into and essentially vandalizing a bear family’s vacant hut. She samples and renders judgments over their bowls of porridge, chairs, and beds. Goldilocks doesn’t like Papa Bear’s or Mama Bear’s belongings; the physical characteristics are just too extreme. But Baby Bear’s stuff is “just right,” from temperature to sturdiness to the bed’s cozy comfort. Like so many legendary children’s stories, there are many renditions of this odd little tale. The first published version, by 19th-century poet Robert Southey, had an angry old woman breaking into the bears’ hut and sampling the wares of three male bears. Some literary historians suggest Southey borrowed from the story of Snow White, who breaks into the dwarves’ house, tastes their food, sits on their stools, and then falls asleep on one of their beds. In one early version of “Goldilocks,” the intruder was a fox, not a woman; later she became a girl variously called Silver Hair, Silver-Locks, and Golden Hair. But the “just right” principle is preserved throughout.
So many creatures have this just-right characteristic embedded in their biology that scientists have given the phenomenon its own rather unscientific name: the Goldilocks Effect. It is so common because biological survival in this hostile world often calls for a balancing act between opposing forces. Too much or too little of something, such as heat or water, often hurts biological systems, most of which are obsessed with homeostasis. A full description of many biological processes involves this “just right” idea.
Four things proven to help baby’s brain
The behaviors proven to aid and abet brain development in the womb—especially important in the second half of pregnancy—all follow the Goldilocks principle. We will look at four of these balancing acts:
• weight
• nutrition
• stress
• exercise
And there’s not a pregaphone in sight.
1. Gain just the right weight
You’re pregnant, so you need to eat more food. And if you don’t overdo it, you will grow a smarter baby. Why? Your baby’s IQ is a function of her brain volume. Brain size predicts about 20 percent of the variance in her IQ scores (her prefrontal cortex, just behind her forehead, is particularly prescient). Brain volume is related to birth weight, which means that, to a point, larger babies are smarter babies. The increase slows as baby reaches 6.5 pounds: There is only 1 IQ point difference between a 6.5-pounder and a 7.5-pounder.
The fuel of food helps grow a larger baby. Between four months and birth, the fetus becomes almost ridiculously sensitive to both the amount and the type of food you consume. We know this from malnutrition studies. Babies experiencing a critical lack of nutriment have fewer neurons, fewer and shorter connections between the neurons that exist, and less insulation all around in the second trimester. When they grow up, the kids carrying these brains exhibit more behavioral problems, show slower language growth, have lower IQs, get worse grades, and generally make poor athletes.
How much do you need to eat? That depends upon how fit you are going into the pregnancy. Unfortunately, 55 percent of women of childbearing age in the United States are already too fat. Their Body Mass Index, or BMI, which is a kind of a “gross domestic product” of how fat you are, is between 25 and 29.9. If that’s you, then you need to gain only about 15 to 25 pounds to create a healthy baby, according to the Institute of Medicine. You want to add about half a pound a week in the critical second and third trimesters of pregnancy. If you are underweight, with a typical BMI of less than 18.5, you need to gain between 28 and 40 pounds to optimize your baby’s brain development. That’s about a pound a week in the critical last half of pregnancy. This is true for women of healthy weight, too.
So the amount of fuel is important. There is increasing evidence that the type of fuel you eat during the critical period also is important. The next balance comes between foods that a pregnant mom wants to eat and foods that are optimal for a baby’s brain development. Unfortunately, they are not always the same thing.
2. Eat just the right foods
Women have strange experiences with food preferences during pregnancy, suddenly loathing foods they used to love and craving foods they used to loathe. It’s not just pickles and ice cream, as any pregnant woman can tell you. One woman developed a craving for lemon juice on a burrito—a need that lasted for three months. Another wanted pickled okra. A surprising number crave crushed ice. Women can even desire to eat things that aren’t food. Items that regularly make the Top 10 List of Weird Pregnancy Cravings include baby talcum powder and coal. One woman wanted to lick dust. Pica is a common disorder: a craving lasting longer than a month for eating things that aren’t food, like dirt and clay.
Is there any evidence you should pay attention to these cravings? Is the baby telegraphing its nutritional needs? The answer is no. There is some evidence that iron deficiencies can be consciously detected, but the data are thin. Mostly it’s a matter of how a person uses food in her daily life. An anxious person who is comforted by the chemicals in chocolate might grow to crave chocolate whenever she feels stressed—and a woman will feel stressed a lot during pregnancy. (This craving for chocolate reflects a learned response, not a biological need, though I think my wife would disagree.) We actually don’t know why a pregnant woman’s random cravings occur.
That doesn’t mean the body doesn’t have nutritional needs, of course. The pregnant woman is a ship with two passengers but only one galley, and we’re looking to stock this kitchen with the right ingredients for brain growth. An infant’s body needs 45 different nutrients for healthy growth. A whopping 38 of these are critically involved in the development of the nervous system. You can look on the back of most pregnancy-formulated vitamin supplements to see the list. We can look to our evolutionary history for some guidance on what to eat to get these nutrients. Since we know something of the climate in which we developed for millions of years—one that supported ever-increasing brain girth—we can speculate about the type of foods that helped it along.
Caveman cuisine
An old movie called Quest for Fire opens with our ancestors seated by a fire, munching on a variety of foods. Large insects buzz about the flames. All of a sudden, one of our relatives shoots out his arm, clumsily grabbing an insect out of thin air. He stuffs it into his mouth, munches heartily, and continues staring into the fire. His colleagues later dig around the soil for tuberous vegetables and scrounge for fruit in nearby trees. Welcome to the world of Pleistocene haute cuisine. Researchers believe that for hundreds of thousands of years, our daily diet consisted mostly of grasses, fruits, vegetables, small mammals, and insects. Occasionally we might fell a mammoth, so we would gorge on red meat for two or three consecutive days before the kill spoiled. Once or twice a year we might run into a beehive and get sugar, but even then only as unlinked glucose and fructose. Some biologists think we are susceptible to cavities now because sugar was not a regular part of our evolutionary experience, and we never developed a defense against it. Eating this way today (well, except for the insects) is called in some circles the paleo diet.
So it’s a bit boring. And familiar. Eating a balanced meal, with a heavy emphasis on fruits and vegetables, is probably still the best advice for pregnant women. For the non-vegetarians in the crowd, a source of iron in the form of red meat is appropriate. Iron is necessary for proper brain development and normal functioning even in adults, vegetarian or not.
Miracle drugs
There is a lot of mythological thinking out there about what you should and should not eat—not just during pregnancy but your whole life long. I had an honors student at the University of Washington, the thoughtful type of kid who has to sit on his hands not to answer a question. One day he came up to me after class, breathless. He was taking an entrance exam for medical
