Obesity has become a global pandemic, a complex condition influenced by various factors including lifestyle, genetics, and hormonal mechanisms. Recent scientific evidence highlights the significant role of gut microbiota in modulating energy metabolism and its connection to obesity and related metabolic consequences. Modifications of gut microbiota composition have been associated with variations in body weight and body mass index. While lifestyle modifications remain the primary approach to managing obesity, new therapeutic strategies involving prebiotics and probiotics are being explored to promote a healthier gut microbiota composition, similar to that found in non-obese individuals. This article explores the mechanisms through which gut microbiota influences obesity and the potential benefits of prebiotic supplements in weight loss.
The Gut Microbiota: A Key Player in Obesity
The human intestinal microbiota is a complex ecosystem comprising bacteria, viruses, archaea, fungi, and phages, deeply involved in host metabolism. The gut microbiota is predominantly involved in the fermentation of indigestible carbohydrates into SCFAs, which have been found to exert multiple effects on energy homeostasis and are crucial for intestinal health. The gut microbiota plays an important role in the absorption, storage, and expenditure of energy obtained from dietary intake.
The gut microbiota (the collective genomic content of microorganisms) in humans contains ~40 trillion microorganisms. The dominating bacteria phyla in humans, accounting for 90% of the gut microbiota, are Firmicutes and Bacteroidetes. There are currently >274 genera within the Firmicutes phylum, including Bacillus, Lactobacillus, Mycoplasma, and Clostridium.
How Gut Microbiota Influences Weight
Several mechanisms explain the role of gut microbiota in obesity development. Some mechanisms have been proposed to explain the role of gut microbiota in obesity development. One is related to the energy regulation and ability of the microorganism to ferment dietary polysaccharides not digested by humans [32]. Fermentation of dietary fibers results in SCFA generation. Once absorbed, SCFAs can induce lipogenesis and increase triglyceride stores through molecular pathways. SCFAs have shown to activate the carbohydrate responsive element-binding protein and the sterol regulatory element-binding transcription factor 1, both involved in lipogenesis. Furthermore, SCFAs can suppress the fasting-induced adipocyte factor, which inhibits lipoprotein lipase, inducing triglycerides accumulation in host adipocytes [32]. Obesity-associated microbiota increases the efficiency of calorie uptake from ingested foods and affects energy balance by influencing energy use and storage [20].
- Energy Regulation: Gut microorganisms ferment dietary polysaccharides that humans cannot digest, leading to the production of short-chain fatty acids (SCFAs). These SCFAs, such as acetate, butyrate, and propionate, play a vital role as substrates for glucose metabolism and can influence lipogenesis (fat production) and triglyceride storage.
- Low-Grade Inflammation: Obesity is often associated with chronic low-grade inflammation and insulin resistance. Alterations in gut microbiota composition, often induced by a high-fat diet, can increase gut permeability, leading to the translocation of bacteria or lipopolysaccharides (LPSs) into the bloodstream, triggering inflammation.
- Gut-Brain Axis: The gut microbiota is also involved in the regulation of food intake by affecting hormones that influence metabolic function and areas in the brain associated with eating behavior [27]. This so-called “gut microbiota-brain axis” represents a bidirectional signaling axis that regulates body weight by balancing appetite, storage, and energy expenditure [22]. The gut-brain axis exerts a substantial physiological impact on mood, behavior, and stress responsiveness.
- Calorie Uptake: Obesity-associated microbiota can increase the efficiency of calorie uptake from ingested foods, affecting energy balance by influencing energy use and storage.
- Altered SCFA Composition: Alterations in diversity and microbial richness are thought to be associated with altered SCFA composition, energy homeostasis, and inflammation.
Gut Microbiome and Obesity
Reports on the composition of the gut microbiota in obese individuals are not uniform, obese humans showed an increased Firmicutes/Bacteroidetes ratio in the fecal microbiota, and reduced microbial diversity and richness seem to be a recurrent finding. The obese phenotype was transmittable via intestinal microbiota alone in germ-free mice [30] and human beings [31] and was reversed in germ-free mice following co-housing with mice transplanted with the lean microbiota [31]. These findings show the transmissible, rapid, and modifiable nature of interactions between diet and gut microbiota in obesity and metabolic syndrome. Those alterations in diversity and microbial richness are thought to be associated with altered SCFA composition, energy homeostasis, and inflammation.
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Prebiotics: Fueling Beneficial Gut Bacteria
Prebiotics are non-digestible food components that promote the growth and activity of beneficial microorganisms in the gut. They are essentially food for the good bacteria, helping them to thrive and outcompete harmful bacteria. Prebiotics are different from probiotics. Probiotics are strains of beneficial bacteria that you can try to intentionally add to the body through fermented foods like yogurt or via supplements, while prebiotics are meant to “feed” good strains of bacteria already living in the gut. “Prebiotics are nondigestible fibers and compounds found in certain foods [like fruits, vegetables, and whole grains] that nourish and stimulate the growth of beneficial gut bacteria,” notes Alexa Aboudaram, owner and nutritionist at Navigating Nutrients, based in Charleston, South Carolina.
How Prebiotics Work
Prebiotics are undigestible fibers or compounds found in plant-based foods that nourish and stimulate the growth of beneficial gut bacteria. They play a crucial role in maintaining a healthy gut microbiome, which can have positive effects on digestive health, overall well-being, immune function, and nutrient absorption. These non-digestible fibers can be found in foods like onions, leeks, artichokes, wheat, bananas, and are particularly abundant in chicory root. They enhance the well-being of the gut by stimulating the growth and function of beneficial gut bacteria.
