Those who use a flexible approach to dieting such as IIFYM track protein, carbohydrates and fat daily. With IIYFM, no food is off limits so long as daily macro numbers are being hit consistently. However, it is typically recommended that a variety of foods be consumed each day to ensure adequate vitamin, mineral and fiber intakes.

Most individuals have a pretty good grasp on what IIFYM, macronutrients, vitamins, and minerals are, but may not know as much about fiber. The purpose of this article is to discuss what dietary fiber is, why we need it, where we can get it from and how to incorporate it into an IIFYM dietary approach.

To start this process and obtain your macro numbers, start with our macro calculator.

What is Fiber?

The Institute of Medicine defines dietary fiber as the “nondigestible carbohydrates and lignin that are intrinsic and intact in plants.” They further define functional fiber as “isolated, nondigestible carbohydrates that have beneficial physiological effects in humans.” Total fiber is defined as a combination of dietary and functional fibers. However, it should be noted that there is much debate over the exact definition of a fiber.

For the purposes of this discussion, you can think of fiber as food matter that passes through the stomach and small intestine without digestion by our digestive enzymes. This food matter enters the large intestine where it comes into contact with bacteria that colonize both the walls and lumen of the large intestine.

Make tracking fiber easier with dialed in macro calculations for your Macro Blueprint.

These bacteria contain enzymes that are able to ferment some of the food matter that our human enzymes are unable to digest, producing a number of compounds including short-chain fatty acids (acetate, propionate, and butyrate). Short-chain fatty acids can be absorbed and used for a number of purposes in the human body

Acetate: Absorbed in the large intestine, passes through the liver and can be used as an energy source throughout the body.

Propionate: Absorbed in the large intestine and is used as a fuel source in the liver. It may also contribute to a reduction in cholesterol through inhibition of HMG-CoA Reductase, the rate-limiting enzyme in cholesterol synthesis.

Butyrate: Absorbed by the cells lining the colon and is used as a preferred energy source. It may also reduce colon cancer risk by promoting normal cell growth.


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Types of Fiber

Fiber sources are typically classified based on their solubility in water.

Soluble Fiber: These include compounds such as gums, beta-glucans, pectins, and some hemicelluloses. Due to their solubility in water, they form viscous solutions and are also highly fermentable by bacteria in the lower GI tract.

It’s recommended that individuals consume a level of fiber daily that meets or exceeds the 14g of fiber per 1000 Calorie minimum set by the Institute of Medicine.

Insoluble Fiber: These include compounds such as cellulose, lignin, and some hemicelluloses. They are insoluble in water, nonviscous and poorly fermentable, primarily contributing to stool bulk.

Health Benefits of Fiber

Although a human can live without consuming fiber, there are a number of potential health benefits to consuming a diet high in fiber:

Increased Satiety: High fiber diets have been found to increase satiety. This is thought to be due to the viscosity of soluble fiber. By forming a viscous gel in the stomach, gastric emptying is slowed and ultimately results in an increased feeling of fullness. This may also contribute to reduced caloric intake and help prevent weight gain.

Reduced Cardiovascular Disease Risk: Diets high in fiber have been found to be associated with reduced blood cholesterol levels. The reduction in cholesterol is thought to be due to multiple mechanisms. First, the viscosity of soluble fiber can prevent cholesterol absorption in the intestine. In addition, the short-chain fatty acid propionate has been showed to inhibit cholesterol synthesis in the liver.

Improved Blood Glucose Control: A meal high in fiber can slow the rise in blood glucose as the meal is digested and absorbed. This is thought to be due to the effect of fiber on reducing gastric emptying and also slowing nutrient absorption in the small intestine.

Reduced Colon Cancer Risk: Both soluble and insoluble fiber may play a role in a reduction of colon cancer risk. Soluble fiber can be fermented into short chain fatty acids, including butyrate, which may help to promote normal growth and development of cells lining the large intestine.

In addition, fermentation of soluble fiber decreases the pH in the large intestine which helps to promote the growth of “beneficial” bacteria which can out-compete other bacteria and result in a healthier gut microbiome. On the other hand, insoluble fiber can increase stool bulk and dilute substances that may be potentially detrimental to cells lining the intestine.

Increased Regularity: Diets high in fiber, especially insoluble fiber, can increase stool bulk and improve regularity.


