This study aims to systematically review original articles investigating the link between spectral acoustic measures in healthy talkers and perceived speech intelligibility, according to the PRISMA guidelines. Twenty-two studies were retained. Eighteen papers investigated vowel acoustics, one studied glides and eight articles investigated consonants, mostly sibilants. Various spectral measures and intelligibility estimates were used. The following measures were shown to be linked to sub-lexical perceived speech intelligibility ratings: for vowels, steady-state F1 and F2 measures, the F1 range, the [i]-[U] F2 difference, F0-F1 and F1-F2 differences in [è-A] and [q-è], the vowel space area, the mean amount of formant movement, the vector length and the spectral change measure; for consonants, the centroid energy and the spectral peak in the [s]-sound, as well as the steady-state F1 offset frequency in vowels preceding [t] and [d].To conclude, as speech is highly variable even in healthy adult speakers, a better understanding of the imprecisions in healthy spontaneous speech will provide a more realistic baseline for the investigation of disordered speech. To date, no acoustic measure is able to predict speech intelligibility to a large extent. There is still extensive research to be carried out to identify relevant acoustic combinations that could account for perceived speech variations (e.g. vowel and consonant reductions) and to gather normative data from a large number of healthy speakers. To that end, speech-related terms (e.g. intelligibility, comprehensibility, severity) need to be clearly defined and methodologies described in sufficient details to allow for replication, cross-comparisons/meta-analyses and pooling of data.