So many factors impact your weight beyond the number of calories you eat or how much you exercise. One of the most significant factors in weight balance is the health and balance of your gut.

As the largest immune organ in your body, the gut contributes to many aspects of your health and physiology. Malnutrition and weight imbalances, including obesity, being underweight, and nutrient deficiencies, result from the interplay between many factors. These include genetics, lifestyle habits, environmental exposures, and microbial characteristics, especially in your gut microbiome. 

The millions of microbes that colonize the digestive tract make up your gut microbiome. These bacteria, yeasts, and other microbes play essential roles that impact processes all over your body and are essential for the maintenance of your health. These microbes influence everything from mood to hormones, skin, metabolism, autoimmunity, and inflammation, including facilitating the gut-weight connection. 

A holistic health approach to weight balance looks at the health of your gut and aims to heal and keep the gut healthy using diet, lifestyle, supplements, and integrative therapies. Understanding how the gut influences your appetite, metabolism, and weight can help you take control of your health and regain a weight that is healthy for your body!

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The Human Gut: A Brief Overview 

The digestive system is made up of the gastrointestinal tract (mouth, esophagus, stomach, small intestine, large intestine, and anus) and the liver, pancreas, and gallbladder. Your digestive system allows you to digest nutrients from the foods that you eat into components that you can absorb and convert into energy. It also processes and excretes the waste products of digestion. In addition, the gastrointestinal tract plays an important role in maintaining immune system function and balance so that your body can protect itself from harmful pathogens while tolerating innocuous food, friendly microbes, and self-antigens.

Beginning at birth, your body accumulates microbes that inhabit your skin, gut, other organs, and tissues. Your gut microbiome diversity becomes established within the first few years of life and is influenced by genetics as well as external factors, including breastfeeding, diet, and environmental exposures. 

In the digestive tract, this collection of over 1,000 species of bacteria, along with viruses, fungi, and other microorganisms, make up your gut microbiome. The most common bacteria in the gut microbiome are members of the Bacteroidetes and Firmicutes species.

These microbes in the gastrointestinal tract have evolved alongside the human host to perform many functions that we cannot accomplish on our own. For example, the gut microbiome supports intestinal development and function, micronutrient absorption and synthesis, hormonal regulation, and the metabolism of medications or other toxicants.

The diversity within your gut microbiome influences your digestive function as well as many other processes throughout your body. The way you digest and absorb nutrients is regulated and influenced by the microbes in your gut. Research shows that the gut microbiome plays an important role in the harvest, storage, and expenditure of energy from the foods that you eat.

How Does Gut Dysbiosis Impact Weight?

When the microbes in your gut are not in balance, dysbiosis occurs. Gut dysbiosis involves a lack of beneficial bacteria and/or overgrowth of potentially pathogenic (bad) bacteria that leads to a loss of overall bacterial diversity. This leaves your gastrointestinal tract more vulnerable to infections or overgrowth of disease-causing or invasive microbes and disrupts the normal functions that the gut microbiome plays. 

This imbalance usually results from the interplay of several factors, such as a diet that is high in refined sugars, processed foods, and poor-quality fats and low in omega-3 fatty acids, fiber, and phytonutrients; pathogenic infections that occur from contaminated food or water; chronic antibiotic use; low stomach acid which can occur with chronic use of antacids and proton pump inhibitors; and poor dental hygiene. In addition, lifestyle factors such as acute or chronic stress and traumas, inadequate sleep, regular alcohol consumption, and smoking can all contribute to gut dysbiosis and inflammation that can impact weight.

A growing body of research is exploring the connection between gut health and weight and the role that the bacteria in your gut play in influencing your body composition. This emerging science gives us a deeper understanding of the complex factors that impact weight and insight into new approaches to achieving a balanced weight.

