In his last post Loren Cordain wrote:
'....Neel's hypothesis has become "one of the orienting
concepts of nutritional and biomedical anthropology" .....
So very true, and not just anthropology but nutritional biochemistry
and molecular biology too. Just about every paper on the origins of
obesity and diabetes mentions it. It's as if Neel's hypothesis is
considered proven beyond reasonable doubt.
Loren suggested I might elaborate on the mechanisms behind our
hypothesis (1) that 'ultra' high protein diets selected for the insulin
resistant genotype rather than cycles of feast and famine (ie the
thrifty genotype hypothesis).
The mechanism relates to both the high protein intake as well as the
simultaneously low carbohdyrate intake. We hypothese that the need to
spare carbohdyrate for the brain and fetus which use glucose as their
preferred fuel would have required metabolic mechanisms that
re-directed glucose away from the muscles. That's exactly what insulin
resistance does best! What's more insulin resistance in the liver
promotes gluconeogenesis even in the face of the moderate insulinaemia
which accompanies high protein meals.
We have had the opportunity to revise the hypothesis for World Review
of Nutrition and Dietetics (in press). Here is the abstract from that
paper (I'd appreciate any new feedback):
TimesInsulin resistance may
provide valuable insights into past human existence and diet. A
critical role is proposed for the quantity and quality of dietary
carbohydrate in the pathogenesis of the insulin resistance and
hyperinsulinemia which characterise the metabolic syndrome,
non-insulin-dependent diabetes mellitus (NIDDM) and heart disease. Our
hypothesis, the carnivore connection, proposes that an
insulin-resistant genotype evolved to provide survival and reproductive
advantages to populations adapted to a high meat, low plant food (low
carbohydrate) nutritional environment.
Unlike true carnivores, humans have a limited capacity for
gluconeogenesis even on a high protein diet. Insulin resistance would
have maximised gluconeogenesis and redirected glucose away from muscles
facilitating the preferential utilisation of glucose by the brain,
fetus and mammary gland. But about 10,000 years ago, following the end
of the last Ice Age, carbohydrate intake increased with the development
of agriculture in the Middle East and Europe and the selection pressure
for insulin resistance was relaxed. Hence the prevalence of the
insulin-resistant genotype decreased in Europeans and other groups
exposed to a high carbohydrate diet for sufficiently long.
The Mongoloid ancestors of both Pima Indians and Nauruans occupied the
Siberian mammoth steppe during the final 20,000 years before the end of
the last Ice Age. These groups depended on a high meat diet and did not
develop agriculture until 2,000 years ago. Australian Aborigines never
developed agriculture and until this century ate an animal-based diet.
Thus Pima Indians, Nauruans and Australian Aboriginals have had only
recent exposure to a high carbohydrate diet and currently have among
the highest rates of NIDDM in the world. While their traditional
carbohydrate foods have a low glycaemic index and stimulate only modest
increases in plasma insulin, westernisation is associated with the
intake of refined, high glycaemic index carbohydrate which results in
pronounced postprandial hyperinsulinemia. In this context the insulin
resistant genotype is disadvantageous and predisposes to the
development of the metabolic syndrome, NIDDM and heart disease.
(1) Brand Miller JC, Colagiuri S. The carnivore connection: dietary
carbohydrate in the evolution of NIDDM. Diabetologia 37: 1280-1286,
1994.
Best wishes Jennie
Jennie Brand Miller PhD
Associate Professor in Human Nutrition
Department of Biochemistry G08
University of Sydney
NSW 2006 Australia
Phone: (61 2) 9351 3759
Fax: (61 2) 9351 6022