Fiber intake can heavily shape our gut microbiota profile — that’s the trillions of bacteria in your digestive tract that help you to break down food — which may in turn play a key role in controlling stress responses resulting from intense exercise.
What’s concerning is that many athletes are advised to follow an eating plan that is higher in simple carbohydrates and protein, and low in fat and fiber. Athletes sometimes forego high-fiber foods so that their meals can provide a quick source of energy as well as minimize indigestion and gas.
My Experience:
I have a mixed relationship with fiber. During weeks of hard training, it becomes harder to take fiber from natural sources. After a long ride or run, proteins & carbs are critical. The last thing I want is to fill up on fiber from broccoli or apples and be unable to eat enough. Hard days training days with 3+ hours of training, of back to back session require big eating, and our bodies can require in excess of 4000calories, even for an age-grouper.
Using a CGM (continuous glucose monitor) was an eye opener for me. The relationship between blood glucose levels and fiber is remarkable. Eating too many carbs gives a spike in blood sugar levels, which is often accompanied by a crash. This can increase stress and fatigue – the last thing you want when your body is already stressed from tough workouts, and life in general. Adding fiber, fat & protein before eating carbs helps manage blood sugar. The rise is steady, and blood sugar returns to baseline rather than crashing lower than baseline.
This in itself is a key factor in making sure enough fiber is added into our diets, either through supplements or natural sources.
What is dietary fiber?
Fiber is the part of food, usually from plants, that our body cannot digest, i.e. they have no caloric value. There are two classifications of fiber: soluble and insoluble.
Soluble fiber is water soluble, and turns into a gel-like substance. They tend to have a pre-biotic effect, meaning it acts a source of energy for our gut-microbiome. Good source of soluble fiber include:
Fruit: Apples, pears, berries
Vegetables: carrots, artichoke, onions
Legumes: lentils, beans, peanuts
Seeds
Insoluble fiber is not water soluble and cannot be broken by our gut microbiota. It helps in keeping you fuller longer, slowing digestion as well as regulating blood glucose levels. It also helps in stool formation and preventing constipation. Insoluble fiber is found in various food sources such as:
Whole grains: Wheat, barley, oats, etc
Legumes: Lentils, beans, peanuts
Nuts & seeds
Benefits of consuming more dietary fiber
- Controls blood sugar
High fiber foods sit lower on the glycemic index (GI). Endurance athletes in particular need to maintain stable blood sugar levels for optimal performance. The spikes and dips which result from high GI or processed food do nothing but leave us exhausted
- Feeds good bacteria
As mentioned earlier, fibre feeds gut bacteria which keeps our systems firing on all cylinders and enhances immune function. A poor gut biome means less energy, poorer recovery and out-of-whack hormone production, all of which impact training performance.
- Lowers Cholestrol
- Reduces GI Distress
- Reduces risk of various diseases including: Type 2 diabetes, colon cancer, obesity, heart disease
How much fiber should we be consuming?
A good range is from 25g to 50grams based on personal experience & tolerance. Its best to minimize fiber before and during training, especially non-soluble fibers should be avoided or minimized. In addition, it may be important to reduce fiber around harder or longer workouts and races. Longer sessions are a great time to test fiber ingestion to see what sits well with you, so you know how you react going into race day!
