Low Carbohydrate - Popular Diets: Obesity

Content provided by the Faculty of the Harvard Medical School

Low carbohydrate

Books: Dr. Atkins' New Diet Revolution; The South Beach Diet

First published in the 1970s, Dr. Atkins' Diet Revolution launched the low-carbohydrate diet craze, which enjoyed a resurgence in the late 1990s. The diet is a carnivore's dream, focusing largely on high-protein meats and poultry (along with eggs and full-fat dairy products), while banishing most carbohydrates such as bread, rice, and pasta. One popular permutation of the low-carb diet is the South Beach diet, which also restricts carbohydrates but urges people to avoid saturated and trans fats (found in meat and processed foods) and to favor healthier, unsaturated fats (found in nuts and fish). It also allows more whole grains, fruits, and vegetables, making it a more balanced approach.

Rationale. The low-carb eating strategy is based on the biological fact that eating carbohydrates raises blood sugar levels, which triggers an outpouring of insulin from the pancreas. The theory goes a step further, claiming that high insulin levels produce hunger, so people who eat carbohydrates take in more calories and gain weight. The antidote to carbohydrates is fat, which is more satisfying and filling. So, people on a high-fat diet eat less and lose weight. Low-carbohydrate diets also tend to cause dehydration. To make up for the lack of carbohydrates in the diet, the body mobilizes its own carbohydrate stores from liver and muscle tissue. In the process, the body also mobilizes water, meaning that pounds are shed as urine. The result is rapid weight loss.

Does this theory translate into actual weight loss? Yes and no — it depends on the individual and the time period. Some people lose a substantial amount of weight on a low-carb diet, while others lose little, and some actually gain weight. And for those who lose, the effects typically aren't permanent. After a few months, weight loss tends to slow and reverse, just as happens with most other diet types.

The American Heart Association cautions people against the Atkins diet, because it is too high in saturated fat and protein, which can be hard on the heart, kidneys, and bones. The lack of fruits and vegetables is also worrisome, because these foods tend to lower the risk of stroke, dementia (advanced memory loss), and certain cancers. Most experts believe South Beach and other, less restrictive low-carbohydrate diets offer a more reasonable approach.

Bottom line. Low-carb diets work for some people and not others. There's no evidence that their short-term effects produce better long-term weight loss than other diets. Equally important, we know little about the long-term health effects of high-protein, high-fat, low-carb diets.

Last updated:	June 20, 2007