Is my gut flora linked to being overweight?
Your gut microbiome is probably linked to excess weight through multiple mechanisms, but a proven causal relationship in humans is still lacking. A varied diet that supports your gut microbiome is worthwhile, but specific supplements for weight loss have not yet been proven effective.
Yes, your gut microbiome is probably linked to being overweight, but whether it is a cause or a consequence is not yet fully understood. People with obesity more often have a different gut microbiome than people with a healthy weight. In people with excess weight, bacteria from the Firmicutes group are found more frequently, for example. These are linked to greater energy extraction from food and changes in satiety hormones, which can lead to eating more and gaining weight.
Gut bacteria produce substances such as short-chain fatty acids and indole, which drive the production of gut hormones like GLP-1 and GIP. Those hormones regulate your feeling of fullness and your weight. A disrupted gut microbiome can throw that hormone production out of balance. How large that effect is in practice still needs to be established more precisely.
Another mechanism operates through the gut wall. A disrupted gut microbiome can make the gut wall 'leaky' to bacterial building blocks known as lipopolysaccharides (LPS, fragments of bacterial cell walls). These then enter your bloodstream and cause low-grade inflammation. That leads to insulin resistance, which is closely associated with excess weight and type 2 diabetes. Several review studies identify this mechanism as relevant, although the exact magnitude in humans has not yet been precisely measured.
There are also indications that the gut microbiome communicates with your brain via nerve pathways, hormones and the immune system, thereby influencing your eating behaviour. Mouse studies have demonstrated this convincingly: when the gut microbiome of people with obesity is transferred to germ-free mice, those mice gain more weight. However, that evidence cannot simply be extrapolated to humans.
Treatments such as faecal microbiota transplants, probiotics and prebiotics are being investigated as approaches to obesity. The results are promising, but the studies in humans are still too small and too short. There is currently insufficient evidence that any specific probiotic or prebiotic reliably helps with weight management. Larger and longer clinical trials are needed for that.
All claims are based on seven PMIDs (35421277, 34321848, 29667480, 26459447, 35134709, 39673174, 39040013, 38636809), including multiple reviews and overview studies. Most human evidence is associative; causal evidence comes largely from animal models.
Can your gut microbiome influence inflammation in your body?
Your gut microbiome can influence inflammatory processes throughout your body via the gut wall. Eating more fibre and exercising regularly are the most well-supported ways to influence this favourably.
What are the signs that your gut flora is out of balance?
There are several recognisable signals, of which abdominal complaints such as persistent pain, diarrhoea, or constipation are the best supported. If you experience prolonged bowel complaints after a course of antibiotics or an infection, discuss this with your GP.
Is there a real connection between your gut microbiome and your mood or brain?
There is a biologically plausible and, in animal research, robustly supported connection between your gut microbiome and your brain, but causality has not yet been proven in healthy humans. A varied, fibre-rich diet is the most concrete step you can take right now.
Can your gut microbiome affect your cholesterol?
Your gut microbiome influences your cholesterol through bile acid conversion and the fermentation of fibres. Eating more fibre is the most concrete and safe step to take; supplements such as berberine are not yet sufficiently substantiated for daily use.
Does my gut microbiome change as I get older, and does it matter?
Your gut microbiome certainly changes as you get older, but whether that is harmful depends strongly on which direction that change goes. What you eat has a major influence on this, so that is a concrete area to pay attention to.
Can your gut microbiome influence your risk of heart disease?
Your gut microbiome influences your heart health through metabolic by-products that can promote arterial hardening, high blood pressure and blood clots. The association is plausible, but how best to modify the gut microbiome to protect your heart has not yet been sufficiently proven: always discuss major interventions with your doctor.