The difference between acute and chronic effects and the impact they have can be challenging to determine. Secondary natural products do not have a direct nutritive impact and this can make the consequences of their ingestion difficult to determine. One of the measurable outcomes from secondary natural product ingestion is bitterness which can be measured both in terms of binding to a receptor and through a physiological sensation. The naming of natural products can be based on derivation, chemical or biological characteristics and these can be demonstrated. The biological activity may be a consequence of the compounds as produced or their metabolites or breakdown products. Examples of these can be found and of synergies between different compounds and metabolites. The ‘Magic Bullet’ concept can apply to some bioactive secondary natural products but is less useful in foods and food systems. The complexity of the potential effects of secondary natural products is illustrated by studies of mutagenicity and carcinogenicity.