Effect of gut bacteria on sugar cravings-From the second brain: You may know how gut health or gut bacteria can affect nearly every aspect of human health. But not only that your gut bacteria can interfere with your food choice also. You will know why your gut is called your second brain. You may wonder how your gut bacteria can tell you what to eat more sugar, more processed foods. Here we will explore how your gut bacteria can affect your mental health as well as your food choice step by step.
Why you need to be cautious about added sugar as well as processed carbohydrates. Because those foods become the top food villains to kill your health in the modern world. And most people are unknowingly consuming such foods. Those foods can make you overweight, diabetic, increase your chance of heart disease, high blood pressure, impair cognitive function, raise the uric acid level, and more. And your gut health is a reason to consume those foods.
Effect of gut bacteria on sugar cravings-From the second brain
Gut-brain connection-enteric nervous system to central nervous system
You may aware that our fatty brain cells are made up of billions of neurons involved in numerous brain signaling. You may also hear that your gut has also a large concentration of neurons called the enteric nervous system (ENS) that controls many critical functions. (1)
Data from the last decade we have learned our brain has an intimate connection with our gut. The enteric nervous system is connected with the central nervous system via biochemical signaling called a Gut-brain axis. (2, 3)
That’s why the gut is also called the second brain.
Gut bacterial ecosystem
Before jumping into the Gut-Brain axis we need to know about the gut bacterial ecosystem. The human body is a residence of a dynamic population of microorganisms such as bacteria, fungi, and viruses that live together in a harmonic and dynamic equilibrium. They are of so many varieties researchers yet to understand them all. Those microorganisms are bacteria in major and mostly reside in the gut. And the number of those microorganisms is much higher. The number of microorganisms inhabiting the GI tract has been estimated to exceed 100 trillion, which encompasses ∼10 times more bacterial cells than the number of human cells. (4)
Both friendly and harmful bacteria exist in your gut
Some of them are friendly to human health, some are neutral and some are harmful. For example-short chain fatty acids produced by bacteria by digesting fiber affect the brain numbers of ways such as controlling appetite and also used as an energy source. (5) While pathogenic bacteria release toxins, harm to the gastro-intestinal tract, interferes with other important functions of the body leading to the development of many health disorders. On the other hand, friendly bacteria generally modulate our immune system, protect against external bacteria, viruses, germs, or similar, and act as gatekeepers in the intestinal barrier. (6) And all they are living with the host i.e. the human body like an ecosystem.
We need a balance between both types of bacteria
Collectively both good and bad, living inside your digestive system, they’re known as the gut microbiota. When there is an imbalance of bacteria among good or friendly and bad types, also called this condition as dysbiosis, many health problems begin to develop.
Nobel laureate Eli Metchnikoff (1845–1916) said that “the majority of diseases begin in the digestive tract when “good” bacteria are no more able to control “bad” bacteria”. Gut dysbiosis has been linked to the development of several disorders like (inflammatory bowel disease, celiac disease, obesity, metabolic disorder, and more) (7)
In mammals, the gut is the largest immune organ. Your gut bacteria have a very important role in educating and shaping the immune system. An uneducated, untrained strong immune cells can become hostile against your own body cells. That’s why autoimmune diseases are increasing day by day. And the development of the ecosystem of a baby begins from its mother’s womb. C-section babies and natural vaginal delivery babies had different bacterial ecosystem. Moreover, in a study on 596 births in the United Kingdom, C-section babies are missing key microbes. I will come later on this with more elaborately.
The relation between Gut bacteria and Brain-your mental health
The gut-brain axis (GBA) consists of bidirectional communication between the central and the enteric nervous system. That links emotional and cognitive centers of the brain with intestinal functions. Strong evidence suggests that microbiota residing in the intestine has an important role in bidirectional interactions between the gut and the nervous system. It interacts with the Central Nervous System by regulating brain chemistry and influencing neuro-endocrine systems associated with stress response, anxiety, and memory function.
