Posted on 04/22/2011 9:49:13 PM PDT by neverdem
Obesity is on the rise in nations across the globe, and more than diet and genetics may be to blame. A new study suggests a third factor is at work: DNA-binding molecules that can be passed down from mother to child in the womb. The finding could explain why what a woman eats while pregnant can sometimes influence the weight of her child—even into adulthood.
Scientists first began to suspect that a mother’s diet could affect the weight of her offspring in 1976. Studying the Dutch famine of 1945, when the German army cut off food supplies to western Holland, researchers found that people born to mothers who were pregnant during the famine were more likely to be obese as adults. Rat studies at the University of Auckland in New Zealand bolstered the findings: mothers who were undernourished during pregnancy gave rise to obese adults. One possible explanation is that the moms are somehow programming their children to live in a food-scarce world by increasing their appetites and ability to store fat—and if the children grow up with plenty to eat, they become overweight.
In the past few years, researchers have begun to suspect that so-called epigenetic modifications are behind this programming. Often these are chemical tags called methyl groups that can bind to DNA, where they act a bit like a volume knob, turning up or down the activity of certain genes. In a 2005 study at the University of Auckland, for example, researchers found that they could prevent obesity in rats born to starved mothers by removing methyl tags from their DNA. A recent survey of methyl groups on the DNA of adult people has also suggested that these tags are linked to obesity. But in that study, the authors could not determine whether the epigenetic changes were a consequence of being overweight or the cause of the obesity in the first place.
To determine if epigenetic changes can trigger obesity in humans, researchers at the University of Southampton in the United Kingdom and colleagues analyzed the diets of 78 pregnant British women using diet questionnaires that were crosschecked by blood tests that detect the residues of certain foods. When the babies were born, the researchers extracted DNA from their umbilical cords. Nine years later, they measured the body fat of the children using a low-dose x-ray scan. Infants with more methylation of a gene known as retinoid X receptor-α (RXRα), which codes for a protein involved in the development of fat cells and fat metabolism, were more likely to be obese at age 9.
The team repeated the study on another 239 pregnant women in the United Kingdom, this time measuring the body fat of the children at the age of 6, the earliest age at which they expected to see major differences in obesity. The relationship held: Of the 78 genes the researchers examined for epigenetic marks, only the methylation of the RXRα gene showed a strong relationship with obesity. As the percentage of the RXRα genes that were methylated went from 40% to 80%, the children’s percentage of body fat crept up from 17% to 21%, the team reports this month in Diabetes. The authors suspect that methylation inhibits the ability of the RXRα protein to play its normal role in the development and metabolism of fat cells, resulting in obesity.
Overall, a statistical analysis showed the methylation of the RXRα gene explained about a quarter of the differences in the children’s fat levels. The team could not find any DNA sequence changes in the RXRα gene or other genetic differences in the children that could explain the result. And when the researchers examined the mothers’ diets during pregnancy, they found a link between low carbohydrate intake early in pregnancy and methylation of the RXRα gene.
It’s not uncommon for pregnant mothers in the United States and the United Kingdom to follow a low carbohydrate, Atkins-style diet, says epidemiologist and lead author Keith Godfrey. That may send a starvation-like signal to their fetuses, which puts the children out of sync with the high-calorie world into which they are born. The findings, he says, could also help explain the obesity epidemic in countries like China, where the children of poorly nourished mothers are now obese, middle-aged adults.
Still, the researchers can’t be certain that the mother’s diet caused the epigenetic changes. But the strong correlation has experts excited. “It’s a pivotal finding,” says Jeffrey Craig, a geneticist at the Murdoch Childrens Research Institute in Melbourne, Australia. “This is the first time an epigenetic change detected at birth has been shown to predict a clinically important finding,” he says.
“This suggests that even in normal pregnancies, the fetal environment has major effects on subsequent development,” adds fetal physiologist and co-author Peter Gluckman of the University of Auckland. Mark Hanson, a cardiovascular physiologist at the University of Southampton and a co-author of the study says: “Five to 10 years ago, we thought obesity would be controlled by genes and there was nothing we could do. The fact that these changes are epigenetic means we can do something about it, possibly by targeting these children for interventions early in life.” One possible intervention, he says, is administering micronutrients like folic acid that can alter epigenetic tags.
