Have you experienced drowsiness after eating a large meal? Has an important presentation made your stomach turn? Seeing a special someone made you feel butterflies in your stomach? If you have (and you most likely have), then you know how strong the connection between the brain and the gut is.

Scientists have found that many chronic metabolic diseases, type 2 diabetes, mood disorders and even neurological diseases, such as Parkinson’s disease, Alzheimer’s disease, amyotrophic lateral sclerosis (ALS) and multiple sclerosis, are often associated with functional gastrointestinal disorders (1). The importance of the association between the gut and the brain is gaining momentum with each new study. However, the way HOW the signaling between these two integral parts of the body exactly works hasn’t been clear until recently.

It was thought for a long time that the only “communication channel” between the gut and the brain was the passive release of hormones stimulated by the consumed nutrients. Hormones entered the bloodstream and slowly notified the brain that the stomach is full of nutrients and calories. This rather slow and indirect way of passing messages takes from minutes to hours.

But now, a recent study (2) has elegantly proven that the gut can message the brain in seconds! Using a rabies virus enhanced with green fluorescence, the scientists traced a signal as it traveled from the intestines to the brainstem of mice, crossing from cell to cell in under 100 milliseconds – faster than the blink of an eye.

The researchers had also noticed that the sensory cells lining the gut were quite similar to the receptors in the nose and on the tongue (3). The effects, however, differ. In the mouth, the taste of fatty acids triggers signals to increase hunger, whereas in the small intestine, fatty acids trigger signals of satiety. This means that the discovered “gut feeling” might be considered as a sixth sense, a way of how the brain is being signaled when the stomach is full.

This new knowledge will help to understand the mechanism of appetite, develop new and more effective appetite suppressants and help those struggling with weight and problematic eating patterns.

REFERENCES
(1) Pellegrini C et al (2018) Interplay among gut microbiota, intestinal mucosal barrier and enteric neuro-immune system: a common path to neurodegenerative diseases? Acta Neuropathol 136:345. doi:10.1007/s00401-018-1856-5

(2) Kaelberer et al (2018) A gut-brain neural circuit for nutrient sensory transduction. Science 361(6408):eaat5236. doi:10.1126/science.aat5236

(3) Bohórquez and Liddle (2015) The gut connectome: making sense of what you eat. J Clin Invest 125(3):888–890. doi:10.1172/JCI81121

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Psychobiotics are helpful bacteria (probiotics) or support for these bacteria (prebiotics) that influence the relationship between bacteria and brain. The human digestive system houses around 100 trillion of these bacteria, outnumbering the human body cells 10:1. Probiotics provide a great deal of functions vital to our well-being, like supporting the digestion process and improving the absorption of nutrients. Based on the latest research, helpful gut bacteria that can also positively affect the brain – psychobiotics – benefit people suffering from chronic stress, poor mood, or anxiety-like symptoms (1).

There are 3 ways psychobiotics can affect your mental health:

  • Brain chemicals like serotonin, dopamine, and noradrenaline can be produced in the intestines directly by gut microbiota.
  • Battling with and protecting from stress by modifying the level of stress hormones.
  • When an inflammation occurs, inflammatory agents are elevated throughout the body and brain and can cause depression and other mood and cognitive disorders. Psychobiotics can affect the brain by lowering inflammation.

Lactobacillus and Bifidobacterium are the most popular probiotics with respect to mental health (1).

Disruption of the balance of gut bacteria is quite common due to the use of different kinds of medications, antibiotics, artificial preservatives, poor food and water quality, herbicides, stress, and infections (2, 3, 4).

In order to support a healthy microbiota, one should start from eating a diverse range of foods rich in different plant sources. Foods that contain lots of fiber or are fermented also promote the growth of beneficial gut bacteria. Excessive consumption of sugar and artificial sweeteners should be minimized. Managing stress levels, exercising on a regular basis, not smoking and getting enough sleep are also important for keeping microbiota in good condition. When taking antibiotics, one should make sure to consume probiotics so the body can maintain the bacteria it needs to stay healthy.

