Fiber is getting a lot of press in the wellness world lately, and for good reason. As more evidence emerges on its relationship with our gut microbiome, its role in our overall health is becoming better understood. With much of America consuming far too little, Athletes would benefit from consuming recommended amounts of fiber and also learn how to strategize intake around their training regimen.
What is Fiber?
Fiber is a non-digestible component of plant-based foods such as vegetables, fruits, grains, legumes, nuts, and seeds. Anything from an animal like eggs, beef, fish, and poultry will not have naturally occurring fiber.
Soluble Fiber: It gets its name due to its solubility in water. It actually forms a gel during digestion which helps to slow the rate of digestion. Rich sources include but aren’t limited to: Legumes such as black/navy/red/kidney, chia seed, flaxseed, brussels sprouts, broccoli, and cabbage.
Insoluble Fiber: You guessed it- not soluble in water. This one makes its way into the large intestine (aka: colon) before being fermented by certain bacteria that live there. It also helps regulate bowel movements. Rich sources include but aren’t limited to: Legumes, whole wheat, green beans, cauliflower, and nuts/seeds.
The cool thing about fiber-rich foods is that they are generally rich in both soluble and insoluble fiber, but may have more or less of the other, so you don’t need to get caught up in tracking individually.
Why is it Important?
Fiber is beneficial for a host of reasons, and research continually emerges regarding its benefits.
Digestion:
You may have heard that fiber encourages regular bowel movements, and it’s true! Adequate fiber intake actually keeps you regular because it’s a bulky agent that helps move your stool down your digestive tract. Fiber’s helpful role in digestion is also linked to prevention of colon cancer (which is actually more common in people <50 years of age than many other cancers). Note that adequate hydration is essential with a high or low fiber diet to help soften stools.
Weight Management:
Due to fiber’s bulky structure and slow rate of digestion, it has an incredible ability to make one feel full, stay full, and may prevent overeating. It’s also linked with prevention of type 2 diabetes in part due to its satiety, and also stabilizing blood sugar due to the slower digestion rate.
Heart Health:
A high fiber diet can contribute to a healthy heart by keeping total and LDL cholesterol in healthy ranges. Fiber has the ability to bind molecules and therefore may decrease overall absorption of fat. It can bind bile acids (the stuff that helps you break down fat) and increase excretion, preventing lipids from hanging around in circulation, which reduces the overall body store of cholesterol.
Immune System Function:
Our gut (intestines) is integral to our immune system, and the microorganisms that reside there are a huge part of the equation. Fiber is literally food for the healthy microbes living there. Certain fibers are even considered prebiotics: fiber that serves as food for probiotics, the types of microorganisms beneficial to our health.
How Much Should I Be Eating?
Most adults should consume 30-38 grams of fiber daily from food, and current estimated daily fiber intake of most Americans is a mere 15 grams. There is currently no upper tolerable intake level for fiber, so it’s difficult to discern just how much is too much, but intakes may exceed the recommended amount and are generally well tolerated if consumed from a variety of sources from whole grains, fruits, vegetables, legumes, and nuts. Very high intakes may contribute to excess flatulence, bloating, and diarrhea and likely differs between individuals.
However, I caution highly active individuals who struggle to maintain weight from consuming beyond the recommended daily amount due to the early satiety fiber brings which may lead to under-consumption and inadequate fueling.
If you fall short of the daily fiber recommendation, try increasing your fiber incrementally to avoid any gastrointestinal distress. If you go from an average of 15g fiber daily to 30g right away, it could actually cause temporary gas and bloating mentioned above. Hydration with adequate fiber intake is imperative to avoid gastrointestinal distress.
Should I Take a Supplement?
Food containing naturally occurring fiber such as whole grains, vegetables, fruits, nuts, and seeds should be the primary way you consume fiber. Consuming fiber-rich foods ensures you eat a variety of fiber types (soluble and insoluble), and also countless other nutrients that contribute to a healthy and diverse diet. Due to evidence of fiber’s health benefits, many packaged bars and cookies add fiber to their products to improve the nutrition. While this is still advantageous, these are best suited for supplementing a healthy diet and not recommended to be relied on for the majority of your fiber intake. Supplements may be warranted for certain medical conditions per your physician’s recommendation.
The following sample day shows how 38 grams of fiber can be met in ~2000 calories.
Breakfast: 1 c 2% plain, unsweet Greek yogurt, 1 c Kashi Go peanut butter cereal, 1/2 c mixed berries
Fiber: 12g | Calories: 488
Lunch: Salad: 2 c (lightly packed) mixed field greens, 3/4c quinoa, 1/2 c black beans, 1/4 c shredded carrot/cherry tomato, 3 oz chicken, 2 tbsp shredded cheddar, 3 tbsp avocado ranch
Fiber: 13.65g | Calories: 580
Snack: 1, 4 oz apple, 1 string cheese, 1/4 c almonds
Fiber: 5.7g | Calories: 309
Dinner: 5 oz flank steak, cooked in canola oil, 1 1/2 c roasted potatoes cooked in olive oil, 1 1/2 c roasted broccoli cooked in olive oil
Fiber: 10.7g | Calories: 602
Dessert: 3 Dove chocolates
Fiber: 0g | Calories: 120
Total Fiber: 42 Total Calories: 2099
How Can Fiber Be Detremental To Athletes?
One of the reasons fiber is beneficial for health is also why it can be detrimental to athletic performance if intake is timed incorrectly. Due to fiber’s slow digestion, it is not advantageous to consume fiber rich foods within an hour before exercise. Digestion causes blood flow toward the digestive tract, limiting oxygen and nutrient delivery to your working muscles which hinders performance.