Many of these effects appear to be bacterial strain-specific, suggesting a potential role of certain probiotic strains (live microorganisms considered as friendly) as a novel adjuvant strategy for neurological disorders. (8)
A myriad of recent studies has revealed that gut bacteria seem to be intimately related to mental health. More specifically, both the function of the Central Nervous System and its stress‐triggered dysfunction, have emerged as targets of gut bacterial imbalance. (9)
The study of the gut microbiome has increasingly revealed altered gut bacterial composition can induce impaired brain function and mental health, promote the development of depression and anxiety, changes in cognitive function and behavior, and more. (10, 11, 12, 13)
And impaired mental health, brain function, increased mental stress depression anxiety can result to eat more comfort foods.
Does the gut microbiota manipulate eating behavior?
High Sugar diet and alteration of gut bacteria
In general simple sugars are digested in the small intestine and to some extent in the mouth. They are unlikely to travel to the large intestine where most gut bacteria are colonized. Although it has low comparative to the colon small intestine also has a colony of bacteria. We don’t need too much bacteria in our small intestine. And if you have SIBO or small intestinal bacterial overgrowth you can also have irritable bowel syndrome or IBS. (14)
And apart from that, we have limited capacity to absorb the sugar in the small intestine. And absorption is also impaired with absence or impaired presence of sugar transporter in the intestine. Both these factor contributes to the escape of sugar from the small intestine to the colon. Unabsorbed sugar may contribute to fermentation in the presence of bacteria with the production of gas and other bacterial by-products. (15)
Researchers demonstrate both fructose and glucose block the production of a key protein called Roc, required for colonization of beneficial bacterium such as Bacteroides thetaiotaomicron in the gut. On the other hand, some other bacteria had colonization advantage with high fructose and glucose diet. Interestingly they didn’t found the same result with complex carbohydrates like polysaccharide. (16) Whole food like complex carbohydrates that consists of dietary fiber while glucose or refined carbohydrates from processed foods and fructose don’t.
That indicates the consumption of glucose and fructose from highly sugar-loaded processed foods gives benefits to some intestinal bacteria. That further results in altered gut bacteria.
So where are the researches?
In animal studies-sugar altered gut bacteria
In mice, high-Glucose or fructose diet causes changes in the gut microbiota and increase intestinal permeability. (17)
In another study, high fructose consumption had increased pathogenic bacteria in the gut, imbalanced microbial community structure in the gut, and impaired intestinal barrier function in mice. And researchers found inflammation and neuronal loss in brain region Hippocampus in high fructose feed mice. (18)
Other studies also reported the change of gut bacteria and increased intestinal permeability with a high fructose diet. (19)
Sugar change gut bacteria- human studies
However, these studies are mostly animal studies. Animal study always doesn’t have a similar result in a human.
In humans study published in the journal of Gut Microbes, researchers found high fructose diet reduced friendly bacteria that participate in carbohydrate metabolism in the overweight or obese teenager. (20)
Similarly, researchers found altered gut bacteria with children with excess body weight with another study.(21)
Other studies found an imbalance of gut bacteria in people with non-alcoholic fatty liver and also obesity. Apart from that, a study found peoples suffering from IBS showed a high prevalence of fructose mal-absorption up to 64%. That means a large part of consumed hadn’t gone into the blood from the intestine. Interestingly, from another study, also people tested negative for fructose metabolism disorder showed abdominal symptoms after fructose ingestion suggesting fructose intolerance as a highly common condition (6, 22)
And numerous problems can begin to develop if you have an imbalance between friendly and harmful bacteria.
Alternatively reduced fructose diet showedimprovement in symptoms of IBS including abdominal discomfort, bloating, gas, and diarrhea in adults and children. Researchers also indicated reduced absorption of fructose as well as intestinal inflammation. (23)
As per a 2020 editorial paper published in the journal of Nutrients recent studies have shown that high intake of sugars increases the relative abundance of harmful bacteria in the gut. Not only that, high sugar intakes simultaneously have shown decrease friendly bacteria, which can reduce the effects of toxins released by harmful bacteria, as well as reinforce gut barrier function. That further promotes chronic low-grade inflammation and metabolic dysregulation. (24) And with chronic inflammation, chronic diseases begin to develop in your body.
