Question: My wife is on a diet that isn’t especially radical but it does emphasize protein over carbohydrate. I’m a relatively serious cyclist (2,000 miles per year) and during the cycling season I follow a high-carbohydrate diet. Would switching to my wife’s high-protein diet help or hinder my cycling performance? —Jim B.
Coach Fred Mantheny Replies: High-protein diets are popular—and controversial. Some athletes push the protein, as do many dieters.
Protein advocates suggest a diet of only 40 percent carbohydrate with 30 percent protein and 30 percent fat. However, the overwhelming opinion of researchers, nutritionists, athletes, and coaches is that diets high in protein and/or fat aren’t optimum for athletic performance.
The biggest problem is low carbohydrate levels. If you eat the large amount of protein recommended, there’s little room left in the diet for adequate carbohydrate to sustain endurance activities. You might have to eat so many extra carb calories that you gain unwanted weight.
Carbohydrate is the body’s energy source. It’s converted to glycogen, the muscle fuel that allows you to train and ride hard. Endurance performance is partially limited by the ability to deliver oxygen to the working tissues, but it is also limited by fuel. Even with a great ability to consume oxygen (VO2max), if there’s no glycogen in your muscles, you won’t go fast.
High carbohydrate intake is also important because the body makes glucose from carb. Glucose is the only fuel your brain can use. If levels are low, your body protects the brain by manufacturing glucose from whatever is available—even cannibalizing protein in muscle tissue. you’ll feel lethargic, you’ll ride slowly, and your sweat will smell like ammonia from the byproducts of breaking down your muscle tissue for energy. Don’t go there.
Years of research have shown that eating about 65 percent of your diet as carbohydrate and only 15 to 20 percent each of protein and fat is best for endurance performance as well as for general good health.