I'm planning my hydration and nutrition for the Zion 100k in early April. It isn't carved in stone yet, but the following is the approach I've taken to narrow it down.
You shouldn't do what I do; your best choice for hydration and nutrition during training and racing is unique to you. However, there are excellent starting points that are grounded in many years of research. In my own approach to finding what works best for me, I started with some of those fundamental ground rules. If you want to learn much more of the science, listen to Science Of Ultra episodes 4, 7, and 13 - the knowledge in those episodes form a substantial basis for plan development.
I started with two fundamental questions. First, to what extent do I want to drink vs eat? Second, how much do I need to drink and eat?
To answer the first question, to what extent do I want to drink vs eat, I considered one major driving factor: I want to maximize my rate of absorption of whatever I consume so that it gets into my blood stream as quickly as possible. From that standpoint, it was important to avoid fats and avoid fiber in what I consume because both of those slow down gastric emptying, which is how quickly the stomach moves its contents into the small intestine, where absorption occurs. Most of the food at aid stations have fats and/or fiber. I decided to use aid stations only when I felt cravings for what they had to offer and to otherwise rely on liquids for my hydration and calories if possible.
The most important source of calories while running is carbohydrates because the body has a limited store of available carbohydrates to mobilize for use during running. On the other hand, fats are something that even very lean people have plenty of for fueling single day ultra events. Protein, as you learned in Science Of Ultra episode 11, is not a substantial source of calories during running. What type of carbohydrates is best and how much can I absorb? In episode 13, we learned that most people can absorb 60 g of carbohydrates per hour (which is close to 240 Calories), that this number is not very different among people, and that exercise doesn’t lower this number. Those last two points are something that likely came as news to many listeners. The 60 gram limit is due to the saturation of glucose carriers, which are the molecules that actively transport glucose into the cells of the intestines. When they are working maximally, you’ll be able to absorb about 60 grams of glucose-based carbohydrate each hour. With simple sugars (sweet stuff), it takes a lot of molecules to get to 60 grams. More molecules increases the likelihood of GI upset, which we discussed in episode 16. It turns out that maltodextrin, a form of glucose based carbohydrate is made of much larger individual molecules. With maltodextrin, you get fewer molecules in the same 60 grams (so less GI upset) and maltodextrin is digested and absorbed to increase blood glucose levels just as quickly as the smaller and simpler glucose based carbohydrates. Maltodextrin also isn’t sweet tasting, because it is a large molecule and doesn’t activate the sweet taste receptors in our mouths. So, there is little chance of it progressively putting me off the taste as the hours tick by, which happens with stronger flavored drinks.
Now, it is also the case that many people can absorb even more carbohydrate if that carbohydrate is in a form that is absorbed but doesn’t rely on the glucose carriers. That molecule is fructose - fruit sugar. People can absorb up to another 30 grams per hour of fructose (which is almost another 120 Calories). Here is where more people need to be particularly careful and experiment because fructose is more likely to cause GI upset. For myself, I’ve taken honey and maple syrup on runs in the past. These have a high percentage of their calories coming from fructose (agave syrup often has even more). They tend to give me the runs - that is, I need the bathroom - which is something we want to need as little as possible, or at least to keep under voluntary control. So, adding fructose into my home-brew is something I will do slowly as I continue to experiment.
I’ve looked back at all the commercial products I’ve used in the past. There are three that I’ve liked the best…they haven’t turned my stomach, they keep my energy levels up, and I generally feel that work the best for me. Looking at their ingredients list, they are the three (out of the many products I’ve tried) that have maltodextrin as the primary energy source. That observations gives me an added level of confidence in my choice of energy source.
Now, how much fluid do I need to consume? By weighing myself naked before and after runs in different environmental conditions and terrain, and adjusting for any fluids I consumed while running, I’ve slowly gotten a sense of how much I sweat. My sweat rate increases as I acclimate to warmer environments, which is expected. One thing to be careful of while making these observations is that urinating during a run is non-sweat weight loss and confounds the results. So, runs where I haven’t needed to urinate until a while after the run are the most accurate. I suppose I could take an extra bottle and collect my urine - I would need to actually carry it back home. A container that has volume markings would allow me to urinate into the container, measure how much that is, and then dump it on a thirsty bush. Back home I can remove that urine weight from the measurements by converting volume to weight (actually mass) knowing that 1 liter = 1 kilogram (2.2 lbs). Though the mass of urine varies from this based on several factors, the differences are too small to worry about in these calculations. Generally speaking, I lose about 0.7-1.0 liters per hour on the majority of my runs. This varies significantly based on conditions for sure, and I’ve determined the rate for enough conditions that I have a good starting point for most training sessions or races.
