Modified carbohydrates: Wave of the (sports nutrition) future?


What if we could modify the chemical structure of nutrients to alter their digestion, absorption, and metabolic effects during exercise? Could this enhance performance? These are the questions posed by a recently developed sport supplement containing hydrothermally modified starch.

What is hydrothermally modified starch?

Starches are the primary storage form of carbohydrate in plants. They can be found in potatoes, legumes, fruit, wheat, corn, etc. Interestingly, food scientists have found ways to modify the structure of starches by exposing them to specific amounts of moisture (hydro), heat (thermal), and/or chemicals. These modifications have a range of applications such as improving cooking outcomes, altering food forms/characteristics, and increasing food shelf life. In addition, modification can influence carbohydrate digestion and absorption in ways that may interest endurance athletes.


Should endurance athletes be interested?

Maybe... but with a few caveats.


Despite the interesting process by which starches can be modified, the result (relevant to athletes) is essentially nothing new—carbohydrates that are absorbed at different speeds. In other words, starch modification is another way of influencing the glycemic index of carbohydrate. We discussed the glycemic index in a previous blog as well as a potential role of slow carbs.


The glycemic index is a rating system for the speed and magnitude of the blood glucose response following ingestion. High glycemic index carbohydrates result in rapid and large spikes in blood glucose following ingestion whereas low glycemic index carbohydrates cause a more prolonged/milder increase.


Importantly, glycemic responses influence hormones and metabolism. Specifically, increases in blood glucose result in the release of insulin from the pancreas, which signals skeletal muscle to take up and store glucose. Insulin also has the effect of reducing fat oxidation. Thus, high glycemic index carbohydrates cause large increases in insulin and favor carbohydrate oxidation whereas low glycemic index carbohydrate ingestion reduces the insulin response and increases fat oxidation.


As carbohydrate is our primary fuel during high-intensity endurance exercise, but we store it in relatively small amounts compared to fat, it is logical to hypothesise that the increase in fat burning with low glycemic index carbohydrate may allow us to save our precious carbohydrate until we need it the most (e.g. the end of a race). Moreover, nutritional supplements that enhance fat burning may be of interest to certain athletes focused on physique, weight loss, etc. Whether or not these hypotheses are actually true is questionable, which has been discussed recently


It is likely based on these premises that many have flocked to a newly developed sport supplement containing a hydrothermally modified corn starch with a very low glycemic index. However, an examination of the research suggests that this supplement, much like any other low glycemic index carbohydrate nutritional option, is not all it’s cracked up to be.


.. an examination of the research suggests that hydrothermally modified corn starch, much like any other low glycemic index carbohydrate, is not all it’s cracked up to be.

What does the research say?

We conducted two studies to evaluate the physiological and performance responses with ingestion of this modified starch supplement. In the first, trained male cyclists completed approximately 1.5 hours of intermittent cycling followed by a performance test consisting of 10 maximal 2-3 minute sprints (1). Thirty minutes before exercise, subjects consumed 60 grams of sucrose or modified starch. During exercise, they consumed 60 grams per hour of sucrose or the same amount of modified starch. Additionally, in order to assess whether the slow absorption and consequent prolonged release of carbohydrate into the blood stream with modified starch permitted the intake of less overall carbohydrate while maintaining performance, a third trial was completed in which subjects consumed half as much modified starch during exercise (30 grams per hour).

Our findings aligned with most others investigating low glycemic index carbohydrate and performance. Modified starch substantially reduced the blood glucose response and increased fat oxidation during exercise, but performance was not improved and even declined in the lower dose modified starch trial. Moreover, we observed severe symptoms of gastrointestinal distress with modified starch intake. This is perhaps not surprising considering that slow absorption necessitates carbohydrate sitting in the gut for longer periods of time.


Modified starch substantially reduced the blood glucose response and increased fat oxidation during exercise, but performance was not improved and even declined in the lower dose modified starch trial.

As the results of this study definitively discouraged further use of modified starch during exercise, we designed a second study to assess it solely from a pre-exercise perspective (2). As such a situation is more common in runners, we recruited 10 trained males to run for 1 hour at moderate-high intensity followed by a 5km time trial. Thirty minutes prior to exercise, the runners consumed 75 grams of sucrose, modified starch, or a placebo. Additionally, we sought to determine how exactly modified starch influenced fat oxidation. To do this, we used a technique called microdialysis to measure the rate of fat breakdown in abdominal adipose tissue (belly fat).


... we observed severe symptoms of gastrointestinal distress with modified starch intake.

Again, as with the first study, modified starch reduced blood glucose responses. While this was associated with increased fat oxidation before exercise, modified starch did not alter fuel metabolism or adipose tissue breakdown (lipolysis) during exercise suggesting that whatever changes occurring at rest were effectively overridden during exercise. Also, performance was similar in all conditions.


Modified starch has slower absorption, may cause more GI problems and have no or even a negative effect on performance

Summary and implications

Hydrothermally modified starch supplements may enhance fat oxidation and promote stable blood glucose concentrations during exercise. However, the characteristics that contribute to these perceived benefits, that is slow absorption, may also upset your gut. Moreover, there is no evidence to suggest enhanced performance.


Most importantly, modified starch works in the same fashion as low glycemic index carbohydrates in general. So, if you want to avoid simple carbohydrates that spike your blood glucose, save your money and look for whole food low glycemic alternatives.


References

  1. Baur, DA, Vargas, F de CS, Bach, CW, Garvey, JA, and Ormsbee, MJ. Slow-Absorbing Modified Starch before and during Prolonged Cycling Increases Fat Oxidation and Gastrointestinal Distress without Changing Performance. Nutrients 8: E392, 2016.

  2. Baur, DA, Willingham, BD, Smith, KA, Kisiolek, JN, Morrissey, MC, Saracino, PG, et al. Adipose Lipolysis Unchanged by Preexercise Carbohydrate Regardless of Glycemic Index. Med Sci Sports Exerc 50: 827–836, 2018.

  3. Burdon, CA, Spronk, I, Cheng, HL, and O’Connor, HT. Effect of Glycemic Index of a Pre-exercise Meal on Endurance Exercise Performance: A Systematic Review and Meta-analysis. Sport. Med. 47: 1087–1101, 2017.

  4. Donaldson, CM, Perry, TL, and Rose, MC. Glycemic index and endurance performance. Int J Sport Nutr Exerc Metab 20: 154–65, 2010.

  5. Roberts, MD, Lockwood, C, Dalbo, VJ, Volek, J, and Kerksick, CM. Ingestion of a high-molecular-weight hydrothermally modified waxy maize starch alters metabolic responses to prolonged exercise in trained cyclists. Nutrition 27: 659–65, 2011.