However, food and fiber tolerance prior to exercise depends on the person, as well as activity type, intensity, and duration. Certain athletes with sensitive stomachs may need to limit fiber two hours or more prior to training, so experiment with what works for you. For reference, a banana is considered well tolerated by most athletes close to exercise, and an 8in banana has about 30 grams of carbohydrates and 3.5 grams of fiber . Some endurance and ultra-endurance athletes with sensitive stomachs may also benefit from limiting fiber the night preceding a key race depending on their history.
Timing meals and snacks before key races/competition can be helpful for avoiding GI issues during a race. Ideally, consuming a high carb, lower fiber meal 2-4 hours prior to endurance activities can improve performance. The further out the meal, the more likely one is able to tolerate a higher volume of food and higher fiber amount because the body has time to digest it. Limit fiber content of a meal 4 hours out to ≤10 grams or less depending on event type/duration and personal tolerance history.
Check out the following list of foods and their fiber content so you can strategize how you can boost fiber in everyday meals, and limit fiber close to key workouts and competition.
Foods With ≥4g of Fiber Per Serving
Grains:
¾ c high fiber cereal
1 slice high fiber bread
½ c cooked quinoa
½ c cooked farro
½ c cooked barley
½ c cooked teff
½ c cooked muesli
Starchy Vegetables:
½ c cooked beans (black, white, kidney, garbanzo, etc)
½ c mashed sweet potato (skin off)
Fruit:
1 large apple with skin
1 medium pear with skin
½ c raspberries
Non-Starchy Vegetables:
1 cooked artichoke
Nuts/Seeds:
¼ c almonds
¼ c walnuts
1 tbsp chia seeds
Foods With 3g of Fiber Per Serving
Grains:
1 slice high fiber bread
1, 10in whole wheat tortilla
½ c cooked sorghum
1 whole wheat English muffin
Starchy Vegetables
½ c green peas
1 medium (2 ¾ in diameter) potato, skin on
½ c mashed potatoes (skin on)
½ c steamed edamame
Fruit
1, whole orange (3 in diam)
1 c sliced strawberries
1 medium (8in) banana
Non-Starchy Vegetables
10 baby carrots
⅓ c cubed avocado
1 c fresh or ½ c cooked green beans
½ c cooked brussels sprouts
1 c raw chopped jicama
Nuts/Seeds
¼ c shelled pistachios
¼ c pecans
2 tbsp ground flaxseed
Foods With 2g of Fiber Per Serving
Grains:
½ c cooked brown rice
½ c cooked oatmeal
Starchy Vegetables:
½ c cooked butternut squash
Fruit:
½ c blueberries
1 c diced cantaloupe
Non-Starchy Vegetables
1 c raw or ½ c cooked broccoli
3-4 c lightly packed raw or ½ c cooked spinach
1 c chopped raw or ½ c cooked kale
1 c shredded fresh cabbage
1 c (or 1 whole) bell pepper
Nuts
¼ c shelled sunflower seeds
¼ c pepitas (green pumpkin seeds)
2 tbsp peanut butter
Foods With ≤1g of Fiber Per Serving
Grains:
1 slice white bread
1 small white dinner roll
½ a white bagel (or other flavored, white flour based)
1 English muffin
1 c cooked cream of wheat
Starchy Vegetables:
1/c c corn
½ c mashed potatoes (w/o skin)
Fruit:
1 c diced watermelon
1 tbsp raisins
3 dried dates
Non-Starchy Vegetables:
1 c raw celery
1 c raw or ½ c cooked beets
1 c raw sliced zucchini/yellow squash
Sources
Kaczmarczyk, M. M., Miller, M. J., & Freund, G. G. (2012). The health benefits of dietary fiber: beyond the usual suspects of type 2 diabetes mellitus, cardiovascular disease and colon cancer. Metabolism: clinical and experimental, 61(8), 1058–1066. doi:10.1016/j.metabol.2012.01.017
Van Horn L, McCoin M, Krisetherton PM, Burke F, Carson JA, Champagne CM, Karmally W, Sikand G. The evidence for dietary prevention and treatment of cardiovascular disease. J Am Diet Assoc. 2008 Feb;108(2):287-331. Review.
Brown L, Rosner B, Willett WW, Sacks FM. Cholesterol-lowering effects of dietary fiber: a meta-analysis. Am J Clin Nutr. 1999;69:30-42.
Pereira MA, O’Reilly E, Augustsson K, Fraser GE, Goldbourt U, Heitmann BL, et al. Dietary fiber and risk of coronary heart disease: a pooled analysis of cohort studies. Arch Intern MEd. 2004;164:370-76.
Position of the Academy of Nutrition and Dietetics: Health Implications of Dietary Fiber. Dahl, Wendy J. et al. Journal of the Academy of Nutrition and Dietetics, Volume 115, Issue 11, 1861 – 1870
Burke LM, Hawley JA, Wong S, Jeukendrup AE. Carbohydrates for training and competition. J Sports Sci. 2011;29(suppl 1):17S-27S
Barron, E., Cano Sokoloff, N., Maffazioli, G., Ackerman, K. E., Woolley, R., Holmes, T. M., … Misra, M. (2016). Diets High in Fiber and Vegetable Protein Are Associated with Low Lumbar Bone Mineral Density in Young Athletes with Oligoamenorrhea. Journal of the Academy of Nutrition and Dietetics, 116(3), 481–489. doi:10.1016/j.jand.2015.10.022
Melin A, Tornberg AB, et al. (2015). Low‐energy density and high fiber intake are dietary concerns in female endurance athletes. Scandinavian Journal of Medicine & Science in Sports, 26(9), 1060-1071.
