Do mothers who diet during pregnancy predispose their children to be heavier? That's the intriguing suggestion of a new study done in the United Kingdom, and the latest addition to a field known as epigenetics.
Epigenetics is a funny story (though not raucously so) in biology. In my first biology textbooks in middle or high school, an 18th-century French biologist named Jean-Baptiste Lamarck was the chump of the chapters on evolution. Before Charles Darwin formulated his ideas on adaptation and natural selection, Lamarck speculated that organisms could pass down traits that they'd acquired during their lifetime. For example, if a giraffe gradually stretched out its neck by reaching for high leaves, it could pass on that stretched-out neck to its young. Poor Lamarck's theory was tragically easy to disprove. If you cut off a mouse's tail, after all, it still has babies with tails. Genes are the units of heredity. We get our DNA from our parents, and nothing we do during our lifetime changes our DNA.
Except for when it does. These days, scientists are gaining appreciation for epigenetics: factors above the level of the gene that we can pass down to our children. Sorry for all the joshing, Jean-Baptiste. Genes are still the most important unit of inheritance, but we now know that the way our DNA is coiled and packaged inside our cells affects how its instructions are carried out. Factors in our lifestyles can cause changes in that packaging, and we can pass on those changes to the next generation.
Epigenetic change can also happen in utero. A human's DNA is locked in as soon as sperm and egg combine, but factors in the womb--our first environment--can have epigenetic effects on the DNA in our rapidly multiplying cells.
That brings us back to pregnant mothers. Previous studies have shown a connection between famine in utero and obesity in adulthood. If a mother can't get enough food, does she somehow mark the genes of her fetus so that it clings to calories in later life? A slow metabolism is helpful in a time of famine, but not so much in a time of fast food. Studies in animals have suggested that epigenetic changes are responsible for the link between a pregnant mother's diet and her offspring's adult weight.
Looking at DNA from the umbilical cords of newborns, the authors of the new study set out to find epigenetic changes that were linked to the children's weight many years later--and to their mother's diets.
The authors studied two groups of women and their children living in the UK. They interviewed the women when they were 15 weeks pregnant about their diets. When the babies were born, their umbilical cords were frozen. Six or nine years later, the researchers tracked down these children (between the two groups, there were 317) and measured their body fat. They also extracted DNA from the frozen umbilical cords.
The researchers looked at a certain kind of epigenetic change called methylation--a chemical tag attached to the DNA that makes it less legible to the cellular machinery. In both groups, they found that increased methylation around one particular gene in the umbilical cord DNA was strongly correlated with higher body fat when the children were older. This marker in the newborns' DNA, that is, partly predicted what their bodies would be like as six- or nine-year-olds.
Additionally, methylation at that same gene seemed to be linked to the mothers' carbohydrate intake in early pregnancy. Mothers who reported eating low levels of carbs had babies with higher levels of methylation. The increase in methylation was not linked to higher fat or protein intake, just to low levels of (reported) carbohydrates.
It's hard to rigorously measure the nutrients in a person's diet from their answers on a questionnaire. And even if the correlation is real, it doesn't prove the mother's diet is causing the methylation or the higher fat level in her child. Furthermore, we don't know whether these children will grow up to be overweight adults. But the study's suggestion is tantalizing. Could women who follow Atkins or South Beach, or another diet sold to them in the name of health, be predisposing their unborn children to a lifetime of weight struggles?
As researchers continue to solidify the links between our lifestyles and epigenetics, new diagnostic tests and treatments may become possible. A DNA test at birth could reveal a person's risk for various diseases based on epigenetic factors--instead of, or in addition to, their genetic risk. And scientists might even develop treatments that target DNA packaging and methylation.
Or maybe someone will just start selling another fad diet. Epigenetics: the new Atkins!