The pleasantness of a food declines with consumption and this phenomenon has been demonstrated reliably in the short-term. To investigate long-term effects of repeat consumption on pleasantness, preference and intake, 21 volunteers consumed either a salty snack (french fries) or sweet snack (chocolate) every day for 15 days. Four dependent variables were measured: pleasantness ratings, ranked preference, frequency of consumption and ad libitum intake. Daily pleasantness of taste ratings decreased across the exposure period only for chocolate. Ranked preference for chocolate declined during the sweet snack condition and increased during the salty snack condition. Preference for french fries remained the same during the salty snack condition and increased during the sweet snack condition. Frequency of consuming chocolate outside the laboratory decreased during the sweet snack exposure. No such pattern was found for french fries in either condition. Ad libitum intake in the laboratory remained the same over time for both foods. Short-term sensory-specific satiety within the eating episode was consistent over time. Therefore, long-term monotony effects were found only for pleasantness, preference and frequency of eating chocolate following repeated exposure, but these changes had no impact on ad libitum intake. Systematic, repeat exposure to a single food provides a useful paradigm for investigating the development of monotony.

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Physical activity promotion in this population has the potential to improve the quality of life and reduce health risks associated with sedentary lifestyles.

As the dietary supplement industry is now a multi-billion dollar industry, there is growing pressure, and a subsequent need for research to establish the efficacy and safety of these products particularly for adolescent users. The psychological and educational components of such use cannot be ignored as they play an equally important role in the health and safety of adolescents.