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Margaret McCartney: Promising miracle diet fixes isn’t fair on anyone

BMJ 2017; 358 doi: (Published 25 September 2017) Cite this as: BMJ 2017;358:j4226

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The most recent meta-analyses for low-carb diets.

In support of the points made by George D. Henderson I would add that the correct definitions set by Feinman et al (1) are <130g carbohydrate per day for a low-carb diet and 20-50g carbohydrate per day for very-low-carb diet. This means that the 2017 meta-analysis that McCartney cites is not relevant, as it incorrectly defines low-carb as <45% of total calories from carbohydrates.

With that in mind the most recent meta-analysis between correctly defined low-carb and low-fat for weight loss was published in December 2015 by Mansoor et al (2), this is not cited by McCartney.  They found that "Compared with subjects on low-fat diets, subjects on low-carbohydrate diets experienced significantly greater weight loss, greater triglycerides reduction and greater increase in HDL-cholesterol after 6 months to 2 years of intervention."

Also, the most recent and relevant meta-analysis was published in July 2017 by Meng et al (3), this was also not cited by McCartney. It concluded that "The results suggested a beneficial effect of LCD intervention on glucose control in patients with type 2 diabetes. The LCD intervention also had a positive effect on triglycerides and HDL cholesterol concentrations, but without significant effect on long term weight loss." Although this meta-analysis showed that in the long term those living with type 2 diabetes didn't lose any more weight than each other, the end result was that individuals following a low-carb diet do become healthier with better glucose control than those following a low-fat diet.

I agree that low-carb isn't a ‘miracle diet’ but surely given that starchy carbohydrates digest down into sugar, and no-one is suggesting sugar itself is a good food for someone living with type 2 diabetes, a lower carb diet is a logical dietary option. An option which does now have a reasonable evidence base.

1) Feinman, Richard D. et al. Dietary carbohydrate restriction as the first approach in diabetes management: Critical review and evidence base Nutrition , Volume 31 , Issue 1 , 1 – 13

2) Mansoor, N., et al. (2016). Effects of low-carbohydrate diets v. low-fat diets on body weight and cardiovascular risk factors: A meta-analysis of randomised controlled trials. British Journal of Nutrition, 115(3), 466-479. doi:10.1017/S0007114515004699 S0007114515004699

3) Meng, Yan et al. (2017)Efficacy of low carbohydrate diet for type 2 diabetes mellitus management: A systematic review and meta-analysis of randomized controlled trials. Diabetes Research and Clinical Practice , Volume 131 , 124 - 131 abres.2017.07.006 

Competing interests: No competing interests

04 October 2017
Samuel G. Feltham
Director of the Public Health Collaboration