The obesity epidemic is one of the fastest growing threats to public health. More than 70 percent of American adults are currently overweight or obese, with other countries catching up quickly. This is putting our population at higher risk of a wide variety of preventable diseases. Despite a multi-billion dollar diet industry, we continue to get larger and larger. Could this really be entirely due to our unhealthy diets? New research on gut bacteria and weight gain suggests that this dangerous trend is not just due to our food choices, but to changes in our gut bacteria.

Links Between Gut Bacteria and Weight Gain

Several major studies have linked gut bacteria and weight gain. Mice fed high-calorie diets are more likely to gain weight when they have certain imbalances of gut bacteria. Humans, similarly, are more likely to be obese when they have high levels of specific gut bacteria such as Firmicutes. Our microbiome is an integral part of our health, so these imbalances can also lead to vitamin malabsorption, fatigue, depression and a wide variety of common conditions.

This is significant because the balance of human GI bacteria, also known as our microbiome, is rapidly changing. Cultures that eat a lot of whole grains and vegetables have very different kinds of bacteria in their intestines. As our eating habits change, our gut bacteria are rapidly changing in response. Our food choices do not just add to the number of calories we eat, but also the way these calories are processed. But how can gut bacteria cause weight gain and even obesity? The circadian rhythm of the GI tract may be the link.

The Innate Rhythms of the GI Tract

Like all organ systems, our GI tract has a distinctive circadian rhythm. This rhythm is partially set by external factors, especially what times we eat. This, in turn, affects gut bacteria. Bacteria, like humans, partially set their internal clocks by what times they are most active. When we eat, they also must “eat.”

Changing our mealtimes or our sleep-wake cycles can dramatically alter the circadian rhythms of bacteria in our GI tract. Some bacteria flourish under these changes and can quickly become the predominant bacteria in our intestines when we rapidly change our sleep-wake cycles. In turn, these bacteria appear to contribute to weight gain and obesity. Until recently, this was believed to be the reason for the link between jet lag and weight gain. However, new research suggests that the bacteria themselves may affect our intestinal circadian rhythms as much as our internal clocks affect them.

Can Gut Bacteria “Hijack” the Circadian Rhythm?

Researchers studied how a high-fat diet affected two populations of mice: one with a typical microbiome and one bred to have no GI bacteria at all. The ones with no GI bacteria handled their unhealthy diet much better than the other group. When researchers looked closer at the data, this appeared to be due to an intestinal protein called NFIL3.

Mice that had a normal microbiome had higher levels of a protein called NFIL3. NFIL3 is an important cue for the intestines, telling them how much fat to absorb. It is released in a cyclic manner, which helps our circadian rhythm to regulate food intake. Mice with no bacteria produce extremely low levels of NFIL3 on a cyclic basis and thus absorb very little fat even when eating a very high-fat diet. Gut bacteria appear to somehow stimulate NFIL3 production regardless of the time of day, effectively hijacking the circadian rhythm of the intestinal tract. This indiscriminate absorption of fat may, in turn, be one of the mechanisms by which some gut bacteria cause weight gain.

Establishing a Healthy GI Tract

Maintaining a healthy and diverse microbiome is key to whole-body health and a reasonable weight. If you are struggling to develop healthy intestinal bacteria, consider the following strategies:

• Eat a great deal of fiber, especially from plant foods such as whole grains, fruits and vegetables.
• Refuse refined and processed foods such as white sugar that encourage the growth of less healthy bacteria.
• Enjoy fermented foods such as yogurt and sauerkraut.
• Use fewer antacids and other medications that interfere with gut bacterial health.
• Keep your sleep-wake cycles steady, as these can affect your bacterial balance.
• Consider taking a daily probiotic supplement to keep a steady intake of beneficial bacteria.

These simple changes can change your microbiome in positive ways by seeding your intestines with the right kind of bacteria while discouraging the growth of bacteria that contribute to obesity.

For many Americans, our diets have led to a vicious cycle. Our dysregulated circadian rhythm leads to changes in bacteria, which, in turn, further affect our circadian rhythm. This can lead to obesity and other dangerous health conditions. However, there is hope. There are ways to achieve balance in your gut bacteria and thus change the way your body metabolizes food, stopping the cycle once and for all.