Stable isotope analyses of body tissues and exhaled breath can be useful in considerations regarding diet, but the effects of metabolism-altering drugs on body δ¹³C and δ¹⁵N are not known. Hair samples and exhaled breath were sampled from 212 university students. Carbon and nitrogen isotope values were related to gender, age, diet, activity, and drug consumption. δ¹³C of exhaled CO₂ became heavier with increasing consumption of caffeine and tobacco. δ¹³C values of hair were significantly higher than exhaled CO₂ and became heavier with increased consumption of meat, alcohol, caffeine, and tobacco. δ¹⁵N of hair was significantly correlated to meat intake. In addition, there were numerous biological and sociological correlations between subjects in the study. Males and females differed in their likelihood of consuming meat, seafood, alcohol, appearance enhancing drugs (e.g., diet pills or exercise supplements), vitamins, and other drugs. Subjects who consumed alcohol were also more likely to consume nicotine and caffeine.