Also, read 8 foods that can inflame your body from inside.
Altered gut bacteria act negatively in other parts of the body
Gut health affects nearly every aspect of your health. For example
A study found reduced expression of intestinal tight junction protein ZO-1 and occludin in the colon which controls intestinal permeability against unwanted invader to the bloodstream in mice fed with high glucose and high fructose diet. In blood, the high glucose and high fructose significantly increased intestinal permeability and fructose increased permeability by 2.5 fold. And that further increased inflammation. (25)
In normal intestinal barrier doesn’t allow the passage of unwanted foods, toxins, or other harmful pathogens from the intestine to blood circulation. The barrier allows foods to enter into blood circulation after breaking down to a particular size by stomach acids, enzymes, and gastrointestinal movements. But when intestinal permeability is increased it allows passage partially digested food, toxins, and bugs from the intestine. That can lead to myriad health problems. (26)
Studies suggested the role of altered gut bacteria in the development of inflammatory diseases such as arthritis, inflammatory bowel disease, obesity, diabetes, cardiovascular disease and anxiety, and depression. (27, 28)
In overall imbalance in the bacterial ecosystem in the gut with a decrease of beneficial bacteria along with the increase of pathogenic bacteria can impact your overall health and associated with numerous diseases.
How Gut bacteria can affect sugar craving?
We have already talked about the relation of gut bacteria to the brain. Gut bacteria directly stimulate afferent neurons of the enteric nervous system to send signals to the brain via the vagus nerve. (29)
The vagus nerve is a central actor in this communication axis, connecting the enteric nervous system to the base of the brain at the medulla.
A review published in the journal of Bioessays, researchers indicated gut microbes may manipulate eating behavior by hijacking the nervous system. Gut bacteria may manipulate eating behavior by generating a craving for food according to their need to suppress competitors or inducing an environment of dissatisfaction until we eat foods that enhance their fitness. They demonstrated by gut bacteria can manipulate the eating behavior of mammals in several ways including (30)
Gut bacteria create pain signaling
Pain signaling due to the release of toxins by bacteria when certain nutrients are absent and manipulate to consume such nutrients. Detection of simple sugars and other nutrients regulates virulence and growth for a variety of human-associated bacteria. These bacteria directly injure the intestine in the absence of certain nutrients and create pain signals.
Changing taste receptor expression by gut bacteria
Changing taste receptor expression of the host of bacteria. Changes in taste receptor expression and activity have been reported after gastric bypass surgery, that also changes gut microbiota and alters satiety and food preferences
Gut bacteria hijack the host’s nervous system
Gut bacteria may manipulate their host’s eating behavior by hijacking the host’s nervous system through the microbiome-gut-brain axis. Evidence suggests that the vagus nerve through which gut bacteria connect with the brain regulates eating behavior and body weight. For example blockade of the vagus nerve has been reported to cause drastic weight loss. On the other hand, activity appears to drive excessive eating in satiated mice when stimulated by stress neurotransmitters. That suggests that gut microbes that produce such neurochemicals may contribute to overeating via mechanisms involving vagus nerve activity. Interestingly activities like exercise, yoga, and meditation are known to enhance parasympathetic (to a calm and composed state) outflow from the vagus nerve thought to strengthen willpower and improve the balance between food intake and calorie burn. However, increased vagus activity is not always associated with health.
