This study aimed to verify the impact of the variables age, sex, weight, and energy expenditure on zinc intake in healthy adults in the city of São Paulo, Brazil, in order to evaluate the variables that compose the recommendation of the nutrient to facilitate the adequacy of intake, avoiding its excess or deficiency.
Regarding age, the results showed that the variable does not correlate with zinc intake, but it is known that inadequate chewing, reduced absorption of nutrients, and the use of medications may affect the need for daily intake of the nutrient in older individuals (22). Therefore, more studies need to be conducted with older individuals, to understand the relationship between this group and the consumption of micronutrients.
Results indicate that the difference in zinc intake between men and women is due to the difference in energy expenditure between sex.
The study by Yeung, 2021(23) shows that zinc intake presents no statistically significant difference between sex when compared through the energy adjustment method. Therefore, unlike how the IOM conducts its studies (24), the variables were analyzed without sex distinction.
As for the bodyweight variable, the results indicate a low correlation with zinc intake, corroborating a 2011 study, in which no statistical significance was found for intake of any micronutrient when associated with muscle mass (23). Furthermore, no statistical significance of the weight variable was observed in the linear regression, suggesting that body weight is a confounding variable associated with energy expenditure for adults. In addition, it is worth noting that extrapolations of nutritional recommendations from adults to older adults considered that nutritional needs, as well as intake, digestion, and excretion, would be the same among different ages (25), impairing calculations of micronutrient recommendations for specific age groups.
Meanwhile, Pearson's correlation coefficient shows a statistically significant correlation between energy expenditure and zinc intake for adults, suggesting that this variable can be considered a reference for the nutrient recommendation. Moreover, according to the IOM, the EER is defined as the average intake needed to maintain the balance of a healthy individual and has as variables age, body weight, height, and physical activity factor (12). Therefore, according to predictive energy equations (12,15–17), individuals of the same age, weight, or height may have different nutritional needs according to their metabolic rate. With these considerations mentioned, this study proposed a linear regression between energy expenditure and zinc intake that proved to be statistically significant (p = 0.004) and also showed to be better than using the mean as a reference [F (1, 77) = 8.728 p = 0.004; R²=0.091]. The value found in the linear regression for each individual would be the actual daily recommendation of zinc. Therefore, the recommendation of the nutrient becomes individualized to consider physiological, environmental, and genetic factors, which, according to the workshop entitled "The Development of the DRIs 1994–2004: Lessons Learned and New Challenges", published in 2008 by the IOM, these factors require consideration because they can influence the need for each nutrient, suggesting that further studies should be conducted in this direction (26).
Despite the results obtained, the method used to investigate nutrients (24-hour recall on 3 different days) may represent a limitation because its use depends on memory recall and requires a well-trained investigator to get accurate estimates of the portions consumed. However, it is a widely used method and provides reliable estimates of the average intake of the population (27).
Regardless of the limitations considered, this study is important to understand the zinc requirements of healthy adults and to explain the significance of using energy expenditure as a reference variable for micronutrient intake guidelines.