Poor maternal nutrition appears to change the child's “phenotype” … a term that refers to physiological attributes that arise from the interactions between a person's genes and their lifestyle, including their diet in the womb and during infancy.
For example, a Swedish study published two years ago showed that children born to mothers who ate vegetables only three to five times per week were 71 percent more likely to develop type 1 diabetes, compared to children of women who ate vegetables daily during pregnancy (Brekke HK et al. 2010).
Now, the findings from a novel Harvard clinical study adds to growing evidence that maternal nutrition can influence a child's health prospects.
Low maternal omega-3 intake linked to babies' obesity risk
Adequate intake of omega-3 fatty acids during pregnancy may lower the risk of childhood obesity by almost one-third, according to new research from Harvard Medical School (Donahue SM et al. 2011).
Conversely, maternal diets high in omega-6 fatty acids (from vegetable oils) and low in omega-3s (from fish or fish oil) appeared to increase a child's risk for obesity.
Harvard researchers led by Emily Oken, M.D., determined children's risk of obesity by measuring their body mass index (BMI) and taking skinfold measurements at the scapula and triceps.
The study authors also estimated the mothers' omega-3 intake – based on the women's self-reported weekly fish intake – and measured the levels of omega-6 and omega-3 fatty acids in the babies' cord blood at delivery.
(Omega-3s and omega-6s compete for absorption into cell membranes, and diets high in omega-6s can limit the proportion of omega-3s.)
The Harvard team concluded that higher maternal omega-3 intake and higher omega-3 blood levels in newborns reduced the risk of childhood obesity.
The Harvard group then calculated the odds for obesity in the women's offspring at age three, and looked for links to the mother's omega-3 fatty acid intake and/or the level of omega-6 and omega-3 fats in cord blood at delivery.
Oken and her co-workers reported the odds of obesity in three-year-olds were between two and four times higher when cord blood had a high ratio of omega-6 to omega-3 fatty acids.
In contrast, the odds of obesity were 32 percent lower when maternal consumption of omega-3s was high or if the ratio of omega-3 to omega-6 intake was at or close to the recommended 1:3 ratio.
In other words, mothers who get too few omega-3 and too many omega-6 fats during pregnancy might raise their baby's odds of becoming obese.
As they wrote, “A higher ratio of cord plasma omega-6 to omega-3 polyunsaturated fatty acids was associated with higher sub-scapular and triceps [skinfold thicknesses] and odds of obesity,” they said.
Mothers' omega-3 intake generally inadequate
Dr. Oken and her colleagues reported that, at mid-pregnancy, only about one-fifth of the expectant mothers in their study reported eating more than the widely recommended two fish meals per week.
And only about half of these relatively frequent fish-eaters were estimated to achieve the widely recommended intake of DHA of at least 200mg per day … because they reported eating mostly lean white fish.
Worse, a mere three percent of the women in the study were estimated to get the recommended 200mg of omega-3 DHA per day during their last month of pregnancy.
As Oken's team noted, the last month of pregnancy is when large amounts of omega-3 DHA are transferred from mother to baby to support brain development.
Judging by their study participants' behavior, the authors hypothesized that even pregnant women who meet the two-meals-per-week intake guideline don't consume enough fatty, omega-3-rich fish … such as salmon, tuna, sardines, and mackerel.
Omega-3s and obesity risk: An overview
The Harvard team's report included an important caveat:
“These findings need to be confirmed by others. It will also be important to demonstrate that making deliberate changes to a woman's fat intake during pregnancy has desirable effects on weight and fatness in children.” (Donahue SM et al. 2011)
Two years ago, a team at Germany's Technical University Munich reported that they were undertaking just such a study … so we'll keep an eye out for their findings (Hauner H et al. 2009).
Although imbalances in fatty acid intake – too few omega-3s and too many omega-6s – promote the development of adipose (fatty) tissue in animals, very few clinical studies have tested this in people.
Indeed, when Norwegian researchers gave pregnant mothers either omega-3-rich cod liver oil or omega-6-rich corn oil from mid-pregnancy until three months after delivery, they found no link between the infants' omega-3 or omega-6 blood levels through the first three months of life and their BMI at age seven (Helland IB et al. 2008).
But body mass index is not a very accurate indicator of excess body fat, since people with more muscle mass than average have a high BMI without being overweight or obese.
Nor is the skinfold method used in the Harvard study perfect, because it estimates body density, not body fat percentage, which must be estimated by applying a mathematical formula … an approach with its own room for error.
However, as the American Heart Association says, “… children and adolescents assessed to have a skinfold measure greater than the 95th percentile are more likely to have excess body fat as opposed to increased lean body mass or large frame size.” (AHA 2011)
The Centers for Disease Control and Prevention defines overweight in children as having an age-adjusted BMI at or above the 95th percentile … and CDC recommends use of the triceps skinfold test for further evaluation when a child's BMI exceeds this level.
Finally, we should note that when it comes to the proposed capacity of omega-3s to help adults control their weight, the clinical evidence is mostly positive, but much too limited and mixed to be conclusive … see the “Omega-3s & Weight/Fitness” section of our news archive.
American Heart Association (AHA). Overweight in Children. Updated March 29, 2011. Accessed at http://www.heart.org/HEARTORG/GettingHealthy/Overweight-in-Children_UCM_304054_Article.jsp
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