I am old enough to remember when an obese person was a rarity. So was someone who was “stick-thin.” We ate a widely varied, mostly-unprocessed diet containing lots of meats, fats, dairy and poultry products, and natural starches, like potatoes and yams. Desserts were most often fruits, with an occasional sweet pastry for holidays and special occasions. We were all what was considered “normal,” in those days. A layer of fat under our skin of roughly one to two inches. A svelte movie starlet was about a size 12 or 14. Very few of us were emaciated, and very few were obese. Diabetes was RARE.
Are you doing low carb?
Yes, I’m LC (less than 10g of sugars a day) but I had to cut back on fat and calories in order to lose weight. Once I’ve lost the weight, I’ll maintain with straight LC.
The LC crowd is right one one thing - you can’t gain weight if you don’t eat carbs. But I’ve found that I can’t lose a lot of weight if I eat a lot of fat. I won’t gain, but I won’t lose. Calories do count in that sense.
As a 40 year old woman with PCOS and hypothyroidism, I had to do more.
My next to youngest, 17 year old son, had outgrown the ‘dress’ pants he was to wear today for Easter. He is 6’3 and 165lbs, he has 31 in waist and 36 inseam (try finding pants/jeans for that!). He was 10 lbs at birth; and was off the chart at his first birthday. By his second birthday he was average in weight (started running...never walked) and has been average to below average ever since. He is a HS athlete (basketball, baseball) so he is physically active/fit. He is at that point where he can eat a full meal; and a second one (like he did today...our relative didn’t want to ‘put away leftovers’) then come home and eat two bowls of cheerios before bed.
Did you have gestational diabetes? Did you eventually become type 2?
From the second link in the 5th paragraph, the abstract states:
Regression analyses including sex and neonatal epigenetic marks explained >25% of the variance in childhood adiposity.Check the abstract. P represents probability. P = 0.002 means that you would expect those results 2 times out of a thousand results if the results were just random. In sample populations, it's considered significant when P is less than P = 0.05, i.e. you would expect a random result happens less 5 percent of the time.
Hence, you want larger samples for smaller margins of error and the exhortations for the replication of results.
Right, in many cases the doctor or the husband are guilty of pressuring women to restrict their pregnancy weight gain to unhealthy limits.
However I still say that in some cases it is the women themselves who are being vain.
There is so much celebrity idolatry in our culture, and the media set up --as examples for us to emulate-- celebrity women who stay slim and chic while pregnant -- while pointing to the celebrity's cute little "baby bump." It's a narcissistic thing.
Do you know women who have done this? Have you ever been pregnant? I ask because your remarks don’t reflect what I encountered in my work. I’ve worked in a medical environment and have had contact with many, many pregnant women and with their doctors. I’ve also examined the medical records of thousands of pregnant women. I’m a mother myself with a number of pregnancies. And I never heard or saw or read about a woman who said, “I have to keep my weight down so I’ll look like Jennifer Anniston.” What I do hear them saying is, “I know I shouldn’t gain 75 pounds but I’m crazed with hunger, and if I don’t eat I get low blood sugar. Put an ox on the kitchen table and I’ll eat it all by myself.”
Sometimes women also don’t gain enough weight not because they’re vain or their husbands and doctors pressure them, but because they are so terribly nauseated.
Yep I've had four kids. And I gained at least 40 pounds with each pregnancy, thank you very much! (And lost ... well ... most of it with each post-pregnancy)
Do you know women who have done this?
Yes, two people very close to me (relatives) did. Once their children were born, they also insisted on giving them skim milk to drink -- another terrible mistake, since human childrens' brains need a higher fat content to develop properly, than is available from skimmed cow's milk.
I’m shocked! Those poor children.
However, my husband and his whole family are overweight. I can also say that the reason they are overweight is because they eat a lot. It is really that simple.
My girls and I are constantly mad because my husband will eat everything in the house. We have to hide food, so it is there when we want to eat it.
I really bought into the whole "it's just my genes" thing, until I spent time around heavy people. I had no idea that a family could put away that much food.
I have never had to diet or watch what I eat, and I also have a complete sweet tooth. However, I don't gorge myself to death, because I don't like feeling overly full.
I really think that is the big difference between skinny and fat people. They don't stop until they can't fit another bite. I stop way before that, because I hate that feeling.
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