Research Based Interview with Dr. Louise Burke on Athlete Nutrition

burkeProf. Louise M. BurkeGiven your expertise in carbohydrate and fat metabolism, what is your take on the “train low, race high” approach that suggests endurance athletes should train with low carbohydrate availability but replenish their glycogen stores for competition? Should they plan this type of strategy within their training and nutritional programmes or will something like this be achieved “by chance” anyway?

There is good hypothetical and research support for the idea that training with low glycogen stores increases the “strength” of the exercise stimulus —in other words the signalling response to a given exercise load is increased when it is done with low glycogen concentrations, producing a greater increase in the synthesis of many of the proteins associated with adaptation to exercise. We can measure greater increases in markers of the signalling, transcription and translation processes of protein synthesis, as well as an increased abundance of the proteins —especially, enzymes and transporter proteins that are involved in fat and carbohydrate metabolism in the muscle. This has been dubbed “training smarter” —or an attempt to get more “bang” for your training “buck”. Another model of “train low” is to do your workout in an overnight fasted state and without the intake of carbohydrate during the session.

The problem is that apart from a single study, undertaken by previously untrained individuals who trained one leg “low” and the other leg “high” for 10 weeks (the Hansen study), no other researcher has been able to show that the cellular advantage in the muscle turns into an enhanced performance outcome. There are many ways to explain this apparent disconnect between what’s happening to the muscle machinery and how well an athlete can complete an exercise task. An obvious one is our inability to measure small changes in competitive performance that might be useful in the real world of sport. I suspect, however, that the main issue is that the studies have been too crude in their design. Most have compared the difference between Black and White —where 50% or 100% of all training sessions are done with the “train low” model compared to a “train high” control, and in some cases, where the training model consists of repetitions of the same clamped sessions of exercise. This doesn’t represent the real world where athletes undertake complex and periodised training programs, featuring a variety of workouts each of which has different characteristics and goals. This is essentially what the “art” of coaching is all about —it tries to assemble a variety of different types of training to build within the athlete all the different elements that will make them better able to do their sport.

Within an endurance training program, some sessions need to be done with a focus on training as hard as possible to develop the capacity for speed, high power outputs and high exercise intensities. These can’t be supported in the absence of good glycogen stores. Other sessions train body systems to tolerate the metabolic disturbances associated with the high levels of acidity achieved as a by-product of the oxygen independent utilisation of glycogen. Again, these sessions are hard to do effectively when glycogen is depleted. Optimal performance of endurance sports is achieved when carbohydrate availability to both the muscle and the central nervous system is high, so it’s important to include some training sessions under similar conditions and practices that will occur on race day. Apart from learning or fine tuning the behaviours that need to occur during an event, practising the intake of carbohydrate during exercise can train the gut to tolerate and increase its capacity to absorb this carbohydrate. In other words, some of the training that needs to be done to develop a well-rounded endurance athlete needs to involve high carbohydrate strategies. Choosing a study design that suddenly removes 50 or 100% of this type of training isn’t likely to produce a useful outcome. It might help to adapt the athlete in one way, but at the expense of the other characteristics that are important. A fairer study or implementation of “train low” strategies would be to integrate them into some of the sessions which focus on aerobic metabolism and the capacity to oxidise fat as an exercise fuel, but to leave the high intensity sessions intact. This would help to enhance this particular aspect of metabolism, without interfering with other goals.

“Train Low” tactics have been used by athletes for decades, often happening by chance, or by design following the observation that a chance happening produced good results. Many successful athletes do some of their workouts in the morning before breakfast (i.e. fasted), or they do lengthy runs or rides without consuming carbohydrate. Sometimes this is just practical —for example, they are running trails in a forest without feedzones or coffee shops —and sometimes it is deliberate —for example, they might be restricting calories to try to lose body fat. Sometimes, during high volume training loads, workouts are scheduled back to back in the day leaving insufficient time for effective refuelling for the second session. The athlete might have learned that this schedule leads to a good training outcome without realising that part of the effect is gained from the low glycogen training. Furthermore, they may have learned via trial and error that it is best to devote the first session to a high intensity or quality workout, while the second session needs to be more of a “recovery” or lower intensity training bout. Now we understand more about the mechanism of action however, we can make sure this happens more deliberately rather than by trial and error. It’s good to avoid making errors when you can!

