Stanford Study Backs Seasonal Eating for the Healthiest Microbiome

Stanford Study Backs Seasonal Eating for the Healthiest Microbiome

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Did Ancient Man Have Colitis?

Did you know that people living a preindustrial lifestyle seem to be free of digestive issues like colon cancer, colitis, and Crohn’s disease?1,2 One possible explanation is a diet closely connected to the seasons. And now, one of the last remaining hunter-gatherer tribes on earth confirms our gut microbes were meant to change seasonally!

If you are a regular reader here at LifeSpa, this may be old news . . . you probably already eat seasonally, enjoy our monthly recipes, and utilize the grocery and superfoods lists we publish free each month as part of the yearlong 3-Season Diet Guide. Or you may have read my book The 3-Season Diet.

Never heard of it? Sign up for free and start eating seasonally now! It truly is the easiest and healthiest diet, now backed by Stanford University research.

What the Hunter-Gatherer Diet Does to the Body

In a Stanford University study published in the journal Science, researchers found microbes in members of the Tanzanian Hadza tribe change dramatically with each season, in sync with seasonal dietary changes.

The study shows certain microbes in the gut one season may almost disappear the next, suggesting dramatic microbiome changes take place seasonally. Researchers concluded that the Hadza tribe’s gut microbes and digestion are cyclical, in sync with the precise biorhythm of nature.1,2

In addition to their dramatic microbiome seasonal shifts, the Hadza microbiome is significantly more diverse than a Western-cultured microbiome. They carry a powerful stable of gut microbes extremely skilled at breaking down fiber.

The Hadza microbiome has more enzymes for breaking down animal-based carbohydrates during the dry season, and more enzymes targeting plant-based carbohydrates in the wet season.

Microbes in the digestive system manufacture enzymes that change seasonally. They do so to help digestion of seasonal foods, as well as to boost immunity in winter, decongest the body in spring, and dissipate heat during the long, hot summer.

For the Hadza, the combination of a higher-fiber and seasonally changing diet (from dry-season hunting to wet-season foraging) has left them seemingly free of colon cancer, colitis, and Crohn’s disease.1,2

Meet Your Seasonal Microbes 

In another study measuring seasonal variation of the human gut microbiome, diet and gut bacteria of a group of volunteers were evaluated over the course of a year. During summer, when a higher concentration of produce and complex carbohydrates was in the diet, there was a surge in complex carbohydrate-digesting bacteria, called bacteriodetes, along with a decrease in actinobacteria, which have been negatively correlated to fiber content.5,6

The more carb-digesting Bacteroidetes you have compared to Firmicutes, the higher the risk for obesity. It was also found that Actinobacteria increase in winter. Actinobacteria increase with the amount of fat consumed and decrease with fiber, suggesting a higher-fat diet in winter and early spring is supported by a related seasonal eating shift in the microbiome.5,6

Seasonal eating provides the right foods to be digested by the right microbes that inoculate the gut in a seasonal manner. Chronically eating out of season leaves the body ill equipped to digest in the way we were designed. Other studies suggest that receptors for food, digestive enzymes, nutrients, and even neurotransmitters change seasonally.1,2,7

How the Body Adapts to Seasonal Shifts 

eat wheat cover

In my book Eat Wheat, I cite research showing how the starch-digesting enzyme amylase naturally increases in the body during fall and winter. This is aligned with when more starchy tubers, wheat grasses, and grains are in abundance and harvested.

Amylase decreases in spring and early summer, when the diet shifts to be more vegetable-based. During the season when starches are harvested, the body’s amylase enzyme surges.7

If you eat a high-carb, high-starch diet 24/7, 365, instead of only during late summer months (when carbs and starches are naturally available), carbohydrate-digesting bacteria, such as Bacteroidetes, can overpopulate the gut and drive excess glucose (sugar) into the bloodstream, possibly contributing to today’s current epidemic of prediabetes.8,9

We carry microbes that digest carbs in late fall and winter and microbes suited to digest more fat and fiber in spring. Carbohydrates and fat are the two major sources of fuel for the body. Nature shifts the fuel supply in order to change the population of microbes in the gut, so one does not predominate and overwhelm the body. A gut with too many carb-digesting microbes can drive excess sugar into the blood sugar. Excess fat (found in diets such as the Keto Diet) has side effects as well.10,11

Another way the body responds to seasonal change is the parasympathetic nervous system (often referred to as the “rest-and-digest” nervous system) increases the body’s digestive potential in fall and winter. It does this in order to more effectively break down denser and more concentrated fall- and winter-harvested foods, such as nuts, seeds, meats, and root vegetables.3

Seasonal Microbe Symphony

Microbiome microbes come from the soil that nourishes the plants we eat.

