The idea that children's brains are affected by their diet is not new, but perhaps the most dramatic example is now a distant memory. Until well into the last century, nearly one percent of inland children had "cretinism" with severe learning problems, stunted growth, thickened skin, and enlarged tongues. In 1789 Michael Malacarne, an Italian physician living in the Alps, observed that the mothers of these children always had goiters, swellings in their necks due to enlarged thyroid glands, a problem that was very common in inland areas. A folk remedy for goiter was dried seaweed which was rich in iodine and; in 1917, David Marine showed that giving iodine made goiters shrink in a group of Cleveland schoolgirls. The makers of table salt soon began adding iodine, which is abundant in sea salt, and both goiter and cretinism quickly disappeared.
Is it possible that other nutrients in children's diets can also make a significant difference in how well they think? A new study of ours just published in the Frontiers of Evolutionary Neuroscience suggests that children with identical family backgrounds can have quite different scores on tests of mental ability depending on their intake of two quite similar fats.
While dietary fat is often maligned, some polyunsaturated fats that come from our diets are crucially important to our ability of think. Because the special form of omega-3 fat called DHA plays a very important role in the brain, we thought that children with more omega-3 in their diets might do better on mental tests. Since our bodies cannot make them, these omega-3 fats must come from our diets, with seafood being the richest source. In the brain, omega-3 DHA helps nerve cells to grow faster and larger and to make more connections with other nerve cells - the connections that enable us to think.
Laboratory animals with less omega-3 in their diets have smaller nerve cells and brains, and fewer neural connections, and are much less able to learn. Unfortunately, another kind of omega fat that also comes from the diet, omega-6, uses the same chemical machinery as omega-3; so large amounts of omega-6 in our diet can decrease the level of omega-3 in our bodies So we suspected that while eating plenty of omega-3 fats might increase children's mental abilities, having a lot of omega-6 could have the opposite effect.
We also thought that these effects of dietary omega-3 and omega-6 fats could be stronger in girls. Girls not only need omega-3 for their own brains; they also need to set aside some omega-3 for their future children. Not counting water, more than ten percent of our brain is DHA, so newborn babies and infants need a lot of it from their mothers. Because there isn't enough omega-3 in a mother's daily diet to meet these demands, she has to rely on omega-3 stored in her body fat to provide the omega fats her baby needs. (In fact, much of girls' development seems organized around getting these brain-building fats for future motherhood - but that's another story.)
To test these ideas, we looked at the relationship between dietary fats and test scores in more than 4,000 American children between six and sixteen years old. Of course many other factors like family size and income and the parents' schooling are known to be predictive of a child's test scores; if we didn't make appropriate adjustments for these influences the effects of diet might not be visible. Considering all these factors together, we found that dietary omega-3 significantly increased cognitive test scores for both sexes; and the boost was twice as great in girls as in boys. We also found that having more omega-6 in the diet led to lower test scores in the girls. For girls with high omega-3 and low omega-6 levels, test scores were fifteen percent higher than those with high omega-6 and low omega-3.
Many studies have shown that infants who get more omega-3 have better mental development, and some other studies have found a similar connection between omega-3 in the diet and mental ability in older children. But ours is the first to look at the difference between boys and girls and to consider the role of omega-6 fats. Our result is striking because we measured over 40 different dietary elements, and only the two omega fats had any significant effect on cognitive performance.
Together with many others, our study supports the idea that dietary and body fat have special significance for women. This issue is critical now because of the large and ever-increasing amounts of soybean and corn oil in the American diet, oils that are very high in omega-6 and low in omega-3. Not only are most processed foods laden with corn and soybean oil, but large amounts of corn are also fed to cattle and poultry. Given this food-production system, the potential harmful effects highlighted in our study are probably all around us.
Foods that come from the water are rich in both iodine and DHA, and it seems likely that these foods played an important role in the diet of our ancient ancestors and helped them to develop the large brains of which we are so proud. But just as those living away from the seacoasts were prone to iodine deficiency, many of us today may be suffering from omega-3 deficiency, which also affects how well our brains work.
Our study suggests that those with more omega-3 and less omega-6 in their diets score better on mental tests, and experimental research with animals suggests that this relationship is causal. For example, animals fed a Japanese-style diet-high in omega-3 and low in omega-6 did much better on learning tests than a comparison group fed a high-omega-6, low-omega-3 American-style diet. According to international tests, the same seems to be true for Japanese and American children as well. All of these ideas are explored more fully in our forthcoming book, Why Women Need Fat, available in late December.
Written by Will Lassek and Steve Gaulin