Dietary fiber

Dietary fiber is carbohydrate found in plant cell walls that partly resists human digestive enzymes.^{1Haff and Triplett (eds.), Essentials of Strength Training and Conditioning, 4th ed., p. 200.} Examples include cellulose, hemicellulose, beta-glucans and pectins.^{1Haff and Triplett (eds.), Essentials of Strength Training and Conditioning, 4th ed., p. 200.} Some fibers slow stomach emptying and briefly increase fullness; others add bulk and water to stool, easing constipation.^{1Haff and Triplett (eds.), Essentials of Strength Training and Conditioning, 4th ed., p. 200.} Some soluble fibers reduce cholesterol absorption, while prebiotic fibers feed gut bacteria.^{1Haff and Triplett (eds.), Essentials of Strength Training and Conditioning, 4th ed., p. 200.}

The IPTA textbook assigns fiber 4 kcal per gram before digestion costs and roughly 2 kcal per gram afterward.^{2International Personal Trainer Academy, Certified Personal Trainer Textbook, p. 486.} Low-fiber diets have been linked with constipation, heart disease, colon cancer and type 2 diabetes.^{3Haff and Triplett (eds.), Essentials of Strength Training and Conditioning, 4th ed., p. 203.} The dietary reference intake (DRI) is 21 to 29 g a day for women and 30 to 38 g for men, depending on age and life stage.^{3Haff and Triplett (eds.), Essentials of Strength Training and Conditioning, 4th ed., p. 203.} Average US intakes fall below those recommendations.^{4Haff and Triplett (eds.), Essentials of Strength Training and Conditioning, 4th ed., p. 197.}

In practice

• Sources include beans, peas, bran, many fruits and vegetables, nuts, seeds and whole grains such as oatmeal and popcorn.^{1Haff and Triplett (eds.), Essentials of Strength Training and Conditioning, 4th ed., p. 200.},^{3Haff and Triplett (eds.), Essentials of Strength Training and Conditioning, 4th ed., p. 203.}
• The US recommendation works out to 14 g per 1,000 kcal; Helms and colleagues suggest capping fiber at about 20% of carbohydrate intake because very high intakes can upset digestion, reduce absorption of some nutrients and cause bloating.^{5Helms et al., The Muscle & Strength Pyramid: Nutrition, 2nd ed., p. 97.}
• Keep the meal before competition low in fiber so it leaves the stomach quickly and is less likely to cause gut trouble.^{6Haff and Triplett (eds.), Essentials of Strength Training and Conditioning, 4th ed., p. 218.}
• Fruit and vegetables provide fiber and support satiety, helping clients feel they’re eating more during a calorie deficit.^{7Helms et al., The Muscle & Strength Pyramid: Nutrition, 2nd ed., p. 111.}