This new research is what Me and Niklas Ekstedt, discuss in our book Happy Food. We’ve interviewed researchers around the world and read hundreds of scientific reports. We believe that there is important research taking place in the vanguard, and that it’s important to deepen our knowledge about it. The picture that is emerging is already showing that the links between the intestines and the brain are stronger than we could have ever imagined.

Your intestinal bacteria altogether weigh about 1.4 kilograms (3 lbs), roughly the same as your brain. There are unfathomable numbers of them – about 40 trillion according to new calculations – and they are present in the billions in every gram of mucus that covers the walls of your colon.

These trillions of inhabitants, currently residing in your very private intestinal basement, are in direct contact with the brain. They communicate via nerve cells that surround the intestine. These nerve cells are as numerous as those found in the entire spinal cord, and they are connected to the large vagus nerve, one of the largest nerves in the body – which is in turn part of our autonomic nervous system, the one we can’t consciously control ourselves.

However, there are other communication pathways in what researchers are calling the “Gut-brain axis,” and in those cases it’s about both the hormonal system and the immune system.

Every type of neurotransmitter that your brain uses can be made by your intestinal bacteria in their microscopic workshops, including key players for our emotional life, like dopamine and norepinephrine. 95 percent of the body’s production of the “happiness hormone” serotonin is created in the intestine.

Even the ancient Greeks knew that the stomach and the psyche were connected. Nevertheless, our healthcare system continues to promote the belief that the brain is an autonomous entity, leading a completely independent life separate from the rest of the body.

Through years of patient research, a conclusion has emerged: If we treat our intestinal bacteria well, they can help us to become more stress-resistant, clear-headed, happy, and harmonious. The food we eat also seems to play a role when it comes to depression and other psychological diseases.

This summer, I attended a science conference in Bethesda, outside of Washington D.C, in the US. There, researchers from all over the world were studying the link between the intestine and the brain. Their message was clear:

• We now know that there is a correlation between the quality of food we consume and how we feel.

• It’s time to proceed with more research and more expansive studies that will enable us to better understand the connection and to develop treatments.

Western junk food, with its excess of sugar and refined fats, as well as its lack of fibers and healthy micronutrients, has long been linked to global epidemics of obesity, diabetes, and heart disease. Now, we see one research group after another reporting data indicating that even the epidemic of poor mental health has been linked to the same underlying causes.

Of course, there are many different reasons as to why we may feel depressed, and food can’t solve all problems on its own. But when we get sick or anxious, many parts of the body are affected, the intestinal flora being one of them. When our bacterial system is in a state of imbalance, our immune system is weakened. It can easily become a downward spiral in which we feel worse and worse. Often, the cause may be in the intestine.

In fact, time after time, the common denominator turns out to be our intestinal flora. For example, in early animal experiments, researchers have observed that feces transplanted into mice from depressed people caused the animals to show depressive behavior. When the mice feces were passed on to other mice, the depressed mood followed.