The bottom line is that it can be useful to design a program to include some workouts of “low glycogen” training or training in a fasted state. The best time to focus on these strategies would be during baseline training or a return from injury where the focus is on regaining conditioning and enhancing aerobic and “fat burning” characteristics. As you change to a focus on higher quality training closer to the competition season, you would reduce the emphasis or frequency of such sessions. In any case, I would coincide “train low” strategies with sessions based on lower-moderate intensity work. There are many different ways to achieve this that appeal to different sports or individual athletes: 1. Do a long slow session first thing in the morning on water only. 2. Do a high quality workout well-fuelled after breakfast, then follow up with a protein-rich low carbohydrate snack/meal and a moderate intensity “recovery” session a couple of hours later 3. “Mix and match” a little —for example, to start a session fasted, then consume carbohydrate later in the session before doing some tempo work. All these examples would ensure that “train low” strategies don’t interfere with the quality of the total program. They would also be balanced by other workouts done with better fuelling strategies and a focus on training at high intensity or with good skill and technique. The use of specific “train low” strategies should be adapted to the athlete’s experience —it may work for some but not for others.

What are your thoughts on high fat, low carbohydrate diets for highly trained athletes? Could these induce an adaptive ketosis?

We started some serious research on this idea about 20 years ago based on the idea that even the best trained athletes could further adapt their “fat burning” capacities by eating a low-carbohydrate, high-fat diet while continuing to train hard. We and other research groups found that the muscle could adapt to this in as little as 5 days, and the changes included increased levels of fat transporter proteins that help to ferry fatty acids to the site where they are oxidised in the muscle (the mitochondria) as well as increased amounts of fats stored inside the muscle, ready to be mobilised as an exercise fuel. Our interest was never to make the athlete rely solely on fats and restrict carbohydrate through. I don’t see the sense in this —fat is less efficient as a muscle fuel in terms of the amount of ATP it produces per volume of oxygen consumed. Furthermore, carbohydrate can be metabolised with oxygen independent pathways to produce higher rates of ATP turnover —i.e. to fuel exercise of higher intensity/power outputs/speeds. So unless you are happy to be an athlete who can just do lots of lower intensity exercise for long periods, you want to be as “metabolically flexible” as possible. That means you want to have all fuel systems working as efficiently as possible and to be able to quickly switch your emphasis on different fuel systems.

Our idea was to program a special strategy in the week before an endurance or ultra-endurance race —a short-term period of “fat adaptation” followed by a switch back to carbohydrate fuelling strategies, so that the athlete would be at the starting line with good carbohydrate stores plus an ability to burn them more slowly because they can utilise more fat at sub-maximal intensities. Seemed like the best of both worlds for an endurance athlete! We wanted to keep the fat adaptation period as short as possible, because you feel awful trying to exercise with depleted glycogen stores and it interferes with training quality. We weren’t sure how long the adaptation to being a better fat burner would last once you switched back to having more carbohydrate in the system. Perhaps a day or two —in fact, maybe you adapt and de-adapt in the same sort of time frame. Over a series of studies we refined the program to 5 days of high-fat low-carbohydrate eating while still training with some high intensity sessions, followed by 1 day of rest and a carbohydrate loading diet, and the usual race day strategies of a pre-event carbohydrate-rich meal and plenty of carbohydrate during the race. We found clear proof that this protocol led to an increased capacity to burn fat, despite plenty of glycogen and good fuel support from blood glucose supplies. It was intriguing!