Research suggests that the composition of the gut microbiota differs between lean and obese humans. When the microbiome is out of balance (dysbiosis), it impacts levels of chronic low-grade inflammation in the body. This occurs in part due to the release of lipopolysaccharide (LPS), a toxin derived from the intestinal microbiota that can contribute to weight issues, such as obesity and/or malnutrition. 

An imbalanced microbiome can contribute to a leaky gut, which makes it more likely for toxins and other substances to cross into the bloodstream, where they can trigger increased inflammation that is associated with various conditions, such as autoimmune diseases and weight imbalances. Studies show that imbalances in gut microbiota cause increased permeability of the gut wall that allows for endotoxin to leak into the bloodstream and ultimately results in micro-inflammation that has been associated with obesity. Research has found that butyrate-producing gut bacteria like Faecalis Bacteria help to decrease gut permeability by decreasing zonulin levels and lowering inflammation. 

Not only do these microbial communities impact nutrient absorption and energy regulation, but they also help to make key nutrients themselves. For example, bacteria in your gut produce short-chain fatty acids (SCFAs) like butyrate by fermenting partially- and non-digestible carbohydrates like prebiotic fibers and resistant starches, especially from plant foods. In turn, these SCFAs help to nourish your gut, keep the microbiome balanced, impact energy balance and blood glucose levels, impact the gut-brain axis, and regulate your appetite and metabolism to reduce the chance of obesity.

The Gut-Brain Axis and Appetite Regulation

Your body needs energy to carry out all of the processes it requires to survive and thrive. Usually, this energy is derived from the food you eat. Genetic, metabolic, hormonal, and neural factors influence your appetite, how much, and how often you eat. 

When you eat food, your intestinal tract can assess your nutritional status and send messages to the brain via the gut-brain axis about your current state. The brain can then regulate food intake via hormonal and neural signals that help you maintain stable energy and metabolism. 

This complex orchestration of energy balance is largely controlled by the gut-brain axis or gut microbiota-brain axis. This bidirectional communication network between the gut and the brain involves signals that are coordinated via the immune system, hormones, neurotransmitters like serotonin, and vagus nerve signaling via the enteric nervous system. 

Hormones, or gut-brain peptides, including leptin, cortisol, insulin, estrogen, ghrelin, neuropeptide Y, Glucagon-Like Peptide-1, peptide YY, and cholecystokinin are released into circulation to signal the level of need for more energy and impact the activity of appetite neurons to help make sure your body gets the energy it needs. For example, your satiety hormone leptin is released primarily from fat cells and binds to its receptors in the brain to signal that you have enough energy, and the brain can inhibit food intake and increase energy expenditure. On the other hand, ghrelin is the hunger hormone that stimulates appetite and increases food intake and fat storage when the stomach is empty. These hormones also impact taste sensation and carbohydrate metabolism. 

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Many of these appetite-regulating hormones are also produced by and influenced by gut bacteria. Research suggests that microbes can manipulate human appetite and eating behavior directly by producing hormones that regulate appetite and indirectly by stimulating the production of auto-antibodies that interfere with the normal regulation of appetite.

The vagus nerve (cranial nerve ten) is the main nerve of the rest and digest (parasympathetic) division of the autonomic nervous system (ANS) that helps to regulate many processes your body carries out without you having to consciously think about it, including digestion, heart rate, blood pressure, and breathing. The vagus nerve is an essential route of communication between the brain, gut, and immune system. 

Neurotransmitters (including GABA, serotonin, norepinephrine, dopamine, acetylcholine, and melatonin) are produced by both your brain and gut bacteria that facilitate messaging, impact your mood, and regulate your appetite and weight. Bacteria such as Escherichia coli, Bacillus cereus, B. mycoides, B. subtilis, Proteus vulgaris, Serratia marcescens, and Staphylococcus aureus manufacture dopamine while B. infantis raises tryptophan, which is converted into serotonin. In fact, over 50% of the dopamine and the vast majority of the body's serotonin is produced in the gut. 

