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Are Your Gut Bugs Making You Gain Weight?

If you have been following our blog posts for a while, you know that Jaci and I love to talk about all things “gut health.” You also know that the health of your digestive system has a massive impact on your overall health and wellbeing- both from a physical and mental standpoint. In our last blog post, Jaci alluded to the influence that your gut bacteria (aka your microbiome) might be having on your body weight. Believe it or not, there is a significant association between gut health and obesity. And with obesity rates steadily increasing, we would be amiss not to consider this association and incorporate strategies to improve the microbiome into weight management programs.

So how exactly does the health of your gut and the bacteria within it influence your weight? Before I explain, it is interesting to note that the gut microbiota of obese individuals has been found to differ from that of lean individuals. Those with obesity have tend to have a less diverse population of bacteria within their gut (a more diverse microbiome is associated with better gut health) and have a greater proportion of a certain type of bacteria (called Firmicutes) than their lean counterparts (1). While this does not prove anything per se, it does suggest that the gut microbiome has a role in obesity and an individual’s propensity to gain excess weight. Perhaps even more interesting is that weight loss surgery (ie. gastric bypass) has been shown to affect gut bacteria. The levels of a division of bacteria called Bacteroides actually increased post-surgery, bringing the gut micobiome of the surgical patient more closely in line with that of lean individuals (1).

At the risk of geeking out too much on all of you, I do want to allude to some interesting previous studies looking at what are called “germ-free mice.” Germ-free mice are raised in a sterile environment and do not have any bacteria in their gut. It was animal studies using these mice that initially suggested a link between obesity and the gut microbiome (2). Mice raised in a normal, non-sterile environment have a 40% higher body fat content than germ-free mice, despite consuming less food than their germ-free counter-parts (3). Even more fascinating (especially for a gut geek like myself) is the fact that when the gut bacteria from the normal mice was transplanted into the germ-free mice, there was a 60% increase in body fat within 2 weeks without any corresponding increase in calorie consumption or difference in energy expenditure (3). Crazy, right?

Taking all of this together, it is obvious that the gut microbiome has an influence on the development of obesity. But what are the exact mechanisms underlying this relationship? While we still have a lot to learn about the role of gut bacteria in many aspects of health and disease, research has shed some light on a few ways in which gut bacteria can lead to excess fat accumulation and difficulties losing weight.

Energy Harvesting

One proposed way in which the gut microbiome can contribute to the development of obesity is through extracting more energy from food (4). At the end of the day, obesity is due to an imbalance between energy intake and energy expenditure. So, if your gut bacteria are more efficient at harvesting calories (aka energy) from the food that you ingest, then you will be consuming more calories overall. While the excess calorie intake resulting from this mechanism is likely small, it can still have important long-term consequences for body weight and metabolism.

Metabolic Changes

In addition to extracting more calories from the food that you consume, your gut bacteria can influence metabolic pathways and cause a shift towards increased fat storage (4). Consumption of choline, a nutrient obtained from red meat and eggs, has been linked with changes in gut bacteria and the production of TMAO (aka trimethylamine-N-oxide – try saying that 3 times fast!), a substance that has been associated with cardiovascular disease and atherosclerosis (plaque build-up in the arteries) (5). This suggests a strong possible link between the consumption of choline-rich foods, the gut microbiome, and an increased risk for metabolic disease (ie. metabolic syndrome and diabetes) and obesity.

Chronic Inflammation

Inflammation has been implicated as one of the key players in obesity and is associated with many different disease processes including cardiovascular disease, diabetes, and fatty liver disease (4). High-fat diets have been linked to changes in the gut microbiome that lead to inflammation of the intestinal lining and increased intestinal permeability, aka “leaky gut.” (4) Leaky gut, a term we have alluded to in previous blog posts, refers to when the tight junctions (the spaces between the single layer of cells lining the intestinal wall) have been damaged, thereby disrupting in the integrity of the intestinal wall and allowing everything from undigested food particles to bacteria to “leak” through the wall and into the blood stream. LPS (aka lipopolysaccharide – another tongue twister), a component of the gut bacterial cell wall, can also permeate the leaky intestinal wall and end up circulating in the blood. LPS is a potent inducer of inflammation within the body and contributes to increased fat tissue accumulation, impaired blood sugar regulation, insulin resistance (prediabetes and diabetes) and, therefore, obesity (1, 4).

Appetite and Cravings

We have alluded to the importance of the gut-brain axis in previous posts, and its role in obesity is no exception. Believe it or not, there is evidence suggesting that the bacteria in your gut can actually manipulate your food preferences and appetite. Germ-free mice have been found to prefer more sweets and have a greater number of sweet taste receptors in their gut compared to normal mice (4). Perhaps even more interesting is that individuals who crave chocolate produce different urine microbial end-products compared to individuals who are “chocolate indifferent,” despite eating the same diets (6). While these findings do not prove anything, they certainly speak to the incredible role that our gut microbes have in our behaviors surrounding food. The fermentation of carbohydrates by bacteria within the intestines actually produces substances known as short-chain fatty acids (SCFAs) that alter the secretion and gene expression of gut hormones that control satiety (4). In other words, how satisfied and full that you feel following a meal is directly related to the bugs in your gut. When we say that gut health matters, we are not kidding around!

All of this is fascinating (or at least a nerd like me thinks so!), but how does it help us in regards to weight loss? It all comes down to eating and living in a way that nourishes and supports your gut and the trillions of bacteria that live within it. Eating a diet rich in plant-based foods (fruits, vegetables, legumes, and fiber-rich grains), eliminating potential food triggers (which can be done with an elimination diet), limiting added sugars, cutting out processed foods, adding in gut-healthy supplements and probiotics (see our post on Gut Health Supplements and our “Supplement Favorites” page), and reducing stress. And you don’t have to figure out how to do any of this alone! A licensed health care practitioner, dietician, and health care can all be valuable resources in your weight loss and gut health journey.

Lastly, be sure and reach out to us if you have any questions regarding this or any of our previous blog posts and keep on following us for more helpful information regarding all things health and wellness.

Continue to follow your gut,


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