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Fiber is Your Friend by Jeanne Rosner, MD

Updated: Mar 10, 2020

As a nutrition educator, I teach throughout my community to middle school students and adults. The main tenet of my teaching is to eat food as close to its natural source—as close to nature—as possible. Foods like fruits, vegetables, whole grains, nuts, seeds and legumes. When you eat food close to the source, you are getting nutrient-rich food filled with vitamins and minerals as well as an abundance of fiber. 

Fiber is your friend!

So, what exactly is fiber? Fiber is the outer, structural part of plants. Humans lack the enzymes to break apart the bonds within the plant, which is why fiber is indigestible. As a result, fiber does not provide us with energy or many calories when used as a food source. Most, if not all, of the fiber we ingest flows through the digestive tract (esophagus, stomach and small intestine) untouched until it reaches the large intestine. In the large intestine, the fiber nourishes the microbial community that resides there, or it gets eliminated in our stool.

There are two types of fiber: soluble and insoluble, and each performs a variety of healthful functions in the human body. Examples of soluble fiber sources are oats, flaxseeds, avocados, legumes, Brussels sprouts, apples, strawberries, citrus fruits and blackberries. Insoluble fiber sources can be found in whole grains, legumes, nuts and seeds, and vegetables such as green beans, celery, cauliflower and carrots. It is important to eat a diet rich in both types of fiber to reap the many health benefits of this amazing nutrient.

I teach my students to try and minimize their intake of processed foods. I often say, “Eat an orange rather than drink the orange juice” (which is minimally processed). When you eat an orange, you are getting many vitamins, minerals and FIBER. When an orange is processed to orange juice you will still get the orange’s vitamins and minerals but the juice is lacking in all that beneficial fiber. The presence of fiber in fruit has the health benefit of limiting the fructose (fruit sugar) absorption. Additionally, the fiber is full of nutrients called polyphenols (phytonutrients with health-promoting effects), so when the fiber is removed in the juicing process, so too are these healthful polyphenols.

A few unique facts about fiber:

  • Fiber does not freeze or can well. 

  • Processed food lacks fiber because fiber reduces the shelf life of food. The food industry wants processed foods to be more shelf-stable and, with fiber, this goal is not achieved.

  • Fiber causes the cook time of food to be longer.

  • When grains are refined or processed, some nutrients are removed. Vitamins and minerals can be added back (enriched) to these processed food items. Fiber in its original form cannot be added back to a food source, but rather it is in the form of cellulose. Researchers still do not know whether the health benefits of added fiber can mimic those of fiber in whole grains, for example.

There are numerous health benefits attributed to eating a diet rich in fiber. These include:

  • Aids in blood sugar stabilization. Fiber slows glucose absorption in the small intestine, thereby reducing a rise in blood sugar levels. It also decreases the insulin response.

  • Lowers cholesterol in the body.

  • Most fiber passes intact through the digestive tract to the large intestine where the bacterial enzymes digest it. Fiber fuels the microbial community (microbiome) there. It increases microbial diversity, which ultimately protects us from Western diseases. Fiber gets fermented in the large intestine and promotes beneficial bacterial growth. In addition, short chain fatty acids are produced, which help nourish and keep our colonic cells healthy.

  • Can lower colon cancer risk (via the short chain fatty acids that nourish the colonic cells).

  • Aids in healthy digestion.

  • Helps with weight control by helping keep you feeling fuller for a longer time.

  • Can help prevent obesity.

  • Decreases heart disease risk.

  • May play a role in decreasing breast cancer risk.

  • May help lower risk for diverticular disease.

  • Reduces inflammation, which will help decrease the risk for chronic diseases.

The daily recommendations for fiber are as follows:                19-50 years old: Men, 38 grams/day; Women, 25 grams/day                > 50 years old: Men, 30 grams/day; Women, 21 grams/day

When eating a processed food item, pay attention to the nutrition facts label on its outer wrapper. Look at the number of grams of carbohydrates and the amount of fiber listed on the label. The ratio of grams of carbohydrates to grams of fiber is important to note. Aim for foods with a ratio that is < 5:1 to ensure the food is a good source of fiber. Try to limit foods that have higher carbohydrates-to-fiber ratios, as they lack sufficient fiber.

To illustrate this point, let’s look at the nutrition facts label of MultiGrain Cheerios. The per-serving listing shows that carbs are 24 grams and fiber makes up 3 grams. Calculate the ratio, C:F = 24/3 —> 8:1. With a ratio of 8, this food falls into the undesirable category. It is a food item that is lacking in sufficient fiber and should be eaten sparingly or not at all.

Keep in mind, there are a few medical conditions that preclude a fiber-rich diet, including diverticulitis; a narrowing of the bowel due to a tumor or an inflammatory disease; history of bowel surgery; or if you are undergoing treatment such as radiation that damages or irritates your digestive tract.

For most of us, eating food closest to its natural source will provide plentiful amounts of dietary fiber. Eat an abundance of fruits, vegetables, whole grains, nuts, seeds and legumes. Your body will thank you for it. Remember, fiber is your friend.


Lustig, Robert H. "Chapter 12: Fiber - Half the "Antidote" Fat Chance: Beating the Odds Against Sugar, Processed Food, Obesity, and Disease. NY, NY: Hudson Street, 2013.

Weil, Andrew, MD. Eating Well for Optimum Health, The Essential Guide to Food, Diet and Nutrition: Alfred A. Knopf, 2000.

Michael Greger, The Five to One Fiber Rule, video:

Jeanne Rosner, MD

Jeanne Rosner is a board-certified anesthesiologist who practiced pediatric anesthesia at Stanford Medical Center for nearly 20 years. In 2011, she began teaching nutrition classes in her son’s 5th-grade science class. It was an “aha” moment for her. She realized that learning and teaching about nutrition, health and wellness in her community was her destiny. 

Since retiring from anesthesia, Jeanne has been a nutrition educator in the San Francisco Bay Area, at Woodside Elementary School, Menlo School, the Boys and Girls Club of the Peninsula and Peninsula Bridge School. She teaches middle school children the importance of eating food closest to the source, making good food choices and eating in a balanced and moderate way.  Jeanne started SOUL (seasonal, organic, unprocessed, local) Food Salon in 2014. SOUL Food Salon’s mission is to educate and empower people to be healthier. She holds small gatherings (salons) at which experts in the health and wellness community share their knowledge on how to lead a healthier life.

instagram: @soulfoodsalon

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