As I’ve gone deeper into endurance cardio sports like trail running and ski touring, I’ve started using sports nutrition gels and found them extremely helpful.
This post is an overview of how to make your own similar product and some information about why gels have the ingredients that they do. TLDR; Skip to the bottom for my recipe
There are many commercial nutrition gel products out there. The one most people are probably familiar with is Gu, which is a flavored carbohydrate gel that comes in disposable foil sachets which tear open. Each serving is 100kcal and looks like this:
These have worked really well for me, but I have some problems:
Gu and others seem to be aware of at least the convenience problems with the packets and you can instead buy a soft flask with a twist nozzle that holds 5 servings of Gu. They also sell large 15 serving pouches which you can use to top up your flask.
I tried this system out and I can say that it solves the sticky pockets and dose problems very well, but the other problems remain and are actually worse since Gu doesn’t sell 15 serving pouches for all their flavors.
Instead of buying the 15 serving pouches, we can instead make our own goop to go in the soft flask pretty easily. First, we should understand a bit of theory about what we are making.
The theory behind these gels is simple: during endurance cardio, your cells need glucose to produce energy and do work. This glucose first comes from your blood, but as you use up that small reserve, your body starts breaking down glycogen stored in muscle and liver tissue to create more glucose.
If your endurance exercise is long and high-intensity enough, you’ll eventually burn through most of your stored glycogen and “hit the wall.” It’s worth noting that your body is far from out of energy in this state, this is because your body has immense reserves of energy stored as fat. This energy in fat can’t be converted to useful energy at the same rate as glucose though, so you can think of glycogen depletion as a power limited state. The time to reach glycogen depletion depends on several factors, including metabolic efficiency, which can be trained over time. Well-trained athletes can sustain higher power output while mostly burning fat, allowing them to go faster and further without hitting the wall, but eventually everyone hits their limit. The obvious solution to this problem is to continuously consume simple carbs during a workout. This is all that Gu is. Carbs that extend the time taken to deplete glycogen.
For more in-depth information on the metabolism of performance, I highly recommend Training for the Uphill Athlete.
The primary carbohydrate used for energy is glucose but rather than use glucose directly, we will instead use the glucose polymer Maltodextrin. Maltodextrin is rapidly converted to glucose in the body. There are two reasons for this choice:
Maltodextrin alone won’t get us a good product though because most people can’t absorb more than about 60g/hr of glucose. This limit is caused by the intenstinal uptake process being limited and so trying to consume more than this leads to sugar accumulation in the gut and discomfort. We can get around this problem by introducing another sugar: Fructose.
Fructose is another monosaccharide like glucose, but glucose and fructose are absorbed by different transport proteins in the intestine. If you consume pure glucose, you can saturate your glucose transport process while your fructose transport process is completely idle. By adding some fructose to our gel, we can use both pathways to surpass the 60g/hr limit. Even if we aren’t getting close to the 60g/hr limit, we can still reduce the chances of gut distress due to unabsorbed sugars.
Many commercial products use a 2:1 ratio of glucose to fructose, so we will do the same. The optimal ratio seems to depend on individual preference and training. Some super hardcore athletes who have “trained their gut” can tolerate higher fructose ratios and seem to benefit from more uptake. I think casual athletes are probably served well by the classic 2:1 ratio. One of the benefits of a DIY gel is that this ratio can easily be tweaked.
Since it’s challenging to swallow spoonfuls of powder, especially while cycling, running, or skiing, we will combine our carbs with water to make a gel. If you go ahead and make a gel with just glucose, fructose, and water, you’ll run into a few problems though:
To solve the crystallization problem, a little sodium alginate does the trick well. This is a thickening/gelling agent and a little bit of it seems to prevent crystals from forming very effectively. Similar ingredients are used in ice cream manufacture to prevent ice crystals from forming and although the problem is different, this solution works well.
For sodium content, I used sodium citrate. The Bro Science™ is that the citrate salt is less upsetting to the stomach than the chloride because of an osmolarity argument similar to glucose vs. maltodextrin. Gu seems to buy into this and also uses sodium citrate rather than sodium chloride in their gels.
For flavor, I went with simple orange citrus since it’s easy to get right. All you need is citric acid and some essential oil. I guessed at the quantities for these ingredients by trial and error comparison to the orange Gu flavor.
Weigh out your maltodextrin and fructose and add them with water in a blender. Blend until fully combined then add remaining ingredients and blend again. You’ll get a nice smooth mixture you can pour into your soft flask. This recipe makes just enough gel to fill a single 150ml soft flask.
Our total batch is 6 servings at 43.7g/serving. Each serving contains:
At time of writing, you can buy all the ingredients on amazon at these approximate prices:
That brings our cost per kcal to $0.0062 or $0.62 for a 100kcal serving, quite a bit cheaper than Gu. Not bad considering that we have to buy all our ingredients in small retail quantities.