Study under review: The Ingestion of 39 or 64 g·hr-1 of Carbohydrate is Equally Effective at Improving Endurance Exercise Performance in Cyclists
The ingestion of carbohydrates during exercise has been well established to improve performance. Some of the reasons are seen in Figure 1: it sustains a high rate of carb oxidation (more carbs per minute can be burned), maintains blood glucose levels (it prevents exercise-induced blood-sugar dips), spares muscle glycogen (one of the muscle’s fuel sources), and improves the central nervous system’s response to fatigue. Not surprisingly, carbs and exercise have become like peas and carrots … always together!
While there is little doubt that carb intake will bolster performance during extended exercise, questions remain as to the optimal amount of carbohydrate that should be ingested. Guidelines from the American College of Sports Medicine (ACSM) suggest intakes of 30-60 grams per hour during exercise, although benefits have been seen from as low as 16 grams per hour and as high as 105 grams per hour. Interestingly, carbs may even be of benefit without swallowing them. Simply using a carbohydrate mouth rinse can improve performance in a one-hour time trial! This means that part of the performance boost is mediated by the brain: when the brain thinks there's carbohydrate coming, it lets the muscles work a bit harder.
While a dose-response relationship between performance and carb intake has been observed up to 78 grams per hour, other studies have seen no improvements at 47 grams per hour compared with 27 grams per hour. A number of reasons could explain these differences in the published research: the gender of the participants, their body size, their level of fitness (trained athletes have greater glycogen stores), their sport (e.g. endurance athletes vs. sprinters), their diet (their usual carb intake, notably), their hydration status and fed or fasted state before the test, the type of carbohydrate consumed for the test, the duration of the test, etc. The sample size of the study is also important, as small studies may not have the statistical power to detect small, yet meaningful, differences.
Because optimal carb intake is not yet known for certain, the authors of this new study set out to examine the dose-response effect of an hourly ingestion of zero to 64 grams of carbohydrate during exercise in trained male cyclists.
Ingesting carbs during extended endurance exercise is a well-known way of improving performance. However, the optimal amount is up for debate. Guidelines state that 30-60 grams per hour is effective, but many other studies have found effects at both lower and higher doses. The goal of this study was to see how performance was affected by varying carbohydrate intake during exercise in trained male cyclists.
Other Articles in Issue #10 (August 2015)
Put down the apple and have some chedda
Although both cheese and meat are lumped into the “watch out!” category in hearthealth recommendations, dairy products often show neutral or positive associations with cardiovascular health. But how do cheese-rich diets fare in randomized trials when compared to other diets? This trial tested three diets against each other in a highly controlled fashion: a cheese diet, meat diet, and high-carb diet.
All up in your krill: The story on krill
Oil thus far has been fairly simplistic: it’s better than fish oil and more expensive. But there’s a reason why you can’t draw conclusions based off few studies, and successful results in one condition don’t apply to other conditions. This trial gives some of the first pieces of evidence for possible negative metabolic effects of krill oil.
Omega-3: kid-tested, mom approved?
While heart health gets much of the attention for fish oil benefits (which, incidentally, are often overstated), outcomes in children typically show more promise. This study, involving children and their parents living on the island of Mauritius, explored possible behavioral benefits to fish oil supplementation. And not just the childrens’ behavior, but the parents’ as well!
A thorough trial of carb intake for diabetes
There are few conditions where carbs play as direct of a role as in type 2 diabetes. Yet the recommended carb intake levels for this condition aren’t so different than for the general population. That may change at some point, due to trials like this one, which is more highly controlled and thorough than previous lower-carb & diabetes studies.
- Interview: Elke Nelson PhD
- Interview: Marguerite McDonald, MD
“B” is for breakouts
B vitamins are commonly thought of as harmless, due to being water-soluble. As nutrition junkies know, that view lacks nuance, and B vitamins can indeed be harmful in certain situations. As an example, this elegant series of experiments sheds new light on the mechanism by which vitamin B12 may impact acne formation.
Wellness, Not Weight
By Cristen Harris, PhD
Salt in the wound
Science and mystery often go hand in hand, and this is a perfect example: when you have a skin infection, you tend to have more salt in the infected skin. But why is that? Well, where there’s smoke, there’s fire. The salt is probably doing something in regards to immune response, and it’s possible that how much salt you eat could also play a role. Resist the urge to skip to the end of this mystery -- the buildup is worth it.
Carbs-protein or protein-carbs …
Does food order matter? Grandma always said “You have to eat your vegetables first if you want dessert!”. If you substitute “carbs” in for dessert, grandma might have hit another one out of the park. It’s possible that simply switching the order of what you eat might benefit blood sugar control, which would be a relatively easy way to address the thorny public health issue of type 2 diabetes