Each plant seasonally attracts certain microbes from the soil, creating a symbiotic relationship. Plants seem to benefit from certain microbes, while those microbes seem to benefit from the nutrients of certain plants.

With each seasonal shift, soil microbiology changes, plant chemistry changes, and microbes attached to the roots, stems, and leaves of each plant shift like a changing of the guard.

When we eat these plants in season, we consume nutrients in the plant, as well as microbes attracted to and attached to that plant. We are also ingesting foods the microbes love.

These microbes create a microbial community within us. In fact, microbes make up 90% of nucleated cells in the human body!

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Why You Should Eat Seasonally

Dangers of Eating out of Season

When we do not eat seasonally, our microbiome quickly disconnects from nature’s intelligence and much of our genetic dependence on seasonal microbes is lost.

Let me share a quote from the book The Forest Unseen to illustrate this point:4

Sudden changes in the diet can disrupt this elegant molding of the rumen community and its environment. If a deer is fed corn or leafy greens in the middle of winter, its rumen will be knocked off balance, acidity will rise uncontrollably, and gases will bloat the rumen. Indigestion of this kind can be lethal.

David George Haskell, The Forest Unseen

Deer have a four-chambered stomach. The first chamber, called the rumen, is for storage. The rumen allows for deer to gather a lot of food at once and digest it later. The deer brings the food back up into their mouth and chews it again. This process is called “chewing their cud.” It is also called ruminating! Animals that can do this are called ruminants.12

In other words, when an herbivore eats out of season, it causes a drastic shift in its microbiology, leading to severe indigestion that can actually kill the herbivore. Cows, for example, when taken from pastures and fed grain, have to be medicated to settle their stomachs.

I realize we are omnivores, not herbivores, but clearly this is food for thought! We are as connected to nature’s cycles as herbivores, albeit in a slightly different way. If eating out of season can kill a deer, is this a message to respect the diet right in front of us?

There is no doubt microbes in our intestinal tract change according to diet and seasonal influences. Perhaps we are more resilient to these changes than deer, but are we immune to them?

Without a diet rich in seasonally changing microbes, our intestines are often populated by space-occupying microbes that, while not necessarily bad, are not beneficial either. They take up real estate in the intestines and can affect the gut, its immunity, and many other adaptive processes to function less than optimally.

Without the influx of seasonal microbes to boost digestive strength and support a diverse community of essential bacteria, we can become extremely vulnerable and often hyper-sensitive to our environment and foods.

Are you sensitive to certain foods or notice your digestion is less than ideal? Try a seasonal diet and let us know what you find!

3-season diet guide

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Dr. John


  4. Haskell, David George. The Forest Unseen. Penguin Books, 2012.

5 thoughts on “Stanford Study Backs Seasonal Eating for the Healthiest Microbiome”

  1. I got advice from Ayurvedic doctor to follow a Vata pacifying diet year around. I guess that is the power of Ayurveda, that through a consultation one can get advice about diet how to balance onces doshas.

  2. In many parts of the world the seasons are more or less the same. Israel where I am, the Middle East, the differences between seasons are very minimal. I am a vegetarian close to 20 yrs, and me and my wife eat the same diet all year around. A lot of beets and avocado, sweet potato and regular potato, different pumpkin and squashes. Buckwheat and Quinoa.Coconut Oil and Organic Honey(from Argentina). Thin slices of Pumpernickel Bread and organic Spelt bread, organic butter and Ethiopian Tahini. These are the staple of or diet. No changing because the seasons here are only two: hot summer without any drop of rain May-November, and warm winter with some rain.

    • I understand your situation but here in Canada there is quite a difference in produce available in the spring and summer. I should say LOCAL produce. Of course I can get watermelon flown in from California but as the article points out that is not a local food that normally would be available in the freezing cold. I rather chose local foods such as root vegetables, small amount of local fruits such as apples, pears and berries and small amounts of pasture raised meat that keep my body warm and sustained during the cold winter months.

  3. I’ve had this question for a long time. I also live in a climate that is different than the “North”. Here in Mexico, near Central America, we have the “Rainy Season” that is too hot and wet to grow anything but tropical fruit. Then in the cooler “Dry Season”, we can grow many greens and veggies. However, almost none (with the exception of tomatoes) is “native”. Things like bananas & papayas & Chaya grow year-round, while other tropical fruits have a season. There are only two native “vegetables” I can name.

    Not only that, but I also travel North . . . into a totally different climate. So . . . I really do WANT to “eat with the seasons”, I just don’t know how to do that!


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