How Your Gut Affects Your Weight

The bacteria in your gut influence your digestion, immune system, mood—and possibly even your ability to lose weight. It turns out your gut is capable of much more than just causing stomachaches in stressful situations. It hosts a complex ecosystem of trillions of bacteria, collectively called the gut microbiome. With over 1,000 species and 7,000 bacterial strains, the cells in your gut outnumber the rest of your body’s cells tenfold. These multitaskers play a crucial role in breaking down food to aid nutrient absorption and ensure a well-functioning digestive system.
Additionally, they assist your immune system in fending off invaders like the flu virus. In fact, 70–80% of immune cells are located in the gut. Researchers are increasingly recognizing that the gut may have an even greater impact on overall health than previously thought.
There’s been a significant rise in studies showing the influence of gut bacteria on nutrient absorption, cardiovascular risk, autoimmune diseases, and even mood. These hard-working microbes often have surprising effects.
Recent research on the gut-brain connection suggests that probiotic-rich foods and supplements might one day be used to treat depression. A 2015 UK study found that healthy participants who consumed prebiotics (fiber-rich carbohydrates that serve as food for probiotics) had lower concentrations of the stress hormone cortisol and responded to positive and negative stimuli similarly to those taking antidepressants or anti-anxiety medications.
How Your Gut Influences Your Weight
Your gut flora can lay the foundation for weight gain or weight loss. “People who consume a lot of saturated fats tend to have higher levels of Firmicutes bacteria and other microbes that are particularly efficient at extracting calories from food".
“When these individuals switch to a Mediterranean diet rich in colorful fruits and vegetables, whole grains, beans, and limited meat, the number of Firmicutes decreases, fostering a microbiome that stores energy less efficiently. This makes it easier to maintain a healthy weight.” A 2017 study published in the International Journal of Obesity found that a diverse gut microbiome can help protect against weight gain.
Additionally, some experts suggest that gut bacteria—especially a lack of diversity in the microbiome—can trigger junk food cravings. “A recent theory posits that low bacterial diversity in the gut allows individual strains to exert greater influence, sending signals to the brain that prompt you to eat the unhealthy foods they thrive on,” says nutritionist Wendy Bazilian.
On the other hand, a diverse bacterial ecosystem prevents any one strain from dominating and driving sugar cravings. “An unhealthy microbiome can hijack your cravings.”
Nurturing Your Inner Garden

The ecosystem in your gut is often referred to as an “inner garden,” reflecting the diversity of bacteria living and working together in harmony. However, like an untended garden overrun with weeds, the gut microbiome can become unbalanced due to a fiber-deficient, sugar-rich diet, chronic stress, or antibiotics. “These conditions can allow harmful bacteria like Salmonella, yeasts, or parasites to thrive.”
The microbiome begins forming at birth, influenced by factors such as delivery method and whether an infant is breastfed or formula-fed. Vaginal births pass beneficial microbes like lactobacilli to the baby, while breastfeeding provides bifidobacteria and other healthy bacteria.
Post-birth, diet plays the most significant role in shaping gut health. Although researchers are still investigating whether specific bacteria can directly aid weight loss or alleviate gastrointestinal issues, they agree that a balanced microbiome offers numerous health benefits.
A Guide to a Healthy Gut
1. Consume Fermented Foods
Probiotic-rich foods include:
- Fermented vegetables like kimchi or sauerkraut
- Kefir and yogurt
- Kombucha tea
- Fermented soy products like miso, tofu, and tempeh
Small amounts suffice; for instance, one tablespoon of fermented beets can provide a daily dose of beneficial bacteria. Choose yogurts and kefirs with less than 10 grams of added sugar per serving and avoid artificial sweeteners, which can disrupt gut health.

2. Pair Probiotics with Prebiotics
Feed your probiotics with prebiotic-rich foods like bananas, oats, whole grains, beans, and cruciferous vegetables. For example:
- A banana-kefir smoothie
- A stir-fry with broccoli, asparagus, and tempeh
- Brussels sprouts with kimchi
For maximum benefit, eat these foods raw or lightly steamed to preserve prebiotic fibers.
3. Increase Fiber Intake
Fiber-rich foods promote gut health by feeding beneficial bacteria, which produce short-chain fatty acids to regulate the immune system and reduce inflammation. The German Nutrition Society recommends 30 grams of fiber daily for adults.
4. Prioritize Whole Foods
Whenever possible, get probiotics from whole foods rather than supplements. Whole foods contain synergistic nutrients that help probiotics survive and thrive in your gut.
Final Thoughts: Cultivate Your Gut, Reap the Benefits
The bacteria in your gut may be the only microbes you’ll willingly nurture, but the rewards are worth it. A healthy gut microbiome not only supports digestion and immunity but also contributes to mental and physical well-being—giving you every reason to prioritize its care.