The circadian diet, another form of intermittent fasting | Ask the doctors | Health, medicine and fitness
Dear doctor: A yoga teacher in our gym talked about something called the circadian diet. He says it’s good for your gut microbiome. I’ve heard of circadian rhythms, but I don’t see how it relates to the gut. What is a circadian diet anyway?
Dear reader: At the start of the 18th century, astronomer Jean-Jacques d’Ortous de Mairan’s experiments with mimosa plants opened the door to the idea of a biological clock. Since then, researchers have been fascinated by the concept. A few hundred years of study later, they had come to a good understanding of what they came to call the circadian clock, that is, the internal cycle of about 24 hours that coincides with the flow from day to night.
While this cycle is related to the daily pattern of light and dark, it is actually controlled by the body itself. It is widely believed today that in addition to the existence of a master biological clock, located in a light-sensitive part of the brain called the hypothalamus, each individual cell in the body also functions according to a circadian cycle that is clean.
Working together, these synchronization mechanisms form a complex matrix. They play a role in virtually all of our bodily processes, including sleep-wake cycles; metabolism; hormonal activity; body temperature; the cardiovascular, gastrointestinal and nervous systems; organ function; and the gut microbiota. When our internal clocks and the external signals of light and dark get out of sync, we suffer physical consequences. Jet lag and the adverse health effects of night shift work are good examples.
Recent research has revealed new and intriguing links between the gut microbiome and the circadian cycle. A study in mice found that microbes in their intestines produced significantly more of a natural antimicrobial compound during the day than at night. This helped them better fight possible food poisoning during the hours when they were most likely to eat. This may explain why people with chronic sleep disorders have been found to be more susceptible to intestinal infections. The results of another study, which limited the times rodents were given food, suggested that the way the body metabolizes fat depended on what time the food is eaten.
Humans typically eat during the day and fast at night while we sleep. It is basically a form of intermittent fasting, which research suggests has a range of health benefits, such as better blood sugar control, lower levels of inflammation, better healthier blood pressure figures and blood lipids.
In the circadian diet, you eat for a 12-hour window – usually between 7 a.m. and 7 p.m. – and fast for the other 12 hours. The size of the meals is reversed, with breakfast being the largest meal of the day and dinner the smallest. This 12-hour nightly fast eliminates after-dinner snacks and nightly raids on the fridge.
It is important to note that at present, while supporters of the circadian diet discuss its benefits with great certainty, there is a dearth of reliable studies to support their various claims.