The paper develops a framework combining a model of rational behaviour under dietary constraints, an epidemiological model of diet-related mortality, and a life-cycle-analysis model of environmental impact, which permits the ex-ante assessment of dietary recommendations in multiple sustainability dimensions (i.e., taste cost, welfare effect, deaths avoided, reductions in greenhouse gas emissions and acidification). It is applied to compare in a French context the relative effects and efficiency of six popular sustainable diet recommendations. The results confirm the synergies between the health and environmental dimensions: healthy-eating recommendations usually have a positive effect on the environment, although some exceptions exist. Most of the sustainable diet recommendations appear highly cost-effective, but those most commonly promoted on health grounds (e.g., targeting consumption of salt, fruits and vegetables and saturated fat) rank highest in terms of overall efficiency. Moreover, the valuation of benefits indicates that in most cases health benefits are significantly larger than environmental benefits. Overall, the analysis reveals some under-investment in the promotion of sustainable diet recommendations in France. The general lack of enthusiasm in policy circles for informational measures promoting behavioural change may reflect unrealistic expectations about the speed and magnitude of dietary change rather than an objective assessment of the efficiency of those measures.