The problem was that this “glycogen sparing” didn’t appear to improve performance —and we tried it many times over exercise protocols lasting from 2 hours to 5 hours. Finally, the results from two studies explained what was going on. The first study came from our collaboration with Trent Stellingwerff and Lawrence Spriet in Canada. They looked at some of the muscle we collected from our fat-adapted athletes and found that although we had up-regulated fat burning, we had interfered with carbohydrate utilisation at the same time. The activity of a key enzyme that helps the muscle shepherd carbohydrate into fuel pathways was reduced. The bottom line was that we hadn’t “spared” muscle glycogen use, but rather, we had “impaired” it. The second study, from Lize Havemann and Tim Noakes Lab in South Africa showed more clearly why this was important. They examined the ability of cyclists to do a 100 km time trial after the fat adaptation/carbohydrate restoration program —a protocol that was more similar to real life performance than what we had been examining in our studies. Overall the differences in 100 km race time between the two different dietary preparations were not statistically significant (although the high carbohydrate trial was actually several minutes faster than the fat-adapted/carbohydrate-restored trial). But during the 100 km, the cyclists were asked to do some sprints —over 1 km and 4 km distances. When intensity was increased, the fat adapted cyclists performed worse. In fact, their times and power outputs for the 1 km sprints were significantly impaired. This showed clearly that lower intensity exercise is preserved in the fat adapted athlete, but “when the going gets tough” and the muscle needs to burn carbohydrate to support higher exercise intensity, the impairment of carbohydrate metabolism interferes with performance. At that point, we stopped being interested in our fat adaptation protocol, because with all the events we work with, athletes need to have “a top gear” or an ability to surge up a hill or sprint to the line. Even if the majority of the event is done at submaximal intensities, the race defining moments need carbohydrate systems fully tuned to produce power. On that basis, I couldn’t recommend adaptation to high fat diets being of use for sports performance for competitive athletes.

Some endurance athletes are known to use an “intermittent fasting” approach to reduce their body fat levels. Is there a rationale for such behaviour?

I am always suspicious when new dietary crazes hit. Are we all talking about the same thing when we use the words “intermittent fasting”? I have heard this term used to describe a whole bunch of different practices —ranging from repeated patterns of 24 hours of eating followed by 24 hours of no intake, to a “warrior” diet in which all food intake is done within a 1-2 hour period each day, and finally the 5:2 diet made popular by a best-selling book. This version proposes that people have two non-consecutive days each week in which they restrict their intake to only 500 calories per day, then they consume their normal food intake on the other days.

I spent some hours reading website blogs and comment forums about this book over the past week. This is the really interesting part, because you learn about what people are actually doing. There are lots of testimonials about the masses of weight and body fat people are losing, but I can promise you that individuals describe lots of different things and give each other totally different advice under the guise of ‘intermittent fasting”. I laughed at one entry on a forum in which someone said “This diet is fantastic. I am losing so much weight. Next week I am going to buy the book and read it”. Other individuals say things like “This diet is so great because I can pig out on as much as I like for 5 days as long as I go super restrictive on 2 other days”. I doubt that will work in the long run.

I think there are two separate issues of importance. The first point is that any food plan that gets someone to reduce their energy intake will produce weight loss. When you get to be as old as I am, you get to see a million dietary crazes that essentially trick people into doing that —from Israeli army diets (where you can eat as much as you like but restrict yourself to apples one day, cheese another, chicken on another day etc etc) to Low carbohydrate diets (stop eating anything containing carbohydrates) to low fat diets (stop eating anything high in fat) to cabbage soup diets (eat as much cabbage soup as you can). These diets “work” while total energy intake is less than it used to be. Whether this is sustained in the long term is the bigger issue. One problem occurs when people start to “cheat” as they get bored or find ways to get around the original rules of the diet. The food industry is good at helping to sabotage popular diets. I remember that the Atkins diet craze lasted a longer time the first time round, because in the original version, once you cut out all the foods in your diet that contained carbohydrate, all you were left with was meat, bacon, cheese and salad. Twenty years later when the book was relaunched to a new population, the supermarket shelves were full of Atkins beer, Atkins chocolates, Atkins donuts and Atkins icecream —calorie-containing foods that had been specially manufactured with artificial ingredients to replace starch and sugars. Obviously this gave people more opportunity to consume calories, just like all the jumbo sized low-fat muffins and 99% fat free confectionery items could be eaten on low fat diets. Bottom line, is that these diets became less effective and even caused weight gain in people who worked out ways to continue to eat too much with another different set of foods. I think that people who get good at scoffing thousands of calories in a couple of hours a day, or on 5 days of the week, will be able to overcompensate for the energy restriction they manage on two days or 21 hours of the day. But until that occurs, they will lose weight. There’s an interesting lesson to learn from Ramadan fasting – most studies don’t report weight loss in observant Muslims over this time , even though they refrain from all food or fluid intake for the prolonged daylight hours for a whole month. That’s because the culture that surrounds this fasting allows feasting at night.

