This is one of three Journal Notes this week that will cover studies from the Journal of the American Medical Association’s special issue on obesity.
Atkins. The Zone. Protein Power. You’ve heard of low-carbohydrate diets; perhaps you’ve even tried one yourself. Recently, low-carbohydrate diets have surged in popularity.
Dr. Atkins’ New Diet Revolution
has been on the
New York Times
bestseller list for almost six years. And, over the past five years, three books on low-carbohydrate diets have sold millions of copies in the United States.
Low-carbohydrate diets are based on the premise that reducing your carbohydrate intake will lower the amount of insulin your body produces. Because insulin is responsible for making blood sugar available for your cells to burn as fuel, less insulin means your cells must turn to your fat stores as its main source of energy. These diets have had a great deal of anecdotal success, prompting more and more dieters to trade in their baked potatoes for juicy steaks.
But the American Dietetic Association and American Heart Association warn against low-carb diets, stating that they can increase the risk of heart disease (by emphasizing sources of animal protein that can be high in saturated fat). They are also concerned that that people who can’t use excess protein effectively will run the risk of osteoporosis, and liver and kidney disorders.
In a study published in the
Journal of the American Medical Association’s
(JAMA’s) April 9, 2003 special issue on obesity research, scientists analyzed results from studies on 94 low-carbohydrate diets to determine the efficacy and safety of these diets. They found that based on current research, it is not possible to conclude that low-carbohydrate diets really work to lower weight.
The researchers analyzed data from 107 journal articles describing 94 low-carbohydrate diet interventions. The studies had been conducted between January 1, 1966 and February 15, 2003, and involved 3268 participants.
Of the 3268 participants, 633 received
carbohydrate diets (60 grams per day (g/d) or less of carbohydrates); 71 participants were on
carbohydrate diets (20 g/d or less of carbohydrates). The remaining participants, on
carbohydrate diets, ate 60 g/d or more of carbohydrates.
From these studies, the researchers evaluated average changes in weight, cholesterol, fasting serum glucose, fasting serum insulin, and blood pressure among adults following low-carbohydrate diets.
The studies evaluated in this review were highly varied with respect to their design, carbohydrate intake (0–901 g/d), total calories (525–4629 kcal/d), diet duration (4–365 days), and participant characteristics (baseline weight 126–478 pounds). Such variability makes it harder to draw overall conclusions about the effectiveness of low carbohydrate diets.
The researchers found that among obese participants, weight loss was significantly associated with longer diet duration and restriction of calorie intake. However, there was no significant association between weight loss and reduced carbohydrate intake for obese or non-obese participants.
Low-carbohydrate diets did not adversely affect cholesterol levels, fasting serum glucose, fasting serum insulin levels, or blood pressure.
Despite the limitations of the studies included in this analysis, the authors conclude that if people without diabetes can tolerate a low-carbohydrate diet better than a higher-carbohydrate diet, it may be an effective way to achieve short-term weight loss without negative health consequences. However, they suggested that weight lost on low-carbohydrate diets was more likely due to decreased caloric intake and increased diet duration than reduced carbohydrate intake.
This conclusion supports the tenet that weight loss occurs when the number of calories expended outnumbers the number of calories ingested. In other words, restricting calories for a longer duration is more important for weight loss than restricting certain types of calories. On the other hand, low-carbohydrate diets may make it easier to accomplish this goal, because, for many people, it is easier to eat a large bowl of pasta than a 12-ounce steak.
Low-carbohydrate diets did not appear to have negative effects on the participants’ health. However, this analysis could not say whether low-carbohydrate diets were safe for people who were older, or had diabetes, high blood pressure, or high cholesterol.
One aspect of weight loss that this study was not able to account for was calories expended through physical activity. Regular exercise is vital, not only to weight loss, but to overall health. As such, it should be an integral part of any weight loss program.