Fiber – Friend or Foe of Athletes?

Athletes often have a unique approach to fiber. Some do not address its existence or significance at all. Others, on the contrary, anxiously avoid its intake because they fear potential consequences such as increased bloating and flatulence, which could complicate their ability to perform well during training. This concern is justified, but it only applies to situations where the amount of fiber in the diet is so large that it leads the gut microbiota to produce more gases. The result is a situation where the eater avoids consuming all typically rich representatives of fiber, namely legumes, root vegetables, or nuts, seeds, and whole grain products.

This is a real shame because once the significance of fiber in the diet is properly understood and its impact on metabolism behavior is realized, it is only a short step to finding a way to work with it effectively to one's advantage.

The benefits of adequate fiber intake are clear:
- it supports intestinal peristalsis,
- exhibits anti-inflammatory effects in the intestines,
- influences the metabolism of water in the intestinal tract,
- is a crucial source of nutrition for probiotically behaving microorganisms in the intestines,
- through microbial activity, it supports immune functions or brain activity (thanks to the production of neurotransmitters headed by serotonin),
- reduces the glycemic index of the diet, thereby influencing the distribution of quick energy in the body.

However, the proverbial "too much of anything is harmful" applies to fiber as well. Its excess is not welcomed with a smile in practice, with a number of consequences:
- bloating and flatulence,
- risk of irritation of the intestinal mucosa,
- impaired absorption of certain nutrients (headed by minerals).

It is therefore necessary to find the right amount for each individual. This is often a stumbling block because the ideal dose is one that does not cause any problems (currently or in the long term). Moreover, the factor of gradual adaptation to fiber intake comes into play, where the digestive tract is able to (along with microorganisms) adjust to the "load" and function very well even with a highly above-average intake of this indigestible component of food. In terms of specific numbers, the situation is as follows:

1. The recommended daily intake of fiber for the adult population is most often in the range of 25-35 g.

2. Just because something is recommended universally does not mean it is the optimum for the respective individual. The actual (though still statistically averaged) daily fiber intake for adults following the Western dietary model is around 10-15 g. And because we know what health consequences this subpar brings, in the initial phase of dietary adjustments, it makes sense to aim for these generally recommended values.

3. If we ask what the ceiling is in the field of fiber intake, we encounter two limits:

A) The first is the antinutritive nature, where with an increasing volume of this component, the absorption of minerals from the diet worsens.
This is not just theoretical information; in practice, these problems are fought by, for example, the vegan part of the public, but athletes feel this most and fastest.

B) The second limit may be the pattern in the form of the ability of human metabolism to handle absolutely atypical amounts of fiber for today's era, as pointed out by some anthropological studies of our ancestors from the Paleolithic period.
It shows that the diet of hunters and gatherers could represent over 100 g of fiber. Given the conditions we are in today, aiming for these goals is not a complete victory. The reasons are understood by anyone who dares to try such a dietary concept themselves.

As you might have noticed in Lucie's sample meal plans published in previous articles, not only do we monitor fiber intake, but we also keep it at significantly above-average levels. We have several reasons:

1.  We aim to support the diversity of the intestinal microbiota and increase the activity of probiotic microorganisms.
Adequate fiber indeed has a positive impact on immune functions. Due to the high load and level of stress Lucie undergoes, it is reasonable to think this way and prevent diseases whose cause stems from weakened immunity.

2. A higher proportion of fiber can prolong the process of releasing carbohydrates into the blood and thus reduce blood glucose levels.
This has double value when the diet is based on a significantly low-fat concept (fats also lower the glycemic index of the diet). Lucie benefits from this among other things during longer training sessions, where we excluded the consumption of any sources of fast sugars (in the form of ionic drinks).

3. With an increasing intake of fiber, the energy yield from food decreases.
Since Lucie is in a reduction regime, this property of all fiber sources meets our requirements.

4. Last but not least, fiber retains a larger amount of water in the intestines.
This is an advantage that we exploit very successfully in the pre-match dehydration process.

So how is Lucie doing with specific values of fiber in her diet?

The average daily intake of fiber ranges from 45-55 g. There are days, however, when it climbs above 70 grams. Here I must emphasize that this is not intentional, but the outcome of a situation where Lucie is forced to prepare her food due to daily travel to trainings. It is organizationally easiest to pack something that tastes good, preparation does not take much time, does not spoil, and is consumable even "on the go" (a typical example is hummus, which is indeed a rich source of fiber and in the situation of two servings a day, pushes the values of fiber intake beyond the normal norm).

For everything to work as it should, it is necessary to address not only the total fiber intake but also its form and processing method.
In terms of forms (types) of fiber, we consider the following:

- For higher values of fiber intake, it is reasonable to intentionally reduce the amount of insoluble fractions that unnecessarily burden digestion.
This involves avoiding, for example, sources of bran, or choosing peeled forms of rich fiber sources (a typical example is the preference for peeled lentils).

 - If we decrease the share of insoluble fiber, it is logical to increase the presence of soluble fractions.
These exhibit prebiotic properties and are strongly hygroscopic (retain water). We therefore try to preferentially include foods in the diet that predominantly contain soluble forms. It is possible to exploit the potential of supplemental nutrition, which in this field offers possibilities like psyllium or inulin. However, it is always more advantageous to use the potential of real foods. In terms of availability, the most advantageous source in our conditions is the ordinary onion. One of the rules that Lucie (fortunately) accepts is to get at least one whole onion (in a cooked form) on the everyday plate.

If we have under control the ratios of soluble and insoluble fractions of fiber, we also pay attention to the methods of their preparation:
Because fiber is indigestible for the human digestive tract, it is advantageous to reduce this burden with thermal preparations of its sources. There is one overarching rule here - with the increasing amount of fiber in the diet, it is desirable to also thoroughly thermally process its high-proportion sources. This means longer cooking, stewing, baking, or preparation in a pressure cooker. Not respecting this procedure risks an undue load on the digestive tract, so it is necessary to pay adequate attention to it.

As the date of the match approaches, we will gradually reduce the amount of fiber, due to the need to accelerate metabolic processes, which are an integral part of the process of tuning peak form. This topic will still be addressed in our series.

Note in conclusion: If any of the readers have the tendency to copy Lucie's diet, they should know in advance that Lucie worked her way up to the fiber intake values mentioned above within the course of dietary adjustments over the past two years. It is therefore my professional duty to warn of the many risks stemming from a quick transition from conventional eating patterns to Lucie's current diet.