Gut bacteria manipulate through hormone
Microbes produce a variety of neurochemicals similar to mammalian hormones involved in mood and behavior. The figure is not a smaller one. More than 50% of the dopamine and the vast majority of the body’s serotonin has an intestinal source. Many bacterial cultures have been shown to produce dopamine. In contrast, the enzyme produced by the body degrades bacterial origin hormone in the intestine. However certain bacteria have shown to raise blood tryptophan a precursor of serotonin. Gut bacteria both commensal and pathogenic bacteria produce peptides that control hunger, satiety, and food intake by vagus nerve signaling. In contrast, humans and mammals produce anti-hormone antibodies against bacterial manipulation. But these antibodies also act as auto-antibodies against mammalian producing hormone.
Scientists indicate that hormonal manipulation of human’s eating behavior can be two ways
- By directly producing peptide that controls hunger and food intake.
- And by indirectly stimulating hormone antibodies that interfere with mammal’s appetite-regulating hormone.
Inducing the host to supply their preferred nutrients
By inducing their host to supply their preferred nutrients that promote their fitness at the expense of host fitness. (30)
In chocolate testing, scientists found people who had a desire for chocolate had different microbial breakdown products in their urine than those who hadn’t despite eating identical diets. (31)
Studies have linked the inconsolable crying of infant colic with changes in gut microbiota including reduced overall diversity, with the change of types of bacteria compared to controls. Scientists also found the gut microbes of obese humans are less diverse than the microbiota of their lean twins which support that lower diversity may affect eating behavior and satiety. And several studies including clinical studies suggest a role for probiotics in weight loss, reducing body fat in humans. Similarly, probiotics that increase microbiota diversity in humans are predicted to reduce cravings more than control. (30)
Probiotics in the improvement of mental health
Gut bacteria have shown to modulate mental health through the gut-brain axis. Friendly bacteria probiotics not only had shown to restore the gut bacterial ecosystem but also shown to improve mental health.
In many animal studies microbes affecting their hosts’ mood and behavior. Some bacteria appear to calm down anxiety while some increased anxiety-like behavior. In a clinical study probiotic (Lactobacillus casei) intake improved mood significantly whose mood was initially in the lowest tertile. (30) In another example, healthy women who took fermented milk with probiotics had shown higher emotional resilience compared to the control group. (32)
Probiotics had shown to improve mental health in many studies
Drinking yogurt containing live bacteria for three weeks improved the mood of people whose mood was initially poor. (33)
A 2017 systematic review of 10 clinical studies assessed the effects of probiotics intake on mood, anxiety, and cognition. Scientists found most of the studies had positive results in alleviating symptoms and improvement of mental health. (34)
Another narrative review of electronic databases from their inception to December 2017 in English with the inclusion of human and clinical studies found probiotics seem to potentially produce a similar significant beneficial effect in mental health. (35)
Other clinical studies also reported improvement of mental health with probiotics supplementation. (36)
In summery impaired gut health affect nearly every aspect of the health including eating behavior. That’s why gut health is very important. The gut restoration process takes several processes, like following an autoimmune paleo diet and restricting hard digestible foods, allergic foods, sugar-laden foods, and similar for a period. Supplementing with probiotics, collagen protein with glutamine, foods with Zinc, restoration of stomach acid for digestion and acidity, etc are followed. Then slowing re-introducing foods in a controlled manner and identifying foods that cause allergic reactions and eliminating those permanently.
Probiotics or friendly bacteria
A good probiotic supplement help to restore and maintain the gut bacterial ecosystem. However, if you are critically ill don’t use probiotics and also consult with your healthcare provider who had proper knowledge before supplementation. Fermented foods with Probiotic such as kefir, yogurt or curd, kimchi, etc with friendly bacterial culture promotes gut health, reduce gut inflammation and diseases.
On the other hand foods with prebiotics or dietary fiber pass through the small intestine mostly undigested and fermented in the large intestine by gut microflora. This process promotes the growth of the friendly bacteria in your gut, helps them to produce essential nutrients in return. Mostly plant-based foods contain varying amounts of fiber with higher amounts in foods like beans or legumes, whole grains if tolerated, and other vegetables and fruits. However, more is always not better. Too much fiber in the diet may increase gastrointestinal symptom especially in conditions like SIBO, IBS, and IBD.
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