Unfortunately, sometimes environmental exposures, chronic stress, a lack of sleep, poor gut health, and microbiome imbalances can throw this gut-brain signaling system out of balance. When this occurs, it can dysregulate your appetite and influence your weight.

One way these impacts lead to changes in weight is by influencing the balance of microbes in your gut. Microbes in your gastrointestinal tract can have a significant impact on these signaling and regulation systems. The gut microbiome can influence your appetite and eating behavior, reward and satiety/fullness pathways, mood, taste receptors, and vagus nerve function to impact communication within the gut-brain axis.

Research shows that the vagus nerve regulates eating behavior and body weight with blockage to its signaling, resulting in weight loss and overstimulation of vagal pathways, leading to excessive eating behavior. Microorganisms in your gut can produce certain neurochemicals that can also stimulate vagal nerve activity and thereby contribute to overeating.

Functional Medicine Lab Testing for Gut Health

A functional medicine approach allows for uncovering underlying factors that contribute to gut health and weight balance that can guide a personalized approach to healing. Functional medicine lab testing, including comprehensive stool analysis, intestinal permeability tests, and organic acids testing, can provide valuable information that can guide a weight management plan aimed at your unique gut and body. 

Comprehensive Stool Analysis

A comprehensive stool analysis like the GI360 Profile Test by Doctor’s Data or the GI-MAP + Zonulin from Diagnostic Solutions provides insights into microbial diversity and imbalances, inflammation, digestion, and immune function. Including a measure of zonulin helps also evaluate if leaky gut is occurring, which may further reflect dysbiosis and contribute to inflammation and gut-brain axis dysfunction.

Intestinal Permeability Testing

Increased intestinal permeability or “leaky gut” can result from dysbiosis and inflammation in the gut. When this occurs, there is a loss of regulation of the normally tight barrier of the gut wall that allows food, pathogens, and other toxins to pass across the gut wall and into the bloodstream. Obesity and its metabolic complications, such as metabolic syndrome, high cholesterol, type 2 diabetes, coronary heart disease, high blood pressure, and stroke, are associated with the chronic inflammation that occurs with leaky gut. 

Zonulin is a molecule that modulates the tight junctions between gut cells. As stated above, it can be measured along with the GI-MAP. However, it can also be measured separately with the Zonulin Test by Diagnostic Solutions in a stool sample as a biomarker of intestinal permeability. 

Organic Acids Test

Organic Acids Testing, like the one by Mosaic Diagnostics, is a urine test that can be completed easily at home. It measures byproducts of gut bacteria and yeasts that can occur with dysbiosis and provides information about vitamin and mineral levels, oxidative stress, neurotransmitter levels, and oxalates to give a picture of overall gut health.

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Role of Probiotics and Prebiotics in Weight Balance 

Probiotics are beneficial live organisms that can be supplemented or derived from food to help enhance the microbiome. In addition to targeted supplements of various probiotic strains,  probiotics are found in fermented foods like yogurt, kefir, sauerkraut, and kombucha.

Prebiotics provide food for gut bacteria. These non-digestible fibrous carbohydrates, such as inulin, fructooligosaccharides, galactooligosaccharides, fructans, lactulose, resistant starch, polydextrose, pectin, arabino-oligosaccharides, xylooligosaccharides, beta-glucans, and guar gum stimulate the growth of beneficial microbes within the gut.  

Overall, obesity is associated with lower microbial diversity and richness and imbalances in certain types of microbes. For example, an increased Firmicutes/Bacteroidetes ratio in the fecal microbiota has been seen with obesity. 

Synbiotics contain a mixture of prebiotics and probiotics and can help to favorably modulate the gut microbiome and weight. Various probiotic strains, along with prebiotics, help to modulate physical, biochemical, and metabolic parameters that reduce weight imbalances like obesity. Targeted probiotic supplementation results in beneficial changes in gut microbiota, lower insulin resistance, and greater satiety or sense of fullness. Probiotics can support the maintenance of a balanced weight by reducing the number of calories you absorb from food, regulating appetite-influencing hormones, and reducing inflammation.

