As debates heats up about American cyclist David Zabriskie's mostly vegan diet and how this might impact his performance in the Tour de France, Dr Ross Tucker takes a look at the energy demands of the TdF.
The Wall Street Journal ran this piece on American cyclist David Zabriskie who is taking part in the Tour de France on what is mostly a vegan diet. There's the fine print (or the asterisk in the headline) that says that he is 'allowing' himself salmon for its nutritional value, but mostly, he's going with the non-meat options.
The energy demand of the Tour
The Tour is obviously a massive energy challenge - five to six hour days in the mountains are extremely energy costly. Read this post detailing the roughly 6.00kCal per day energy requirements for a cyclist here. And that's just the average - the high mountain stages reach the 8,000 kCal mark.
The challenge for a Tour rider is that they have to replace huge amounts of energy in a relatively short space of time - some is taken in on the ride, then the rest must be squeezed into a relatively narrow window after exercise, before sleep. Strenuous training also has an "anorexic" effect in that it kills the appetite, and so generally, whatever energy deficit is there after cycling must be replaced in a space of maybe five to six hours. That would equate to around 700 kCal per hour.
And so Tour riders are not just great cyclists, they have to be great eaters. A study by Klaas Westerterp looked at Tour de France energy balance and found that the average energy cost of a day in the Tour was 6,100 kCal, and the riders managed to replace about 6,000 kCal per day over the three weeks. In other words, they almost matched energy use.
Over the course of the Tour, a rider will lose some weight and their hormone function does change for the worse over the three weeks of the race (cortisol up, testosterone down, for example). So getting energy balance as close to optimum is of course vital.
The "vegan diet" and energy/nutrient intake
In terms of the Zabriskie "vegan + salmon diet", the question is how did the riders manage to almost on top of their energy use per day? And the first significant point is that cyclists actually ingest huge amounts of energy during cycling. It was found that 49% of the daily energy intake was achieved during the day's stage.
That's almost 3,000 kCal on the bike, and it's achieved with the intake of 94grams of carbohydrates per hour during racing (which made up 70% of the energy intake on a stage, so the riders do eat foods and get energy from fat and, to a lesser extent, proteins).
This means that much less has to be replaced after the stage, but highlights the importance of eating on the ride - if you don't, then you leave a significant 'mountain' to climb after the day's racing.
In the course of a 24-hour day, the energy came from the following sources: 5% from proteins, 62% from carbohydrates and 23% from fat.
For Zabriskie then, or anyone who wants to eliminate meat from the diet, the primary issue is whether it's still possible to get the energy intake right, and also to get the right levels of protein in. There's some evidence that protein ingestion aids recovery, so while it may be small as an overall percentage of energy intake, it may play a vital role in getting through the Tour.
Managing fuel for optimal performance
Now, I don't know enough about Zabriskie's diet to comment on its specifics. Also, I'm wary of going into that area given that I'm not a dietician and shouldn't claim to know specifics anyway. And in all my interaction with any athletes, my interest has been more the practical management of diet for elite performance, not saying "eat X not Y", or "add A, B and C to your diet".
However, I will say this. A vegan diet does present challenges to meeting the energy and nutrient requirements of a Tour, because animal products make protein and fat ingestion easier, and are more energy dense. But, a vegan-like diet does not make them impossible, for three reasons.
First, there are many ways to get nutrients in, it's sometimes a matter of getting creative (which, for a professional athlete on the road, can be very, very difficult).
The second reason is that the evidence from Westerterp suggests that half the energy replacement happens during the day's riding, and is mostly in the form of carbohydrates. That would not affect Zabriskie. So in reality, his challenge is to replace another 3,000 kCal, not the full 6,000 kCal per day.
Awareness and proactive diet management
The third reason that any diet can be effective, in my experience, is that awareness of nutrition is often a crucial factor that enables effective nutrition.
That is, simply being made more aware of diet improves diet in those individuals who want to improve. This is why dieticians are often so interested in educating their clients about their food choices, and why tracking daily food intake helps. There are studies, for example, showing that keeping a food diary assists weight-loss without any other intervention - awareness leads to effectiveness.
And so my interpretation of the success of vegan or vegan-like diets (Zabriskie is one. Scott Jurek, I'm told, is another) is that often, they may be effective because the person going onto the diet is consciously aware that there are some practical limitations that must be overcome, and this awareness, combined with the more methodical approach to diet, helps the athlete eat better than they might have done before.
In other words, a diet that may be sup-optimal in concept can be more effective than an optimal diet, because the athlete is more invested, more aware, more careful.
The diet debate
There's going to be debate about whether a vegan diet is optimal or not. Whether meat is better than vegan. I could play devil's advocate, and bring up the concept of a paleo-diet, for example, which is the very opposite extreme that says that high protein is the way to go, that our bodies "evolved" for that diet and that our reliance on carbohydrates is sub-optimal and unnecessary.
This is even being applied to endurance exercise, and while I don't agree with it for exercise, there are cases and some compelling reasons why it can't be dismissed out of hand. Then there are those who will argue for high carbohydrate. And those who argue for everything in between - the diet world is full of new ideas, fads and revolutions, and the sciences are only really just scratching the surface.
The bottom line is that a Tour de France rider must replace the energy, and the nutrient (both macro and micro) composition of the diet must be carefully managed. I think that a vegan-like diet is possible, but may introduce some challenges.
However, those can be overcome (in the case of Zabriskie, by adding salmon, among other things), and in the end, provided one is sensible and balanced in the diet, performance can be optimised regardless of the global view of diet.
That is, don't argue "vegan" vs "meat", rather take a systematic view of everything in it, and that might reveal that barring the very far extremes (the zero carb diet, for example), the body is good enough to go on a range of different fuels!
Dr Ross Tucker, is Health24’s FitnessDoc and has a Ph.D. in Exercise Physiology from the University of Cape Town and a Post-Graduate degree in Sports Management from the UCT's Faculty of Commerce. He is currently employed at the University of Cape Town and Sports Science Institute of South Africa, and works as a consultant to various sporting teams, including South African Sevens, Canoeing, Rowing and Triathlon SA. He also blogs on www.sportsscientists.com)