How your microbiome plays a key role in regulating your metabolism, inflammation, and appetite

In some circles, September is considered to be a second January, AKA another shot at resolving to curb or enhance various behaviors in order to achieve your goals. One such resolution may, for some, may include healthy weight loss—you know, the kind that focuses on diet rather than dieting and reasonable levels of targeted physical activity.

Of course, there are many reasons you might not be seeing the results of your healthy lifestyle reflected on the scale. One, however, is quickly becoming a central player not just within this conversation but in dialogues regarding a broad spectrum of health questions: your gut microbiome. There is a relationship between your weight and the 100 trillion bacteria living within your digestive tract. Status: It’s complicated.

When I call Emeran Mayer, PhD, author of The Mind-Gut Connection, and Professor in the Departments of Medicine, Physiology, and Psychiatry at UCLA, he says that research is still in the early stages, but explains what scientists know so far. First, he describes a couple of studies used to prove a connection. In one version, lean, germ-free mice raised in sterile environments were transplanted with bacteria-rich feces from genetically-modified obese mice with voracious appetites. They not only gained weight but also developed the same uninhibited food intake as a result.

A similar experiment was done with fecal material taken from obese humans and transplanted into lean, germ-free mice and had the same results—the recipient mice became fat. Then, in another study, researchers took fecal material from formerly-obese subjects (who had undergone bariatric surgery for weight loss) and transplanted it into normal-weight mice. Results were compared with those from mice who received the fecal materials from obese subjects prior to their surgically-induced weight loss. The mice that received the post-surgery fecal materials did not become fat, evidence that there’s a connection between the microbiome, ingestive behavior, and weight regulation.

If you’re starting to worry that the key to shedding excess weight is getting a poop transplant, chill… because actually, the solution may be far more simple (not to mention, more appealing). Dr. Mayer tells me that what we feed our gut microbiata affects its diversity, behavior, and interactions with bodily systems, like the brain, all of which have metabolic implications.

There’s evidence, for example, that a a diet high in fat and sugar and low in fiber changes the composition of the microbiome in ways that negatively impact overall health. One study showed that such a diet decreased the presence of specific microbes while displaying a correlation between those decreases and increases in body weight, fat mass, insulin resistance, and low-grade inflammation.

It’s also been well established, says Dr. Mayer, that microbiome changes caused by high-fat and high-sugar diets decrease the thickness of the mucosal layer lining our intestine, resulting in a condition often referred to as leaky gut. When this occurs, some microbes gain access to immune cells located just underneath the intestinal lining, which can trigger a reaction that has been called “metabolic toxemia.” (The term refers to a low-grade immune activation throughout the body in the absence of any infectious cause.) “While this inflammation can affect any organ in the body, it is the detrimental effects on components of our satiety system that can have important consequences on our appetite and food cravings,” he explains.

Though he concludes from this data that high-fat diets like the ketogenic diet offer little value to your microbiome, he admits that most of the animal studies were done using a diet high in lard as opposed to healthier fats. And Mark Hyman, MD, Director of the Cleveland Clinic Center for Functional Medicine and Author of Food: What the Heck Should I Eat clarifies that this distinction actually makes a huge difference with respect to your microbiome. “The wrong fats—like polyunsaturated fats from seed oils like canola oil—increase inflammation, promote the growth of bad bugs, and create resistance to weight loss,” he says. “The right fats—like coconut oil, avocados, grass-fed butter, fish rich in omega 3s, and extra-virgin olive oil—decrease inflammation and help with weight loss.”

Still, this doesn’t mean you should lose the veggies if you want to lose weight. In fact, Dr. Hyman tells me that fiber, of which plants are the most important source, can actually prevent obesity. “The bacteria in your gut metabolizes the soluble fiber in vegetables, fruits, beans, nuts, seed, and most whole grains, and that’s when the benefits start. This fiber slows the rate at which food enters your bloodstream and increases the speed at which food exits your body through the digestive tract. That keeps your blood sugar and cholesterol in ideal balance—and quickly eliminates toxins from your gut and reduces your appetite,” he explains.

Plant-based foods are also super important to the microbiome-related weight loss equation for other reasons, according to Dr. Mayer. “The fiber in these foods is converted by the microbes into short-chain fatty acids which signal to specialized cells located at the end portion of the small intestine, which is packed with satiety hormones,” he explains. “The increased release of such signaling molecules from these so-called enteroendocrine cells results in boosted satiety and decreased food intake.” Without this information—as before with the leaky gut scenario—you won’t know you’re full and will in turn eat more than you need to.

Suffice it to say that researchers have established a strong connection between weight loss and gut bacteria, but are just beginning to understand the myriad ways in which it functions. What is proving to be effective is having a diet rich in fiber. So fill your plate with veggies and you’re more likely to see and feel the benefits.

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