The relationship between gut health and weight loss

The buzz around the microbiome is hard to miss, as scientists dive deep into understanding the communities of microorganisms living in and on our bodies and how they affect our health.

If you have ever Googled gut microbiome, you have probably seen it linked to almost every health issue out there. While some of these connections may not hold up under rigorous scrutiny, there is compelling research to support an association between the microbiome and weight management [1, 2].

We do not fully understand all the precise mechanisms linking gut health to weight, but this article dives into the existing research to provide insight into how your gut microbes may influence your capacity for successful weight loss.

How your gut can help, and hinder, weight loss

Ranging from vitamins to neurotransmitters and short-chain fatty acids, microbial compounds can influence other bacteria or directly cross the gut barrier, enter the bloodstream, and interact with our cells, ultimately shaping how our body functions. The consequences, positive or negative, hinge on the specific composition of the gut microbiome.

Microbiome transplants

Faecal microbiota transplantation (FMT) involves transferring microbiota from one individual, or animal, to another. It is an invaluable technique in microbiome research because it tracks changes in the host organism, showing the specific impact of microbial species.

FMT studies in both animals and humans have demonstrated the powerful influence the gut microbiome has in dictating body weight. In these experiments, germ-free mice, raised in a sterile environment without any microorganisms, played a crucial role.

When germ-free mice were given microbiomes from humans with obesity, they also developed obesity.

In contrast, mice that received microbiomes from individuals after bariatric surgery stayed lean [4, 5]. This suggests FMT might be a potential treatment for human obesity [6].

Microbiome patterns

Gut microbial richness (total bacterial species) and diversity (the abundance of individual bacteria from each species) serve as important markers of gut health. Lower richness is tied to obesity, whereas a more diverse ecosystem is associated with effective weight management [7, 8].

Reduced diversity has also been linked to other markers of poor metabolic health like insulin resistance and chronic inflammation, conditions that frequently co-occur in individuals dealing with weight-related issues [9].

Gut microbiota composition varies with obesity severity. Compared with normal-weight counterparts, obese individuals show clear decreases in the Akkermansia, Faecalibacterium, Oscillibacter, and Alistipes genera, and higher levels of Lactobacillus reuteri, which may contribute to weight gain. Normal-weight individuals show an increased abundance of Bifidobacterium animalis, Methanobrevibacter smithii, and other Lactobacillus species [10, 11]. These microbial signatures could serve as early diagnostic markers for obesity and related conditions.

Possible mechanisms

While these observational studies are significant, studying the underlying mechanisms is crucial for informing new treatments. Below are some of the hypotheses currently thought to contribute to the impact of the gut microbiome on obesity.

1. Energy absorption

Research in obese mice reveals that their gut microbes extract more calories from their diet than lean mice [12]. Studies on germ-free mice carrying an obese microbiome showed a significant increase in total body fat compared with those given a lean microbiome, despite a similar diet and starting weight [13]. Scientists hypothesise that the microbial makeup of patients experiencing weight gain might be more efficient at harvesting energy from the diet [14]. One possible explanation is a lack of specific butyrate-producing species [15].

The takeaway: while our gut microbes are essential for health, an unfavourable composition may contribute to weight gain by extracting extra energy from the diet.

2. Modulating appetite and satiety signals

The gut-brain axis is a two-way communication pathway connecting the gut and the central nervous system [16]. One result of this interaction is the control of food intake. Specific microbial metabolites regulate the release of gut-derived serotonin, which plays a pivotal role in communicating satiety signals to the brain, as well as influencing mood [17, 18]. Your gut microbes also regulate the release of hormones such as GLP-1, which influences hunger signals in the brain [19].

The takeaway: a diverse gut microbial community with the right species can help regulate appetite and food intake, contributing to effective weight management.

3. Inflammation, insulin signalling, and glucose

A dysbiotic microbiome, characterised by low bacterial diversity and a high percentage of disease-causing microbes, can contribute to leaky gut syndrome. This compromises the intestinal barrier, allowing harmful substances to leak into the bloodstream and trigger chronic inflammation [20]. This inflammatory response has been shown to disrupt insulin signalling, leading to glucose variability and potentially contributing to weight gain.

The takeaway: the interplay between the gut microbiome, leaky gut, inflammation, and insulin signalling reveals potential new ways of managing these issues by targeting the root cause, an imbalanced gut microbiome.

The best foods for gut health and weight loss

Understanding the connection between gut microbes and obesity is like the chicken-and-egg dilemma: which comes first? While research has not reached a clear answer, it is likely that gut microbes play a substantial role in both the onset and progression of obesity. Dietary interventions that manipulate the gut microbiome and host metabolism have been successful in restoring gut health, reducing inflammation, and helping with weight loss [21].

Beneficial microbial changes from dietary interventions can occur within just 24 hours.

• Prebiotic-rich foods. Prebiotics nourish beneficial gut bacteria, and increasing prebiotic fibre intake can dampen the brain’s response to high-calorie food stimuli [23], which may help prevent overeating. Try leeks, mushrooms, flaxseeds, cabbage, and almonds, particularly as replacements for ultra-processed foods.
• Fermented foods. Kimchi, sauerkraut, and yoghurt contain live probiotic strains that support gut health [24]. Regular consumption has shown benefits including improved digestion, enhanced immunity, and weight loss.
• Colourful fruit and vegetables. The vibrant colours come from phytochemicals that nourish a diverse range of microbes, fostering the community richness and diversity associated with a healthy weight [25]. Polyphenols in oolong tea, and proanthocyanidins from grape seed and cranberry, are associated with improved gut barrier integrity and reduced inflammation.

Key takeaways

• The connection between the gut microbiome, health, and weight management is well established, but the exact mechanisms are still being determined.
• The richness and diversity of the microbiome, and the presence or absence of specific bacterial species, have been linked to obesity and poor metabolic health.
• Gut microbes can influence weight through energy absorption, appetite regulation, gut permeability, and inflammation, all of which can disrupt insulin signalling.
• The quickest and most effective way to shape your microbiome is through diet, with positive changes observable within 24 hours.
• Prebiotic-rich foods, fermented foods, and colourful fruits and vegetables can enhance gut health and support weight management.