The Lowdown on Low Carbs
10/11/04 04:00 PM
Loc: Seattle, WA
The Lowdown on Low Carbs
In America recently, the new road to weight loss has been paved with high-protein, low-carb diets. In the past few years, an estimated 32 million carb-conscious Americans began taking cues from the well-known Atkins and South Beach diets, which forbid or severely limit eating bread, pasta, potatoes and other starches. These diets also blacklist refined flours, so out go the sugary sweets—cookies, donuts, cakes or candies. One effect of this anti-carb quest is that Americans now spend some $2.5 billion a year on low-carb products in hopes of shrinking their waistlines but keeping their food choices ample. As the food industry stocks hundreds of new, low "net" carb items onto supermarket shelves, some of the beleaguered heavy-carb industries—for instance orange and potato growers—have attempted to re-position their products as healthy "smart carbs."
But are low-carb diets really good for us?
Ironically, the study often credited with helping kick start the low-carb craze—published by Duke University in 20021—enrolled just 51 patients for a diet that lasted six-months. That's not a very long time for something that could potentially affect the rest of your life.
"Nobody knows the long-term effects, since it hasn't been carefully studied," says Eric J. Topol, M.D, chairman, Cleveland Clinic department of cardiovascular medicine. "It's all about total calories and good versus bad carbohydrates. So you're taking a risk if you, and your diet, don't take these points into account."
New studies, however, are being launched that will examine the low-carb diet's long-term effect on weight, arteries, cholesterol, body composition, bones and kidneys. But for now, the verdict is still out. There are, however, some things we do know.
"Long-term scientific evidence has proved that foods like fatty cuts of meat, cheese, cream, and butter—allowable foods on the Atkins diet—are all high in saturated fat and cholesterol," says Melissa Stevens Ohlson, M.S., R.D., L.D., nutrition program coordinator in preventive cardiology and rehabilitation. "These are the same foods associated with increases in blood cholesterol and risk for heart disease."
In addition, foods high in saturated fat have a direct impact on the flow of blood in arteries. Studies conducted on high-fat versus low-fat meals have shown that the arterial wall is narrowed after a high-fat meal, restricting the flow of blood. If you already have some narrowing of the arteries, this means further constriction of the arteries that could increase the risk of having a heart attack or stroke.
"Conversely, the foods that low-carbohydrate diets discourage are precisely the foods that have been shown to protect the body from heart disease—a variety of fruits, vegetables, legumes [dried beans, lentils, split peas] and unrefined whole grains," says Ohlson. These foods provide the body with vitamins, minerals and phytonutrients that are essential to good health.
Ketones may be key
In high-protein diets, the body's normal fuel for energy—carbohydrates—are in severe short supply, so it compensates by burning fat. But this inefficient means of providing the body with an alternative source of energy also produces toxic byproducts known as ketones, in a process called ketosis. Some ketones leave the body via the lungs, while others must be excreted by the kidneys, a process that not only can overwork the organs, but also one that requires lots of water.
"Most of the weight loss in the first two weeks of a low-carb diet is from fluid loss," says Sethu Reddy, M.D., chairman, Cleveland Clinic department of endocrinology, diabetes and metabolism. "This can cause problems like dehydration."
But along with the ketones, the kidney may also excrete beneficial electrolytes, such as calcium, magnesium and potassium. "During ketosis," says Dr. Reddy, "the kidneys excrete potassium, and the potassium level in the blood can drop to a dangerous level. This has the potential to lead to muscle fatigue and heart arrhythmias."
Other experts question whether the excess protein in low-carb diets might leach calcium from bones, weakening them. The salt and water depletion that occurs during ketosis may cause hypotension (low blood pressure), fatigue, fainting, constipation and kidney stones. Some experts fear ketosis may impair metabolism of insulin and liver function. And most important, the impact that ketosis may have on people who have diabetes, high cholesterol or high blood pressure has yet to be determined.
Finally, consider this: most dieters go off a diet at some point—that's human nature. And when the weight returns, they jump back on the dieting bandwagon, returning again and again to the "induction" or the extreme, limited-eating phase of the diet. "Repeated return to the induction phase makes for yo-yo dieting," says Dr. Reddy. "The body's metabolism shifts to become more efficient and conservative— leading to fat gain."
1. Westman EC, Yancy WS, Edman JS, Tomlin KF, Perkins CE. Effect of 6-month adherence to a very low carbohydrate diet program. Am J Med 2002;113(1):30-6.
Source: Cleveland Clinic Magazine 2004
http://www.clevelandclinic.org/ (site is in frames, so you have to do a site search for this specific article)
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