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BMJ 2010; 341 doi: (Published 15 September 2010) Cite this as: BMJ 2010;341:c4970

Could a low carbohydrate diet save your life?

Low carbohydrate diets can help some people lose weight, but their impact on lifespan may well depend on what replaces the carbohydrate. Diets that switch carbohydrates for proteins and fats from animal sources were associated with a small but discernible increase in mortality in a recent study, whereas low carbohydrate diets rich in proteins and fats from vegetables seemed protective.

Researchers explored associations between diet and death in two large and established cohorts of US health professionals with more than 20 years of follow-up. Significant results emerged from analyses comparing adults at the two extremes of the dietary spectrum—men and women in the lowest and the highest tenths of a dietary score derived from food frequency questionnaires. Low carbohydrate diets based on animal products were associated with worse mortality from all causes (adjusted hazard ratio 1.23, 95% CI 1.11 to 1.37), from cardiovascular disease (1.14, 1.01 to 1.29), and from cancer (1.28, 1.02 to 1.60). The link between low carbohydrate diet based on vegetable products and a low mortality seemed driven by a lower risk of cardiovascular death (0.77, 0.68 to 0.87).

Observational studies, even big ones, have let us down many times before, however. It’s still impossible to know whether these associations are real or the result of statistical artefact such as confounding, says an editorial (pp 337-9). Surely we can find the time and money for at least one big trial looking at the long term impact of diet on chronic illness and mortality?

Measures of doctors’ performance should be adjusted for case mix

Healthcare providers and policy makers continue to grapple with the problem of how to rate individual doctors in a way that is fair and accurate …

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