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Gut Microbes and Circadian Rhythms
According to Ayurveda, your body is designed to be better able to digest the foods that are in season.
In addition, the strength of your digestive system also changes seasonally—with stronger digestion in the winter and weaker digestion in the summer.
This wisdom is now supported by many studies that have found in animals and humans alike, a dramatic shift in the species of gut microbes occurs from one season to the next. (1-3)
In one study, researchers evaluated the gut microbiota of free-ranging primates and found that each winter, their microbiomes would shift to be able to digest tough, fibrous foods like bark, mature leaves, and other more dense foods available only in the winter. (1)
Come spring and summer, the microbes in their guts would shift to certain species of Prevotella that are better equipped to digest starches and easier-to-digest carbohydrates found in young leaves, fruits, and berries.
In another study, 60 members of the Hutterite community—who eat a traditional farm-to-table diet—agreed to have their gut microbiomes evaluated seasonally to determine any microbial seasonal shifts.
Once again, the researchers found a strong shift in gut microbes each season. During the summer and autumn, carbohydrate- and starch-digesting Bacteroidetes were more dominant. In the winter, tough, fiber-digesting Actinobacteria were more dominant. (4)
The mechanism for this is now more understood than ever before. Science is emerging about circadian rhythms—the light/dark cycles that take place every 24 hours and each season.
Circadian rhythms have shown to be responsible for the seasonal microbial shifts in the gut which regulate digestive acumen, immunity, and more. (5)
The daily and seasonal shifts of the gut microbes regulate our diurnal rhythms that turn on and off body functions daily, such as digesting during the day, and sleeping and detoxifying at night. (5)
These studies not only explain why humans are better off digesting their food during the day and sleeping at night, but they also offer emerging evidence that we have evolved as seasonal eaters, and may be better served adhering to a seasonal diet.
While there is a significant microbial shift in the gut from just changing the diet, the last study cited suggests that these shifts are first and foremost in response to the changing light/dark seasonal circadian cycles.
A changing diet is secondary to circadian rhythms. Remember, the seasonal foods are also growing in connection to the circadian rhythms and seasonally changing soil microbes as well. (6)
Based on the emerging science, it is plausible to link the growing number of food intolerances and digestive imbalances to the consumption of gluten, dairy, grains, lectin, nuts, seeds and other more-difficult-to-break-down, fall- and winter-harvested foods.
By letting your circadian digestive clock reset each season by eating organic, microbial-rich seasonal foods, your diet, your microbes and your digestive strength will naturally adjust to the foods of that season.
Eating basically the same foods season after season and year after year will lead to an overpopulation of gut microbes engineered to digest the foods you regularly eat.
These types of microbial overpopulations can cause digestive-related health issues. Linking overpopulations of certain microbes to disease states is a new and exciting area of research… Stay tuned for more on this!
Each winter, the foods available in the Northern Hemisphere shift to a higher-fiber, higher-fat, and higher-protein diet.
Seasonal foods, such as meats, nuts, seeds, grains and legumes, all require a stronger digestive system. This is provided by a new stable of winter microbes better able to digest hard-to-digest winter foods.
To break down these foods, the stomach is required to produce more hydrochloric acid. Hydrochloric acid helps break down the anti-nutrients in grains and the harder-to-digest proteins in meats.
Digesting winter food also keeps us warm in the winter. Digestive acids, along with winter-based fermented foods (made with warming lactic acid fermentation) provide a welcomed increase of internal heat during the winter months.
During the summer, the body could be overheated by the same diet and the same digestive microbes. Summer foods are cooked on the vine and much less digestive heat is required to break down the leafy greens, fruits, and berries of summer, which are actually cooling to the body.
Eating cooler, easier-to-digest foods in the summer allows us to not overheat during the hot summer months. In the winter, harder-to-digest foods boost digestive acids, provide a better winter fuel reserve, internal heat, and much-needed winter body insulation.
The takeaway here is that we should be seeking out easy-to-digest foods in the summer—fruits and vegetables that have been cooked on the vine all summer, and harder-to-digest, more dense, heating, and insulating foods in the winter.
Eat Less Meat This Summer
The amount of meat that was eaten by traditional cultures was not nearly as much as we might think. The centenarians (who live to be over 100 years old) in different parts of the world all eat meat, but very little.
On average, they eat only about 10 percent of their diet as animal protein, according to National Geographic researcher and author, Dan Buettner.
During the colder winter months, animal protein intake would go up—as hunting may have been one of the only sources of food in the more extreme cold climates.
During the summer months, animal protein intake should decrease while plant-based foods should be eaten in greater quantities.
Here in the west, many still eat meat 2-3 times a day, which is both unsustainable for the planet and an amount of animal protein that was never consumed by our ancestors.
Excess consumption of meat has its health risks, and the summer months are a great time to dial down the meat and eat way more beans, green veggies, fruits, nuts, and seeds.
The following reasons for consuming less meat may help you make the decision to eat a summer plant-based diet with only 10 percent of your diet as animal protein.
7 Reasons to Eat Less Meat
- In 2012, the Harvard School of Public Health evaluated over 120,000 meat eaters. After 28 years, those who ate the most meat (2 servings a day) had a 30% increased risk of dying compared to those who did not eat red meat.
- In a 2010 study published in the journal, Circulation, 84,000 nurses were evaluated for 26 years. Those who ate 3 servings of meat per day had a 29% increased risk of chronic heart issues compared to those who ate only half a serving per day.
- Red meat is high in an amino acid called carnitine. When the carnitine is digested by the microbes in the gut, they produce a toxic by-product called trimethylamine-N-oxide or TMAO. In a 2013 study published in the New England Journal of Medicine, 4000 otherwise healthy patients who had the highest levels of TMAO had a 50% increased risk of a cardiovascular event over the next three years.
- In 2011, the American Institute for Cancer Research suggested that you should reduce consumption of cooked red meat to less than 18 ounces per week and avoid processed or packaged meats to reduce cancer risk.
- In a 2012 study in the journal Stroke, 125,000 people were followed over a period of 22 years. For every one to two ounces of processed meat eaten per day, there was a 30% increased risk of a stroke.
- In a 2011 study in the American Journal of Clinical Nutrition, Harvard researchers followed more than 200,000 men and women for 28 years. For every two ounces of processed meat eaten, there was a 32% increased risk of type 2 diabetes.
- It takes 7-8 pounds of feed to produce just one pound of beef. It takes 1000 tons of water to make just one ton of grain and the vast majority of grain is produced to feed beef and pork. As our population grows, this way of eating is simply not sustainable.
What is now known from the ancient wisdom of seasonal eating is that the circadian rhythms of nature change the microbes in the soil, on the foods we eat, and in the gut.
These microbes regulate the daily diurnal and nighttime nocturnal functions of the body. Ayurveda hacked into the intelligence of these rhythms thousands of years ago!
- Nutrition Action Health Letter. June 2013 Cover Story.