n-3 ratio (2-3:1 vs. 10:1), higher protein, higher micronutrient density, a neutral acid-base balance, a lower sodium:potassium ratio and higher fibre [7]

“Although dairy products, cereals, refined sugars, refined vegetable oils, and alcohol make up 72.1% of the total daily energy consumed by all people in the United States, these types of foods would have contributed little or none of the energy in the typical preagricultural hominin diet” [7]

* It should go without saying that those are old Australian statistics and may not reflect the rates of disease in Australia currently or those in other developed countries. 

** I drew the line at anatomically modern humans, which is a little later than where most in the Paleo community draw the line (2.5 million years ago, when early hominids ate more animal food).  Drawing the line at anatomically modern humans makes the point well enough (that we are likely well adapted to a HG diet and lifestyle).  You have to draw the line somewhere, if you go back 2.5 million years, why not 3.5 million years, 5, or even 55?

*** One could argue that HGs are genetically protected against chronic diseases, but this is unlikely seeing as they are usually more susceptible to chronic diseases when exposed to the western diet and lifestyle 

**** This is just a summary of what they found.  It doesn't mean that it's optimal, although is a move in the right direction.  I disagree with the lean meat, low salt, high protein and low SFA, and don't think acid-base and GI is important.

Further Reading:
(1) An Evolutionary Approach to Chronic Disease
(2) Evolutionary Health Promotion: A Consideration of Common Counterarguments
(3) Guest Post – Professor Gumby - essay 001
(4) Origins and evolution of the Western diet: health implications for the 21st century
(5) Plant-animal subsistence ratios and macronutrient energy estimations in worldwide hunter-gatherer diets
(6) The western diet and lifestyle and diseases of civilization

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