Evidence of a vegetarian diet permanently shaping the human genome
MOLECULAR BIOLOGY AND EVOLUTION (OXFORD UNIVERSITY PRESS)
In a new evolutionary proof of the old adage, 'we are what we eat', Cornell University scientists have found tantalizing evidence that a vegetarian diet has led to a mutation that -- if they stray from a balanced omega-6 to omega-3 diet -- may make people more susceptible to inflammation, and by association, increased risk of heart disease and colon cancer.
The discovery, led by Drs.
Tom Brenna, Kumar Kothapalli, and Alon Keinan provides the first evolutionary
detective work that traces a higher frequency of a particular mutation to a
primarily vegetarian population from Pune, India (about 70 percent), when compared
to a traditional meat-eating American population, made up of mostly Kansans
(less than 20 percent). It appears in the early online edition of the journal Molecular
Biology and Evolution.
By using reference data from the 1000 Genomes Project, the research team provided evolutionary evidence that the vegetarian diet, over many generations, may have driven the higher frequency of a mutation in the Indian population.
The mutation, called rs66698963 and found in the FADS2 gene, is
an insertion or deletion of a sequence of DNA that regulates the expression of
two genes, FADS1 and FADS2. These genes are key to making long chain
polyunsaturated fats.
Among these, arachidonic acid is a key target of the
pharmaceutical industry because it is a central culprit for those at risk for
heart disease, colon cancer, and many other inflammation-related conditions.
Treating individuals according to whether they carry 0, 1, or 2
copies of the insertion, and their influence on fatty acid metabolites, can be
an important consideration for precision medicine and nutrition.
The insertion mutation may
be favored in populations subsisting primarily on vegetarian diets and possibly
populations having limited access to diets rich in polyunsaturated fats,
especially fatty fish.
Very interestingly, the deletion of the same sequence might have
been adaptive in populations which are based on marine diet, such as the
Greenlandic Inuit. The authors will follow up the study with additional
worldwide populations to better understand the mutations and these genes as a
genetic marker for disease risk.
"With little animal
food in the diet, the long chain polyunsaturated fatty acids must be made
metabolically from plant PUFA precursors. The physiological demand for
arachidonic acid, as well as omega-3 EPA and DHA, in vegetarians is likely to
have favored genetics that support efficient synthesis of these key
metabolites." say Brenna and Kothapalli in a joint comment.
"Changes in the dietary omega-6 to omega-3 balance may
contribute to the increase in chronic disease seen in some developing
countries."
"This is the most
unique scenario of local adaptation that I had the pleasure of helping
uncover", says Alon Keinan, a population geneticist who led the
evolutionary study.
"Several previous studies pointed to recent adaptation in
this region of the genome. Our analysis points to both previous studies and our
results being driven by the same insertion of an additional small piece of DNA,
an insertion which has a known function. We showed this insertion to be
adaptive, hence of high frequency, in Indian and some African populations,
which are vegetarian. However, when it reached the Greenlandic Inuit, with
their marine diet, it became maladaptive."
Kaixiong Ye, a postdoctoral research fellow at Keinan's lab,
further notes that "our results show a global frequency pattern of the
insertion mutation adaptive to vegetarian diet, with highest frequency in
Indians who traditionally relied heavily on a plant-based diet."