Medical research related to low-carbohydrate diets

This article summarizes a sampling of the studies that exist related to this diet trend. It is not a complete listing of all relevant research. For general information about low-carbohydrate diets see the main article.

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Synopsis

Because of the substantial controversy regarding low-carbohydrate diets, and even disagreements in interpreting the results of specific studies, it is currently difficult to objectively summarize the research in a way that reflects scientific consensus.

Although there has been some research done throughout the twentieth century, most directly relevant scientific studies have occurred in the 1990s and early 2000s and, as such, are relatively new and the results are still debated in the medical community. Supporters and opponents of low-carbohydrate diets frequently cite many articles (some times the same articles) as supporting their positions. It is worth noting that one of the fundamental criticisms of those who advocate the low-carbohydrate diets has been the lack of long-term studies evaluating their health risks.

Specific Studies

The following is not a complete list of all relevant research but a selected list of articles demonstrating some of the breadth of scientific knowledge available on this subject.

Journal of the American Medical Association: 2003

Bravata et al., 2003^[1] conducted a literature search study of low-carbohydrate diet studies conducted between 1966 and 2003. The paper stated the following conclusion.

There is insufficient evidence to make recommendations for or against the use of low-carbohydrate diets, particularly among participants older than age 50 years, for use longer than 90 days, or for diets of 20 g/d or less of carbohydrates. Among the published studies, participant weight loss while using low-carbohydrate diets was principally associated with decreased caloric intake and increased diet duration but not with reduced carbohydrate content.

Studies have shown that carbohydrate reduction did not significantly contribute more to weight loss than simply reducing calories. It is worth noting that the article does state that

Low-carbohydrate diets had no significant adverse effect on serum lipid, fasting serum glucose, and fasting serum insulin levels, or blood pressure.

Annals of Internal Medicine: 2004

Two significant studies can be found in the Annals of Internal Medicine in 2004.

Stern et al., 2004^[2] conducted a one-year study of 132 obese adults. The conclusions state the following.

Participants on a low-carbohydrate diet had more favorable overall outcomes at 1 year than did those on a conventional diet. Weight loss was similar between groups, but effects on atherogenic dyslipidemia and glycemic control were still more favorable with a low-carbohydrate diet after adjustment for differences in weight loss.

Meta-analytic summaries

Meta-analysis is a method to succinctly summarize and combine the results from multiple individual studies. The following meta-analyses of low carbohydrate diets are limited to randomized controlled trials that directly compare low carbohydrate diets to other diets. Some of the studies listed above are randomized controlled trials and are included in these meta-analyses.

A meta-analysis of randomized controlled trials by the Cochrane Collaboration in 2002 concluded^[3] that fat-restricted diets are no better than calorie restricted diets in achieving long term weight loss in overweight or obese people.

A more recent meta-analysis that included randomized controlled trials published after the Cochrane review^[4][5][6] found that "low-carbohydrate, non-energy-restricted diets appear to be at least as effective as low-fat, energy-restricted diets in inducing weight loss for up to 1 year. However, potential favorable changes in triglyceride and high-density lipoprotein cholesterol values should be weighed against potential unfavorable changes in low-density lipoprotein cholesterol values when low-carbohydrate diets to induce weight loss are considered."^[7] Although studies from Stanford University and Duke University were not meta-analytic, their results favored the low-carbohydrate approach,^[8][9] as opposed to the aforementioned study which questions which is better.

Notes