Genetic Adaptations to Diet and Climate
News Sep 29, 2015
At the genetic level, any 2 people are more than 99% the same. The variations that exist can be as small as a difference in a single DNA building block—called a single nucleotide polymorphism (SNP)—or as large as whole sections of the genome being copied or moved. These variations may underlie differences in susceptibility to disease, response to drugs, or reaction to environmental factors.
An international team of scientists led by Dr. Rasmus Nielsen of the University of California, Berkeley, wondered whether the genomes of people who live in a challenging environment for a long period of time show adaptations to that environment.
The Inuit, natives of Greenland, live in extremely cold conditions that can hover in the negative digits in winter. They eat a specialized diet, including seals and whales, that’s rich in protein and omega-3 polyunsaturated fatty acids. Although their ancestors arrived in Greenland less than 1,000 years ago, they lived for thousands of years before that under similar conditions in the Arctic.
The scientists analyzed SNPs from 191 Inuit (once known as Eskimos) and compared them with SNPs from 60 Europeans and 44 Han Chinese that were part of other genetic variation studies. The research was funded in part by NIH’s National Human Genome Research Institute (NHGRI).
The team found marked differences in a cluster of genes that code for proteins that help process dietary fatty acids. One SNP was the same in almost all the Inuit, but only about 2% of the Europeans and 16% of the Han Chinese had it. Some variants were significantly associated with the fat composition of red blood cell membranes, which had previously been measured in a group of Inuit. These membranes reflect how fatty acids were processed from foods eaten during the past 2 to 4 months.
The team found another region of genetic variation common to the Inuit that includes genes thought to be involved in the regulation of brown and brite fat cells. These cells affect heat production in response to cold exposure.
The scientists noted that several of the genetic differences in the Inuit were associated with other characteristics, including a lower height and weight and lower levels of fasting insulin and LDL cholesterol levels, which could potentially protect against heart disease and diabetes.
The original focus on fish oil and omega-3s came from studies of Inuit, Nielsen explains. They seemed quite healthy on their traditional diet, which is rich in fat from marine mammals, so many thought that fish oil might protect against cardiovascular disease.
“We’ve now found that they have unique genetic adaptations to this diet, so you cannot extrapolate from them to other populations,” Nielsen says. “A diet that is healthy for the Inuit may not necessarily be good for the rest of us.”