High Fiber Foods

A number of foods are high in fiber [5]. Below are examples of a number of high fiber foods (all values listed for 100g raw food):

FoodsCaloriesCarbohydrates (g)Fiber (g)
Brussel Sprouts439.03.8
Sweet Potato8620.13.0
Bran Cereal39380.416.1
Brown Rice36776.33.6
Wheat Bread26744.46.7
Nuts and Seeds
Flax Seed53428.927.3
Peanut Butter58921.68.0
Sunflower Seeds58420.08.6
Black Beans34262.415.5
Navy Beans33760.815.3
Pinto Beans34762.615.5
White Beans33360.315.2

In addition to the aforementioned foods, many other foods are fortified with fiber. Examples of fiber-fortified foods include high fiber tortillas, some protein and/or granola bars (e.g. Quest Bar) and some cereals (e.g. Fiber One).

How Much Fiber Should I Eat?

The Institute of Medicine (the group that establishes the DRI’s) recommended an adequate intake of fiber, which is 14g fiber per 1000 Calories consumed. Based upon average daily caloric intake, this works out to be a minimum intake of around 25g daily for women and 38g daily for men. However, it is important for each individual to base their daily fiber minimum upon their own daily caloric requirements.

Average fiber intake in the United States is around 15g daily. Clearly, the average American is well below the recommended daily fiber intake.

To avoid confusion, it’s ideal to count fiber along with other carbohydrates consumed and aim for a consistently high fiber intake daily.

Although no upper limit for fiber consumption has been set, it should be noted that extremely high fiber intakes are likely not optimal for health. Most individuals will experience GI distress as daily fiber intake exceeds their level of tolerance. This may also result in suboptimal nutrient digestion and absorption.

Therefore, it is recommended that individuals consume a level of fiber daily that meets or exceeds the 14g fiber per 1000 Calorie minimum set by the Institute of Medicine, but at the same time is below the amount that results in adverse GI symptoms.

This is why when we created the IIFYM Macro Calculator, we set fiber at a range that is proven to aid in digestion and gut health without interfering with macronutrient absorption.

Individuals with extremely high caloric requirements (e.g. 4000+ Calories daily) may not be able to tolerate the 14g/1000kcal minimum without GI symptoms. These individuals instead should aim for a high fiber diet that is below the threshold at which symptoms appear.


How to Incorporate Fiber into IIFYM

Now that we have discussed some of the basics of fiber, it is important to also discuss how to fit fiber into an IIFYM approach in order to make progress towards your goals and also receive the number of health benefits of a high fiber diet.

Some individuals who follow IIFYM don’t count fiber towards their daily calorie or macro totals because fiber cannot be digested by human enzymes. However, these individuals may not be aware that many types of fiber are fermentable by bacteria in the digestive tract. Which helps produce a number of products such as short-chain fatty acids which can be absorbed by the human body and used for energy (as previously discussed).

Find out your starting macros to assist you with your fiber intake, let one of our skilled coaches build your Macro Blueprint.

Although some of the fiber consumed in the diet can be fermented (primarily soluble fiber), not all fiber consumed is fermented. As a result, the best estimate for the caloric composition of fiber is 1.5 – 2.5 Calories per gram depending upon the composition of the fiber source.

This is less than carbohydrates which contain 4 Calories per gram. However, to avoid confusion it’s best to count fiber along with other carbohydrates consumed and aim for a consistently high fiber intake daily.

Minimum Daily Fiber Requirements

To ensure an individual is progressing towards their goals with IIFYM and also consuming adequate fiber daily it is recommended that they include a daily fiber minimum. The macronutrient plans provided through include a daily fiber minimum to ensure that fiber intake is adequate as macronutrient needs are met.

An individual should exceed their daily fiber minimum while also hitting their macros by consuming a variety of food from all food groups. Having a fiber minimum will ensure adequate consumption and ensure an individual eats fruits, vegetables, and whole grains daily in order to hit their fiber minimum (however, those experienced with IIFYM are likely doing this since they eat a variety of foods to hit their numbers daily).

Take Home Points:

  • Fiber primarily refers to carbohydrates consumed in the diet that cannot be digested by human enzymes. However, many types of fiber can be fermented by bacteria in the colon. Therefore, fiber does have a caloric value and should be counted towards an individual’s daily totals. The easiest way to do this is count fiber towards your carbohydrate total for the day.
  • There are a number of health benefits of a high fiber diet including; increased satiety, reduced cardiovascular disease risk, improved blood glucose control, reduced colon cancer risk and improved regularity.
  • Healthy individuals should aim for a fiber intake of at least 14g per 1000 Calories consumed daily. However, excessive fiber should be avoided if it causes individual GI distress.
  • To ensure adequate fiber intake while following an IIFYM approach individuals are encouraged to aim for a fiber minimum each day, while also hitting their macro numbers through consumption of a variety of foods.