To eat or not to eat? The impact of food intake in proximity to the start of exercise. A conversation with the medical coordinator of the 70.3 Ironman World Championships, and sports psychology take 2. All that, today on Tri Talk.
Welcome to Tri Talk your podcast source for triathlon tips, training, news and more. New listeners since episode 52 come from New Zealand and Colorado. In New Zealand, I hope you enjoy the Stroke and Stride sprint-distance series that has just kicked off, and in Colorado, where the climate is not as nice as New Zealand this time of the year, I hope you are taking my advise on recovery from the last episode and not doing anything. My goal at Tri Talk is to help you swim, bike, and run faster, to meet your personal triathlon goals. Whether you are an elite or amateur triathlete, we cover sprint distance to Ironman distance. I’m your host, David Warden, and this is Tri Talk episode 53.
This episode was scheduled to be the third and final part of our series on periodization. That series will actually conclude in episode 54 because I will be wrapping up that subject with a conversation with the father of modern periodization, Dr. Tudor Bompa, who has agreed to an interview next week. We are so lucky to able to have the opportunity to hear from this giant in endurance sports, the man who really condensed all the knowledge and brought periodization to athletes all over the world.
Let’s get onto the good stuff! Have you ever found yourself nearing the middle of a workout, and suddenly you just feel flat? Your energy drops, you feel fatigued, and start to count the minutes until the workout is over? Maybe the same workout the previous week, you felt great, full of energy and able to meet the intensities you had planned for the workout. And we’re not talking about a 2-hour workout where it is normal to start to feel fatigue at the end, but a workout where you began to feel crappy just 15-20 minutes in.
While there are many factors that could have created that fatigued state so early in a workout, including sleep and recovery, there is another potential overlooked cause. How soon before your workout you last ate. I’m guessing that many of you are thinking that particular type of fatigue would be caused by eating too far in advance of a workout, and that eating close to the workout would ensure you had enough energy. The following results might surprise you.
Dave Costill, one of the leading sports physiologists, published a study in the Journal of Applied Physiology that looked at the effects of a feeding 45 minutes prior to exercise. This study took 6 trained males, with a VO2max ranging from 53-65, indicating a good level of fitness for all the test subjects. On two separate occasions, the men performed a 90-minute running trial.
On the first run trial, the men took in 75 grams of glucose, or about 300 calories, 45 minutes prior to exercise. What happened in that 45 minutes is what you might have expected to happen. Blood glucose spiked by 38% in that 48 minutes. When I first read this I thought “Sweet! Does this mean if I plan my meals and workout right, I can go into a workout with my blood sugar at its peak? But, just 15 minutes into the workout, the athletes blood glucose dropped by 300% to just a fraction of what it was even before the athletes took in the glucose 45-minutes before exercise. Over the next 60 minutes, the athletes’ blood glucose did begin to climb again, but it never even reached the level it was at prior to the workout. In fact, several of the test subjects couldn’t even finish the 90-minute time trial because they felt exhausted at 75 minutes.
Now, the same group of athletes did the same test over a week later. This time their last meal was several hours prior to the run test. Their blood glucose levels were the same 45 minutes before the trial, and those levels stayed the same until they began to exercise. To compare from the previous week, the blood glucose levels of the athletes in the second week were 40% lower than they were the previous week at the moment they began to exercise. They did not experience the spike in blood glucose that had had the week before. As they began to exercise at the same intensity as the previous week, the subjects blood glucose began to rise steadily through the first 75 minutes by 26%, while the week before with the pre-exercise meal the athletes had had their blood glucose cut in half at 75 minutes.
Your probably thinking that this doesn’t make sense. The athletes who ate 45-minutes before had a decrease in blood glucose after 15 minutes of exercise, and the athletes who did not eat had an increase through the first 75 minutes. How can that be?
The answer is insulin. Just like a diabetic who has to understand the impact of their diet and the timing of their diet, the same thing applies to an athlete. Carbohydrates digested in that 45-minute window, when the body is at rest, stimulates insulin secretion, which causes the muscles to use an enormous amount of glycogen when exercise starts, leading to a dramatic decrease in available blood glucose leading to hypoglycemia and early fatigue.
Now, does this mean that you should not take in glucose or carbs during exercise? Not at all. This same study showed that insulin levels did not increase when the glucose was taken in during exercise, and in fact it steadily increased the glucose in the blood when taken in during exercise.
