Serotonin plays many crucial functions in the human body. Though we most often associate it with regulating our mood, did you know that most of our serotonin is used to regulate critical movements in the intestines? Or that it plays a function in regulating our sleep cycles and appetite?

These interconnected systems that rely on serotonin may explain why people suffering from depression may also experience digestive and sleep disorders. Low levels of this important chemical can throw all these systems off balance.

To produce serotonin, the body needs to covert it from tryptophan, an essential amino acid that must be obtained through our diet.

While it's important to always consult with your primary care physician if you're suffering from long bouts of depression, insomnia or digestive issues, adding in some serotonin-boosting foods may be effective in reducing or reversing some conditions.

Research has shown that people who ate certain types of nuts also had higher serotonin metabolite levels. Also, soybeans, which have not received the best press lately thanks to many being genetically modified, are also an excellent source of tryptophan. Try fermented soy such as miso or tempeh for more digestible soy food that's easier to break down.

A note about chocolate. The cacao bean is one of the most plentiful sources of plant-based tryptophan. This is of course, excellent news for chocolate lovers. However—processed chocolate products are most often mixed with sugar, high fructose corn syrup and conventional dairy products. There's also a high risk of artificial flavors, preservatives and other questionable ingredients that can trigger both digestive discomfort and increased depression due to sugar crashes. So if you're adding in cacao products, make them pure as possible—dark chocolate with a cacao content over 70 percent—and even raw cacao beans.

1. Spirulina
2. Spinach
3. Almonds
4. Walnuts
5. Brazil nuts
6. Hazelnuts
7. Sunflower seeds
8. Sesame seeds
9. Pumpkin seeds
10. Lentils
11. Kidney beans
12. Chickpeas
13. Soybeans
14. Watercress
15. Mushrooms
16. Peanuts
17. Parsley
18. Cauliflower
19. Kale
20. Broccoli
21. Chocolate

Keep in touch with Jill on Twitter @jillettinger

Image: Xanetia