In the paper, the current state of research is presented with reference to carbon and nitrogen stable isotopes ratios (δ) in various food products (vegetables, fruits, meat, and milk) produced using conventional and organic farming methods. The δ value denotes an amount of heavy and light isotopes in a sample. The δ¹⁵N value in vegetables and fruits is affected, among other thing, by a soil and fertigation type, as well as by a farming method used previously in the field. The methods consisting in the determination of δ¹⁵N or δ¹³C values can be a useful tool to distinguish between organic and conventional food products; though, this principle does not involve all food products.