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Are high-protein, low-carb diets good for me?

This is an excerpt from Endurance Sports Nutrition by Suzanne Girard Eberle.

Diets touting more protein (and fat) and less carbohydrate, such as the Atkins diet, continue to die a slow death. Nevertheless, some versions continue to remain popular among fitness buffs and athletes seeking to lose body fat and boost their performance. For instance, proponents of the 40–30–30 plan (40 percent carbohydrate, 30 percent protein, and 30 percent fat) shove carbohydrate aside and claim protein to be the most coveted nutrient for athletes. Carbohydrate
is blamed for everything from unwanted weight to low energy levels. How can this be if glycogen (stored carbohydrate) is the body’s preferred fuel during exercise, especially as you pick up the pace?

Take a closer look at this popular, but not necessarily beneficial diet. The 40–30–30 balance of nutrients supposedly keeps the correct balance between two hormones that the body produces, insulin and glucagon. Advocates reason that limiting the intake of carbohydrate keeps the body from producing too much insulin, while consuming protein boosts glucagon (a hormone that counteracts the effects of insulin) levels. This optimal insulin–glucagon balance supposedly maintains blood sugar levels better, improves endurance by increasing the use of fatty acids for fuel, and reduces body fat by increasing the use of stored fat. Incidentally, all the scientific jargon referred to in these diets about good and bad eicosanoids (hormonelike substances that regulate a variety of body functions) as being the key to all health and disease is unfounded and unproved by any published scientific research.

High-protein diets hinge on the theory that carbohydrate, not excess calories, does the damage. Eating high-carbohydrate foods, such as rice and potatoes, raises insulin levels. High insulin levels cause the body to store excess carbohydrate as fat instead of burning it for energy. The result is a feeling of lethargy and fatigue as the blood sugar level dips (insulin moves glucose out of the bloodstream) and a gain in weight as high insulin levels inhibit the ability of the body to access its fat stores. Eating protein, on the other hand, supposedly increases the level of glucagon, which directs the liver to release glucose, thereby replenishing the body’s blood sugar supply. Lower insulin levels also promote the release of fatty acids from the fat cells of the body for use as energy.

Here is a look at the flip side of high-protein, low-carbohydrate diets. First, those who go too low in carbohydrate will pay the price. We have known since the 1930s that a high-carbohydrate diet enhances endurance during strenuous athletic events. As you’ve read in this chapter, consuming carbohydrate before, and especially during, exercise is crucial for endurance athletes. Eating carbohydrate-rich foods (for instance, an hour before exercise) does raise insulin levels and lower blood sugar levels, but this response is temporary. Most healthy, active people experience no negative effects on performance. Refilling glycogen stores following exercise is also simply smart science. Failing to do so will definitely hinder your ability to recover, and thus train, effectively.

Second, fat is an important source of energy, particularly at rest and during low-intensity exercise, and training promotes its increased use as a fuel source. The limited glycogen (stored carbohydrate) reserves of the body, however, remain the limiting fuel source during endurance exercise, even in marathons and ultraendurance events. In addition, the body shifts to burning carbohydrate, not fatty acids, as the pace increases or as exercise becomes more intense. The brain needs a steady supply of carbohydrate too. Seriously, who performs at their best when experiencing a headache and feeling grumpy and irritable? So, although terribly old-fashioned (and definitely unhip among those trying to sell you the latest “discovery”), carbohydrate is still king.

Remember, human sport physiology hasn’t changed in the last 75 years. It still applies to all endurance athletes, from fast to slow. Furthermore, weightloss or fad diets aimed at average people rarely work for active people, especially those serious about their athletic goals. Remember, you’re eating to work out or train, not sit in a rocking chair. The ability to train smart and consistently leads to being fit. Fitness leads to leanness (a healthy weight that you can maintain without heroics), not the other way around.

Third, losing weight is about expending more calories than you consume. The total amount of calories burned during the day is what counts—not whether you burn fat or carbohydrate. (Otherwise, to lose weight, you could simply sleep more, an activity that burns few total calories, but a high percentage of fat calories.) Your body can pull from its fat stores at any time of day or night to compensate for the calories burned during exercise. Besides, if you consume too many calories from any source—carbohydrate, protein, or fat—your body will store the excess calories as body fat. As for high insulin levels causing people to become overweight, the reverse is more likely to be true. Being overweight drives insulin levels up. People have trouble regulating their blood sugar level and consequently feel hungrier, and thus more likely to overeat. Losing weight through a sound exercise program almost always brings insulin levels back down within the normal range.

By the way, it’s not surprising that people can lose weight quickly on highprotein, low-carbohydrate diets because most provide too few calories for active people. Besides, ketosis (when the body turns to burning fat when insufficient carbohydrate is eaten) promotes water loss and curbs appetite. (Every gram of glycogen is stored with almost three grams of water, so as you deplete your glycogen stores, you lose a great deal of water.) Besides dehydration, ketosis also causes bad breath, light-headedness, dizziness, and fainting and can be dangerous in the long run.

Why do some athletes claim that they feel, and perform, better on a highprotein, low-carbohydrate diet? Obviously, we don’t all have the same nutritional needs, and not everyone is an elite athlete who trains for hours every day. Some active people, especially those who have been on carbohydrate overload (eating, for example, fruit, salad, energy bars, bagels, pasta, and more bagels), may lose weight or perform better on high-protein diets simply because they’re eating a more balanced diet. You’d be amazed at how getting enough high-quality protein, iron, zinc, calcium, and a little more fat can make you feel. Perhaps you’ve been “fat-phobic,” that is, eliminating most protein-rich foods, such as meat and dairy products, because they also contain fat. Adding some protein and fat back to a very low-fat diet means that you may eat less because you feel more satisfied and can resist those urges to plow through a box of fat-free cookies in one sitting.

Keep in mind that deciphering complicated formulas and eating specific percentages of nutrients at every meal and snack most likely have little to do with your feeling healthier and performing better. The key lies in eating a balanced diet that tastes good; mixes carbohydrate, protein, and fat at every meal; and meets your energy needs. Eating plenty of carbohydrate, without going overboard, makes sense. Otherwise, someone should tell some of the world’s fastest runners, the Kenyans, that they’re doing it all wrong by eating a diet high in ugali, a starchy corn-based mash that’s rich in carbohydrate.



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