The truth about fiber and calories
Fiber is often referred to as a “0-calorie nutrient”. If you like to count carbohydrates, you may rest the amount of fiber (grams) from the total carbohydrate intake to determine how many carbs you can eat.
Our bacteria found in the intestine are more than happy to eat fiber and they produce certain beneficial substances for us in exchange. Our intestinal and immune cells then use up these nutrients. Is it therefore a 0-calorie nutrient?
What is fiber?
Fiber is a type of carbohydrate that cannot be broken down or used up by our body. Instead, in food for our gut bacteria.
In general, fiber can be divided into two groups: insoluble (able to hold large quantities of water) and soluble fiber (soluble in water and forms a gel-like structure). In reality, there are thousands of fiber types, and each of them feeds different bacteria. This is why it’s so important to eat a variety of plant foods.
Is fiber really a 0-calorie carbohydrate?
In short, fiber itself has ~ 1–2 kcal/g, possibly less. However, there are many factors that affect this number.
Factor #1 — Antinutrient effect
Fiber can bind to other dietary components and inhibit their absorption. This will reduce the energy value of what we eat. It has been shown that fat and protein digestibility is reduced when fiber increases.
Factor #2 — Delay of intestinal transit time
Soluble fiber enlarges the intestines forming a viscous gel that delays the emptying of the intestines leading to higher satiety signals. At the same time, this allows for more complete digestion and absorption of nutrients.
Insoluble fiber has the contrary effect. Food passes more quickly through the intestines and diminishes the absorption of nutrients, reducing the final calorie yield.
Factor #3 — Type of fermentation
When bacteria use up (ferments) fiber produces SCFAs (short-chain fatty acids), which are subsequently absorbed, and used as an energy source by cells from the colon, liver, and even the brain! Thus, these SCFAs can be counted as calories. SCFAs and other substances coming from the fermentation of fiber equal to 2–3 kcal/gr. As a comparison, the utilization of glucose by our cells yields 4 kcal/gr.
This gets even more complicated because some SCFAs are used up by other bacteria instead of our cells. Scientists have proposed to lower the number to 1.5–2.5 kcal/gr fiber.
Factor #4 — Degree of fermentability
Soluble fiber is generally fully fermented by bacteria while insoluble is only done partially.
Factor #5 — Type of fiber and individual microbiome
There are thousands of different fiber structures and each of them feeds a different type of bacteria. Therefore, each specific gut microbiome determines the amount of fiber that is fermented, and the overall energy produced from it.
Tips to increase fiber in your diet
Tip #1 — Eat the skin and peel of vegetables and fruits
Fiber (and vitamins!) are mostly found in the peel and skin of vegetables and fruits.
Tip #2 — Eat whole grains
Fiber is generally found in the most external part of grains.
Tip #3 — Eat beans, peas, and lentils on a daily basis
These are the best when it comes to fiber!
Tip #4 — Don’t juice, eat the whole thing.
Juicing reduces (filtrates) the fiber in fruits and vegetables. Smoothies are a better option even though fiber is broken down in high-speed blenders which reduce the fiber benefits. The best option is always to eat whole vegetables or fruit.
