You may have noticed some short-term mood changes, which follow the consumption of certain foods. You are euphoric after eating sweets and you can hardly focus when you are hungry. However, it may come as a surprise that your eating habits can affect your brain in the long-term, too.
We are all aware that an unhealthy diet is one of the major risk factors for diabetes and other conditions linked to obesity. But bad eating habits could also contribute to the development of some mental and cognitive disorders.
Our food preferences begin to develop in the womb. Studies have shown that that if a woman drinks carrot juice throughout her pregnancy, her child will like its taste later in life. To prove that this connection is relevant when it comes to unhealthy food, researchers have experimented on monkeys.
One part of the examined pregnant primates were fed with healthy food, while the other with fatty food. Once born, the baby monkeys were given access to junk food. Those whose mothers had an unhealthy diet tended to eat significantly more junk food than those whose mothers consumed low-fat food. The scientists examined the dopamine markers of the monkeys to find out how exactly the mothers’ eating habits changed their babies’ brains and affected their taste.
Dopamine is a neurotransmitter responsible for our sense of satisfaction. When we eat our favourite food, the dopamine levels raise, making us feel good. An excessive amount of the same food, however, gradually reduces the dopamine’s effect as the brain sees the level of dopamine is too high and restores the balance by removing dopamine receptors. When you have fewer receptors, you need more dopamine to reach the same level of satisfaction as before, thus you eat more.
Going back to the monkeys experiment, in the brains of the baby monkeys, which were exposed to unhealthy food in the womb, the number of dopamine receptors was significantly reduced. This explains why these monkeys eat more fatty and sweet food — they need a bigger portion of such food in order to feel satisfied.
Heidi Rivera, a researcher from the Oregon National Primate Research Center, notes that the unhealthy diet of the pregnant monkeys resembles the eating habits of the modern western world. According to her, this could explain the growing number of obese children in the US.
Rivera’s research shows that the food we consume during our early development determines our eating habits later in life. But Constance Harrell from the Emory University raises another question: “Could food affect our mental health?”
The findings of a study conducted in 2008 shows that teenagers consume significantly higher amount of sugary soft drinks compared to any other age group. Sugar, especially in the form of highly-concentrated corn fructose, which today we find in almost everything — from soda to salad dressings, bread and yogurt — increases the stress hormone (cortisol) levels in the brain. This puts teenagers at risk of a number of mental issues, including depression and anxiety.
To test this theory, Harrell experimented on adolescent rats. One part of the examined animals were fed with healthy food, while the rest consumed big amounts of fructose. The latter had higher cortisol levels and were tested for depression. They were placed in a maze with two types of corridors — open and bright, and closed and dark. The rats which consumed more sugar tended to spend more time in the dark corridors, which signalled insecurity. Put in an aquarium those rats gave up sooner than the others, which indicated depression. Other experiments on the rats proved the high sugar intake had also affected the animals’ memory.
“We should note that excessive sugar intake is bad not just for our metabolism, but for our psychological health, too,” concludes Harrell.
It is interesting that the same experiment on adult rats did not show the same results. This may prove that the adolescents’ brain is more susceptible. However, the unhealthy food certainly affects our brain at any age.
For example, several studies have shown a link between obesity and the size of the hippocampus — the part of the brain responsible for the memory and learning capability. The relation between the two has been proven by Australian scientists, who had compared the size of the hippocampus to the body mass index (BMI). People in their 60s who are overweight have the smallest hippocampus. And while it is normal for the hippocampus to shrink over time, those obese individuals were reported to have suffered from this change the most. A smaller or shrunk hippocampus causes dementia and memory loss. Separate studies have also shown that overweight people perform worse in memory tests.
Another experiment on mice sheds light on the link between weight and hippocampus. Overweight mice reported higher levels of inflammation in the brain, including the hippocampus, caused by fat cell molecules. Those mice also underperformed in memory tests.
As proven by scientists, the choice of food has much more of an impact than you realise. Feed your brain with healthy food and it will certainly reward you!