Nutrition for Endurance Sports – Supplements

After the introduction into metabolic processes and advice on carbohydrates and protein intake, as well as hydration, I continue the series of articles on diet and endurance sports by talking about supplements.

You’ll notice that I left out fat. This isn’t by accident. Fat is not critical for sports performance, but are an additional source of calories, after satisfying the needs for proteins and carbs. And no, I’m not saying we need to consume fats only for their calorie value. After satisfying our other macronutrient needs, the intake of foods with significant fat content is usually enough to satisfy needs for essential fatty acids and vitamins soluble in fat.

To begin, I’d like to define dietary supplements. According to the Guidebook on dietary supplements, NN 126/2013, they are as follows…

materials produced from concentrated sources of nutritive items or other items with nutritional or physiological effect that serve a purpose of enriching the diet in order to maintain the level of health.

What are nutritive, and what are other items? According to the Guidebook, nutritive items…

are considered to be vitamins and minerals.

Other items…

are amino acids, essential fatty acids, fibers, organs and plant extracts, microorganisms, edible fungi, algae, bees’ products and other items with nutritional or physiological effect.

I’d like to point out a few problems with this definition. First of all, it mentions that we take supplements to additionally enrich our diet in order to maintain health. Additional enrichment, and enrichment as such, means having an additional effect that diet itself cannot achieve. This means that this term does not include replacing items that are missing from our diet, that our body needs, but we can ingest them through the diet. The mere potential of replacement of nutrients is the basic value of dietary supplements.

Secondly, as athletes might’ve noticed, the definition says nothing about enhancing sports performance. And not in terms of upgrading the diet to correct dietary deficits because in that case it overlaps with maintaining health (dietary deficits reflect on both health and performance). Rather to achieve an extra effect we cannot achieve with food. A great example of this is supplementing with creatine or beta-alanine, both of which we cannot ingest through diet in quantities large enough to improve the performance.

So I’d like to propose a new definition, that says that dietary supplements are:

materials produced from concentrated sources of nutritive items or other items with nutritive or physiological effect in order to correct for insuficient dietary intake or enrich the diet in order to maintain health or improve sports performance.

In this article I won’t go into details of the specific supplements. I will only make an overview of the question of taking supplements in order to make the readers ask questions. I’ll be philosophical, evil minds would say.

Do I need supplements?

This is the most common question when it comes to supplements. Since I don’t believe there are no stupid questions, I’ll mark it as such. Because it makes no sense to talk about supplements as a unique category without approaching each and every one individually. Just as it makes no sense to talk about generally mystified… sorry… genetically modified organisms (GMO) as a unique group.

I’ll call on the little sense there is in that question and answer it:

If we’re talking about improving health, then the answer is no. All dietary needs can be satisfied with food. But because of the several more or less justifiable reasons we do not ingest enough of certain nutrients. In that case, supplements can be valuable. So, the value of dietary supplements in this context is in their practicality.

But there’s a catch. Supplements are isolated materials. Isolated from food, which contains many other components that may have a positive or negative effect. Also, almost all nutrients interact with one another. They can interact in a positive way by enhancing absorption, or in a negative way by inhibiting it. The more pronounced interactions are well documented, like the fact that the absorption of iron increases along with vitamin C, [1], vitamin D helps calcium absorption, [2], copper intake inhibits the zinc absorption [3]… There are certainly other subtle, yet undiscovered interactions. If we use supplements as a substitute for deficitary nutrients, we cannot be certain to claim how the lack of „other“ items and the change in interaction will affect our body. No, we don’t exactly know how our body works. Let’s make peace with that.

This is why you should be meeting the dietary needs primarily with food. Not because it’s „natural“.

Next logical question is: „Do I need supplements to enhance my sports performance?“

The answer to the question asked in this way is yes.