The second point to consider is whether totally or severely restricting energy intake for many hours in a day, or several days in a week has any different metabolic outcomes in comparison to more evenly restricting energy intake from day to day. In other words, if you are going to eat 14000 Calories in a week (I am just using round numbers here), is it different if you eat 2000 a day compared to eating a pattern of 500, 2500, 2500, 500, 2500, 2000, 2500 Calories? The argument is that our caveman ancestors only ate sporadically —they feasted when they caught a mammoth and fasted until the next one was caught. Therefore we are allegedly evolved to handle this kind of irregular intake.

I don’t really know if there is good evidence to support metabolic advantages of this hypothesis. I also don’t know whether it fits our more regimented lifestyles either —cavemen didn’t work regular jobs or undertake regular training programs. Whether athletes will sacrifice their training quality if they expend large amounts of energy on the days they are fasting/restricting needs to be considered, although it is possible for the fasting program to be periodised so that the “meagre” days involve low intensity or low volume training. It is interesting to consider that the “female athlete triad” (which also occurs in males) is now thought to occur as a result of big mismatches between energy intake and the energy expenditure devoted to training. This “low energy availability” has been shown to impact bone metabolism and other metabolic function in a matter of days. Would intermittent fasting push athletes towards these types of negative outcome? Dan Benardot, an American sports dietitian, has been interested in looking at the body composition of athletes who “backend” their eating —i.e. skip breakfast and lunch or eat sparingly over the day, then pig out at night. He has published a couple of studies that show that athletes who have the greatest mismatches between the hours of the day in which they eat and the hours of the day in which they train, have higher body fat levels than athletes who spread their food intake more evenly around their training. All in all, it’s a fascinating area that we lack data to discuss definitively.

The bottom line, is that I am not convinced that there is anything particularly special about intermittent fasting, but it might provide a mechanism for some people to consume fewer calories than they expend. How long this lasts is of importance to long term weight control. But, of course it is not the only solution to achieve this goal. There are no “universal” truths in diet or training!

When achieving low body fat is the goal, would you recommend strategies like exercise after an overnight fast, or exercising in the afternoon and skipping dinner before going to bed?

I think I have partially addressed these questions in my last answers, but I will quickly recap. I think both those strategies will enhance the training adaptation to the session just done, if they are correctly executed. The overnight fasted session is an example of “train low”. The exercise followed by skipping dinner is something we are calling “sleep low”, where you restrict the ability of the muscle to refuel after exercise. There is a theory that this could increase the time for which post-exercise adaptation activities of protein synthesis are sustained, so it would make sense to do this after a “quality” or high intensity session where you are giving the muscle a good deal of stimulus/stress. Because you are well fuelled for that session, the session isn’t interrupted and the theory is that you might get a longer/stronger adaptation period afterwards. You might also benefit from having some post-exercise protein before bed rather than totally skipping the meal, but restrict the carbohydrate. We are actually in the middle of a study to test this theory out, so it should be considered an idea at this stage rather than an evidence-based recommendation. Of course, it means that you aren’t refuelled after the session, so what you do the next morning needs to be a low intensity/recovery session because you will have turned it into another “train low” session. So, that is all good in terms of training adaptation, if you periodise the tactics into your program periodically and for the right types of workouts.

But will it help with weight loss? Only if it means that you reduce your total Calorie intake. On paper it would appear to, because you have effectively skipped some meals. In real life that works for some athletes. But it doesn’t for others because they overcompensate afterwards. Some people get so hungry after doing these things that they overeat more than they “saved”. Maybe it is hunger driving this, or maybe it is their brain saying “you’ve been really good, so you deserve to splurge” and they overdo it. It is important to look at the total effect of what happens.

