Raw white potatoes and green bananas are natural, often readily available, and inexpensive sources of prebiotic fibers.
Raw white potatoes are rich in prebiotic fiber—with 10 to 12 grams per one-half medium (3 1⁄2 inches in diameter) potato—and contain zero sugar. (Sweet potatoes and yams have far less prebiotic fibers). Some people become so accustomed to the taste that they eat them just like an apple, although they are most commonly added to a smoothie. You can also ferment them, which gives them a slightly tangy flavor great for adding to salads.
Green bananas and plantains—and I mean green. Not green-yellow, or a little green at one end, but green. So green that they are difficult to peel and virtually inedible, so slice them lengthwise, shell out the pulp, chop it coarsely, and then use it in your prebiotic shake.
Prebiotic fibers are essentially the “water” and “fertilizer” that nourish your bowel flora. These are fibers that you ingest but cannot digest, leaving them for microorganisms in the intestines to consume. Some call prebiotic fibers resistant starch since they are impervious to human digestion and digested by microorganisms. Getting prebiotic fibers is crucial to your health and the success of your diet.
The average (unhealthy) American obtains between 3 and 8 grams of prebiotic fibers per day, about half from grains. Measurable health benefits begin at a prebiotic fiber intake of around 8 grams per day, while maximum benefits occur at an intake of 20 grams per day. We therefore aim to obtain 20 grams each and every day, including replacing the modest deficit left by grain elimination, to stack the odds in favor of cultivating a successful bowel flora garden. As with eating fermented foods, this practice should be continued for the rest of your life. Most people make a daily shake or smoothie that includes one or more of the foods richest in prebiotic fibers, especially a raw white potato, green unripe banana, or 1 to 2 teaspoons of inulin/FOS.
Try to include prebiotic fiber choices from the following list every day:
- GREEN BANANAS AND PLANTAINS: 10.9 grams per 1 medium (7-inch) banana (0 gram net carbs)
- RAW WHITE POTATO: 10 to 12 grams per 1⁄2 medium (0 gram net carbs)(Avoid any raw potatoes with green skin, as this is a fungus. If encountered, peel off the skin.)
- INULIN AND/OR FOS POWDERS: 5 grams per teaspoon (0 gram net carbs)
- HUMMUS OR CHICKPEAS: 8 grams per 1⁄2 cup (13.5 grams net carbs)
- LENTILS: 2.5 grams per 1⁄2 cup (11 grams net carbs)
- BEANS: 3.8 grams per 1⁄2 cup (white beans are the richest with twice this quantity) (12 grams net carbs)
Note: Values for prebiotic content vary depending on the source and the method used to measure.
You can find several recipes for prebiotic shakes and smoothies in both my Undoctored and Wheat Belly Total Health books. A word of caution: During the first week of grain-free living, prebiotic fibers should be limited to no more than 10 grams per day (e.g., half a green banana). Exceed this during the first week and you can provoke unpleasant bloating and abdominal distress. So keep intake low for the first week, and then increase to 20 grams the second week. In addition to using no more than half a banana or half a white potato in the shake recipes at the start, also omit the optional inulin/FOS powder the first week. You can add it later if your abdominal status seems favorable. If you experience unpleasant symptoms even with the low starting quantity, you probably have a worse-than-usual case of dysbiosis; in this case, a more extended course of probiotics and fermented foods should be followed.
Try reintroducing prebiotic fibers after 4 weeks of further probiotic “seeding.” If even this causes distress, then it’s time to seek help from a healthcare practitioner with expertise in correcting severe dysbiosis (thankfully, an uncommon situation) and/or consider whether you have small intestinal bacterial overgrowth, SIBO, that may require additional efforts.