Can your gut microbiome control your appetite and hunger?
Yes, your gut microbiome can influence your hunger and eating behaviour via a direct connection to your brain. Eating more fibre is the best thing you can do right now to support that route.
Gut bacteria have direct access to the brain via the vagus nerve, a large nerve that connects the abdomen to the brain. Specialised intestinal cells that produce hormones sense bacterial activity in the gut and send signals upward along that nerve. This means gut bacteria can help determine how much you eat and even which foods you prefer.
When bacteria break down indigestible fibres, short-chain fatty acids are produced, including acetate, propionate and butyrate. These compounds are not passive: they influence appetite, blood sugar balance and energy expenditure. However, it is important to note that most of the evidence for this comes from animal studies. In humans, very few well-designed studies have been carried out on this topic, so we do not yet know precisely how large this effect is in practice.
The composition of your gut microbiome is also associated with body weight. People with obesity have measurably different bacterial populations than people with a healthier weight. Studies using germ-free animals and microbiome transplants show that these differences are probably not simply a consequence of unhealthy eating, but also play a causal role in weight gain. This makes the gut microbiome a potentially interesting target, although we are still far from translating that knowledge into practical treatments.
Dietary fibre is the most important fuel for your gut microbiome. Western diets contain far too little of it, which impoverishes the microbiome and reduces its ability to perform that protective role. Eating more fibre-rich food is the most concrete, evidence-supported step you can take today, backed by multiple studies. Whether manipulating the gut microbiome through other means, such as microbiome transplants after weight loss, also works remains uncertain for now: only a handful of early studies have been conducted on this.
The diabetes medication metformin illustrates how indirect the influence of the gut microbiome can be: part of this drug's weight-reducing effect is thought to occur through changes in the gut microbiome, in addition to direct effects on the appetite centre in the brain. This mechanism has not yet been fully unravelled, but it illustrates that the gut-brain axis is a genuine route through which appetite can be regulated.
Claims are based on multiple published sources (PMIDs 37058160, 28844808, 27988382, 26459447, 32865024, 33096647, 40163180, 30874963). Causal evidence is strongest for the vagus nerve route and the microbiome-obesity relationship; the SCFA mechanism and microbiome transplants are based primarily on animal research or early human research.
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.
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.
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 influence how long you live?
There are clear indications that the composition of your gut microbiome is associated with how long and how healthily you age, but whether modifying your microbiome extends your life has not yet been demonstrated in humans.
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 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.