Low-carb diets aren’t new, but they remain popular, and that popularity comes at a price. Research on the role of the gut microbiota in health is growing, and although “direction of causality” isn’t 100% clear — does having a disrupted gut microbiota contribute to chronic disease, or does chronic disease contribute to a disrupted gut microbiota? — it is clear that what we eat influences which microbes take up residence in our gut.
Good gut microbes — the bacteria and other “critters” we want in our large intestine — eat certain types of fiber and other carbohydrates that we don’t readily digest higher up in our digestive tract. Microbiota researcher Justin Sonnenburg calls these carbs “microbiota-accessible carbohydrates,” or MACs. Some MACs are deemed “prebiotic” because they enhance growth of Bifidobacterium and Lactobacillus bacteria, and not all MACs are fiber — resistant starch is one example. You can find MACs in whole grains, pulses (beans and lentils), vegetables (especially cruciferous vegetables), fruits, nuts and seeds.
Eating enough MACs protects a source of carbohydrates already in our guts: the mucus layer that stands between what’s passing through your intestines and the layer of cells lining your intestinal wall. Skimping on MACs encourages the types of bacteria that are able and eager to eat that mucus. That’s bad both because these tend to be pathogenic (disease-causing) bacteria, and because degrading the mucus layer could compromise integrity of the cell lining, contributing to inflammation. A large proportion of our immune system lies just on the other side of that cellular barrier, and pathogens passing through that unprotected barrier can lead to infection.
Another consequence of lack of MACs in your diet is that your gut bacteria produce fewer short chain fatty acids (SCFAs) through fermentation. SCFAs benefit us in numerous ways, because they can communicate with our nervous system.
The trendiest low-carb diets are the paleo diet and various incarnations of the ketogenic diet, many of which more closely resemble a standard low-carb diet. Modern-day Paleolithic diets adopted by individuals in Western societies generally lack the high-fiber content of traditional hunter-gatherer societies, and some human studies have found that ketogenic diets have negative effects on the gut microbe community and gut health, but larger studies are needed to confirm this.
What might be better? Plant-based, MAC-rich eating patterns, including vegan, vegetarian, flexitarian and Mediterranean, that are also rich in phytochemicals, which can have anti-inflammatory effects in the gut. Overall, studies suggest that we should focus on getting enough of a variety of plant-based foods, not simply excluding animal-based food. For example, following a Mediterranean diet pattern is associated with a more favorable microbial population and higher SCFA production.
This recipe, inspired by a dish I had five years ago at Portage Bay Cafe, includes good food for your gut microbiota from farro (a form of ancient wheat), lentils, three types of cruciferous vegetables and walnuts.
Farro, Lentil and Cauliflower Salad
This recipe makes a lot, but you could neatly cut it in half. Choose a good quality mayonnaise (ingredients shouldn’t be much more than eggs, oil and vinegar or lemon). You can prep the onions, farro, lentils and cauliflower the evening before if you want, just chill them in the fridge.
1 medium red onion, chopped
1 cup farro (emmer)
1 cup beluga (black) lentils
1 medium head cauliflower or 2 pounds florets
4 cups loosely packed curly kale (cut or torn into bite-size pieces before measuring)
4 cups chopped or ribboned red cabbage
1 cup walnuts, coarsely chopped
1 cup grated Parmesan cheese
½ cup quality mayonnaise
½ cup nonfat or low-fat plain Greek yogurt
½ teaspoon Dijon mustard
Zest of 1 lemon
2 tablespoons lemon juice
½ teaspoon granulated garlic
2 tablespoons walnut oil
1 teaspoon salt, or more to taste
1/2 teaspoon freshly ground pepper, or more to taste
1. Heat 1 tablespoon olive oil in a saute pan over medium heat, add the chopped red onion. When onion starts to soften, reduce heat to low or medium-low and cook, stirring occasionally, until onions are caramelized. You want them to be very soft with golden — not dark brown — spots. This may take up to an hour.
2. Meanwhile, add farro and 1 teaspoon salt to 8 cups water in a large saucepan. This will cook the grains using the “pasta method.” Bring to a boil, then reduce to a simmer, cooking uncovered until the grains are tender but not mushy, about 20 to 25 minutes.
3. Add 1 teaspoon salt to 6 cups water in a medium saucepan. Bring water to boil, add lentils, then reduce heat to a simmer, partly cover and cook until lentils are tender but not mushy (about 20 to 25 minutes).
4. While grains and lentils are cooking, preheat oven to 425 F. Cut cauliflower florets into bite-size pieces. Toss in a large bowl with 1 tablespoon olive oil and ½ teaspoon salt, then spread on a baking sheet. Place sheet in oven and roast until cauliflower pieces are golden brown in spots, tossing the pieces after 10 to 15 minutes of roasting, then checking on them about every 5 minutes.
5. Allow farro, lentils and cauliflower to cool to room temperature. Refrigerate if making ahead.
6. Wash, dry and tear or cut the curly kale, and chop the cabbage or cut it into 2-inch narrow ribbons. Chop the walnuts and grate the Parmesan cheese. Add all dressing ingredients to a small mixing bowl and whisk to combine.
7. When ready to serve, place all salad ingredients in a large bowl and gently toss to combine. Pour the dressing over the mixture and gently toss again. Taste, and add additional salt and freshly ground pepper if desired. Serve.