However (how did you know?)! I mentioned that need might be too strong of a word because it suggests the necessity and I used it to keep it in accordance with the former. It would be better to ask Can supplements enhance sports performance“. To avoid too much philosophy in a short space, I would like to conclude. Supplements aren’t necessary for enhancing sports performance, except when a person achieves their genetic and training maximum. Also, certain supplements can be an extra stimulus for progress, but this effect is secondary to training, general diet, hydration and rest.

How to know which supplement works?

The process of a supplement entering the market should go something like this:

  1. Lab research on safety
  2. Lab research on effectiveness
  3. Research on effectiveness in practice
  4. Affirmation of effectiveness from multiple independent sides
  5. Entering the market

Unfortunately, the process often goes like this…

  1. Lab research on safety
  2. Entering the market

…or in different combinations of points 1-5 while missing at least one of them.

The consequence of the incomplete process is insufficiently researched supplements on the market that often have no effect. The Guidebook on dietary supplements, NN 126/2013 does not demand the proof of effect before registering a supplement, unless it has a medical claim, such as Iron helps the normal cognitive development in children. In this case, registering a supplement requires documentation, including scientific data and opinions from scientific research institutions and experts supporting the claim.

Even in a generally ideal process of entering the market there is some doubt about the effectiveness. For example, in the moment when pharmaceutical company testing their own products become involved in the research process. I’m not saying they directly meddle with results, even though that happens too. More often they don’t publish the negative results and publish only positive ones, which creates a wrong impression that most of the literature takes the side of (positive) effect of the supplement. This problem is at least partially decreased by the requirement of the author of research to state the source of financing the project, and a potential conflict of interest. I believe that haters of big pharma couldn’t wait for this part. But I’d like to warn not to fall into the trap of labeling every supplement whose effect has been proven worthwhile by the industry as bad or ineffective. That’s simply not the case because many scientific achievements of mankind were financed by this industry.

My advice is to not trust everything you hear and read, but instead seek advice from an expert.

I can feel it’s working!

The fact that a supplement is selling (well) does not mean it’s efficient. Considering the counterattack „But I can feel it’s working“, you should know that our perception is easily misguided. It falls under the influence of many factors we’re not even aware of, and some cannot be measured through our impressions without instruments and scientific methods. It’s very common for a person that starts taking a supplement to (un)consciously make other changes in diet/training/rest and pin the effects produced on supplements.

If it’s natural, then it’s safe!

It’s not.

Even if we neglect the fact that the difference between anything natural and artificial in the universe (or Earth) is fictional, you must know that „natural“ origin does not imply health safety. Cocaine is natural, but does that mean it is medically safe? Or cyanide? It is a classic logical mistake called „appeal to nature“ which would be smart not to use when deciding on supplements. Or in fact on any other life decision.

Cost to benefit ratio

In the end, as with every life decision, one must take into account the cost-benefit ratio. Money is for most people a very limited resource and one must ask him/herself is there a way to use it that will have a better effect on health or sports performance that buying the supplement X? In other words, is it worth the money? When we think about it, we often conclude that a large number of supplements aren’t worth it even if they have a certain effect, and that investing into quality diet, training and rest provides far better results.

Don’t expect me to talk about all supplements related to endurance sports out there because new ones make the market on a daily basis. I’ll talk about those that work and those that are most popular, but don’t work. If you feel I’ve left out any, feel free to comment, so I could write part two of the article.


  1. Hallberg, Leif, Mats Brune, and Lena Rossander. “The role of vitamin C in iron absorption.” International journal for vitamin and nutrition research. Supplement= Internationale Zeitschrift fur Vitamin-und Ernahrungsforschung. Supplement 30 (1988): 103-108.
  2. Gallagher, J. C., et al. “Intestinal calcium absorption and serum vitamin D metabolites in normal subjects and osteoporotic patients: effect of age and dietary calcium.” Journal of clinical investigation 64.3 (1979): 729.
  3. Evans, G. W., Patrick F. Majors, and W. E. Cornatzer. “Mechanism for cadmium and zinc antagonism of copper metabolism.” Biochemical and biophysical research communications 40.5 (1970): 1142-1148.