Dietary Fiber: When to Avoid It and When to Consume It?

While carbohydrates, protein, and fat are at the center of an athlete's nutrition, dietary fiber is one of the essential but often overlooked components of a healthy and balanced diet.

Even though we constantly emphasize that you should limit the intake of dietary fiber before and during sports activity and when filling your glycogen stores, dietary fiber should be a regular part of your diet due to its numerous health benefits.

In this blog, you'll learn what dietary fiber is and why you should consume plenty of it.

What is dietary fiber?

Dietary fiber is a special type of carbohydrates that are not digested or absorbed in the small intestine and enter the large intestine intact in order to be fermented by microbes.

Dietary fiber is found in foods of plant origin, such as fruit, vegetables, whole grains, beans, and legumes. They include non-starch polysaccharides, resistant starch, resistant oligosaccharides, and lignin.

Based on its characteristics, it is roughly divided into fermentable and non-fermentable dietary fiber and soluble and insoluble dietary fiber.

Soluble dietary fiber is able to bind water and form a gel that helps to normalize stool – it softens it in case of constipation and solidifies it in case of diarrhea. It also increases the viscosity of the bowel content, slowing down the emptying of the stomach and absorption of nutrients. In simple terms, it makes you feel full and prevents a drastic increase of blood sugar. Soluble dietary fiber binds cholesterol in the digestive tract, reduces its absorption, and stimulates the excretion of cholesterol from your body.

Examples of foods that contain soluble dietary fiber are:

• oats,
• barley,
• legumes (beans, lentil),
• fruit (apple, orange),
• vegetables (carrot, Brussels sprout),
• chia seeds,
• and flax seeds.

Insoluble dietary fiber does not dissolve in water and preserves its form when passing through the digestive tract. This type of dietary fiber increases the amount of stool, softens it, and speeds up bowel movement, which boosts regular stool excretion and prevents constipation.

The alimentary sources rich in insoluble dietary fiber are:

• wholegrain wheat,
• bran,
• nuts,
• seeds,
• some vegetables (green leaf, cucumber),
• potato peels,
• and some fruit (strawberries, grape).

In plant foods, soluble and insoluble dietary fiber are present together but in a different ratio. In cereal grains they are found in an equal ratio, while in fruit and vegetables insoluble dietary fiber is a little more prevalent.

Fermentable dietary fiber represents food for intestinal bacteria. Through the process of fermentation, intestinal bacteria transforms it into various substances, such as gasses or short-chain fatty acids, which also contributes a small amount of energy (2 kcal or 8 kJ per 1 gram of fiber). The newly-formed short-chain fatty acids support the health of intestinal cells, boost the immune system, and stimulate anti-inflammatory interactions in the gut.

The rest of dietary fiber, not fermented by bacteria, travels further through the digestive tract and is excreted almost untouched. And yet, it provides several benefits, from slowing down the emptying of the stomach and providing a sensation of satiety to reducing the levels of total and LDL cholesterol, which reduces the risk of cardiovascular diseases.

Main benefits of dietary fiber

In addition to all the mentioned benefits of dietary fiber, there are other significant benefits you should be aware of:

• Oral health: dietary fiber is good for your oral health. Foods rich in fiber require more chewing, which stimulates saliva production and cleans your teeth. It is not surprising that dietary fiber is known to prevent dental caries and dental erosion.
• Weight management: foods rich in fiber provide a longer sensation of satiety after a meal. Consequently, we consume less food which could prevent obesity.
• Cancer prevention: it is known that dietary fiber which travels through the large intestine reduces the risk of pancreatic cancer, colon cancer, and rectal cancer by absorbing bile acids and carcinogenic substances. The newly-formed short-chain fatty acids due to the fermentation of intestinal bacteria also contribute to a reduced risk of colon cancer.
• Reduced risk of diabetes type 2: soluble dietary fiber in the intestine forms a gel that slows down the absorption of glucose and fat into the blood, which also results in more stable blood sugar levels.
• Boost the immune system: the task of the immune system is to defend your body from foreign substances and bacteria, viruses, and other microorganisms. The intestine is the largest organ of the immune system, as it contains about 80% of all immune system cells. To preserve the wellbeing of the immune cells in your intestine, you need to take care of the intestinal bacteria. And these function well if they have access to the right food - dietary fiber.

The recommended intake of dietary fiber and food content

Due to all the health benefits of dietary fiber it is recommended that you intake at least 30 grams per day, which many people don't do. 

You can find dietary fiber in foods of plant origin, and its main sources are wholegrain cereals, legumes, nuts, seeds, fruit, and vegetables.

FOOD	Dietary fiber content in 100 g of food
Linseed	38.6 g
Dry plum	17.8 g
Wholegrain wheat flour	12.2 g
Peanuts	11.7 g
Sesame seed	11.2 g
Oats	10.6 g
Buckwheat porridge (raw)	8.26 g
Peas	7.25 g
Walnut	6.14 g
Wholegrain pasta (raw)	6 g
Wholegrain bread	6 g
Wholegrain rice (raw)	3.2 g
White pasta (raw)	3 g
Broccoli	3 g
White bread	2.4 g
Paprika (red)	2.1 g
Potato	2.07 g
Apple	2.02 g
Lettuce	1.76 g
Orange	1.6 g
White rice (raw)	1.39 g

A few tips to help you reach the recommended dietary fiber intake:

1. Include a bowl of salat or some vegetable soup to your lunch.
2. Add seeds to your oatmeal.
3. Have fruit or nuts for a snack.
4. Replace white pasta, white rice, and white bread with the wholegrain version.
5. Occasionally replace animal protein with plant protein, such as peas, beans, or lentil.

Example of meals on rest days:

• Breakfast: oatmeal with a spoon of linseed, Greek yoghurt, and berries.
• Morning snack: piece of rye bread, chicken breast, and fresh paprika.
• Lunch: a bowl of mixed salad, baked new potatoes, turkey steak, and grilled vegetables.
• Afternoon snack: apple, small portion of nuts.
• Dinner: buckwheat porridge with stewed vegetables and egg.

Dietary fiber in sports

Dietary fiber is undoubtedly an important ingredient of a healthy lifestyle.

Since dietary fiber is difficult to digest, its intake should be limited before, during, and after physical activity and when filling your glycogen stores.

But during a period of rest or low-intensity exercise, you should consume plenty of fiber. With the high amount of energy gels, energy bars, soda, and other energy-rich foods you consume regularly, your digestive system will love some fiber.