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Nearly all of us have gone on a diet at one time or another. And nearly all of us have gone off that diet before it changed our lives forever. The problem isn't necessarily willpower. It may actually be bacteria that override directions from the brain.

Skinny people, especially svelte doctors and trim dietitians, and even some professionals who have not worked out their own weight issues, are always telling fat people that their problem is a lack of willpower. Calories in have to equal calories out, they say over and over again, so if you weigh too much, they problem is that you are eating too much. And if you are eating too much, the problem is your lack of willpower. Your fat is your fault.

Or maybe it isn't.

Bacteria Power May Be Greater than Brain Power

There is an increasing body of scientific evidence that bacteria in the gut override signals in the brain to cause you to eat the foods that give them an edge over competing microbes. Microorganisms, primarily in the large intestine, may send signals to the vagus nerve, the long nerve down the middle of your body that regulates both heartbeat and appetite, to cause you to eat the foods that are good for them rather than the foods that are good for you.

Dr. Carlo Maley, a PhD director of the Center for Evolution and Cancer at the  University of California at San Francisco, stated in a press release that "Bacteria are manipulative. There is a diversity of interests represented in the microbiome, some aligned with our own dietary goals and others not."

A paper Dr. Maley wrote with Dr. Joe Alcock, an MD, and other scientists, published in the journal Biofactors, explains that different kinds of bacteria have different nutritional needs. Provatella bacteria, for instance, thrive on carbohydrates. They generate chemicals that send a message to the nervous system for their hosts to eat more sugar. 

Bacteria in the genus Bifidobacterium, a kind of "friendly" or symbiotic bacteria, thrive on fiber.

They send out signals that encourage their hosts to eat fiber-rich fruits, vegetables, and grains. Many other kinds of bacteria are generalists, and can survive on many kinds of nutrients, but have their preferences for maximum growth. Many different kinds of bacteria can hijack the nervous system and override the signals from the brain that encourage dietary restraint so that dieters indulge in foods not so much because they want them as because the bacteria in their digestive tracts insist on them.

One Hundred Million Chances to Stimulate Your Appetite

The vagus nerve connects to over 100 million neurons that line the digestive tract. The activities of these millions of neurons or orchestrated by the vagus nerve, and the vagus nerve in turn sends signals from those neurons to the brain. This important nerve can be "toned down" so that appetite decreases, or become hyperactive so that appetite greatly increases.

Bacteria release neurotransmitters such as dopamine, which stimulates the appetite when they aren't getting the nutrients they want.

They can release serotonin to increase stomach activity and bowel movement when they want to "clear out" the digestive tract for their preferred nutrients. They can even change the digestive tract's taste sensors so that certain foods taste better or worse.

Continue reading after recommendations

  • Alcock J, Maley CC, Aktipis CA.Is eating behavior manipulated by the gastrointestinal microbiota? Evolutionary pressures and potential mechanisms. Bioessays. 2014 Aug 8. doi: 10.1002/bies.201400071. [Epub ahead of print].
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  • Photo courtesy of Alex "Skud" Bayley by Flickr:

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