Updated: Jan 3, 2019
Fiber is probably the most overlooked carbohydrate despite offering so many advantages for our health and well-being. In almost every meal plan that I have came across online, the importance of carbohydrate is always being singled out as a very important nutrient for strength trainees looking for muscle growth and good workouts. IIFYM (if it fits your macros) approach made it even worse because the only thing that matters now is that the carbohydrates fit your caloric budget, no matter the source or quality. What if I tell you that fiber is significantly more important for your health than the amount of carbohydrates you are consuming?
While I have nothing against simple carbs like glucose, fructose, maltose, lactose and sucrose, more complex carbs such as polysaccharides can offer more than just sugar. Other than micronutrients they can offer fiber as well.
What is fiber?
Fiber is an indigestible carbohydrate that comes from plant cells wall, both primary and secondary. The energy that our body needs is within that wall. There are many types of fiber and the exact fiber composition depends on plant maturity. Depending on the fiber type, it can have a very beneficial role in regulating your digestion and absorption of nutrients.
Fibers are divided into two main categories: water soluble, and water insoluble. Water soluble fibers, as the name suggest, dissolve in hot water. Water insoluble fiber do not dissolve in water and maintain their structure. Soluble fibers delay gastric emptying and increase transit time through intestine while insoluble fibers speed up the transit time and increase the fecal bulk. Lets look at the chart below to compare different food sources.
Both soluble and insoluble fibers offer many health benefits. Below I will list the most important effects of fiber that makes it a super food.
1. Reduced absorption of lipids
Both types of fibers can reduce the absorption of lipids simply by binding with fatty acids, cholesterol, and bile acids in the intestines. Lipids that are bound with fiber cannot be absorbed in this form and they typically just pass through intestines and get excreted in the feces. Specific types of fibers that can reduce absorption of lipids are gums, pectins, beta glucans, hemicelluloses, and lignin.
Foods rich in this type of fiber: onions, leafy greens, apples, pears, plums, oranges, oats, barley, bran, nuts, legumes.
2. Lowers serum cholesterol concentrations
This effect is connected with the events described above. As the amount of lipids and cholesterol excreted in feces increases. As bile acids are crucial in digestion of fats, there is a decrease in the cholesterol absorption which leads to decreased cholesterol content of liver cells. This promotes removal of LDL cholesterol from the blood.
Beta glucans are most effective at lowering cholesterol, and they can be found in oats and barley. Additionaly, psyllium, resistant dextrins, methylcellulose and pectins can also aid with lowering of the cholesterol.
3. Delays glucose absorption and lowers blood glucose level
Fiber naturally decreases the absorption of nutrients in the intestine and helps lower blood glucose level. By creating a viscous water layer on top of the enterocytes in the small intestine, fiber slows down the absorption of nutrients, and as a result, lowers blood glucose concentration levels. This also keeps related hormones in check, such as insulin and glucagon like peptide l, and blood sugar levels in a good range.
Types of fiber that affect this are gums, pectins, beta glucans, psyllium, and resistant starch.
Foods rich in this type of fiber:
Onions, leafy greens, carrots, apples, oats, barley, rye, legumes.
4. Delays gastric emptying
Fiber increases the transit time of food in our digestive system by delaying the release of partially digested food from the stomach to the small intestine. As a result, nutrients remain longer in the stomach creating fullness effect. Also on average, 14 g of fiber can reduce energy intake by 10% when you are not tracking your macros. This means that simply by consuming 24 g of fiber you can be in a 20% energy deficit. This is a great way to reduce appetite when you are dieting to lose weight, and especially when you enter the single digit body fat numbers.
5. Prebiotic benefits
Most fermentable fibers promote colonic growth of health promoting species of bacteria, directly improving the gut health. Food that is generally rich in these fiber are green peas, chickpeas, lentils, navy beans, soybeans, lima and field peas.
6. Short chain fatty acid generation
The main products of fermentable fibers are short chain fatty acids and lactic acid. The short chain fatty acids include acetic, butyric, and propionic acids. These acids have many important effects on our overall health. Lets look as what benefits they provide us with.
-Inhibition of cholesterol synthesis
-Improved colonic blood flow
-Enhanced immune function
-Provision of energy (1.5 - 2.5 kcal/gram)
-Increased water and sodium absorption in the colon
-May be protective against colon cancer through acidification of luminal environment
Many insoluble fibers can absorb water fearing carcinogens and prevent their interaction with colonic mucosa. On the other hand, fermentable fibers can inhibit an increase of tumor cells and delay tumor formation through short chain fatty acids. As a result, eating lots of plants and legumes can provide you with a real detox and improve your health.
As we have seen above, consuming fiber provides you with many health benefits including improved digestion, stabilized blood glucose levels, lowered blood cholesterol, improved immune system, lowered risk of cancer and lowered risk of cardiovascular diseases. This only increases the importance of fiber in your diet and especially the amount of fiber that you should be consuming on a daily basis.
Recommended fiber intakes are 25 g for women and 38 g for men. For athletes and individuals that are strength training, this would be a minimum. Remember that most plants and fruits contain a mixture of different types of fiber, and the best way to cover your daily recommended intake would be to have a mixture of your favorite veggies and fruits from the list above, that way you can easily include them on a daily basis. Mobile apps like MyFitnessPal can offer you a convenient way to track your fiber intake provided that you use the correct verified values.