New research raises the intriguing possibility that eating more fruit during pregnancy could boost the intelligence of a normal, healthy baby.
Researchers found that each additional daily serving of fruit that pregnant women consumed corresponded with an increase in cognitive scores for their children one year after birth. The study, at the University of Alberta, analyzed data from 688 children in the Canadian Healthy Infant Longitudinal Development, or Child, study.
The findings, published in the journal EBioMedicine in April, are preliminary and best seen as a suggestion for future studies on mammals and in randomized human trials, experts say. Still, the study is striking. Only one other food—fish—has been linked to enhanced cognitive development in normal, healthy offspring, experts say.
Piush Mandhane, an associate professor of pediatrics at University of Alberta and one of the two senior authors of the paper, says he was surprised by the strength of the findings. He sought out a colleague to double check the results using fruit flies, which are often used in experiments to model learning and memory. Those tests came up with similar results.
Still, “we don’t want pregnant women to go out and eat a tremendous amount of fruit,” Dr. Mandhane cautions. “It’s a single study, and we haven’t looked at the health effects of increased fruit intake.”
Consuming large amounts of fruit during pregnancy could raise blood sugar, a particular problem for women with gestational diabetes, or lead to increased weight gain, experts say.
Many people eat less fruit than is recommended. Half of the pregnant women surveyed for the study didn’t meet the U.S. government’s guidelines of 1½ to 2 cups of fruit a day. Dr. Mandhane says his advice to pregnant women “is to meet the recommendations.”
The study is one of relatively few to look at how prenatal nutrition can improve normal cognitive outcomes. Most such research has focused on nutrient deficiencies that cause abnormal development. For example, strong evidence indicates that inadequate levels of folic acid early in pregnancy can lead to neural tube defects, and that sufficient iron and iodine are critical for normal brain development.
Omega-3 fatty acids, primarily found in fish, are building blocks of brain-cell membranes, and many studies have found an association between women who eat more fish during pregnancy and children who score higher on cognitive-assessment tests. But randomized trials, using fish-oil supplements rather than actual fish, have been inconclusive. Also unclear is whether high fish consumption goes hand in hand with other factors that may contribute to good cognitive outcomes.
“Is it the fruit consumption or is it that women who eat fruit have other healthy behaviors?”Emily Oken, a professor of population medicine at Harvard Medical School and professor of nutrition at Harvard T.H. Chan School of Public Health, says about the latest study. The research is “really suggestive, worth exploring in more depth,” says Dr. Oken, who is co-principal investigator of Project VIVA, a large longitudinal study of pregnant women and their children in Massachusetts.
Dr. Mandhane is co-research leader of the Child study, which enrolled 3,600 pregnant women from the general Canadian population between 2008 and 2012. He says his team decided to look at what factors help to predict neurodevelopment at 1 year of age, after adjusting for family income, the mother’s education, whether she took vitamin supplements, whether she breast-fed her baby and other variables. They had extensive data of the mothers’ diets, including their components, total calories and statistical measures of empty calories and general healthiness of diet, he says.
“Fruit kept coming back to the top of the list as a factor associated with cognitive development,” he says. “Most surprising was how big an effect it was. When my data analyst showed me, I said you’ve got to do it again, I just don’t believe it.” The data included very limited information on the specific types of fruit the women consumed.
The babies were measured on the widely used Bayley Scales of Infant and Toddler Development. Cognitive scores continued to rise in relation to the mothers’ prenatal fruit consumption up to about six or seven daily servings, when the effect maxed out. At that age, the Bayley scales measure things like infants’ ability to stack blocks or remember a penny was hidden under a cup.
Dr. Mandhane asked a colleague, François Bolduc, associate professor of pediatric neurology, to work together on the investigation. Dr. Bolduc is known as the “fly guy” at University of Alberta because of the more than 300,000 Drosophila, or fruit flies, in his lab. He and his research team alter the insects’ genes and test how fast they learn and how well they remember scents. The tiny domestic nuisances are remarkably quick learners.
Although wild Drosophila are big consumers of fruit left on a kitchen counter, in the lab they are fed a gel made from cornmeal, yeast and sugars. For the experiment, the prenatal diet of a group of flies—given when the flies were mating and laying eggs, and to the larvae before they pupated—was enhanced with a combination of orange and tomato juices.
Dr. Bolduc exposed the fruit flies in a tube to two scents, one of which was accompanied by a mild shock from an electrical grid under their feet. Two minutes later, after presenting the flies with both odors, he counted how many made their way to one or the other. To test long-term memory, the same choices were given to them a day later, an extensive period in the monthlong life of a fruit fly.
Offspring of fruit flies whose prenatal diet had been enhanced with juices scored 30% higher on learning and more than twice as high on long-term memory tests compared with the insects whose prenatal diet was the usual lab food.
“I think this is the first time anyone was able to enhance the learning and memory of a normal fly,” says Dr. Bolduc. “We tried feeding flies once born to increase their performance, and we could not,” he says. “So it’s something that’s happening in the development of the brain.”
Dr. Mandhane says he hopes future research will answer questions such as which specific nutrients and kinds of fruit are involved in improving cognitive performance, and whether improvements are still present when the babies get older. He is currently working with another colleague to test whether feeding pregnant rats a fruit-juice combination leads to smarter offspring. So far, the data look promising, but they aren’t yet published or peer reviewed, he says.
Ultimately, he says he would like to better understand the optimal diet during pregnancy to aid neurodevelopment in both the general population and infants at risk for intellectual disability.
“Going from an IQ of 100 to 105 makes a little difference. Going from an IQ of 85 to 90 makes a much bigger difference,” says Dr. Mandhane. “That would be a much greater contribution to society.”
HOW MUCH FRUIT SHOULD YOU EAT?
Here are U.S. government recommendations:
- Women, age 19 to 30: 2 cups a day
- Women, age 31 and older: 1½ cups a day
- Men, age 19 and older: 2 cups a day
- A cup of fruit roughly equals:
- A small apple
- A large banana
- Eight large strawberries
- A medium grapefruit
- A large peach
- 1/2 cup raisins or other dried fruit
- Note: Fruit may be fresh, canned, frozen or dried. 100% fruit juice should at most make up half of fruit consumption.
- Source: USDA