As prebiotics are “eaten” by the gut bacteria, they feed those microbes and release fatty acids that travel in the blood through the body. Scientists are still uncovering the exact and complex ways that the types of bacteria in our bodies impact our health, including our weight, fat stores, and metabolism.
- Selective Fermentation: Prebiotics are selectively fermented by beneficial bacteria in the colon, leading to the production of SCFAs.
- Microbial Balance: By promoting the growth of beneficial bacteria, prebiotics help to restore and maintain a balanced gut microbiota composition.
- Gut Barrier Function: Prebiotics can improve gut barrier function, reducing the risk of inflammation and metabolic endotoxemia.
- Satiety and Appetite Regulation: Prebiotics may also increase satiety levels, says Nicole Ibarra, RD, CEO of Altitude Nutrition & Fitness in Redding, California, aligning with research. Additionally, studies show the human gut contains over 600,000 genes, which impact health markers that affect obesity, insulin resistance, or glucose metabolism.
Prebiotic Foods
The best way to add prebiotics to your body is by eating prebiotic-rich food. To keep things simple, Ibarra recommends focusing on accessible prebiotic-rich foods such as garlic, onions, bananas, oats, chicory root, leeks, and apples. She suggests starting small by adding one prebiotic-rich food to each meal or snack you eat. Aboudaram adds that cooking methods can also impact the prebiotic content of your food. Using methods like steaming or roasting instead of frying can help preserve prebiotic content. Some cooking methods for certain prebiotic-containing foods can actually boost prebiotic levels. For instance, a study found that cooking, cooling, and then reheating lentils actually increased their resistant starch levels.
Foods rich in prebiotics include bananas, garlic, onions, leeks, asparagus, and whole grains. Most fruits, vegetables, and whole-grain foods contain prebiotics, so eating a variety of fresh, whole foods is the best way to add more prebiotics to your diet.
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Prebiotic Supplements and Weight Loss: The Evidence
The question of probiotics and prebiotics influence on host metabolism, and specifically on obesity, is actively debated in the scientific literature because of contradictory data and a lack of knowledge of long-term effects.
While research on prebiotic supplements and weight loss is ongoing, some studies suggest potential benefits:
- Reduced Brain Response to Calorie-Rich Foods: A new study led by the University of Leipzig Medical Center is shedding light on the potential link between prebiotics and brain function in the context of obesity. According to the study, published in the journal Gut, consuming significant amounts of prebiotics in one’s diet is associated with a decrease in the brain’s response to high calorie food cues related to reward. These findings may imply a possible connection between the health of the gut and the way the brain makes decisions about food.
- Improved Gut Health and Metabolism: For instance, a clinical trial followed 45 people with obesity and found that a management program that included probiotics, prebiotics, and a low-carb diet successfully reduced weight, body mass index (BMI), and waist circumference. Aboudaram explains that while more evidence is needed to prove that prebiotics can directly cause weight loss, they can help by improving gut health, which is linked to metabolism, according to a study, and to immune health, per another study.
- Increased Satiety: Since prebiotics are fiber, they naturally fill you up faster. The more fiber you fill up with, the less caloric food you’ll have room for. Interestingly, since it’s considered a carbohydrate, each gram is assigned 4 calories on nutrition labels. Besides making you feel full, prebiotic fiber can also reduce the amount of fat your body absorbs from the food you eat.
It's important to note that studies often include other weight loss practices, too, like diet and exercise. That makes it hard to know what (if any) results prebiotic therapy can take credit for. Where researchers have studied probiotics and weight loss alone, the results have been mixed. A 2020 study looking at synbiotics (a combination of probiotics and prebiotics) found they didn’t affect weight loss or body composition.
Considerations for Prebiotic Supplementation
Always talk to your doctor if you have any concerns about changing your diet. You may need to be cautious about your prebiotic intake if you have specific digestive issues or certain sensitivities that make high-fiber foods hard to digest. Prebiotics are important for maintaining gut health, and there is evidence that they may also play a role in weight management and obesity-related diseases.
- Consult a Healthcare Professional: Before starting any prebiotic supplement, consult with a doctor or registered dietitian, especially if you have existing digestive issues or sensitivities.
- Start Slowly: Introduce prebiotic-rich foods or supplements gradually to avoid digestive discomfort.
- Focus on Whole Foods: Prioritize obtaining prebiotics from a variety of fruits, vegetables, and whole grains.
- Cooking Methods: Be mindful of cooking methods, as steaming or roasting can help preserve prebiotic content.
The Broader Picture: Lifestyle and Gut Health
While prebiotics show promise in supporting weight loss, they are most effective when combined with a healthy lifestyle.
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- Balanced Diet: A balance of healthy sources of proteins, fats and carbohydrates is the most important factor in maintaining good gut bacteria. The friendly bacteria survive and thrive when fed high-fiber foods like fruits, vegetables, whole grains and legumes. A low-fiber diet - an eating plan that’s low-carb and high-protein or high-fat - reduces the number of good bacteria.
- Exercise: Exercise is also crucial for maintaining a healthy microbiome.
- Avoidance of Unhealthy Habits: Research suggests that smoking, excessive drinking and poor sleep can upset the balance of microbiota in your gut.