One of the most pressing current questions in healthcare is “does what we eat matter?” The resounding answer is “of course.” But, why? While food provides nutrition for our bodies, there is also a direct and delicate interplay with our mood. Outside of the feelings a specific food may trigger due to memory or other historical associations, our mental state is affected on an even deeper physiologic level. How?
The gut-brain connection:
Research has shown that the gut is essentially a “second brain” and is profoundly affected by the food we ingest. This occurs when bacteria metabolize food in the intestine and produce chemical signals in response. These chemical signals are then sent to the brain triggering the production of various neurotransmitters including dopamine and serotonin. Both neurotransmitters generate strong physical and emotional responses. Of course, dopamine (known as the “feel good” chemical) promotes happy or pleasant feelings while serotonin causes similar feelings of satisfaction. Notably, nearly all serotonin is made in the gastrointestinal tract but only when the bacterial population is optimal and functioning well. A deficit in either can lead to feelings of sadness or depression. Good nutrition promotes healthy bacteria and a healthy gut. This in turn leads to the appropriate production and secretion of neurotransmitters.
Conversely, poor nutritional choices (such as a high sugar intake) promote the growth of “bad” bacteria. These bacteria also generate signals that produce neurotransmitters. However, in this case, neurotransmitters, especially dopamine, may be produced too quickly leading to a requirement for more dopamine receptors in the brain. This requires higher dopamine concentrations in the future to fill the receptors and generate the same feelings of pleasure and satisfaction. This physiological change is very similar to those seen in addictive conditions. The production of key neurotransmitters is affected while at the same time, systemic inflammation increases. Inflammation contributes to a whole host of other health problems including the development of dementia, stroke, and cardiac disease. A better diet also correlates with fewer mood swings and a better mood overall (i.e. less anxiety and depression).
The brain:
As mentioned above, there is a direct link between dietary choices and mood. “Junk” food is linked to high anxiety, increased depression, and decreased mental focus. It has been shown that “junk” food can worsen information processing, memory development/ storage, and decrease concentration. This effect can be viewed similarly to the negative consequences of a nicotine addiction. Importantly, these symptoms are frequently seen in children when brain development is most active.
In addition to these undesirable effects on the brain, mood, and overall well-being, increased sugar and fat intake, as frequently found in “junk” food can also lead to the inappropriate production of testosterone and estrogen. In turn, the body suffers an even greater physical insult as these hormones wreak havoc and alter normal functioning.
The gut:
A healthy well-functioning microbiome is key to feeling well physically and mentally. This has already been alluded to previously but to further expound on this topic one only needs to look at the condition known as “leaky gut syndrome.” While The Cleveland Clinic states that this is not a formal medical diagnosis, Harvard Medical School’s Health Publishing blog did state that “leaky gut” is a condition in which the gastrointestinal structure becomes damaged and permeable (leaky) allowing partially digested food, digestive enzymes, toxins, and bacteria or other parasites enter into the vasculature feeding the intestines. This directly causes inflammation in the gut (think Celiac disease, Crohn’s disease, or irritable bowel syndrome). However, this may have wider-reaching effects as well. Some chronic conditions may be worsened by a “leaky gut” although the evidence is not conclusive at this point. These may include fibromyalgia, arthritis, autoimmune conditions (lupus, type 1 diabetes, etc), and even mental health. One thing to consider is that some anti-inflammatory drugs, prescribed for conditions like arthritis, are also used for depression.
Insulin regulation:
Another factor that may explain the link between dietary choices and overall mental health is the action of insulin. Food intake of any kind stimulates the secretion of insulin based on the breakdown of nutrients and subsequent glucose load. Poor nutritional choices typically increase blood sugar and therefore increase the amount of insulin produced by the pancreas to funnel it to the muscles, brain, and other bodily organs. Foods with a higher glycemic index have been shown to have a higher risk of causing depressive symptoms. These foods also trigger the release of cortisol, adrenaline, growth hormone, and glucagon. All of these cause a stress response. Frequent glucose fluctuations and the release of these stress hormones can affect mood, and cause anger, irritability, and depression.
Practical application:
There is quite a body of research that diet plays a key role in the health of the mucus layer in our intestines. As mentioned above, intestinal integrity is crucial to overall well-being, especially mental well-being. The standard American diet, otherwise ironically known as SAD, is thought to promote intestinal damage and structural compromise. The high level of sugar and fat, in addition to the low level of fiber, promotes inflammation as previously mentioned but constipation as well. It is thought that alcohol and stress can exacerbate this process.
When I reflect on all of this information regarding the link between food and mental health, I am astounded at the impact of my nutritional choices. Thankfully, with knowledge of this tenuous balance also comes awareness of what I can do for myself (or recommend to my friends and family) to help preserve and restore mental health to good standing. Everything comes down to diet! This has been made clear by what has been discussed above. The following are key points to keep in mind when eating to improve mental health.
Eat whole, unprocessed foods - preservatives, artificial colorings or flavors, and other additives are manmade and have various negative (and at this point even some unknown) effects on both physical and mental health.
Sources:
Aetna. (2024). Food & your mood: How food affects mental health - aetna: Foods that help your brain health. Aetna. https://www.aetna.com/health-guide/food-affects-mental-health.html
Firth, J., Gangwisch, J. E., Borsini, A., Wootton, R. E., & Mayer, E. A. (2020). Food and mood: How do diet and nutrition affect mental wellbeing? BMJ, 369, m2382. https://doi.org/10.1136/bmj.m2382
Hafizurrachman, M., & Hartono, R. K. (2021). Junk food consumption and symptoms of mental health problems: A meta-analysis for Public Health Awareness. Kesmas: National Public Health Journal, 16(1). https://doi.org/10.21109/kesmas.v16i1.4541
Marcelo Campos, MD. (2023, September 12). Leaky gut: What is it, and what does it mean for you?. Harvard Health Blog. https://www.health.harvard.edu/blog/leaky-gut-what-is-it-and-what-does-it-mean-for-you-2017092212451
Selhub, MD, E. (2022, September 18). Nutritional psychiatry: Your brain on food. Harvard Health Blog. https://www.health.harvard.edu/blog/nutritional-psychiatry-your-brain-on-food-201511168626
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