Eating With the Seasons: What Fall Foods Can Teach Us About Gut Health

One of my favorite things about the changing seasons is the way the food around us changes.

In summer, farmers' markets are overflowing with tomatoes, berries, cucumbers, and fresh greens. By fall, those foods begin to give way to apples, squash, pumpkins, sweet potatoes, cabbage, and root vegetables.

We tend to think about seasonal eating in terms of flavor, freshness, or supporting local farmers. But I think there's another interesting question worth asking.

What does changing the foods we eat do to the microbial communities living in our gut?

Our Microbiome Responds to What We Eat

One of the most remarkable things about the gut microbiome is how responsive it can be to diet. Different microorganisms have different nutritional preferences and metabolic capabilities. Some specialize in breaking down particular types of dietary fiber. Others use the byproducts produced by neighboring microbes. This creates a complex network of metabolic relationships within the gut.

When we change our diet, we also change the nutrients available to these organisms. Research has demonstrated that significant dietary changes can alter aspects of the gut microbiome in a matter of days. That doesn't necessarily mean every change is beneficial or that the microbiome should be constantly shifting. But it does show us how closely our microbial communities are connected to what we eat.

Why Variety Matters

I often talk about the importance of microbial diversity. A diverse microbial ecosystem can contain organisms capable of performing many different functions, including breaking down a wide range of complex carbohydrates.

One way we can help support this functional diversity is by eating a variety of plant foods. Different plants contain different combinations of fibers, resistant starches, and polyphenols. And these compounds can influence the gut microbiome in different ways.

For example, apples contain pectin, a soluble fiber that can be fermented by certain gut bacteria. Squash and sweet potatoes provide fiber and a variety of plant compounds. Cabbage, Brussels sprouts, and other cruciferous vegetables contain fibers and phytochemicals that interact with our digestive and metabolic systems. Beans and lentils are another excellent source of fermentable carbohydrates, including resistant starches and oligosaccharides.

These foods don't all feed exactly the same microorganisms. That's part of the point. By eating a wider range of plant foods, we provide a wider range of substrates for our gut microbes to work with.

What Makes Seasonal Eating Interesting?

Historically, humans didn't have access to the same foods every day of the year. What was available changed with the seasons, the climate, and the local environment. That meant our diets were often more variable than they are today.

We now have access to strawberries in December and tomatoes in February. There's nothing inherently wrong with that. But year-round availability can make it easy to fall into the habit of eating the same relatively small collection of foods week after week. Seasonal eating offers an opportunity to introduce variety almost automatically. As one group of fruits and vegetables becomes less available, another takes its place. I find this interesting because our microbial communities are remarkably adaptable.

We don't yet have enough evidence to say that eating seasonally, by itself, produces a healthier microbiome than eating a diverse, nutritious diet year-round. But rotating the foods we eat can introduce different fibers and plant compounds, which may help support a broader range of microbial functions.

Fall Foods Worth Bringing to the Table

There are some particularly interesting foods available during the fall months.

• Apples and pears: Both provide soluble fibers, including pectin, along with polyphenols that can interact with the gut microbiome.
• Winter squash and pumpkin: These provide fiber, carotenoids, and other nutrients. They can also be used in soups, roasted dishes, and stews.
• Cabbage and Brussels sprouts: These cruciferous vegetables offer fiber and plant compounds that are being studied for their effects on metabolism and inflammation.
• Sweet potatoes and other root vegetables: These provide fiber and complex carbohydrates. Cooking and cooling some starch-rich foods can also increase the proportion of resistant starch, although the effect varies by food and preparation.
• Beans and lentils: While not exclusively seasonal, they're wonderful additions to fall soups and stews and provide fermentable fibers that support microbial metabolism.

And of course, fermented foods like sauerkraut can add another dimension to a fall diet.

Fermentation transforms food through microbial activity, creating new flavors and compounds. Some fermented foods also contain live microorganisms, depending on how they are produced and stored.

A Simple Experiment for Fall

Rather than thinking of seasonal eating as another set of dietary rules, I'd encourage you to approach it as an experiment.

Visit a farmers' market or look at what's in season in your area. Choose two or three plant foods you haven't eaten recently. Maybe it's a different variety of winter squash, a bag of fresh Brussels sprouts, or a cabbage you decide to ferment. Add them to meals you already enjoy.

You don't need an entirely new diet. You simply need a little more variety. If you're increasing fiber significantly, do it gradually and pay attention to how your digestion responds.

And remember that consistency matters too. The microbes involved in fermenting dietary fibers need a regular supply of the nutrients they use.

Food Is More Than Fuel

One of the ideas I've returned to throughout my work is that food is not simply a collection of calories and nutrients. It's also a source of information and raw materials for the trillions of microorganisms that live within us.

Those microorganisms, in turn, produce compounds that interact with our immune system, intestinal barrier, and metabolic processes.

When we change what we eat, we change part of that internal environment. And when we think about food this way, the changing seasons become an opportunity to explore new ways of supporting our biology.

Fall gives us a wonderful selection of foods to work with. Perhaps the simplest place to begin is to put a few more of them on our plates.