Your gut is teeming with bacteria, some friendly and some not so friendly. It’s not surprising these gut bacteria affect digestion and how you absorb certain nutrients but there’s growing evidence they play a role in body weight too – and changing your gut bacteria could be as simple as changing your diet.
Gut Bacteria, Obesity and Diet
Researchers at Washington State University in St. Louis were interested in what role gut bacteria play in controlling body weight. To get a better idea, they took gut bacteria from human twins, one of whom was obese and the other slender, and transferred the bacteria into the intestines of mice raised in a sterile environment with no gut bacteria of their own. After the transfer, they closely followed their body weight.
The results? The mice that received the gut microbes from the obese human twin gained body weight to the point of becoming obese, while the mice transplanted with bacteria from the lean twin remained slim and trim. In fact, the mice with the gut bacteria from the obese twin put on almost 17% more body fat. This shows the importance gut microbes could play in controlling body weight.
This time the researchers took the research a step further. They put mice that had received gut microbes from the obese twin in with mice that received microbes from the thin twin. They wanted to see if the mice live in the same environment whether it would alter their gut microbe composition and body weight. It did – and diet seemed to be the deciding factor. Obese mice that ate a diet rich in vegetables and fruits and low in saturated fat developed favorable changes in their gut bacteria. In addition, they stopped gaining weight and developed a better metabolic profile and less insulin resistance.
What did the researchers conclude? At least in mice, eating a healthy diet alters the composition of gut flora, increasing the proportion of gut bacteria that help to promote leanness – even in mice that had obesity-prone gut bacteria, to begin with.
In another study, researchers transplanted gut bacteria from humans into mice that lacked gut bacteria. Afterward, they switched them from a mostly plant-based diet to a diet rich in fats and sugar, typical of the processed food diet many people in Western countries eat. The mice quickly developed obesity-prone gut bacteria in their gut and gained weight.
What do these studies suggest? It’s hard to draw a definite conclusion since this was a mouse study but it’s possible you can change your gut bacteria to ones that help with fat loss by changing the composition of your diet.
Gut Bacteria and Body Weight Control
You may wonder what gut bacteria have to do with weight control. As it turns out, plenty. These tiny but very active bacteria vary in their ability to extract energy from food. Some are more efficient at it so more energy ends up being stored as fat. Some are less efficient so there are more wasted calories that don’t end up on your waistline. Interestingly, one theory as to why gastric bypass surgery works for weight loss is it alters gut bacteria. The surgery seems to shift the balance of bacteria in the gut so that there’s a predominance of gut bacteria that promote leanness rather than obesity.
People who are obese have a different composition of gut bacteria relative to people of normal weight. Obese humans tend to have more bacteria from a phylum called Firmicutes, while their more slender counterparts have more Bacteroidetes bacteria. One study showed that Bacteroidetes species increase linearly in the gut as weight loss progresses. Obese people also have a less diverse bacterial population relative to thin people.
Gut Bacteria, Obesity and Health
The gut bacteria that make their home in your intestines are no small force. At any time, there are about a trillion bacteria hunkering down in your intestines. Far from being passive, the bacteria synthesize vitamins such as vitamin K, biotin and folate, keep disease-causing bacteria in check, break down undigested carbohydrates and help with nutrient absorption. They’re also important for a healthy immune system. In fact, we now know that between 60 and 70% of your immune system reside in your gut. Gut bacteria stimulate lymph tissue within the gut so that it produces antibodies against pathogenic bacteria. They also help to break down carcinogens you’re exposed to through diet. They have a lot of diverse functions that are important for health.
When you take antibiotics, it throws off the balance of good bacteria versus bad bacteria in your gut. That’s why it’s common for people to develop diarrhea and other intestinal symptoms when they’re taking them. Interestingly, food producers give antibiotics to livestock to maximize their size and weight. Does a shift in gut microbes contribute to their expansion in size and weight – and do we absorb enough antibiotics when we eat meat to change our own gut bacteria? Still lots of unanswered questions. Age also affects gut bacteria composition. Children have a more diverse population of gut microbes than adults. Geographic location and the environment you’re exposed to is another but this is also influenced by diet. As this and other studies suggest, you can change the composition of your gut bacteria by changing your diet.
What Role Do Probiotics Play in Body Weight Control?
Probiotics are gut microbes from food sources like yogurt and fermented foods. Some people also take probiotic supplements. It’s not clear whether supplementing with probiotic bacteria impacts weight since no one knows what the ideal combination of gut bacteria is for weight control. Taking a probiotic with the wrong combination of gut bacteria may actually promote weight gain.
If researchers are able to identify the best bacterial composition for maintaining a healthy weight, they may be able to custom formulate probiotics that address the issue of weight control. Until then, you have another means of changing your gut bacteria for the better – eat a clean diet, one rich in fruits and vegetables and low in sugar, processed carbs, and unhealthy fats. You’ll take in fewer calories, have a more favorable metabolic profile and more gut microbes to help keep obesity in check.
References:
Medical News Today. “Healthy Diet Discourages Obesity Microbes in Gut”
Nature. 441 (7122): 21-28. (2006)
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