Moms-to-be are often reminded that they're eating for two. It's tempting to take this as an excuse to go for that extra scoop of the ice cream. (Believe me, I've been there.)
But a solid body of research suggests that expectant mothers should be walking away with the opposite message: Pregnancy should be a time to double-down on healthful eating if you want to avoid setting up your unborn child for a lifetime of wrestling with obesity.
Now, research published this week offers tantalizing clues from mice of one way that a poor maternal diet may be laying the groundwork for obesity: by rewiring a part of the brain that's critical to regulating appetite. And these changes appear to happen in the third trimester of pregnancy, suggest the findings, which appear in the journal Cell.
First, it's crucial to stress that we're talking about mouse moms here, not human ones. Researchers at the Yale School of Medicine and the Max Planck Institute for Neurological Research in Germany used them to find out how maternal diet influenced brain development in offspring.
So they played around with feeding mouse mothers a high-fat diet before and during pregnancy and lactation. Pups born to obese mothers "had different metabolic profiles than those of pups from mothers who were on a normal diet," explains study co-author Tamas Horvath, a professor of neurobiology and obstetrics at Yale.
Specifically, he says, the pups whose mothers ate a high-fat diet while they were in utero had impaired connections in brain neurons that regulate glucose and help control when they're hungry and full and how fat gets broken down.
That wasn't entirely unexpected, since plenty of studies in animals and humans have established that obese mothers beget obese children.
What really surprised the researchers, says Horvath, is that these neural changes also showed up in the offspring of mice who weren't obese but were fed the high-fat diet only during lactation. This period of brain development in mice corresponds to the third trimester of pregnancy in humans.
This suggests that even normal-weight moms-to-be need to watch their diet if they want to avoid setting the stage for obesity in their kids, he says. But it also suggests that researchers should look more closely at late pregnancy as a period when it might not be too late to intervene in a mom's diet to help break the cycle of obesity.
"This study is another important piece to the puzzle that early-life influences can have long-lasting consequences to the offspring," says Dr. David Ludwig, a Harvard researcher who studies obesity in children.
He warns, though, that we should be careful in how far we extrapolate the findings to humans. After all, he notes, "humans and rodents diverged in evolution 60 million years ago."
For one thing, Ludwig says, a high-fat diet for rodents isn't the same as one for humans, so we can't apply the findings directly to human moms. But that said, the general principle that nutrition in the womb and during early life is key to long-term health risks like obesity still applies, says Ludwig, who directs the New Balance Foundation Obesity Prevention Center at Boston Children's Hospital. It's not simply genetics or home environment that explains a family's tendency toward obesity, he says.
Last October, Ludwig and his colleagues published a study of more than 40,000 mothers and their more than 90,000 children. To factor out the role of genes and environment, the researchers looked only at siblings, comparing how much weight a mother gained in different pregnancies and how that related to her children's weight years later. Maternal weight gain, he notes, is a good proxy for the quality of diet during pregnancy.
They found that kids born to moms who put on too much weight — which they defined as 40 pounds or more — during pregnancy had an increased risk of becoming obese even more than 10 years down the road.
The takeaway message for expectant mothers, he says, is that, regardless of your genes, what you eat during those 40 weeks of pregnancy really does matter:
"Genes, at this point, are not modifiable, whereas diet and pregnancy weight gain are."
MELISSA BLOCK, HOST:
It's no surprise that many moms-to-be think a lot about what they eat. For some women, intense cravings and big appetites lead to concerns about too much weight gain during pregnancy. Well, now, new research indicates there may be a direct link between a mother's diet during pregnancy and her child's future eating habits and weight. NPR's Allison Aubrey reports.
ALLISON AUBREY, BYLINE: Kim Cooper, who's a mom of two young boys, recalls precisely what she craved during her pregnancies.
KIM COOPER: It's funny, with my first - with my older son, lemon squares. I wanted them and was making them all the time and eating them.
AUBREY: So, sugar.
COOPER: Yes. And the lemon, the tartness.
AUBREY: Now, Cooper says, don't get her wrong, she also ate plenty of healthy things - salads, beans, avocados. So, she did not gain too much weight. And now almost three years later, she says her son is a healthy weight and he knows what he likes to eat.
COOPER: He definitely has the same taste buds. So, anything that I like he generally likes. So, that could be a pretty big indication of what I eat is what he now likes.
AUBREY: Now, it doesn't always work out this way, but new studies suggest there is a fascinating and somewhat complicated relationship between a mom's diet during pregnancy and her babe's behaviors. It's been known for a while that if a mom-to-be is overweight when she conceives or gains too much weight during pregnancy, her child is more likely to become overweight, too. Physician David Ludwig of Harvard says this is well established.
DR. DAVID LUDWIG: Increasing degrees of maternal weight gain during pregnancy consistently increase the risk of that child being obese.
AUBREY: So, the question is why? Is it becomes mom and baby have the same genes, or is it that if a mom eats an unhealthy diet so do the kids?
LUDWIG: Children and mothers share many factors that could promote obesity, such as genes or environment.
AUBREY: And this is likely part of the explanation. But Ludwig's latest research suggests it's more complicated. It often happens that within the same family you can have one sibling who's overweight while brothers and sisters have no weight problem at all. And when Ludwig looked into why, he discovered that the difference in how much weight a mother gained from pregnancy to pregnancy predicted which of her children would be heavier. He looked at more than 40,000 moms and found, for example, if a mom gained more during her second pregnancy compared to her first, then her second child was more likely to be overweight by age 10. So, this shows there's more than genes at work here.
LUDWIG: Correct. And the importance of that is that genes are - at least at this stage - not modifiable. Whereas diet and pregnancy weight gain are.
AUBREY: So, if you want to protect your babe-to-be from the risk of obesity, new research suggests that what moms eat in the last three months of pregnancy may be key. Here's Yale researcher Tomas Horvath.
TOMAS HORVATH: It appears to us, at least, that by changing the diet in that period of development you will have an impact on development of vulnerability to obesity.
AUBREY: Horvath says, in his study, when pregnant mice were fed a high-fat, high-calorie diet, the brains of their pups changed. The diet rewired the part of the brain that's critical to regulating appetite. And this was true of the offspring of mice moms who weren't obese and only were fed a high-fat diet during lactation, a period that corresponds to the third trimester of pregnancy in humans. Now, it's not clear that it works exactly the same way in humans. But remember mom Kim Cooper, who told us that despite a few lemon squares she did eat well towards the end of her pregnancy.
COOPER: More salads and more protein - probably more protein. I don't think (unintelligible) to my diet.
AUBREY: And this healthy pattern of eating has lately influenced her son for a lifetime. Allison Aubrey, NPR News. Transcript provided by NPR, Copyright NPR.