Carb mixes and benefits
It was revealed that certain carbohydrates are used more quickly than others, yet none surpass 60 g/h. Why is this the case? The reason lies within the limits of absorbing carbohydrates into our muscles. It appears that how much ingested carbohydrate our muscles can utilize is restricted by how much our intestines are able to absorb.
Absorption of carbohydrates
Let's examine absorption more closely. Absorption denotes the transport of a nutrient from the intestinal lumen into circulation within the body (right to left in the image here). For this activity, the nutrient must traverse two cell membranes; while these prevent potential harms brought by foreign substances, they also impede nutrients from entering. In many cases, transporters are needed for passage; these proteins, which are embedded in the membranes, facilitate movement of a nutrient across the barrier.
Glucose is absorbed via a transporter known as sodium-dependent transporter or SGLT1. However, the transport capability of this transporter is limited, as it becomes saturated at a carbohydrate intake of about 1g/min (or 60g/h). This explains why consuming more than around 60 to 70 grams per hour does not result in the oxidation of additional carbohydrates; instead the excess carbohydrates simply build up in the intestine.
To maximize carbohydrate delivery to the muscles, our findings suggest a combination of glucose given at 60 g/h and fructose transported by the GLUT5 transporter.
In 2004, Dr. Roy Jentjens from the University of Birmingham conducted the first study to show that a combination of certain carbohydrates can increase oxidation rates over 1g/min (1.26g/min) by more than 25%, which was higher than what was believed until then(1).
Currently there are two known transporters in the intestines: SGLT1 which transports glucose and galactose, and GLUT5, which carries fructose. Research shows that oxidation of carbohydrates from a sucrose beverage is not as high as the oxidation rates for glucose and fructose (or other multiple-transportable carbs).
The best combination with no sure-fire formula.
Our research focused on the combination of carbohydrates that yielded the greatest rate of oxidation. The studies revealed that multiple carbohydrates produced a 75% higher oxidation rate than single-transporter carbohydrates like SGLT1! Our findings were most favorable for these combinations:
- maltodextrin : fructose
- glucose : fructose
- Glucose has a 1 : 1 : 0.5 ratio to sucrose and fructose.
In every situation, the glucose transporter must be filled up and this will not take place if fewer than 60 g/h is swallowed. Along with that, the supplementary second carbohydrate (fructose) needs to be taken in at rates high enough to contribute to the carbohydrate delivery (30 g/h or more). If these amounts are consumed, it gives a 2:1 ratio of glucose and fructose with an intake of 90 g/h. This is often the recommended proportion. Nevertheless, I would like to emphasize that this is NOT a magical ration. If you can tolerate larger intakes, increasing the amount of fructose might even be beneficial and you will move towards a 1:1 proportion while still consuming 60 g/h of glucose or maltodextrin.
Studies have shown that multiple carbohydrates provide better performance boosts than a drink with one single carbohydrate, as well as improved hydration and less stomach discomfort. Thus, new recommendations incorporate this discovery, noting that there are various carbohydrate needs depending on the type of exercise and the athlete's ability.
Liquid, gel or solids?
From a practical standpoint, getting carbohydrates from beverages, gels (2), and low-fat/low-protein/low-fiber energy bars (3) can provide high oxidation rates. Therefore, you have multiple options to meet your personalized carbohydrate intake needs.
Carb mixes can be beneficial for any exercise duration, but are most effective when lasting more than 2.5 hours. In those cases, up to 90g/h of carbohydrate from multiple transportable sources should be consumed. Glucose or maltodextrin should make up around 60 g/h. The ideal mixture we found with the most success was the 2:1 glucose to fructose ratio. That exactly what is in our Hydro Power Endurance Fuel.
For an in-depth look, readers can consult recent reviews on this topic.
- Jentjens, R. L., et al. (2004). Oxidation of combined ingestion of glucose and fructose during exercise." J Appl Physiol 96(4): 1277-1284.
- Pfeiffer, B., et al. (2010). Oxidation of solid versus liquid CHO sources during exercise." Med Sci Sports Exerc 42(11): 2030-2037.
- Pfeiffer, B., et al. (2010). CHO oxidation from a CHO gel compared with a drink during exercise." Med Sci Sports Exerc 42(11): 2038-2045.
- Currell, K. and A. E. Jeukendrup (2008). Superior endurance performance with ingestion of multiple transportable carbohydrates." Med Sci Sports Exerc 40(2): 275-281.
- Jeukendrup, A. E. (2011). "Nutrition for endurance sports: marathon, triathlon, and road cycling." J Sports Sci 29 Suppl 1: S91-99.
- Jeukendrup, A. (2014). "A step towards personalized sports nutrition: carbohydrate intake during exercise." Sports Med 44 Suppl 1: 25-33.