Studies suggest that supplementing with probiotics regulates appetite and helps to control overeating. In particular, some Lactobacillus probiotics seem to help reduce fat mass and improve insulin sensitivity and glucose tolerance. For example, supplementation with VSL#3, a probiotic containing a mixture of Lactobacillus strains, reduces hunger-stimulating hormones and decreases food intake. L. rhamnosus is another probiotic strain associated with weight loss. 

Bifidobacterium probiotics also inhibit weight gain. For example, a study looking at probiotic treatment with L. rhamnosus GG and Bifidobacterium lactis in pregnancy reduced abdominal fat at six months postpartum.

In addition to Lactobacillus and Bifidobacterium species, other probiotics have also been shown to induce metabolic changes that help to reduce weight gain. These include Pediococcus pentosaceus LP28, Bacteroides uniformis CECT 7771, Akkermansia muciniphila, and Saccharomyces boulardii.

Prebiotics supplement this impact on microbial diversity by improving gut microbiota composition via stimulating the growth of Lactobacillus and Bifidobacterium while reducing the population of pathogenic microorganisms, including Firmicutes and Bacteroidetes. Prebiotics may also help with weight balance by improving glucose and lipid metabolism, repairing intestinal permeability, and increasing leptin sensitivity to impact appetite and satiety.

Diet’s Role in Shaping Gut Health and Weight

The composition of the gut microbiota can change rapidly in response to dietary factors. Individual types of microbes are highly dependent on the nutrient composition of your diet. For example, Prevotella grows best on carbohydrates, Bifidobacteria thrives with access to adequate dietary fiber, and Bacteroidetes prefer certain fats for nourishment. 

Diets that are high in saturated fat, sugar, and processed foods while being low in fiber disrupt the balance of the gut microbiomes and can lead to imbalances in weight. On the other hand, an anti-inflammatory diet that supports the health of the gut can nurture a balanced microbiome and help you maintain a balanced weight. Research shows that eating more fiber, plant-based foods, omega-3 fatty acids, fermented foods, and whole grains helps mitigate the adverse health effects of high-fat diets and obesity on the microbiome. 

Fiber-rich foods help to feed beneficial gut bacteria, helping to increase amounts of Bacteroidetes and decrease Firmicutes levels. Improving microbial balance in this way is associated with improved metabolic health, reduced inflammation, and enhanced intestinal barrier function, which can help to keep weight balanced. 

Prebiotic fibers are especially beneficial for the gut and the bacteria residing there. You can incorporate more prebiotics into your diet by eating foods like dandelion greens, Jerusalem artichokes, garlic, apples, jicama, seaweeds, onions, leeks, asparagus, and whole oats. Other prebiotic-rich foods like unripe green bananas and cooled cooked rice and potatoes contain resistant starch, which has been shown to enrich groups of bacteria that help you maintain a balanced weight (Bifidobacterium adolescentis, Ruminococcus bromii, and Eubacterium rectale). 

The composition of the gut microbiota is also highly influenced by the types of dietary fat that you eat. Replacing saturated fats with plant-based monounsaturated fatty acids and omega-3 polyunsaturated fatty acids improves dysbiosis and gut health. 

Phytonutrients, such as polyphenols, also help boost beneficial bacteria. Polyphenols act as a type of prebiotic since they feed beneficial leanness-promoting bacteria like Bifidobacteria and Akkermansia muciniphila in your gut while also having anti-inflammatory benefits that protect the intestinal lining. Polyphenols provide the bright, vibrant colors of fruits and vegetables and are found in plant-based foods such as berries, grapes, apples, coffee, colorful vegetables, green tea, and cocoa.

