Does it matter which carbohydrates you eat?

Well it looks like not all carbohydrates are created equal. Are you surprised? While doing some research, I came across an abstract titled ” Improved recovery from prolonged exercise following the consumption of low glycemic index carbohydrate meals.” I contacted Professor Clyde Williams and he sent me a copy of the paper.

This paper discusses the results of endurance athletes having greater recovery eating a post-exercise meal consisting of low-glycemic index carbohydrates, than athletes who ate a recovery meal consisting of high-glycemic index carbohydrates. This is a fascinating study and seems to be in line with the philosophies of the Primal Triathlete. I have read the paper and I will give you my analysis.

Let me start by mentioning that the authors of this paper are from Loughborough University (United Kingdom). They are professors in the School of Sport and Exercise Sciences and are with the Sport and Exercise Nutrition Research Group.  This study was conducted to determine if either low-glycemic or high-glycemic carbohydrates improved recovery in endurance athletes.

What is the glycemic index? The glycemic index (GI) is a measure of the effects that carbohydrates have on blood sugar.

  • High-glycemic foods – usually rated at 70 or above on the GI scale are usually highly processed foods such as white bread, Corn Flakes, white potato, and sports/recovery drinks
  • Low-glycemic foods– usually rated at 55 or below on the GI scale and are mostly fruits, vegetables, legumes, and whole grains.

Most triathletes/endurance athletes know that a long training session (longer than 1-hr) or training/competing at a very high intensity will deplete muscle glycogen stores and consuming carbohydrates after training is the best way to restore muscle glycogen.  This paper mentions a previous study that shows that eating high-glycemic foods/drinks during a 24-hr recovery period have shown to better restore muscle glycogen when compared to eating low-glycemic foods.

“It would be reasonable to assume that endurance capacity would be greater during subsequent exercise, however this was not investigated.”

This study consisted of nine active males. In order to participate in the study the males needed to be runners and able to run for at least 1-hr at 70% of their VO2max.  Each of the nine participants did the experiment twice (double blind style), the two experiments were conducted the same, the difference being that during one experiment trial they ate high-glycemic foods and the other trial they ate low-glycemic foods. The two main experiments were separated by at least 7 days. During experiment 1, group A ate high-glycemic foods and group B ate low-glycemic foods and then on experiment 2 the diets of the groups were switched.

The participants recorded their diets two days prior to experiment 1, this was done so that the participants would eat the same meals two days before experiment 2. The analysis of the participants recorded diets was 60% carbs, 25% fat, and 15% protein.  That breakdown is certainly not my cup of tea (too many carbs), but I am guessing that is what most conventional endurance athletes diets would look like.

On the first day of the experiment the participants had to run at 70% of their VO2max for 90 minutes.

“This type of workout has been proven to significantly reduce muscle glycogen stores.”

Thirty minutes after the completion of the 90 minute run, the participants (both group A and B) ate breakfast in the lab, 3 hours later they ate lunch also in the lab. They were then given two snacks and dinner to be consumed at home, one snack was to be consumed between lunch and dinner, the other snack consumed between 8pm – 9pm. They were not allowed to eat anything more and could not eat after 9pm. Just to be clear, the breakfast, lunch, dinner and snacks were all part of a 12 hour recovery eating session.  This recovery diet was composed of at least 8-grams of carbohydrates per kg of body mass. The two groups recovery diets were basically the same as far the macro-nutrient content (all approximates):

  • Total = 36oo kcal
  • 560-grams of carbs (72%)
  • 88-grams of fat (11%)
  • 126-grams of protein (17%)

The main difference in the two diets was the glycemic level of the carbohydrates. To get an idea lets look at the dinner for the two groups:

  • High-glycemic group – 255 gram Baked potato, 410-gram canned spaghetti, 50-grams cheese, 40-gram lettuce, 67-gram Mars candy bar, 170-l Lucozade Original
  • Low-glycemic group – 360-gram chilli beans, 200-gram wheat tortilla, 50-gram cheese, 40-gram lettuce, 260-ml orange juice

The next morning the participants showed up after fasting for around 11-hours (9pm to 8am). The participants were instructed to run to exhaustion at 70% of their VO2max.

“Exhaustion was defined as the time at which the subjects were no longer able to maintain the prescribed running speed.”

The results of the run to exhaustion:

One really interesting finding was that before the run the men on the high-glycemic diet, on both trials, reported feeling hungry prior to the start of the run where as the lower-glycemic index group did not report feeling hungry. I wonder if this has to do with greater blood sugar spikes and crashes associated with high glycemic foods? The results are listed below:

  • Low-glycemic group – average running time, 108.9 +/- 7.5 minutes
  • High-glycemic group – average running time, 96.9 +/- 4.8 minutes

Also the fat oxidation rates were much greater in the low-glycemic group, which means they burned more fat for fuel during the run to exhaustion and this is one of the theories as to why the low-glycemic group was able to run more than 12-minutes longer.

While this study certainty doesn’t answer all our questions it is very interesting to see the effects lower-glycemic foods have on recovery and our ability to use stored fat as energy . It is also very interesting that high-glycemic foods can restore muscle glycogen faster but that does not translate to better performance the next day.

In my opinion, the reason why higher-glycemic foods are a poor choice when eating a recovery meal is mostly based on insulin! One thing to note that during this study, both groups burn both fat and glycogen during the run till exhaustion (2nd day). However the low-glycemic group burn much more fat. I believe this is because higher-glycemic foods put much more stress on your bodies insulin response thus your body goes into a “all hands on deck” state of emergency because if you don’t burn the glucose immediately you can die from too much blood sugar. If you repeatedly stress your insulin response (by eating high-glycemic foods) your body is constantly burning glucose thus teaching your body to burn glucose/glycogen as the preferred fuel instead of fat.

During normal everyday tasks our bodies burn a combination of fat and glucose/glycogen for fuel (just like the participants in the study) however if you are constantly producing insulin your body slowly becomes insulin resistant which means your body releases more insulin, the result being your body only burns glucose/glycogen and you stop burning fat. This is probably why the high-glycemic group felt hungry before the run till exhaustion, they were burning glucose/glycogen while they were sleeping instead of fat.

This is yet another reason to re- teach your body to burn fat by staying away from triathlete’s favorite foods – sports drinks, gels, and bars! I would like to hear what you think.


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