Glucose+fructose combinations have been shown to facilitate carbohydrate oxidation in endurance sports. Would this type of carbohydrate combination be advantageous for intermittent sports such as football, basketball or tennis? Is there a difference in carbohydrate oxidation between males and females in these sports?

I think the main advantage of these combinations comes when they are consumed in large amounts —at rates above the 60 g per hour that seems to be the maximal amount of glucose that can be absorbed by the intestine. This becomes useful in events in which glycogen stores are depleted and an additional fuel source can be provided to the muscle in significant amounts. That’s certainly the case in prolonged cycling and ultra-endurance events such as an Ironman race. It might also be the case for marathons run at high intensities. Could it be useful for team or intermittent games? Perhaps for long tennis matches or for the midfielders in football who have high muscle glycogen demands. It might be more so in cases where glycogen stores weren’t adequately filled prior to the match —such as in a tournament situation in grand slam tennis where the player has a line up of singles and doubles matches, potentially going to five sets, with short recovery periods between. I can’t see it being useful in basketball, because the fuel demands are less and aren’t likely to threaten glycogen stores as far as I am aware.

Of course this is all theory and it needs to be put into practice. It would be nice to test it out, and to see if players doing such high-intensity intermittent exercise can tolerate the high rates of carbohydrate intake and empty them from the gut. We know that becomes more difficult at higher exercise intensities. Finally, you need to think about whether the sport would provide the practical opportunities to consume such high rates of carbohydrate intake. The continual change of ends in tennis provides access to drinks and sports foods during play. The rules of soccer don’t. Aussie Rules footballers would get opportunities to consume carbohydrate in reasonable amounts at their quarter time breaks and when they interchange continually through the match. There is no evidence or reason to think that males and females won’t equally benefit from these feeding strategies.

Let’s say an endurance athlete has achieved the highest recommended values of carbohydrate ingestion during exercise; would mouth rinsing with a carbohydrate beverage be as effective as it has been shown to be when exercising in a fasted state?

So, we now know that there are different mechanisms by which carbohydrate intake during exercise can enhance performance. It works by making the brain feel happy and ready to work hard, and this is best achieved by frequent intakes that involve contact with the mouth. Actually swallowing the carbohydrate may not be important, since this mechanism seems to be driven by communication between the brain and receptors in the mouth and throat which tell it that carbohydrate is a good thing. This mechanism will be the major way that carbohydrate exerts its benefit in shorter, higher intensity sports of about an hour duration where getting fuel to the muscle isn’t needed because muscle glycogen stores are sufficient. In longer events where additional muscle fuel needs become important, this is where the carbohydrate needs to be swallowed so that it makes it to the muscle. The longer the event, the greater the benefit from having higher rates of carbohydrate intake since it is now providing a substantial contribution to the muscle fuel bill.

Of course, the muscle and the brain are both benefiting by consumption of carbohydrate in these longer events, since the mouth will still talk to the brain, and the carbohydrate which makes it into the bloodstream will both fuel the muscle and keep blood glucose concentrations stable. I think there is probably some benefit to consuming the carbohydrate at frequent opportunities so that the brain gets its regular “pep talk” and there is plenty of opportunity to swallow the total carbohydrate intake that the muscle is looking for. When I work with athletes who do get lots of access to drinking/eating during their event —such as race walkers who have a feedzone every 2 km— it is much easier to hit 60-90 g/hour targets than in sports where the access is limited to every 30 or even 60 minutes. In other words, it is hard to separate the benefits of the two effects (mouth contact and fuel to the muscle) when you feed endurance athletes frequently during their longer events. I think the brain effect still works even when the athlete has had a pre-event meal and is consuming large amounts of carbohydrate during the longer events. The benefit might be smaller in comparison to the effect on the fasted athlete, but don’t forget, that it is added to the better performance that comes from being well fuelled, so the total effect is the best. We showed this in a recent study of shorter term exercise (see Lane et al, Appl Physiol Nutr Metab. 13(2):134-139, 2013). In a ~1 hour cycling time trial that wasn’t glycogen-limited, a carbohydrate mouth rinse improved mean power by 3.4% after an overnight fast (282 vs 273 W), compared to a 1.8% improvement when a pre-event meal was consumed (286 vs 281 W). But note that the best performance of all involved the combination of the pre-event carbohydrate and the mouth rinse.

