The role of Westernized diets in genetic discordance

Natural selection is a representation of a continuous interaction between the genome of a species and the environment in which it lives in, over the course of time. When the environment undergoes permanent change, there is a discordance between the species’ genome and its environment, which is stabilized by a directional selection that moves the set point of the general population genome. The discordance can manifest itself through disease, increased morbidity and mortality, and a reduction in reproductive success.

Now, we, the humans of today, have a genome that is adapted to the environment of our ancestors; the environment that conditioned our genetic makeup. There is currently a suggestion that the thorough changes in environment (here, I’m concerned with lifestyle conditions such as diet) that the introduction of animal husbandry and agriculture brought with it, came about too early on an evolutionary timescale for our genome to adapt, causing the emergence of several “diseases of civilization”.

The relevance of this for my research, is that chronic illnesses and other health problems that are in part or in their entirety accountable to dietary choices, is likely to represent the most serious threat to public health today.
– 65% of US adults are overweight or obese
– Almost 300 000 deaths annually in the US are ascribed to obesity
– More than 64 million (!) Americans suffer from one or more variants of cardiovascular disease (the leading cause of mortality)
– 11 million Americans have T2 diabetes
– 37 million adults maintain high-risk total cholesterol concentrations (eggs, bacon, and sausages for breakfast, anyone?)
– Cancer, being the second leading cause of death, is estimated to be attributable to nutritional factors in one third of cases

I’m worried!

Before animal husbandry and agriculture entered the stage, the hominin dietary choices would by necessity have been limited to seasonal wild plant and animal foods. When we domesticated plants and animals, the original nutrient contents changed, even more so with the industrial revolution. New foods were introduced as staples, for which our genome had little or no evolutionary experience (in particular the quantitative and qualitative combinations of food and nutrients that followed the industrial revolution).
Currently, about 3/4 of the total energy consumed by Americans are constituted by dairy products, cereals, refined vegetable oils and sugars, and alcohol. In the traditional preagricultural hominin diet, these foods are likely to have contributed close to zero of their energy intake.

But milk! They must’ve drunk milk!
Like all mammals, hominins likely consumed the milk of their own species during the suckling period, after which the consumption of milk products of other mammals would have been inherently difficult considering that it would’ve required the capturing and milking of wild animals (not yet domesticated!). The direct chemical evidence for dairying is from dairy fat residues on pottery, found in Britain, dated to about 4000 BC.

And sugar?
In 2000, the US per capita consumption of refined sugars was 70 kg (compare to 55 kg in 1970). In the past, one of the few concentrated sugars that hominins would have had access to is honey, which would only have seasonal availability, and thus, be a minor dietary component.
In the 1970s, it became economically feasible to produce high-fructose corn syrup (a mix of liquid fructose and glucose) in mass quantities.

Refined oils, salt, and domestic meats are next up.

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5 responses to “The role of Westernized diets in genetic discordance

  1. Hi Eva,

    This is a fantastic article, thank you for taking the time to write it. As you rightly point out in your statistics, Americans are worryingly overweight, as are us Brits. I think attitudes are slowly changing though. It’s becoming cool to exercise – a vital component of stimulating a healthy lifestyle. Let’s hope attitudes towards food begin to follow suit!

    Look forward to reading your future work!

    Dan

  2. Hi Eva,
    I’m really enjoying these articles…I just finished “Whole” by T. Collin Campbell, who I am sure you are familiar with, and your information/focus fits well with his. I’m curious about the 64 million Americans with a variant of heart diseases stat…what diagnosis/marker does this refer to and what is the source? This would work out to
    20%…Scary stuff…

    • the CVD stat is from the American Heart Association: Heart and stroke statisticsโ€”2004 update. It is indeed a lot but it also includes a variety of different diseases, not only hypertension and atherosclerosis. I’m sure you know all that though. I didn’t read that book, but I do know Campbell! I’ve just heard a lot of criticism of the China Study lately so I’m sticking to shorter journal articles for now to be able to consult many sources in the time I have to finish this paper. Then I’ll most likely get into the books again ๐Ÿ™‚

  3. Pingback: Genetic discordance part 2 | envirodiet·

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