NYTIMES article about nutrition
go here for whole article
June 5, 2008
Personal Best
Real Thought for Food for Long Workouts
By GINA KOLATA
DR. MARK TARNOPOLSKY, a muscle physiology researcher at McMaster University in Canada and a physician, knows all about the exhortations by supplement makers and many nutritionists on what to eat and when to eat it for optimal performance.
The idea is that you are supposed to consume carbohydrates and proteins in a magical four-to-one ratio during endurance events like a long run or bike ride, and right after. The belief is that such nutritional diligence will improve your performance and speed your recovery.
Dr. Tarnopolsky, a 45-year-old trail runner and adventure racer, might be expected to seize upon the nutritional advice. (He won the Ontario trail running series in 2004, 2005 and 2006.)
So might his colleague, Stuart Phillips, a 41-year-old associate professor of kinesiology at McMaster who played rugby for Canada’s national team and now plays it for fun. He also runs, lifts weights and studies nutrition and performance.
In fact, neither researcher regularly uses energy drinks or energy bars. They just drink water, and eat real food. Dr. Tarnopolsky drinks fruit juice; Dr. Phillips eats fruit. And neither one feels a need to ingest a special combination of protein and carbohydrates within a short window of time, a few hours after exercising.
There are grains of truth to the nutrition advice, they and other experts say. But, as so often happens in sports, those grains of truth have been expanded into dictums and have formed the basis for an entire industry in “recovery” products.
They line the shelves of specialty sports stores and supermarkets with names like Accelerade drink, Endurox R4 powder, PowerBar Recovery bar.
“It does seem to me that as a group, athletes are particularly gullible,” said Michael Rennie, a physiologist at the University of Nottingham in England who studies muscle metabolism.
The idea that what you eat and when you eat it will make a big difference in your performance and recovery “is wishful thinking,” said Dr. Rennie, a 61-year-old who was a competitive swimmer and also used to play water polo and rugby.
Here is what is known about proteins, carbohydrates and performance.
During exercise, muscles stop the biochemical reactions used to maintain themselves such as replacing and resynthesizing the proteins needed for day to day activities. It’s not that exercise is damaging your muscles; it’s that they halt the maintenance process until exercise is over.
To do this maintenance, muscles must make protein, and to do so they need to absorb amino acids, the constituent parts of proteins, from the blood. Just after exercise, perhaps for a period no longer than a couple of hours, the protein-building processes of muscle cells are especially receptive to amino acids. That means that if you consume protein, your muscles will use it to quickly replenish proteins that were not made during exercise.
But muscles don’t need much protein, researchers say. Twenty grams is as much as a 176-pound man’s muscles can take. Women, who are smaller and have smaller muscles even compared to their body sizes, need less.
Dr. Rennie said that 10 to 15 grams of protein is probably adequate for any adult. And you don’t need a special drink or energy bar to get it. One egg has 6 grams of protein. Two ounces of chicken has more than 12 grams.
Muscles also need to replenish glycogen, their fuel supply, after a long exercise session — two hours of running, for example. For that they need carbohydrates. Muscle cells are especially efficient in absorbing carbohydrates from the blood just after exercise.
Once again, muscles don’t need much; about one gram of carbohydrate per kilogram of body weight is plenty, Dr. Tarnopolsky said. He weighs 70 kilograms, or 154 pounds, which means he would need 70 grams of carbohydrates, or say, 27 ounces of fruit juice, he said.
Asker Jeukendrup, a 38-year-old 14-time Ironman-distance finisher who is an exercise physiologist and nutritionist at the University of Birmingham in England said the fastest glycogen replacement takes place in the four hours after exercise. Even so, most athletes need not worry.
“Most athletes will have at least 24 hours to recover,” Dr. Jeukendrup said. “We really are talking about a group of extremely elite sports people who train twice a day.” For them, he said, it can be necessary to rapidly replenish muscle glycogen.
The American College of Sports Medicine, in a position paper written by leading experts, reported that athletes who take a day or two to rest or do less-intense workouts between vigorous sessions can pretty much ignore the carbohydrate-timing advice.
The group wrote that for these athletes, “when sufficient carbohydrate is provided over a 24-hour period, the timing of intake does not appear to affect the amount of glycogen stored.”
For protein, it is not clear what the window is. Some studies concluded it was less than two hours, others said three hours, and some failed to find a window at all.
Dr. Rennie and his colleagues, writing in Annual Reviews of Physiology, concluded that “a possible ‘golden period’ ” for getting amino acids into muscles “remains a speculative, no matter how attractive, the concept.”
Although studies by Dr. Jeukendrup and several others have shown that consuming protein after exercise speeds up muscle protein synthesis, no one has shown that that translates into improved performance. The reason, Dr. Jeukendrup said, is that effects on performance, if they occur, won’t happen immediately. They can take 6 to 10 weeks of training. That makes it very hard to design and carry out studies to see if athletes really do improve if they consume protein after they exercise.
“You’d have to control everything, what they do, how they train, and also their carbohydrate and protein intake,” Dr. Jeukendrup said. “Those studies become almost impossible to do.”
As for the special four-to-one ratio of carbohydrates to protein, that, too, is not well established, researchers said. The idea was that you need both carbohydrates and protein consumed together because carbohydrates not only help muscles restore their glycogen but they also elicit the release of insulin. Insulin, the theory goes, helps muscles absorb amino acids.
Insulin may stimulate muscle protein synthesis in young rodents and in human cells grown in petri dishes, Dr. Rennie said. But studies in people have shown convincingly that insulin is not required for protein synthesis in adult human beings; it is amino acids that drive protein synthesis. As yet no convincing evidence exists that a special carbohydrate-to-protein ratio makes a noticeable difference in muscle protein maintenance after exercise. “There is no magic ratio,” Dr. Jeukendrup said.
The American College of Sports Medicine is equally skeptical. “Adding protein does not appreciably enhance glycogen repletion,” its paper states.
“Some studies suggested that adding proteins to carbohydrates during exercise can enhance performance,” Dr. Tarnopolsky said. “Many other studies suggested it didn’t do any good.”
Even if there are effects of protein and carbohydrates, they are not important to most exercisers, these researchers say. Serious triathletes and elite runners, who work out in the morning and at night, need to eat between training sessions. But people who are running a few miles a few days a week don’t need to worry about replenishing their muscles, Dr. Phillips said.
Dr. Rennie agreed. “If you are a superathlete, hundredths of a second matter,” he said. “But most Joes and Janes are just kidding themselves,” he said.
Some, like Dr. Jeukendrup, say they use a commercial protein-energy drink after training hard, for convenience.
