Food phytochemicals are increasingly considered to play a key role in the cardiometabolic health effects of plant foods. However, the heterogeneity in responsiveness to their intake frequently observed in clinical trials can hinder the beneficial effects of these compounds in specific subpopulations. A range of factors, including genetic background, gut microbiota, age, sex and health status, could be involved in these interindividual variations; however, the current knowledge is limited and fragmented. The European network, European Cooperation in Science and Technology (COST)-POSITIVe, has analysed, in a systematic way, existing knowledge with the aim to better understand the factors responsible for the interindividual variation in response to the consumption of the major families of plant food bioactives, regarding their bioavailability and bioefficacy. If differences in bioavailability, likely reflecting differences in human subjects’ genetics or in gut microbiota composition and functionality, are believed to underpin much of the interindividual variability, the key molecular determinants or microbial species remain to be identified. The systematic analysis of published studies conducted to assess the interindividual variation in biomarkers of cardiometabolic risk suggested some factors (such as adiposity and health status) as involved in between-subject variation. However, the contribution of these factors is not demonstrated consistently across the different compounds and biological outcomes and would deserve further investigations. The findings of the network clearly highlight that the human subjects’ intervention studies published so far are not adequate to investigate the relevant determinants of the absorption/metabolism and biological responsiveness. They also emphasise the need for a new generation of intervention studies designed to capture this interindividual variation.

Interindividual variability in vocabulary, sentence comprehension and working memory is studied in older people with mild cognitive impairment, very low cognitive impairment and normal state, according to the Mini Examen Cognoscitivo (MEC). In the study participated 71 seniors, aged between 62 to 90 years of age, with low instructional level (from one to five years of regular education). Variability measures were calculated in a test of lexical knowledge, another of working memory, and also in one of sentence comprehension.

The results obtained using a polynomial regression analysis of the absolute residual scores on the MEC, showed that: (a) variability increases in a linear fashion as the MEC score decreases in the case of nouns, and sentences with one proposition that do not follow the canonical order of constituents in Spanish; (b) Performance on the simpler sentences (one proposition and canonical order) and in the most complex ones (two propositions and non-canonical order) variability showed a change in its trend from MEC scores that indicate cognitive deterioration; (c) In relation to performance on the verbs, variability’s change of trend is not linked to cognitive deterioration. We discuss the results in terms of the utility of these measures as potential indicators of cognitive impairment.