Cultural beliefs and practices, and improper use of medications of Saudis may be associated with poor nutritional status. The purpose of this study was assess knowledge, attitude and practice of Saudi adults regarding possible effects of selected food combinations, and effects of medications on nutritional status, in association with gender, age and educational level. A questionnaire was constructed to include demographic information, some food combinations culturally avoided, or scientifically known to adversely affect nutritional status, possible interactions of food with medications, sources of information, and personal experience of adverse effects following certain food combinations. Subjects were recruited from public areas to complete the questionnaire. An electronic version was distributed through social network. A total of  998 questionnaires were completed, with 60.9% females, 66.5% ≤25 years of age, and  75.6% having university degree. Women, and subjects with ≥ secondary school education had significantly higher knowledge score (P= 0.007, and 0.01 respectively). The majority of participants did not know food combinations that can adversely affect nutritional status, especially those having < secondary school certificate. Significantly higher proportion of subjects > 40 years of age believed in traditional taboos (P= 0.038). Attitude was affected by gender. Hearsay and media were major sources of information, with higher percentage of females intentionally seeking knowledge. Nutritional knowledge is poor among Saudis, with folklore, and media being main sources. This might contribute to the increased prevalence of nutrition related diseases. Nutrition education programmes should be introduced early in life through different channels.