How important is the timing of protein ingestion to maximize training adaptation?

Timing of protein intake around exercise is important in the sense that the stimulus of exercise must be added to the stimulus and building blocks provided by protein to maximise the synthesis of protein that is responsible for many of the adaptations associated with training. I don’t think we still know what is “optimal”, and there may be more than one way to get maximum results. Most of the work has been done with resistance exercise, and with the feeding of isolate proteins or single protein-rich foods. So, we are already making some assumptions regarding endurance exercise, intermittent high intensity exercise and other exercise modes. Furthermore, we are translating these studies to the consumption of whole foods consumed in mixtures in meals and snacks. The general tactics that appear to be important are to consume protein-rich foods containing a good source of leucine within the ~20-25 g total protein serve – soon after the completion of exercise, at repeated intervals over the day, and perhaps just before bed.

Moving on to the popular topic of nutritional supplements and ergogenic aids, are there any nutrients that function as effective ergogenic aids?

If we consider ergogenic aids to be products that can directly enhance performance when they are consumed around exercise/sport, then water and carbohydrate are two nutrients that have clear support for such effects in a range of exercise scenarios. Other food components that aren’t technically nutrients can also improve sports performance when consumed acutely in relation to an exercise task —for example, caffeine and nitrate. Then there are the food ingredients which need to be consumed chronically to achieve their benefits, and in many cases, are more effectively consumed in supplement form because the normal dietary intake is lower than needed to get an optimal load —these include beta-alanine and creatine.

For recreational athletes, would you recommend covering all nutritional needs with food, or is there a place for nutritional supplements?

My starting point is always food first. Food usually provides the benefit of lower cost, greater safety, better social and eating enjoyment and greater availability. However, there are several situations in which a nutritional supplement might be useful. These include scenarios in which the athlete is unable to eat sufficient food of the appropriate choice to meet their nutrient needs, or requires an intake larger than dietary amounts to overturn a deficiency state. These scenarios should often be supervised by an appropriate medical or nutritional expert. The other scenario is when the athlete needs to consume nutrients at a time or place where everyday food and drink choices are impractical or unavailable. In these situations, which include the time pre/during/post exercise or when travelling, a sports food or formula food might provide a more practical form of nutritional support. Again, expert input can help the athlete to identify when the situation merits the extra expense of these items, and how to use them to best advantage.

When muscle hypertrophy is the goal, would milk be as effective as protein supplements as a recovery drink?

The key post-exercise formula for hypertrophy outcomes is a source of high quality protein providing about 20-25 g of leucine-containing protein. Other nutrients that could be of value in various recovery scenarios include fluid, electrolytes, carbohydrate, and energy. Milk can provide all of these nutrients at a cheaper cost than most protein supplements. Of course, other dairy products shouldn’t be forgotten —greek style yoghurt can also be a great recovery snack

Is there a place for BCAA ingestion during resistance exercise in addition to whey protein to maximize muscle mass gain?

I don’t feel really confident that we know of the ideal feeding strategy for the pre-during-post resistance exercise scenario to maximise muscle gain. And I think there is more than one way to get good results. We know that leucine turns on the protein synthetic machinery, but that amino acid building blocks are needed to maximise the results. Whether trying to design a strategy that provides leucine (a BCAA) followed up by protein is the best way to go is unclear. There might be some theoretical advantages, and some studies that suggest this is useful. However, there are other studies that show benefits from ingesting certain food-based proteins (especially dairy based) that seem to be more than just the sum of their individual components. There may be dangers in trying to be too clever in that we miss the forest for the trees. There are too many other issues that need to be factored into any scenario to think that one simple solution will address it all. And of course, our research knowledge is mainly limited to studies that measure the acute response of muscle protein synthesis rates to an exercise bout and some sort of dietary intervention. That’s all good, but the bottom line requires a study of several months of following this strategy to measure the real outcomes that we are interested in.

About the author:

Original Source:


Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s