Continuing the series on The Physiology of Nutrition, I present to you the connection between food and mood – serotonin. While it’s easy to see how what we eat has a direct impact on our waistlines, it seems a little foggier how our nutritional choices affect our brains. Even still, we all know intuitively how important food is to our emotions and our moods. After all, who hasn’t gotten angry or upset and wanted nothing other than a super-sizes sundae drizzled with chocolate sauce to calm down? We use food to affect our moods all the time without even thinking about it. But more importantly, our daily nutritional intake can have huge impacts on how we feel, and most of it is due to a little chemical called serotonin.

What is Serotonin?

Serotonin is a neurotransmitter which is highly common throughout nature.  How it works is incredibly simple. Neurons (nerve cell) communicate by specialized areas of their cells called synapses where they are very close together.  The first nerve cell dumps neurotransmitters into the space between, and the second nerve cell on the other side has receptors which recognize the transmitter and respond accordingly.  Below is a basic picture of the scene where this exchange occurs:


How neurotransmitters help synapses fire (this is how your brain works!)

At the same time, as soon as the transmitter is dumped in between the cells, special proteins which are responsible for taking the transmitter back into the neurons start pumping, so the time that the transmitter is in between the cells is short. As the receptors recognize the neurotransmitter, they send signals inside the second cell which pass the signal onward and do whatever other physiological response that particular transmitter dictates. Soon enough, the first cell has all its signal back inside it, and the two neurons are back to their resting state, ready to signal again when the time is right.


A close-up of whats going on (serotonin is one of the white dots)

What is serotonin’s job as a neurotransmitter? It regulates signal intensity. Think of it like a volume control on a stereo: serotonin changes how efficiently neurons communicate with each other, making other signals louder or softer. Most often, it accompanies other transmitters, changing a neuron’s response to that particular signal. Because of this, its used by all kinds of nerve cells all over the body, and serotonin levels can dramatically alter our behavior. Levels too high can lead to sedation, whereas low levels are associated with debilitating psychiatric conditions and sudden infant death syndrome (SIDS).

Serotonin, The Necklace – by Molecule Muse

OK, if you pay enough attention to those annoying medical ads you probably have heard of serotonin. It’s one of the major mood neurotransmitters in our brains. When serotonin levels are low, we’re more depressed, and when they’re high, we’re happier. Many depression drugs target the serotonin system by attempting to artificially boost serotonin levels or sensitivity.  MAOIs prevent the breakdown of serotonin in the body in general, thus artificially raising levels. Zoloft and other SSRIs (selective serotonin re-uptake inhibitors) target the serotonin system by blocking the those pumps which bring the serotonin back in after a signal, causing signals to seem stronger and last longer. For that matter, recreational drugs often target serotonin as well. Mescaline, LSD and other psychedelics mimic serotonin and activate serotonin receptors in the brain. Ecstasy’s main component, MDMA, causes your brain’s neurons to release stored serotonin, causing the happy, euphoric state the drug is named for.

Serotonin in the Gut

But what you probably don’t know is that about 80 to 90 percent of the human body’s total serotonin is found in specialized cells in our guts, not in our brains. In fact, serotonin was tied to food long before it became an important mood hormone.  In many species, its directly tied to appetite – deplete serotonin, and they act like they are starving. They hunt for food, put off mating and egg laying, and generally do whatever they can to find another bite to eat.

In many species, including us, serotonin is key in the functioning of gut muscles, causing contraction of our intestines. As it turns out, our digestive system has its own neural network and largely controls itself without any input from our brains whatsoever. In fact, if you were to cut the main nerve that connects the two, the gut would continue to function independently. In part, that is where serotonin comes in. It is key in the control our digestive muscles during digestion. Serotonin acts on gut nerves which signals pain, nausea and other gut problems.


Stomach, up close

For example, if you eat something that upsets some of your stomach cells, they release copious amounts of serotonin. This flood of neurotransmitter causes the gut to empty, leading to diarrhea. But if the serotonin overflows the gut’s management system, it leaks into the blood, where it stimulates 5HT3 receptors in the brain which induces vomiting. So depending on how bad the insult to your stomach, serotonin levels control how your body reacts. Because of this, some of those anti-depressants, particularly the SSRIs, frequently trigger nausea and vomiting as a side effect.

Our gut uses so much more serotonin than our brains its amazing. In fact, so much serotonin enters our stomachs every day that if it were injected into the body in general it would be lethal. Luckily for us, there are certain gut cells which contain a lot of serotonin transporters which keep the serotonin in our stomachs and out of the rest of our bodies. (Watch the following video if you REALLY want to know the science behind serotonin in the gut):

There’s even rising evidence that serotonin is important in our hunger signaling, particularly in feelings of fullness. Injecting low serotonin doses into the body has caused rats to eat less even though they’re hungry, an effect enhanced by those same MAOIs that increase serotonin levels. Overall, more and more research suggests that serotonin is somehow modulating food intake – but we’re not sure exactly how… yet.

