Role of the Gut Microbiome in Weight Management

Inside your large intestine are trillions of microorganisms, including bacteria, viruses, and fungi, which have a mutually beneficial relationship with your human cells. In exchange for food and shelter in your gut, these microorganisms help to digest your food and produce beneficial chemicals from the fiber you eat. The whole ecosystem of these microbes is called your gut microbiome, and each person’s gut has a unique balance of species that changes over time with diet, lifestyle, and environment. Recent research shows that the gut microbiome is not just a digestive engine but also a driver of metabolic, immune, and mental health, meaning that the state of your gut can provide a useful window into your overall health.

Your gut bacteria affect what you can digest, and what you absorb has a direct effect on weight. Beyond this routine process, your gut microbiome affects weight in other subtle ways: it sends signals to your adipocytes, or fat storage cells, telling them when to use excess calories as energy and when to store them as fat; and the microbes in your gut can modify bile acids (molecules from your liver) into messengers that regulate the body’s absorption of lipids.

Weight loss generally requires burning more calories than you replace via diet and fat storage. Given that the gut microbiome affects not only the degree of caloric absorption from your food, but also the way those calories are used or stored in the body, its impact on weight loss is significant. Individuals who lose weight have also been observed to have meaningful shifts in the patterns of microbes in their gut, suggesting that there is a correlation between weight status and gut flora. Weight loss often occurs as the result of a lifestyle change such as eating healthier foods (not just fewer calories) and exercising more, and these lifestyle changes have their own impact on the gut microbiome.

While there is some evidence to suggest that probiotics can help with weight loss, the field is new, and probiotics may not be right for everyone. Your probiotic use should depend on what your microbiome currently looks like, and the best way to find this out is through microbiome profiling. A gut microbiome profile tells you the list of organisms in your gut, giving you a place to begin understanding the species and strains you could consider augmenting with probiotics.

Yes, in just about every possible way! Inflammation is caused by abnormal immune responses, and a healthy gut microbiome supports the immune system. Gut microbes turn your undigested food into molecules that calm inflammation, protect the walls of the gut, and enable absorption of beneficial compounds like antioxidants in the food you eat. Conversely, individuals struggling with inflammatory conditions like IBD or rheumatoid arthritis have distinct patterns of gut microbiome dysbiosis, or skewed species distributions in the gut, suggesting that the gut and the inflammatory response are a two-way street.

The gut-brain axis transmits information about cravings, satiety, hunger, and palatability back and forth along the vagus nerve. Evolutionary evidence suggests that the tight link between gut and brain could have helped humans avoid poisonous foods and develop the ability to understand a food’s energetic potential, or its calorie content. Appetite regulation is not just about hunger - factors including emotional state, anxiety, and social environment can all impact the body’s ability to process appetite cues.

Gut bacteria play a strong role in satiety, or the sensation of fullness. Your gut microbes send signals to the hypothalamus, a region of your brain, when you’ve eaten enough and feel full. The endpoint of “fullness” or “satiety” may also be mediated by individual differences in the microbiome, as it is clear that two people eating the same foods may have different blood sugar responses and feelings of fullness.

Research has shown that individuals with obesity have distinct patterns of gut microbiota than lean individuals. While the patterns vary among people, hallmarks of obesity in the microbiome include elevated Prevotella and diminished Bacteroides.

Obesity affects both ends of the gut-brain axis. Studies have indicated that obese individuals have distinct patterns of reward circuitry in the brain, and that disorders of the gut-brain axis could drive overeating or lack of satiety, influencing obesity-promoting behaviors.

Gut microbes feed on fiber, which is a type of carbohydrate that human enzymes can’t break down. Without a variety of fiber sources, your gut microbes eat the protective mucus that coats your intestinal walls, increasing your susceptibility to abdominal infections and leaky gut. While the best foods for each person are dependent on the unique strains of bacteria they are seeking to support or reduce, we know that sugar, saturated fat, and artificial sweeteners are universally unhelpful for gut health. In fact, artificial sweeteners have even been shown to modulate the gut microbiome’s behavior over time, suggesting that long-term consumption of  substances like aspartame and sucralose - often found in “diet” or “sugar-free” foods - can cause meaningful damage.

The American diet is notoriously high in refined carbohydrates, sugar, and saturated fat, none of which are beneficial to the gut microbiome. If you find yourself often reaching for foods like pastries, chips, processed meat, white bread, and sweets, you might be eating an American diet. Better alternatives may be the Mediterranean diet, which has been shown to increase gut bacterial diversity, or the traditional Korean diet, which includes fermented foods like kimchi. Even if your diet has been lackluster, there’s good news: research shows that improving your diet even for a few weeks is enough to change your microbiome, although the benefits of healthy eating are cumulative over time.

Your gut bacteria feed on fiber, which means their diet is generally ‘healthy’ by human standards. The fiber in fruits, vegetables, legumes, and whole grains can feed a wide range of microbes in the gut, whereas typically ‘unhealthy’ foods that you might crave like soda and processed foods don’t have enough fiber to survive the journey through the digestive tract to the gut.

Cravings are actually based in the brain, and they are distinct from appetite because they exist regardless of nutritional needs or hunger. Your cravings and their triggers (when you’re stressed, awake late at night, or on your menstrual cycle) may provide insight into your mental health than your gut health.

Feeding your microbes means feeding the entire ecosystem in your gut. Different bacteria prefer different fiber types, so your best bet is to eat a wide range of foods to nourish the whole spectrum of microbes in your gut, including colorful plants, healthy fats like olive oil, and enough fiber.

You may experience signs and symptoms of an unhealthy gut, but determining the exact status of your gut microbiome is difficult without quantitative testing. A stool test kit will give you an analysis of the microbes present in your gut, their abundances, and what this means for overall health. For the broadest view into your gut, choose a test that uses metagenomic shotgun sequencing, a modern method that can pick up on the thousands of viruses, fungi, and bacteria that all inhabit your gut.

Improving your gut bacteria looks different for everyone since no two microbiomes are exactly the same. Aside from what you already know, like getting enough sleep, water, and exercise and managing stress, a gut microbiome profiling service can show you the specifics of your gut and provide tailored recommendations to improve your unique gut ecosystem.