Research paper
Malik VS, Popkin BM, Bray GA, Després JP, Willett WC, Hu FB. Sugar-sweetened beverages and risk of metabolic syndrome and type 2 diabetes: a meta-analysis. Diabetes Care. 2010 Nov;33(11):2477-2483. doi:10.2337/dc10-1079. PMID: 20693348. PMCID: PMC2963518.
Why we cite it
An early and widely cited meta-analysis of 11 prospective cohort studies — 8 for type 2 diabetes (310,819 participants, 15,043 cases), 3 for metabolic syndrome (19,431 participants, 5,803 cases) — reporting RR 1.26 (95% CI 1.12–1.41) for diabetes and RR 1.20 (95% CI 1.02–1.42) for metabolic syndrome, highest against lowest intake.
These are prospective cohorts. A meta-analysis of observational studies gives a pooled association, not a cause, and pooling eleven of them makes the estimate more precise, not more causal.
The often-quoted figure that about half the diabetes association runs through obesity is not this meta-analysis’s result. The paper reports it from an earlier study: ”Schulze et al. (16) suggested that approximately half of the effects of SSBs on type 2 diabetes were mediated through obesity.” Its own analysis says only that the association ”is likely to be mediated in part by an increase in overall energy intake or adiposity”, without a figure.
Excluding the adjusted estimates raised the pooled risk slightly. With the energy- and adiposity-adjusted coefficients removed, the pooled RR for type 2 diabetes was 1.28 (95% CI 1.13–1.45) from the random-effects model. The authors reason that, since the effect is mediated in part by energy intake and adiposity, adjustment for these factors ”will tend to underestimate any effect”; a meta-regression, though, ”did not find adjustment for energy to be a significant predictor of effect”.
The exposure contrast is the highest quantile, ”most often 1-2 servings/day”, against the lowest, ”none or <1 serving/month". The authors' own conclusion is association language: "higher consumption of SSBs is associated with development of metabolic syndrome and type 2 diabetes".
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