For people needing help regarding mental health problems, psychobiotics may be a promising relief. Psychobiotics are well-adapted to the intestinal environment and naturally modulate gut–brain axis communications, thereby reducing the chance of adverse reactions.

It is possible that even simple prescribing of a particular diet may be sufficient to promote the selective proliferation of natural or therapeutically introduced psychobiotics (5). Further research focusing on the strain and dosage of psychobiotics, duration of treatment, and the nature of mental disorders will help to determine the most efficient ways of helping people to improve their mental health.

REFERENCES
Abhari A, Hosseini H (2018) Psychobiotics: Next generation treatment for mental disorders? J Clin Nutr Diet. 4:1. doi:10.4172/2472-1921.100063

Carding et al (2015) Dysbiosis of the gut microbiota in disease. Microb Ecol Health Dis. 26: 10.3402/mehd.v26.26191

Lozano et al (2018) Sex-dependent impact of Roundup on the rat gut microbiome. Toxicol Rep. 5:96–107. doi: 10.1016/j.toxrep.2017.12.005

Paula Neto et al (2017) Effects of food additives on immune cells as contributors to body weight gain and immune-mediated metabolic dysregulation. Front Immunol. 8:1478. doi:10.3389/fimmu.2017.01478

Kali (2016) Psychobiotics: An emerging probiotic in psychiatric practice. Biomed J. 39(3):223-224. doi:10.1016/j.bj.2015.11.004

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Food is addictive. It has been an addiction that has kept mankind alive for thousands of years. Today, hunger is no longer a problem in the developed world; it is quite the opposite. According to the World Health Organization, worldwide obesity has nearly tripled since 1975. Obesity has reached epidemic proportions globally, with at least 2.8 million people dying each year as a result of being overweight or obese.

In order to maximize the nutritional value, humans are hard-wired to prefer foods that have either a high sugar or fat content. The amount of energy obtained from food is measured in kilocalories (kcal) per gram. Fats have the most energy (9 kcal) and carbohydrates (sugars and starches) have the same amount of energy as proteins (4 kcal). However, these nutrients differ in how quickly they supply energy. Sugars and starches have the advantage of being converted into energy faster than fats and protein. Protein is preferentially used for building and repairing different tissues, not as an energy source.

Once a beneficial adaptation of preferring fast digesting or the most energy-rich nutrients, has now become a risk factor for both physical and also mental health (1), making it an inevitable research focus.

In a recent study at the Yale University School of Medicine (2) it was determined that people not only favour fatty or sugary foods, but place the highest value on those that combine both. Participants (tasked to make monetary bids on different food items) were ready to pay the most for cookies, chocolate, cake and other treats that had both high sugar and also fat content. Equally familiar, liked and caloric fatty (e.g., cheese, salami) or sugary foods (e.g., lollipops) were assigned lower values.

Based on surges of activity, brain scans revealed that foods high in both fat and sugar were more rewarding than foods rich in only one category of nutrient.

Unexpectedly, it was also observed that participants were very accurate at estimating the energy density (kcal) of fatty foods, but poor at estimating the energy density of sugar-containing foods.

Once rare, but nowadays common and abundant treats high in both fat and sugar are most rewarding and therefore can very likely contribute to overeating. In addition, it has turned out to be difficult for people to assess the amount of calories in foods with a high sugar content. These findings taken together can help to understand and also hopefully find new treatment options for people struggling with obesity.

  • Hoare E et al (2015) Systematic review of mental health and well-being outcomes following community-based obesity prevention interventions among adolescents. BMJ Open 2015;5:e006586. doi:10.1136/bmjopen-2014-006586
  • DiFeliceantonio et al (2018) Supra-additive effects of combining fat and carbohydrate on food reward. Cell Metabolism 28, 1–12. doi:10.1016/j.cmet.2018.05.018
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