Serotonin and Nutrition

Since it has so many diverse and important roles in the body, serotonin levels are key to health mentally and physically. Because its so common in all kinds of animals, serotonin can be found in a variety of foods. The highest concentrations are found in:

  • walnuts
  • plantains
  • pineapples
  • bananas
  • kiwis
  • plums
  • tomatoes

These foods can boost serotonin levels in the gut, ensuring rapid communication between gut cells. But because serotonin in its complete form cannot pass through the blood-brain barrier, we have to do more than include serotonin-rich foods in our diets: we have to include its building blocks.


In fact, our bodies naturally understand this, and cause us to crave foods rich in tryptophan, an amino acid key to serotonin production in our brains when serotonin levels are low. What foods are high in tryptophan, you might ask? Carbohydrates. All of a sudden those calorie-rich, carbohydrate-packed comfort foods make a whole lot of sense. It’s logical, then, that sad people tend to eat more junk food even when a more nutritious option is available. When we’re depressed or upset, we want higher levels of serotonin to feel better, and packing in as much tryptophan as possible is our body’s way of trying to cope. Studies have shown that ingesting carbohydrates boosts serotonin synthesis and levels. Particularly tryptophan-rich foods include:

  • turkey
  • bananas
  • milk
  • yogurt
  • eggs
  • meat
  • nuts
  • beans
  • fish
  • a variety of cheeses including Swiss and Cheddar

The irony is that not only does mood affect how we eat, but how we eat affects our mood. It’s a two way street. Research has shown that dieters tend to become depressed about two weeks into a diet, about the time their serotonin levels have dropped due to decreased carbohydrate intake. Cutting calories has been shown to reduce tryptophan levels in rats, leading to less serotonin , and even decreases the number of receptors in their brains, so they’re less responsive to the serotonin they have.

Watch out ladies…

Of course, just because that’s how the world seems to work, women have to be even more careful than men when it comes to dieting and serotonin. In women, calorie reduction has a dramatic impact on serotonin and tryptophan levels – an effect not nearly as strong in men. This strange double standard is suggested to be a part of why women are so much more prone to eating disorders. The obvious recourse when it comes to dieting, logically, is that by cutting calories we make ourselves more depressed, which in turn makes our bodies want more carbohydrates and calories to boost our moods. It’s yet another reason our weight tends to yo-yo when we try to diet, especially when carbs are cut, and helping keep serotonin levels in check might just be the solution. For example, cheat. Giving yourself a carb-rich treat every so often can help you maintain higher serotonin levels and keep you in a better mood where you can curb your cravings to eat calorie-craving comfort foods during the rest of the week.

But its not just tryptophan that’s important. It turns out that vitamin levels in our diets can have a dramatic impact on serotonin systems. One of the most important vitamins key to serotonin function is thiamine, one of the components of Vitamin B Complex. Simply altering the levels of thiamine in our diets and ensuring enough intake can have amazing effects. One study, for example, found that supplemental vitamins for a year significantly boosted women’s moods and overall well-being, particularly due to levels of thiamine.

Another Vitamin-B compound, folic acid, is also strongly linked with serotonin levels. Boosting folate levels in older people, who are generally deficient compared to younger adults, has been found to improve their mood and cognitive function. Even in healthy adults higher levels of serum folate have been linked to fewer mood swings and negative moods. And even more impressively, high folate levels can improve other depression treatmentsparticularly with how well anti-depressants work. Exactly how folate relates to serotonin is unclear, though it appears to act through an intermediate compound called S-adenosylmethionine (SAM). SAM increases serotonin levels, but it requires folic acid. Folic acid deficiency leads to low levels of SAM, and subsequently reduced serotonin.

Serotonin and Behavior

One way in which we can help our bodies have healthy serotonin levels is by good behavior. Things we do, behaviorally, have a major impact on serotonin levels. For example, stressing, feeding, and exercise have been shown to have marked affects on serotonin levels in rats. It turns out that sleep and exercise are particularly strongly tied to serotonin. After all, one of serotonin’s major actions in our bodies is as a sedative, so its not shocking that it has close ties with how we regulate our energy.

Exercise to increase serotonin (credit, Frederic de Villamil, flickr)

It’s well established that exercise can boost our moods and make us feel better. One way in which this occurs is by increasing serotonin. Exercise is a cheap and dirty way to boost blood and brain serotonin levels immediately, making it a good alternative to other ways of dealing with stress and depression. But exercise does even more: it helps regenerate neurons. Unlike we’re told when we’re young, our brain cells can and do regenerate, albeit slowly. Increased levels of exercise have been shown to increase neuron production, giving out brains better ability to utilize the serotonin boosts and improve our moods. Exercise also allows our brains cells to function better by making them more flexible, leading to better responses to all neurotransmitters, including serotonin.