You might also recall in an earlier episode of Tri Talk, we discussed the impact of taking in food 30 minutes before exercise to your heart rate. I won’t go into detail since we have already covered this, but as a review, taking in a large meal 30 minutes prior to exercise increases the HR by 10 beats. When running at the same speed, the HR is 10 beats higher then when running 3 hours after eating.
It seems on the surface that a worse-case scenario for an athletes would be to take in a large glucose meal 30 minutes prior to exercise. If you use HR to measure your intensity, you could be robbing yourself of 10 full beats of intensity, and then you might start to feel like you are going to crash 15 minutes into the workout.
Now, this does mean that these effects are universal. There are some athletes who genuinely seem to have a high tolerance both at a hormonal and digestive level, and who eat whatever they want, whenever they want, and it seems to have no effect. But if you have the choice, it seems the best thing to do is not try and eliminate eating about an hour before exercise.
This is easier said then done. The reality is that we are triatheltes as well as husbands or wives, parents, and we have to make a living. It is not always possible to plan our meals and eating so perfectly around training. So let offer a couple of alternatives to meticulous meal planning and timing.
First, if you can, eat something during your exercise, even right at the beginning. This also depends on your tolerance for certain foods, but if you are accustomed to grabbing a bagel when you first wake up, and then getting ready for your run, consider eating the bagel over your first half mile.
Second, although not explicit in the study we jut reviewed, it is implied that eating foods with a low glycemic index would not result in the same type of insulin spike that something like glucose would. There are lots of foods, even carbs, that have a much lower impact on blood glucose and insulin levels. These low glycemic index foods include apple sauce, barley, peaches and most nuts. A list of these foods can be found on page 244 of the Triathlete’s Training Bible. Proteins of course have very little effect on insulin. These are the types of foods that you can take in within that 45-minute window that might have less of an effect on your insulin, and therefore blood glucose depletion.
My title for the podcast “To eat or not to eat” is really a misleading title. Of course you have to eat. But it was catchy. The key is to understand the timing of when, and what you eat. So, if you have been feeling curiously fatigued in your workouts, consider this small change to your diet and training regimen.
By the way, as I read this study, at the very bottom it stated that the study was made possible by a grant from the National Dairy Council. I am not joking. This should not in any way erode the legitimacy of this study. In fact, not only did Dave Costill participate, but so did uber-physiologist Edward Coyle. Since milk is actually a low glycemic index food, maybe the National Dairy council wanted to get the word out on drinking more milk before exercise, I don’t know. But, the really odd thing about this is that this is the second time I have mentioned the National Dairy Council on Tri Talk. It’s like they have a conspiracy to infiltrate the world of endurance sports. Weird.
Moving on! I had the chance to cover the 70.3 Ironman Championships in Clearwater, Florida for Triathlete Magazine just last week. Since Triathlete got me there, I felt it was necessary to put all the best stuff from the event into their podcast. But, while I was there, I snuck in one interview for Tri Talk with Dr. PZ Pierce, the medical coordinator for the championships, having provided the medical support for over 30 Ironman events.
What are the most common conditions that lead an athlete into the medical tent at an Ironman? How can they be avoided? Let’s find out with a quick conversation inside an Ironman medical tent.
That was actually my second trip inside an Ironman medical tent, the first time being as a participant, but I’d rather not talk about that. So it turns out that hyponatremia may not be as common as I thought. Also, loss of fluids other than sweat should be considered in your hydration strategies. Techniques and testing that determine hydration based on sweat alone may put you short of your hydration needs at long distance racing.
By the way, is it just me, or does it say something about the state of triathlon when the medical coordinator says that a half Ironman distance is short? Sure doesn’t feel short to me last time I did one.
Moving on! Back in episode 42 I took a stab at sports psychology. I think it went well, but in trying to take in on twice, I felt it was important to bring in an expert for this second attempt. Why should we be interested in sports psychology? What kind of edge will it give us as athletes? My version of sports psychology has always been to mock my athletes when they tell me they’re tired. It turns out it is much more complex than this. To answer these questions, I enlisted the help of a real sports psychologist.
That’s all for this week. Don’t forget to join me next time was we cover part 3 of periodization, with an interview with Tudor Bompa. I anticipate that this will be a don’t-miss episode. See you next time!