Another way to support your microbiome for weight balance is by incorporating a variety of fermented foods. These foods, like sauerkraut, kombucha, and kimchi, are naturally rich in probiotics.

Calorie reduction also impacts the balance of microbes in the gut. Eating fewer calories increases the abundance of beneficial bacterial species, such as Bacteroidetes and Akkermansia, while reducing bacterial species that contribute to weight gain, like Firmicutes. When looking to reduce calories, though, it is best to avoid artificial sweeteners and additives, which have been shown to disrupt the balance and diversity of gut microbiota. It is also important not to cut out too much carbohydrates and fiber since a low-fiber (low-carbohydrate and high-protein and/or high-fat) diet does not provide enough food for healthy bacteria, resulting in their depletion and dysbiosis.

Addressing Gut Imbalances for Weight Balance: A Holistic Approach 

While some aspects of your gut health and bacteria are influenced by genetics, there are a lot of factors you can influence. Lifestyle and dietary habits can have a dramatic impact on your mix of beneficial and harmful microbes. Since many complex interactions impact weight and gut health, a multifaceted approach addressing stress, sleep, diet, nutrition, supplements, exercise, and environmental exposures can best help to rebalance your gut and metabolism.

A functional medicine approach seeks to understand the interconnectedness of bodily systems and the impact of genetics, lifestyle, nutrition, and environmental factors. Working together with functional medicine practitioners can help you understand the unique factors contributing to your health and weight and uncover the state of the health of your gut so that you can implement a holistic approach to healing and regaining balance. 

Stress plays a key role in appetite and eating behavior and can influence weight in many ways. Stress influences food choices, levels of insulin, glucose, and other hormones, appetite, and the digestion and assimilation of food. Stress can also impact the balance of the gut microbiome as well as vagus nerve function. Therefore, mind-body practices like yoga, breathwork, and meditation can be used to enhance parasympathetic (rest and digest) outflow from the vagus nerve. 

Research shows that balancing vagus nerve function and parasympathetic activity can improve the accuracy of food intake relative to energy expenditure to help lead to a more balanced weight. A mindful approach to eating and a calm state of mind while enjoying nourishing food can also help your microbiome and weight stay balanced.

One great way to manage stress while balancing weight and inflammation is physical activity. Exercise boosts levels of bacteria that produce short-chain fatty acids like butyrate, which contribute to the production of satiety hormones to curb hunger. Moving regularly also helps to regulate inflammation and improve insulin resistance to regulate metabolism. Research suggests that even a few weeks of exercise helps to balance the composition and function of the microbiome to support a more balanced gut health and weight.

In addition to managing stress, getting enough quality sleep is key for weight balance and a healthy microbiome. Growth hormone is released during sleep and is critical for repairing the body's tissue, including the gut. Adequate, well-timed sleep is also important for regulating appetite. Maintain a comfortable, dark, cool sleeping environment and a regular sleeping schedule. 

Addressing weight balance in this way helps balance the gut microbiome so that you can maintain a healthy weight for the long term while keeping your body nourished, rested, and relaxed.

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Summary

The richness and diversity of your gut microbiome influence your health and how well different processes function in your body. When it comes to weight balance, the diversity and richness of the gut microbiota play an important role in the absorption, storage, and expenditure of energy obtained from the food that you eat.

Microbial richness, or the overall number of microbial species in your gut microbiome, along with the diversity or number of individual microbes from different species present in your gut microbiome, influence your health in many ways. The balance of bacteria in your gut influences your immune system, appetite, how much and what type of calories your body absorbs, fatty acid metabolism, and how full you feel from the food you eat and your hunger signals,

The science connecting gut health with weight balance continues to expand as we learn more about the role that the bacteria in your gut play in influencing your weight. This complex relationship gives us new insights into new approaches to achieving a balanced weight. Research has shown that there are therapeutic effects of probiotics and/or prebiotics on body weight, waist circumference, fat deposition, lipid and glucose metabolism, and chronic inflammation.