Sleep, however, is even more important when it comes to serotonin. People have been studying the connection between serotonin and sleeping behaviors for over 50 years. We know that changes in serotonin levels have marked impact on sleeping, with decreases in serotonin leading to apnea or other sleep problems. But only recently have we realized the opposite is true, too. Lack of sleeping negatively affects our brains neuronal signaling, including how it responds to serotonin. Sleep deprivation has been shown to desensitize serotonin pathways, meaning that consistent lack of sleep has a negative impact on our brain’s response to serotonin in general. This means that consistent healthy sleeping patterns are key to maintaining healthy serotonin signaling in our brains and likely our bodies in general.


Go Outside and Be Happy! Light triggers serotonin…

Another, simple way to increase serotonin production is to get outside. Scientists discovered the connection between light and serotonin almost accidentally. They looked at levels of serotonin in recently-dead people, and found higher concentrations of serotonin in those who died in the summer instead of the winter. That got doctors thinking. It was already known that many people have seasonal changes in mood, with more depression occurring during the cold, dark winter than the warm, sunny summer. It had even been found that increasing light levels helped treat non-seasonal depression. Could light be having an impact on serotonin levels? Research suggests yes. They’ve since found that serotonin levels in healthy men are directly correlated to the amount of sunlight in the day, with marked increases as the seasons changed and the sun’s intensity rose, and other research has found strong connections between light and serotonin function. Taken together, these suggest that a walk in the sun or getting away on vacation to somewhere tropical and sunny during the darker months might be able to naturally boost serotonin levels.

There are other behavioral ways to change serotonin levels, too. Rising evidence suggests that our own emotions and moods affect serotonin levels. In other words, trying to boost our moods or rosy our outlooks can help raise serotonin levels. Things you can try:

  • Meditation
  • Relaxation Techniques
  • Talking to Friends
  • Counseling

All these mood-boosting behaviors might just help raise overall serotonin levels, allowing us to keep out of those bad moods later on.

In The End…

Of course, like anything else, it’s balance that counts. Over-eating of carbohydrates and sugars can lead to decreased sensitivity to serotonin, leading to negative mood and physical side effects like obesity. Eating lots of protein can help balance serotonin levels. As it turns out, eating protein before carbs curbs the usual spike in serotonin. And, the truth is, we want to cut down our serotonin sometimes. It is a mild sedative, and eating serotonin-boosting foods in the middle of the day can make us drowsy and less focused. A protein-rich snack instead will help increase energy and keep you going when you need it most.

Even worse, eating too serotonin-boosting foods, while it might feel good for a short time, can lead to a worse crash later on. That’s why a candy bar or a soda are so much worse for us – the sugary energy-upping effect is only temporary, and we’re left with sleep-inducing increases in serotonin instead, leading to a much harder crash. Proper nutritional balance is required for sustained energy throughout the day and a balanced mood. And if you do want a snack with a pick-me-up in terms of mood, try something with less sugar or caffeine but plenty of tryptophan, like nuts – plus nuts are packed with other brain-boosting goodies, too.

In general, though, people don’t get enough of the healthy serotonin boosters in our diets – leading to a lot of grumpiness and overall blah-feelings. We are outside less than we should be, sleeping odd or too few hours, exercising less, and generally eating poorer. All of these are causing our bodies serotonin levels to get out of whack. Understanding the impacts of our actions and what we eat on this important system can help us improve our moods and gut health dramatically without resorting to anti-depressants or other drugs and their side effects, allowing a natural way for us to feel great more often.

You may want to check out the first part of the series if you enjoyed this amazing article: Leptin, The Fullness Hormone


