Systematic review and meta-analysis of clinical trials of the effects of low carbohydrate diets on cardiovascular risk factors – facilitated by Associate Professor Justin Keogh – Summarised below by Professor Chris Del Mar

Reference:

Santos FL, Esteves SS, da Costa Pereira A, Yancy WS, Jr., Nunes JP. Systematic review and meta-analysis of clinical trials of the effects of low carbohydrate diets on cardiovascular risk factors. Obes Rev 2012;13:1048-66

Justin Keogh provided an interesting SR of low carbohydrate diets for CVD risk factors, sent to him by an enthusiastic colleague.

We appraised it using the FAST mnemonic.

‘F’ind seemed odd: few hits for such a search, (~1000 hits, not including some presumed overlap).

‘A’ppraisal was apparently secure: only RCTs were included, (however little was offered in the form of critically appraising the included studies for methodological rigour).

‘S’ynthesis reaped a major flaw: the studies were meta-analysed in forest plots by changes from baseline – not against the controls. This explains the greater effect sizes than expected, and probably represents a fatal flaw: in effect, only the intervention arms of the RCTs were included in a before-after comparison.

‘T’ransfer of the results was therefore not really applicable.

What should we do?

  1. this is a very good teaching tool (a bad example, to see if students can pick the flaws, and a lesson that not all SRs are good!);
  2. perhaps this topic needs systematically reviewing properly (if not done already);
  3. should we write to the journal to set out the flaw? P Coxeter tabled some criticisms (on other grounds) from closer to the publication date. We are probably too late to send in a corrective response.

To read the full article, click on the link below:

Systematic review