Understanding people's food consumption and malnutrition determinants is the main issue for the improvement of public food security and poverty alleviation policies in the developing countries. The recent food crisis in the Sahel and many other low income countries which followed commodities prices increase highlighted the access problem of poor people. Food access problem and food poverty are mostly related to monetary poverty. Yet in some regions, high malnutrition rates are observed despite the income raise. The objective of the thesis is to better understand the households' income # food consumption relationship within the framework of food security in Southern countries. In addition to the standard tools of the microeconomic demand analysis, especially Engel functions, we developed empirical methods to take into account the qualitative perspectives given by the food entitlements and functioning approaches of Sen and the livelihoods approach. The statistical and econometrical analysis draws upon the data of a Malian national survey of 2001 on households' living standards, which paid a particular attention to the food consumption section. The results show that, on the whole, an increase of total expenditures (taken as a proxy of income) raise food consumption quantitatively (calories) and qualitatively (diet diversity). However, living standards comparisons in terms of monetary poverty and calorie needs coverage reveal unexpected cases: monetary non poor households with insufficient calorie intake and monetary poor ones with sufficient calorie intake. The existence of these cases which represent a relatively important proportion of the survey's sample is explained by the choices of budget allocation and the composition of households' food basket. It underlines that the traditional monetary indicator of poverty is not a suitable indicator of food needs satisfaction.