Why Do People Follow This Diet?
Some specific low-carb diet programs, such as Atkins, restrict carbohydrate to the point that the body breaks down fats into ketones, which can either be used either as energy or eliminated from the body via the breath or urine. Diets such as the South Beach and the Zone diets are less restrictive, and some, such as Sugar Busters, seek to eliminate only sugars and high-glycemic-index foods that excessively raise blood sugar.
What Do the Advocates Say?
Advocates contend that the high amount of carbohydrates in typical modern diets is unnatural for humans, who evolved for hundreds of thousands of years while eating a low-carbohydrate diet. They say that the current overconsumption of carbohydrates has led to increasing problems with obesity, diabetes, and other health problems. High-carbohydrate diets are presumed to result in higher insulin levels, which may lead to insulin resistance and related metabolic disorders such as high triglycerides, low HDL ("good") cholesterol, and high blood pressure.
Some scientific authorities do recommend that people with the insulin resistance syndrome (IRS) or type 2 diabetes avoid high-carbohydrate diets, and some recommend a diet lower in carbohydrate than current public health guidelines suggest. Researchers have demonstrated that replacing carbohydrate in the diet with either fat or protein lowers blood triglycerides and raises HDL ("good") cholesterol, and a few studies have also reported improved blood sugar control and increased loss of weight and body fat resulting from these dietary changes.
What Do the Critics Say?
Many nutrition experts disagree with the basic premise of low-carbohydrate diets--the notion that high-carbohydrate, low-fat diets cause obesity and other health problems. In one argument, some nutritionists point to the traditional Japanese diet that is very high in carbohydrates, low in protein, and very low in fat, yet is associated with good health and normal weight in people who follow that diet. Rather than attributing obesity and other problems to carbohydrate intake, these critics blame the overconsumption of calories (from any source) and lack of physical activity as the primary causes of these health disorders.
Critics concede that low-carbohydrate dieters often experience significant weight loss during the initial stages of the diet. However, these critics argue that these diets often have a diuretic effect (in other words, they promote water loss) and that the initial weight loss is due to water loss, not fat loss. Recent research suggests that some people may lose more weight over the course of several months on a low-carbohydrate diet than on one that is equal in calories but higher in carbohydrates, but few studies have been done to determine the long-term effects, good or bad, of low-carbohydrate diets.
In addition, many authorities are concerned that a lower-carbohydrate diet may result in higher calorie intake from fat, which could lead to more difficulties with overweight, insulin resistance, high cholesterol levels, and heart disease risk. Studies of low-carbohydrate diets that are also low in calories and promote weight loss often do not support these concerns, but research on the effects of higher calorie versions of these diets is scarce and conflicting. Increased protein intake as a result of avoiding carbohydrates is also a concern for some critics, since some high-protein diets may increase the risk of osteoporosis, kidney stones, and some cancers.
Critics also express concern that the lack of grains, fruits, and vegetables in low-carbohydrate diets may lead to deficiencies of key nutrients, including fiber, vitamin C, folic acid, and several minerals.
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