A systematic literature search of scientific databases was performed in 2015 by Nicole Darmon (INRA, Université de Aix-Marseille) and Adam Drewnowski (University of Washington). The analysis unveiled that foods of lower nutritional value and lower-quality diets composed of refined grains, added sugars, or fats generally cost less per calorie and tended to be selected by groups with lower socioeconomic status. Findings from multiple countries were unanimous on this point. A number of nutrient-dense foods were available at low cost but were not always palatable or culturally acceptable to the low-income consumer.
The diet cost among food groups
The French INCA2 nutrient composition food database and 2007 food prices shows that the fruits and vegetables food group and the meat/eggs/fish group are the most expensive. The median cost is €0.82/100 kcal for fruits and vegetables and €0.64/100 kcal for meat/eggs/fish. Fats and sweets only cost €0.22/100 kcal, and refined starches and added fats provide energy at the lowest cost (€0.14/100 kcal and €0.06/100 kcal, respectively). Interestingly, dairy products (yogurt, milk and cheese) have an intermediate energy cost (€0.32/100 kcal).
What are affordable acceptable, nutrient-rich foods?
In order to have a balanced diet on a small budget, it is necessary to select particular nutrient dense foods with a low cost(called by expert: the ratio of nutritional quality to price). In general, pulses, nuts, oils, and whole-grain cereals were foods with very good ratios of nutritional quality to price. Among animal products, milk, eggs, poultry, organ meats, and canned sardines are also indicated as foods with a good ratio of nutritional quality to price. Specifically, the consumption of milk and milk products, like yogurt, are rather considered as cost neutral: whereas fruits and vegetables provided 8% of calories while accounting for 17% of the cost, the energy contribution of dairy products was equivalent to their cost – around 11%.
What is the minimum food budget for a nutritionally adequate diet?
Based on all analyses, the minimum food budget for a nutritionally adequate diet was estimated at €3.5/d. However, that amount imposed significant practical limitations: zero food waste, drinking water from the tap, knowing how to cook, and not eating out at all. Below that cost level, the linear programming model failed to come up with a solution. In other words, having a nutritious diet at less than €3.5/d was impossible, not only in practice but also in theory.
How can the model help?
The modeling of food patterns (SAIN-LIM) can help identify foods and combinations of foods that are affordable, nutrient rich, and culturally acceptable. In general, price reductions aimed at promoting healthier foods enhanced the impact of nutrition education and are more effective than education alone. Nonetheless, nutrition education should remain an important component of dietary guidance, since less-healthy food choices have also been shaped by the lack of nutrition knowledge, local attitudes, or by cultural norms. Therefore it is important to ensure that price-based interventions do not run counter to social and cultural norms.
The authors concluded that identifying food patterns that are nutrient rich, affordable, and appealing should be a priority to fight social inequalities in nutrition and health.
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