Carbohydrates and Health

Higher carbohydrate, average protein diets compared with lower
carbohydrate higher protein diets
5.26 Four randomised controlled trials were identified that presented evidence on diets
differing in the proportion of carbohydrate to protein on systolic and diastolic
blood pressure, all of which were included in the meta-analysis (Appel et al., 2005;
Leidy et al., 2007; Claessens et al., 2009; Delbridge et al., 2009). Three trials were
identified in the update search (Aldrich et al., 2011; Gogebakan et al., 2011; Toscani
et al., 2011) (Cardio-metabolic review, incident hypertension and blood pressure
chapter; Update search). The proportion of carbohydrate in the diets varies
between 40-62% energy and protein varies between 15-30% energy.
5.27 An effect is demonstrated, with higher carbohydrate, average protein diets
resulting in less of a reduction in systolic blood pressure (2.17mmHg, 95% CI 0.08,
4.25; p=0.04) as compared with the lower carbohydrate, higher protein diets. Body
weight is kept constant in one of the trials (Appel et al., 2005), but the other three
are weight loss trials. When the difference in weight loss between experimental
groups in these trials is plotted on a forest plot it is proportional for each trial to
the relative reduction in systolic blood pressure. It is not possible, therefore, to
exclude confounding by concomitant weight loss on the effect on systolic blood
pressure. The trials identified in the update search report no significant effect of
diets differing in the proportion of carbohydrate to protein on systolic blood
pressure.
Higher carbohydrate, average protein diets and systolic blood pressure
• Effect
• Limited evidence
• A higher carbohydrate, average protein diet may result in less of a reduction in
systolic blood pressure as compared with a lower carbohydrate, higher protein diet,
but it is not possible to exclude confounding by other variables, e.g. less weight loss
in one of the experimental groups
• The effect is biologically relevant
5.28 No significant effect is demonstrated for diets differing in the proportion of
carbohydrate to protein on diastolic blood pressure (0.81mmHg, 95% CI -0.83, 2.46;
p=0.33). The three trials identified in the update search report no significant effect
of diets differing in the proportion of carbohydrate to protein on diastolic blood
pressure.
Higher carbohydrate, average protein diets and diastolic blood pressure
• No effect
• Limited evidence
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