  1. Pollock JD, & Rowland N (1981). Peripherally administered serotonin decreases food intake in rats. Pharmacology, biochemistry, and behavior, 15 (2), 179-83 PMID: 7312891
  2. Garattini S, Bizzi A, Caccia S, Mennini T, & Samanin R (1988). Progress in assessing the role of serotonin in the control of food intake. Clinical neuropharmacology, 11 Suppl 1 PMID: 3052823
  3. Fernstrom, J., & Wurtman, R. (1971). Brain Serotonin Content: Increase Following Ingestion of Carbohydrate Diet Science, 174 (4013), 1023-1025 DOI: 10.1126/science.174.4013.1023
  4. Haleem, D., & Haider, S. (1996). Food restriction decreases serotonin and its synthesis rate in the hypothalamus NeuroReport, 7 (6) DOI: 10.1097/00001756-199604260-00011
  5. Anderson IM, Parry-Billings M, Newsholme EA, Fairburn CG, & Cowen PJ (1990). Dieting reduces plasma tryptophan and alters brain 5-HT function in women. Psychological medicine, 20 (4), 785-91 PMID: 2284387
  6. Goodwin GM, Fairburn CG, & Cowen PJ (1987). Dieting changes serotonergic function in women, not men: implications for the aetiology of anorexia nervosa? Psychological medicine, 17 (4), 839-42 PMID: 3432460
  7. Wurtman JJ (1993). Depression and weight gain: the serotonin connection. Journal of affective disorders, 29 (2-3), 183-92 PMID: 8300977
  8. Benton, D., Haller, J., & Fordy, J. (1995). Vitamin Supplementation for 1 Year Improves Mood Neuropsychobiology, 32 (2), 98-105 DOI: 10.1159/000119220
  9. Alpert M, Silva RR, & Pouget ER (2003). Prediction of treatment response in geriatric depression from baseline folate level: interaction with an SSRI or a tricyclic antidepressant. Journal of clinical psychopharmacology, 23 (3), 309-13 PMID: 12826993
  10. Williams, E., Stewart-Knox, B., McConville, C., Bradbury, I., Armstrong, N., & McNulty, H. (2007). Folate status and mood: is there a relationship? Public Health Nutrition, 11 (02) DOI: 10.1017/S1368980007000031
  11. Resler G, Lavie R, Campos J, Mata S, Urbina M, García A, Apitz R, & Lima L (2008). Effect of folic acid combined with fluoxetine in patients with major depression on plasma homocysteine and vitamin B12, and serotonin levels in lymphocytes. Neuroimmunomodulation, 15 (3), 145-52 PMID: 18716414
  12. Rueter LE, & Jacobs BL (1996). A microdialysis examination of serotonin release in the rat forebrain induced by behavioral/environmental manipulations. Brain research, 739 (1-2), 57-69 PMID: 8955925
  13. Salmon P (2001). Effects of physical exercise on anxiety, depression, and sensitivity to stress: a unifying theory. Clinical psychology review, 21 (1), 33-61 PMID: 11148895
  14. Chaouloff F, Elghozi JL, Guezennec Y, & Laude D (1985). Effects of conditioned running on plasma, liver and brain tryptophan and on brain 5-hydroxytryptamine metabolism of the rat. British journal of pharmacology, 86 (1), 33-41 PMID: 2413941
  15. Ernst C, Olson AK, Pinel JP, Lam RW, & Christie BR (2006). Antidepressant effects of exercise: evidence for an adult-neurogenesis hypothesis? Journal of psychiatry & neuroscience : JPN, 31 (2), 84-92 PMID: 16575423
  16. Christie, B., Eadie, B., Kannangara, T., Robillard, J., Shin, J., & Titterness, A. (2008). Exercising Our Brains: How Physical Activity Impacts Synaptic Plasticity in the Dentate Gyrus NeuroMolecular Medicine, 10 (2), 47-58 DOI: 10.1007/s12017-008-8033-2
  17. Weitzman, E., Rapport, M., McGregor, P., & Jacoby, J. (1968). Sleep Patterns of the Monkey and Brain Serotonin Concentration: Effect of p-Chlorophenylalanine Science, 160 (3834), 1361-1363 DOI: 10.1126/science.160.3834.1361
  18. Roman V, Walstra I, Luiten PG, & Meerlo P (2005). Too little sleep gradually desensitizes the serotonin 1A receptor system. Sleep, 28 (12), 1505-10 PMID: 16408408
  19. Carlsson A, Svennerholm L, & Winblad B (1980). Seasonal and circadian monoamine variations in human brains examined post mortem. Acta psychiatrica Scandinavica. Supplementum, 280, 75-85 PMID: 6157305
  20. Golden RN, Gaynes BN, Ekstrom RD, Hamer RM, Jacobsen FM, Suppes T, Wisner KL, & Nemeroff CB (2005). The efficacy of light therapy in the treatment of mood disorders: a review and meta-analysis of the evidence. The American journal of psychiatry, 162 (4), 656-62 PMID: 15800134
  21. Lambert GW, Reid C, Kaye DM, Jennings GL, & Esler MD (2002). Effect of sunlight and season on serotonin turnover in the brain. Lancet, 360 (9348), 1840-2 PMID: 12480364
  22. AANHETROT, M., BENKELFAT, C., BOIVIN, D., & YOUNG, S. (2008). Bright light exposure during acute tryptophan depletion prevents a lowering of mood in mildly seasonal women European Neuropsychopharmacology, 18 (1), 14-23 DOI: 10.1016/j.euroneuro.2007.05.003
  23. Perreau-Linck E, Beauregard M, Gravel P, Paquette V, Soucy JP, Diksic M, & Benkelfat C (2007). In vivo measurements of brain trapping of C-labelled alpha-methyl-L-tryptophan during acute changes in mood states. Journal of psychiatry & neuroscience : JPN, 32 (6), 430-4 PMID: 18043767