Eating to beat the bonk



Triathletes like to call it "bonking." Marathoners call it "hitting the wall." But technically it means the glycogen stores in your muscles are bankrupt and your body is running on fumes or not running at all. "When your immediate energy sources are gone, your body has to start breaking down fat reserves for fuel, which is a slow process. At this point exhaustion sets in and you can't go on much longer," says Dr. Sally Harris, a sports medicine specialist and pediatrician in the Department of Sports Medicine at the Palo Alto Medical Clinic and team physician for Stanford's women's basketball, crew, softball and gymnastics teams.

So what is glycogen and how do you get enough of it to postpone the bonk?

Glycogen is the way carbohydrates are stored in the muscles, and it's the reason athletes start "carbo loading" several days before an event: to build up their inventory of this clean-burning fuel.

Carbohydrates--found in breads, cereals, potatoes, yams and, of course, pasta--should be a major part of a healthy diet for anyone, whether you run marathons or not. But for recreational and serious athletes alike the source of their calories can be as important as proper training. It can make the difference between an efficient machine and a sputtering clunker.

The trouble is there is so much conflicting information that many people have given up trying to sort out the fact from the fiction. Yet there is a solid body of evidence out there on what to eat and what to avoid. And whether you're preparing for your first 10K, recovering from the Ironman or getting ready for the ski season, it can aid in your performance and enjoyment.

The recommendations for athletes don't differ that much from a healthy diet for any average Joe, says Harris.

That means about 60 to 70 percent of a person's daily calories should come from carbohydrates, 15 to 25 percent from fat and 10 to 15 percent from protein.

Athletes in some intensive sports, such as weight-lifting or other sports where the muscles are constantly being broken down and need to rebuild, may benefit from some additional protein, but for most people it's unnecessary.

"It's somewhat of a myth that athletes need more protein," Harris said. "If you suddenly increase your training you might also need more protein, but that can be easily met through your diet."

Protein supplements that promise to buff you out like the Michelin Man are "just a lot of hype and a waste of money," she said. "They tend to be low-quality proteins and expensive."

Moreover, the body can't handle mega-doses of protein. "You can't store extra protein, you just pee it out," she said. In addition, "excess protein contributes to dehydration and stresses kidneys."

Lean meats, grains, nuts, beans and dairy products are good sources of protein, Harris said. Even most vegetarians can get enough protein, she said. "The concern with vegetarians is that they may not be getting enough iron," Harris said. If you are a vegetarian, Harris recommends eating an iron-fortified cereal like raisin bran.

Iron, which is found in large quantities in red meat, is a building block for red blood cells that help transport oxygen to the muscle cells, which is an important function in endurance exercise, added Chip Fried, a therapist and nutritionist at the Brauer Medical Clinic in Palo Alto.

Female athletes in particular, Harris said, should also be concerned about not getting enough bone-strengthening calcium. When you're asking a lot from your body, calcium deficiency can often lead to stress fractures and other injuries, she said. She recommends non-fat and low-fat dairy products rather than calcium supplements.

"With all these nutrients you can get it better in the diet than you can from any kind of pill," Harris said, because supplements aren't absorbed by the body as well.

Fats are another area of nutrition where myths and misinformation have congealed. All fats are not equal.

"You want to pay attention to the quality of your fats, not just your overall fat intake," said Laura Brainin-Rodriguez, a nutritionist and registered dietitian who works at Stanford's Cowell Student Health Center and provides nutrition counseling for the university's athletic teams.

Better-quality fats, she said, include monounsaturated fats such as olive, canola and peanut oils, which are associated with a reduced risk of cancer and heart disease.

Fats with Omega-3 fatty acids, she said, have been shown to help our bodies produce anti-inflammatory agents that help with arthritis, asthma and high blood pressure, as well as reducing the risk of heart disease and cancer.

"For athletes, Omega-3s have been shown to improve circulation, which allows more oxygen, water and fuel to go to working muscles, while removing waste products and carbon dioxide."

Omega-3 fats are found high amounts in fatty fish such as salmon, sardines, herring, mackerel and trout, and in smaller amounts in other fish, said Brainin-Rodriguez, who also has a private nutrition consultation practice.

Vegetarians can get the same fats from flaxseed oil or flaxseed, she said, which has been shown to have "very potent anti-carcinogenic properties." Flaxseed is a staple in Scandinavia, she said, and Americans can expect to see it a lot more added to cereals and breads.

Fats to avoid are hydrogenated fats, she said. This includes any food with vegetable shortening or margarine or with ingredients identified on the label as "partially hard" or "partially hydrogenated."

"Hydrogenated fats are the result of adding hydrogen to artificially saturate fat. It produces a class of fats called trans-fatty acids and there is increasing evidence that they are associated with an increased risk of cancer and heart disease," she said.

"It is everywhere. Our fast foods are fried with these fats. The reason for using it is it helps preserve food and it allows you to take a product like corn oil and use it like butter, but it's much cheaper to produce."

Buyer beware, she said: Hydrogenated fats are even in foods that claim to be cholesterol-free.

There are many new products on the market specifically advertised as athletic foods--some good, some pure hype, Harris said. For instance, sports drinks like Gatorade are beneficial only if someone is participating in events longer than 90 minutes in duration, otherwise they provide no advantage beyond water, she said.

Sports drinks are essentially diluted fruit juice containing about 6 to 8 percent carbohydrates, whereas fruit juice contains 12 to 15 percent carbohydrates, she said. The advantage of sports drinks, or diluted fruit juice, is that it empties from the stomach faster, allowing faster absorption into the bloodstream.

Athletic bars, such as the PowerBar, have also exploded onto the market in the last few years. Harris said they're generally nutritionally sound--low in fat and sugar and high in carbohydrates--but "there's no magic in them." Their real benefit is the convenience they provide, allowing you to eat on the run or even stick them, sans wrapper, to your bike frame, as some triathletes are known to do. Of course, it's all part of their effort to beat the bonk.


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