November 20, 2014

An observational study by Pase et al. (1) assessing the link between fruit juice consumption and blood pressure was recently published in the journal Appetite, which suggested that frequent intake of fruit juice was associated with higher aortic blood pressure, a major risk factor for heart disease. On his blog, Professor Mike Gibney of University College Dublin [also a former president of the Nutrition Society (Ireland) and member of several European Union and United Nation committees on nutrition and health] provided his balanced review of this observational study and compared its scientific rigor to a systematic review on the same topic. 

Professor Gibney first briefly summarized the limitations of the cross-sectional study design (small sample size, diets analyzed using a food frequency questionnaire) and the study's major findings, and quoted the authors' conclusion that "frequent fruit juice consumption may be contributing to excessive sugar intake, typical of the Western population, exacerbating the prevalence of hypertension". He then elegantly pointed out a major flaw in the claimed link between fruit juice intake and excessive sugar intake, given the fact that the study did not provide any data on total sugars intake. The authors did not examine the many other dietary sources of sugars (other including table sugar, soft drinks, whole fruits, etc.) so it is impossible to conclude any correlation between fruit juice and total sugars intake. Another alarming limitation of this study, as pointed out by Professor Gibney, was the lack of control for total energy intake: "to fail to report total energy intake and the fraction of that intake contributed by total sugar and added sugar is unfathomable in terms of scientific rigor. It renders this paper utterly useless and casts a shadow on the editorial process of the journal where it was published." Despite these study limitations, "sensational" headlines appeared in the media linking fruit juice to increased blood pressure. 

In contrast, a meta-analysis conducted by Dr. David Jenkins' group at the University of Toronto was then presented as an example of a systematic approach to investigating the link between total fructose intake (rather than one source of fructose) and risk of blood pressure using best-available observational studies. This meta-analysis followed "the strict rules that are internationally regarded as the 'must follow' rules of systematic reviews". After controlling for all known confounding factors including total energy intake, no association between fructose intake and hypertension was observed. 

 

To read the full article by Professor Gibney: http://gibneyonfood.blogspot.co.uk/2014/11/sugar-bad-science-great-headlines.html

(1). Pase MP, Grima N, Cockerell R, Pipingas A. Habitual intake of fruit juice predicts central blood pressure. Appetite. 2014 Sep 30. pii: S0195-6663(14)00462-0.