A Gut Feeling about Body Weight

You’re unlikely to hear a brass fanfare when you reach for the carrot sticks instead of the cookies, nor wild applause when you lace up your shoes for an evening walk instead of collapsing onto the couch. That is to say, all the small decisions you make to manage your weight and your health can feel downright anticlimactic.
But you do have a cheering section for these actions—albeit an invisible one. Every lifestyle choice, no matter how modest, gets noticed and celebrated by a crowd that’s trillions strong: the diverse community of micro-organisms that call your gut home.
New research shows that while the microbes in your digestive tract may not directly cause you to gain or lose weight, they are thought to influence your metabolism and serve as mediators between your lifestyle choices and your body weight.

The ecosystem within

Communities of tiny living organisms exist in different habitats of the human body. “Microbiota” is the name given to the micro-organisms themselves—primarily bacteria, but also fungi (including yeasts), archaea, and viruses—while the entire environment in which they thrive is called the microbiome. The most complex microbial ecosystem on the human body is found in the digestive tract, especially within the colon.

Scientists have discovered the gut microbial ecosystem is shaped in part by our lifestyle choices, bearing the traces of everything from your dietary choices and medications to whether or not you live with pets.

And just as no two thriving forests have an identical proportion of organisms, no two healthy gut microbial communities are exactly alike. A greater diversity of microbes, however, is associated with better health.

Healthy metabolism takes guts

At any given time, many factors contribute to our metabolism and body weight, and in recent years scientists have tried to find out whether our personal gut microbiome is a contributing factor.

As a starting point, they compared the gut microbes in lean people to those with a body mass index above 30—the threshold of obesity. Taken together, these studies revealed no consistent gut microbiota differences between these two groups.

Intriguingly, the weight of some animals can be altered by changing their gut microbes: in some older studies groups of mice consuming the same diet gain different amounts of weight, depending on their gut microbiota.

In one study, researchers collected gut microbes from human identical twins (one obese, one lean); the mice receiving the microbiota of an obese twin increased their body weight more than the mice receiving that of a lean twin, even though all mice consumed the same number of calories.

Some scientists have cut right to the chase in humans, testing whether it’s possible to slim down by “resetting” the gut microbial community through fecal microbiota transplantation, transferring a gut microbiota sample from one person’s colon to another’s. Receiving a lean person’s microbes does not appear to reduce weight in a recipient with obesity, however.

Beyond body weight, gut microbiota are definitely involved in other aspects of metabolic health. Manipulating the gut microbiota through diet or probiotics, for example, may improve blood glucose control in type 2 diabetes.

Gut microbes may also influence food intake by modulating our appetite: a chain of events set off by our gut bacteria produces hormones that help us feel full. This means gut microbes could have an indirect influence on our body mass index—essentially serving as intermediaries between our lifestyle choices and our weight.

Although it’s important to remember that gut microbes function as a complex ecosystem, scientists have managed to single out a few gut bugs that may be particularly important for maintaining a leaner physique.

Akkermansia muciniphila

These bacteria thrive in the mucus layer that lines the interior of the gut. Multiple studies have associated them with metabolic benefits and prevention of obesity, and they appear to work by strengthening the gut barrier.

Christensenella minuta

These bacteria, which are linked with a lower body mass index in humans and seem to prevent weight gain, come “for free” if you have a particular genetic makeup. Thus, these bugs may be one way in which genes manage to contribute to weight.

Shaping your gut microbiota for weight management

Even if gut microbes don’t directly dictate the number on the bathroom scale, we may be able to leverage them to help us achieve or maintain a healthy weight. New lines of research show they’re often a key element that enables us to benefit from our healthy lifestyle choices. Here’s how to get your gut microbiome to support you and your weight management goals.

Mind your diet

Counting calories is a classic strategy for weight management—but the different macronutrients supplying those calories definitely matter to your gut microbes. Through diet, we may shape our gut microbes in a way that facilitates a healthy weight: fibre (think vegetables, fruits, and whole grains) is paramount.

Akkermansia, in particular, is boosted through fructo-oligosaccharides, a type of prebiotic found naturally in banana, onion, artichoke, asparagus, and other plant foods, or through polyphenols such as grape and cranberry extract.

In general, a diversity of plant foods—30 or more types per week—promotes a diverse, well-functioning gut microbiota, while large amounts of red meat and processed foods (especially those containing emulsifiers and artificial sweeteners) are believed to have a detrimental effect on the gut microbiota and may even sabotage weight-loss goals.

Maintain cardiorespiratory fitness

Exercise is a well-known way to keep weight in check, and recent evidence suggests that higher cardiorespiratory fitness in humans goes hand-in-hand with gut microbiota diversity and health-promoting gut microbiota functions.

Aim to keep stress to a minimum

Healthy eating is notoriously difficult when an individual is experiencing stress; moreover, the body’s stress response induces intestinal permeability. Research on the microbiota-gut-brain axis has shown the gut microbiota changes in association with different stressors. It pays off, weight-wise, to manage stress and mental health as much as possible.

Avoid sleep disruptions

It’s well established that people who experience sleep disruptions, including sleep apnea and the “jet lag” induced by night shifts or staying out too late, have a harder time maintaining a healthy weight.

The changes in gut microbiota composition induced by sleep disturbances could be responsible for the metabolic problems that occur, showing the critical importance of getting enough shut-eye to help your bugs take care of you.

Our gut microbes not only bear the traces of our lifestyle choices but may also be an essential part of how these choices lead to a healthy weight. The exciting new area of science linking gut microbes with health could, over time, yield ways to manipulate microbial ecosystems for targeted health effects, offering each one of us personalized strategies for weight management based on our unique collection of gut microbes.

Inflammation: A consequence of poor gut health

Maintaining gut health is crucial for overall health—and one of the main reasons for this is the close link between gut health and inflammation.

Inside our bodies, the walls of the digestive tract cover an enormous surface area. With closely packed cells separated by protein structures called tight junctions, these work as “gates” to let in essential molecules and keep out harmful substances.

When the tight junctions fail to close properly, the intestinal wall becomes too permeable (a phenomenon sometimes called “leaky gut”). Bacterial components get through the gut wall and start to circulate throughout the body, kicking the immune system into high gear and creating a constant low-grade inflammation.

Scientists have linked systemic inflammation with obesity and metabolic dysfunction—and while cause and effect isn’t quite clear yet, this inflammation could be part of what triggers excessive weight gain in the first place.

Supplements for better gut health

Remember that more is not always better in the finely tuned gut environment, so check with a health care practitioner about the dose that’s right for you.

Can probiotics and prebiotics help with weight management?

Probiotics and prebiotics are sometimes employed to manipulate gut microbiota. But despite the health benefits these substances may offer, studies show they may not be especially good for helping us shed the pounds.

Whole-food-based prebiotics, though, may indirectly affect weight by increasing feelings of satiety after eating. One study, for example, found a diet containing high amounts of prebiotic-rich vegetables made people feel fuller while reducing their cravings for sweet, salty, and fatty foods.

Many ongoing clinical trials are testing novel probiotics and prebiotics for weight loss, so watch this space.