Carb Loading: Outdated and Dangerous


It has become a familiar scene at athletic events: sugar and carb-fests before and during marathons, triathlons, swimming competitions, and other sports among amateurs and professionals, even high school athletes and grade school soccer players. They do it for energy and enhanced athletic performance, having been told that loading up on carbs is the ticket to winning.

This common practice is based on decades-old flawed studies that reported that athletes experienced reduced performance when deprived of carbohydrates, performance restored upon restoration of carbohydrates. Thus was born the notion of “carb-loading” (i.e., consuming large quantities of grains and sugars prior to exercise to improve performance). That simple observation has since become a universal practice. It means runners have pasta feasts the night prior to a marathon in the United States, South African triathletes eat bananas and drink sugary energy drinks during workouts, and even aerobic-exercising mothers in Sydney, Australia, load up on energy bars prior to putting on their Spandex. It is common to see participants in athletic events gorging on pasta, fruit, desserts, and a mind-boggling variety of “energy” bars and drinks from sponsors. They then deal with the “wall” of low blood sugar that results after high blood sugar, as well as abdominal distress and diarrhea from the osmotic load created by the exceptional intake of sugar. (This is why dozens of Porta Potties are familiar fixtures along the route at these events.)

Contrary to popular perception, athletes are not impervious to all the problems presented by overconsumption of carbohydrates and sugars; they are just as prone to all the problems associated with both grain consumption and carbohydrates, such as provocation of autoimmune diseases, impaired digestion, high blood sugars, and the phenomena of glycation, and they are not necessarily spared the visceral fat–provoking effects, either, though their extreme exercise habits blunt it. (Go to any athletic event and you will see it: Easily a third of athletes, including serious athletes, are overweight.) The phenomenon of glycation alone can be responsible for prematurely deteriorating joints from cartilage glycation and cataracts from lens glycation, among other health problems.

A fundamental mistake was made in the studies that purport to prove that carb-loading is beneficial for athletic performance: If athletes who have relied to a moderate degree on grains, carbohydrates, and sugars are deprived of them, there will indeed be a decrement in performance upon their removal: reduced endurance; slowed running, biking, or swim times; and a premature feeling of fatigue. This is due to reliance on glycogen stored in the liver as a source for glucose sugar for energy. The glycogen supply in the liver is depleted after 40 to 60 minutes of high-intensity physical effort, and then the athlete will experience a marked reduction in energy and performance unless sugars are made available to replenish glycogen, accomplished via ingesting carbs and sugars. This phenomenon has been observed over and over again after depriving athletes of carbs and sugars for up to a week. Here is one such study.

What was not appreciated in these studies is that if carb and sugar deprivation is extended to 4 to 6 weeks, performance is restored and then exceeds that achieved during carb/sugar-consuming days (yes, athletes do better without carb-loading, though the effect is delayed due to peculiarities of human physiology). Here is another study.  This obligatory delay is due to the slowed conversion from glycogen-dependence to an increased capacity to mobilize energy stored in fat. While liver glycogen can provide less than 1 hour of energy for high-intensity exercise and forces the athlete to continually seek more sugars, body fat—even in a slender person with little excess body fat—provides energy for weeks. And the energy derived from body fat stores involves no loading up on energy drinks, energy bars, or pasta. It means just eating healthy and living off the, well, fat. And that’s how humans have done it for millions of years, running for hours without such modern carbohydrate crutches. The capacity for long-distance running is built into human evolution without the need for sugary drinks or energy bars (though hydration and electrolytes are necessary).

It means that someone who expects to run, bike, swim, or engage in other prolonged, intensive physical activity will need to endure an obligatory 4- to 6-week period of reduced performance before things get better again, and often better than before. But it also means that you will no longer be exposing yourself to the destructive health consequences of carb-loading before and during demanding physical exertion, including fewer visits to the delightful Porta Potti.

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Dr. William Davis

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