Teanne Davis ’22 and Journey Monegain ’22
There’s a constant debate between nature and nurture. Is it because of my genes that I behave the way I do, or is it because of my environment, like the foods I eat and the places I live? This is a question on the minds of many reflecting on their health, especially for parents concerned for the health of their children. Nutrition is essential for child development, but not only for building strong bones. Nutrition is critical for strong brain development, particularly learning and memory, from conception to adolescence.
So is nurturing your child the solitary factor for healthy development? No! Genes play a central role because they carry information that determines traits such as eye color, freckles, and even personality. But just because you are very extraverted doesn’t necessarily mean that your child will have this trait too. Genes are instructions like a blueprint that are passed down. You get instructions from your mom and your dad at birth, and your child will get instructions from you and your partner as well. Just like a blueprint, genes help determine individuality, but both nature and nurture are central to a child’s development.
However we see a person’s genes as the fixed products of a “genetic lottery” we buy into other problematic ideas. If it’s all up to luck it follows that any inequalities that we observe are natural and a product of chance, unaffected by outside forces. This perspective excuses the long legacy of social and institutional discrimination by blaming individuals for having “bad” genes, but also serves as a gateway to eugenic beliefs about getting rid those who don’t have “good genes.” For example, some people try to claim that intelligence is determined by your genes, and that differences in learning outcomes are due to biological differences. However, studies show that nutrition can have huge impacts on a child’s ability to learn. The nutrition children experience is contingent upon social factors though, such as physical and financial access.
For this reason, it’s important to not solely rely on genetics to understand childhood learning and memory, but also consider the environmental stresses that affect health and development. This is where the field of epigenetics comes in.
Epigenetics encompasses both nature and nurture, and studies how the environment influences gene expression. Scientists now understand that your gene expression is not solely determined by what the exact instructions say. Environmental conditions (what is “on top” of your genes, the “epi-” in epigenetics) play a role in regulating what parts of the instructions get read. The body translates these environmental stresses by adding or removing modifying “tags” that tell your cells which genes should be turned on and which genes should be turned off. These tags could change over the course of your lifetime.
To think about this in a different way, let’s now imagine that our DNA is a sweater store filled with beautifully designed sweaters that represent our genes. In this analogy, we can think of epigenetic tags as price tags attached to our lovely sweaters, and the cellular machinery that decides whether to express a gene or not, as “you,” the shopper.
For example, if you are eating healthy foods and exercising daily, you may have epigenetic tags that encourage the transcription of healthy hair genes. A cashmere sweater has a price tag for $1? Yes! This tag encouraged you to “buy” this sweater, and thus transcribe and express those genes. However, if you’re instead exposed to environmental stresses such as pollution and lack of access to healthy food, costlier tags might be added. Uh oh…that same cashmere sweater now has an epigenetic tag for $2,000. Absolutely not, this sweater will remain at the store, and that gene will be “off”. This is called gene silencing, because the gene will not be expressed.
Researchers have found evidence that this sort of gene silencing and other epigenetic changes can be affected by nutrition, which can then have consequences for learning and memory.
When tackling the relationship between nutrition and a child’s development, it is important to understand the difference between undernourishment and nutrient deficiency. Undernourishment is the condition of not eating enough food or having a diet that lacks proper nutrition and food variety to be in good health. Nutrient deficiency is the lack of one or more essential vitamins or minerals. In subsistence farming communities in Gambia, seasonal variation such as rainy or dry climates limited the availability of specific foods. Researchers discovered that maternal nutrition around the time of conception was shown to have permanent long term effects on DNA methylation (the shopping tags that control which sweaters (genes) are purchased or not (turned on or off)) in offspring from childhood to adulthood. Maternal undernutrition can lead to fetal growth restriction and underweight babies. In addition to undernourishment, nutrient deficiency is important for the progression of a child’s learning and memory as well.
Researchers have conducted a series of studies focused on the impacts of choline, an essential nutrient for movement, memory, and cognition. It’s abundant in food products like meat, fish, dairy, eggs, and certain vegetables, which tend to be more expensive than less-expensive, more processed alternatives. This might partially account for why people in Western countries don’t get the recommended daily intake.
To study the consequences of this dietary deficit, one research group examined the effects of a choline deficiency on human cells and in rats. In groups of cells or rats that were choline deficient, there was an observed decrease in the methylation of a gene that codes for something called a cell-cycle-inhibitor. To use our sweater analogy, it was on a sale too good to ignore. As a result, the cells “bought” too much of this gene, which would likely lead to limited growth and would derail the normal development of important brain structures.
The Western diet
On the opposite end of nutritional concerns, scientists have also worried that we might have too much of certain nutrients in our diets. Specifically, they’ve looked into what is being called the Western diet (WD) which describes a diet that is high in sugar and saturated fat due to the high consumption of processed foods.
In one study, rats fed a WD had different patterns of methylation in brain regions associated with learning and memory. While the exact mechanism is unknown, the researchers suspect that the effect of this tagging on genes might lead to lowered cognitive function. Another research group found that rats that had unrestricted access to a WD had decreased expression of an important brain factor that helps the brain develop new connections between neurons. Behaviorally, they observed that these rats had an impaired ability to learn, which also implicates the WD as having possible, enduring effects on learning. These two studies suggest that the WD might be creating a mess in our genetic sweater store, causing us to end up with too little expression of genes that are helpful for learning and memory, and too much of some of the unhelpful ones.
These studies aren’t without limitations, though. The rat studies included in this paper, like many in the field, only experiment with a small number of specimens, which limits the validity and generalizability of their findings. We can’t, for example, conclude that just because we observe something in rats, that the exact same thing is happening with humans. Furthermore, we still don’t fully understand the effects that a certain nutrient or diet might have on the entire body. Maybe in some pathways it’s helpful but in others it could be harmful. Given these limitations, we don’t mean to present any of these studies as telling absolute truths. Rather, we see them as starting points for further exploration, and early indicators of the link between nature and nurture.
These findings tell a story of how nutrition epigenetically influences development. But what do we do with this information as we start to learn it? If it is our environment that plays a role in shaping us, what can we do to make sure that that influence is helpful, not harmful?
We can start by asking critical questions about what we see now. Why do some children face undernourishment or deficiency? Why do some have to depend on the Western diet, while others do not?
If we take a look at nutrition, a lot of it comes down to food access, both physical and financial. Low income families might have to prioritize buying less expensive foods, but these tend to be highly processed, nutritionally poorer, shelf stable foods. It’s no surprise then, that income is significantly associated with health outcomes. Worse yet, some families might find themselves living in food deserts, which are areas in which residents don’t have access to healthy food options. If a child grows up with these environmental disadvantages, research suggests this might make it harder for them to learn and grow.
Knowing this, we must be cautious of what interventions epigenetics research is used to support and develop. Our public health policy should not simply instruct parents to make better dietary choices for their children, when not all choices are available. Instead, we should try to improve the nutritional environment so any resulting epigenetic influences on a child’s learning and memory are the healthiest and fairest they can be.
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Non-Journal Citations and Multimedia
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