The final issue to tackle is electrolytes. The major electrolytes lost in sweat are Na, Cl, and K. Concentrations of each of these in sweat is wildly variable among people, and it changes substantially with acclimation and even over time in a race. The research has shown that people who are given access to a variety of foods and drink will tend to self-regulate sufficiently. So, I’ll probably choose the foods and drinks that I need to do alright over time just by listening to what I want. This seems to be true for the stuff in foods and drinks but not for the water itself. In general, thirst is not a good way to gauge water needs because people tend to under drink over time. We learned that their is a long history of evidence showing this in episodes 4 and 7. That science goes against some of the dogma in the running world, but exploring these issues critically is one of the reasons that Science Of Ultra exists.
I do not know the concentration of electrolytes in my sweat as I have not yet had it tested. I might have it measured by a colleague this year. I’ve decided to start with average sweat concentrations and then bump this up just a little bit because I am a salty sweater - I can have a chalky face and shirt after a long run in warm conditions. The mean concentrations reported vary from study to study because the numbers themselves are highly variable and studies like this are done on different populations of people, often with small subject pools. The numbers I used to start came from a publication by the authors in episodes 4 and 7 where they demonstrated that the amounts of other electrolytes, such as calcium and magnesium, sometimes reported in sweat in the past, have likely been overestimated. The source of those errors was not ensuring the the skin was fully clean prior to starting sweating and subsequent sweat collection. Build up of those other substances on the skin over time ended up in the sweat giving erroneously high values. When the skin was thoroughly cleaned first, it was discovered that levels of other electrolytes are very small in sweat and can probably be ignored in my hydration home-brew.
If an event is very long, like a 100 mile race, I am sure that I will want solid foods from aid stations at some point and those are likely to contain sufficient amounts of the minor quantities of those other components lost in sweat. Right now, my home-brew has close to a gram of sodium, 600 mg of chloride, and 250 mg of potassium per liter. I’m not done and I’ll continue to experiment. Moreover, that may be right for a segment of one race or training day, but the changes that take place over time and from day-to-day in my sweat concentrations will ensure that it is never exactly right. Which brings me back full circle to aid stations. I will use aid stations on a ‘that looks great’ basis. I will think about what may be at an aid station as I’m getting close and scan what’s there when I arrive. If something really peeks my interest, I’ll go for it without hesitation.
I purchase all of the ingredients in my home-brew from commercial sources as raw materials: organic tapioca maltodextrin, organic fructose, sodium chloride, potassium chloride, and sodium citrate. I am still dabbling with flavor and may develop a scheme to have different flavorings in concentrated form or I may use a commercial hydration drink mix to supplement for flavor. In the end, I may decide to just use the three products I mentioned earlier that have worked for me in the past. For now, this is a fun endeavor and it saves a lot of money. I’m not going to name any particular products because this is not meant as an endorsement of any product and because it really doesn’t matter to you. What will work for you will be different. But, don’t take that phrase ‘we are all an experiment of one’ to the ridiculous. We are all human beings with a vanishingly small amount of our DNA that differs from me to you. All the fundamental functions and principles apply to all of us and the data from decades of rigorous research does form a solid foundation for all of us. It is important that we start there and then adjust and try different things in the safe environment of training where you can always get to safety if you have made an error in calculating how much you needed to bring or if you suddenly have GI upset or anything else that could go wrong.
Now, for the personal and practical. I don't care for drop bags. In a 100 mile race, I'll have crew. For 100k, probably not. At my upcoming Zion 100k, I won't have crew. So, I'll have to rely on aid stations, drop bags, or a combination. I've checked out the race sponsor electrolyte drink and it's ingredients are close enough to my mix, to form a basis for my strategy. I've also confirmed by using it in training. So, while the above is true for training and for drop bag resources, at my 100k I'm planning on carrying 1.1 L of drink in a waste pack along with a couple of gels that I like. Because the drink is low in electrolytes, I'll carry salt capsules (sodium, potassium, chloride) for backup. Pickles are great for electrolytes and orange juice has a remarkably high potassium concentration - good real food options at aid stations. I'll drink the fluids between each aid station and slam extra at an aid station if I'm thirsty at all. I'll then grab another 200 Calories of food - in gels or Oreo cookies most of the time - and pickles, orange slices, or salt capsules as I like. The drink will have about 200 Calories per liter.
*throghout, I've used a capital 'C' for Calories. A nutritional Calories is actually 1000 calories of energy or 1 kilocalorie (kcal). When you read a food label, regardless of how they write the caloric content, the number is in Calories/kcals - even if a lowercase 'c' is used on the label.