How Gut Bacteria Help Make Us Fat and Thin

Intestinal bacteria may help determine whether we are lean or obese

For the 35 percent of American adults who do daily battle with obesity, the main causes of their condition are all too familiar: an unhealthy diet, a sedentary lifestyle and perhaps some unlucky genes. In recent years, however, researchers have become increasingly convinced that important hidden players literally lurk in human bowels: billions on billions of gut microbes.

Throughout our evolutionary history, the microscopic bacteria in our intestines have helped us break down tough plant fibers in exchange for the privilege of living in such a nutritious broth. Yet their roles definitely extend beyond digestion. New evidence indicates that gut bacteria alter the way we store fat, how we balance levels of glucose in the blood, and how we respond to hormones that make us feel hungry or full. The wrong mix of microbes, it seems, can help set the stage for obesity and diabetes from the moment of birth. Fortunately, researchers are beginning to understand the differences between the wrong mix and a healthy one, as well as the specific factors that shape those differences. They hope to learn how to cultivate this inner ecosystem in ways that could prevent—and possibly treat—obesity.

The Research

An early hint that gut microbes might play a role in obesity came from studies comparing intestinal bacteria in obese and lean individuals. In studies of twins who were both lean or both obese, researchers found that the gut community in lean people was like a rain forest brimming with many species but that the community in obese people was less diverse.

To demonstrate cause and effect, scientists conducted a series of experiments with so-called humanized mice. First, they raised genetically identical baby rodents in a germ-free environment so that their bodies would be free of any bacteria. Then they populated their guts with intestinal microbes collected from obese women and lean women. The mice ate the same diet in equal amounts, yet the mice that received bacteria from obese women grew heavier and had more body fat than mice with microbes from a thin woman. As expected, the fat mice also had a less diverse community of microbes in the gut.

In a study in the British Journal of Nutrition, obese women who took a probiotic supplement lost twice as much weight and fat over about six months—and were better at keeping it off—as those who took a placebo.

Unhealthy gut bacteria also produce food cravings: A study published in BioEssays suggests that some microbes may drive us to eat doughnuts or another tempting treat. These gut bugs send chemical messages to the brain that sway our appetite and mood—perhaps making us feel anxious until we gobble a square of dark chocolate or a T-bone steak.

This research has intensified concerns about the profligate use of antibiotics in children. A study has shown that when young mice are given low doses of antibiotics, they develop about 15% more body fat than mice that are not given such drugs. Antibiotics may annihilate some of the bacteria that help us maintain healthy body weight. Antibiotic use varies greatly from state to state in the U.S., as does the prevalence of obesity, and intriguingly, the two maps line up—with both rates highest in parts of the South.

What all of this research suggests is that healthy gut bacteria is crucial to maintaining normal weight and metabolism. Unfortunately, several features of the modern lifestyle directly contribute to unhealthy gut flora:

• Antibiotics and other medications like birth control and NSAIDs
• Diets high in refined carbohydrates, sugar, and processed foods
• Diets low in fermentable fibers
• Dietary toxins like refined seed oils and trans fats
• Chronic stress
• Chronic infections

What Can You Do to Improve Your Gut Health??

1. Healthy diet
   Diet is an important factor in shaping the gut ecosystem. A diet of highly processed foods, for example, has been linked to a less diverse gut community in people. An unhealthy diet somehow prevents the virtuous bacteria from moving in and flourishing.
2. Eat the foods that promote good gut health
   Two keywords to help you here: fiber and fermented.
3. Supplement
   Probiotics are a type of good bacteria, similar to the ones that already reside in your gut. Ingesting these organisms aids digestion helps change and repopulate intestinal bacteria. Some common strains associated with gut health include Lactobacillus acidophilus and Bifidobacteria bifidum.
4. Avoid the foods that damage the intestinal lining
   Avoid highly processed and refined foods, as these contain chemicals from manufacturers that are often not absorbed well, such as the sweetener high fructose corn syrup.
5. Drink water
   Water naturally improves digestion
   Hopefully, research will inspire a new generation of tools to treat and prevent obesity. One promising approach is to identify the precise strains of bacteria associated with leanness, determine their roles and develop treatments accordingly. Another proposal is enriching foods with beneficial bacteria and any nutrients needed to establish them in the gut—a science-based version of today’s probiotic yogurts.

No one in the field believes that probiotics alone will win the war on obesity, but it seems that, along with exercising and eating right, we need to enlist our inner microbial army.