Your gut and the 12-hour fast


Here are some take-home messages for human health from the recent Commonweal symposium on the microbiome—the trillions of bacteria, viruses and fungi that live on and in our bodies.

The good ones can be our friends. From an evolutionary standpoint, they want us to survive so they can survive. We can work with them. We want them to outnumber the bad bacteria that promote disease.

Good microbes in our guts eat fiber from vegetables and fruits. If we don’t give them plenty of fiber, they start eating the mucus lining of our intestines. This promotes a “leaky gut” that allows bacteria to enter our bloodstream, which in turn promotes inflammation and disease. Eat plenty of fiber, meaning vegetables and fruits (which have many other benefits in terms of vitamins and related nutrients). Avoid refined flours and sugars, which lack fiber and promote obesity.

Good bacteria are found in probiotic, and especially fermented, foods—yogurt, kefir, kimchi, sauerkraut and miso. Have a probiotic food daily, including when you take antibiotics. Take a probiotic supplement if you don’t eat these foods daily.

Vegetables and fruits grown organically in healthy soil are good for the earth and for you. You will benefit from their good bacteria.


The 12-hour fast

Researchers from the University of California, San Diego and the Salk Institute have done extensive work with mice showing that restricting food intake to an eight to 12-hour period is beneficial. Mice fed at liberty throughout 24 hours become obese and diabetic, whereas mice eating the same calories in an eight to 12-hour window stay at normal weight and do not develop diabetes.

These researchers have not yet done human studies, as funding is scarce. Many previous studies on mice have been shown to be helpful for humans, however, as we share a similar metabolism. The Salk Institute writes, “The daily feeding-fasting cycle activates liver enzymes that break down cholesterol into bile acids, spurring the metabolism of brown fat—a type of ‘good fat’ in our body that converts extra calories to heat. Thus, the body literally burns fat during fasting. The liver also shuts down glucose production for several hours, which helps lower blood glucose. The extra glucose that would have ended up in the blood—high blood sugar is a hallmark of diabetes—is instead used to build molecules that repair damaged cells and make new DNA. This helps prevent chronic inflammation, which has been implicated in the development of a number of diseases, including heart disease, cancer, stroke and Alzheimer’s.”

It’s easy and beneficial to do a 12-hour fast. It’s safe for most people, but consult your doctor if you are taking meds for diabetes, have type 1 diabetes, or have any other questions. Eat enough healthy food during the day, and see if it works for you.


Sadja Greenwood, a Bolinas resident, is a retired physician formerly active at the University of California, San Francisco.