Association Between Dietary Protein Intake And The Risk Of Depressive Symptoms In Adults

Objective:Depression is a worldwide common mental disorder.The association between dietary factors with depression has been well established.But previous studies on the association between dietary protein and the risk of depressive symptoms were controversial,and the epidemiological study on the association between dietary protein sources and the risk of depressive symptoms was limited.We conducted this study to explore the associations of total protein intake and protein sources with the risk of depressive symptoms.Furthermore,we also examined the dose-response relationship between dietary protein and the risk of depressive symptoms.Methods:This cross-sectional study used data from the National Health and Nutrition Examination Survey(NHANES)for the years 2007-2014.Adults aged 18 or older were included.Dietary protein intake was obtained from two 24-hour dietary recall interviews.Dietary protein intake(g/kg/d)was categorized into four groups according to the quartiles of protein intake:lowest intake group,medium intake group,higher intake group and highest intake group.The lowest level intake group was set as the reference group.For protein intake from different food sources,participants who consumed protein from each food source more than 0 g were divided into three groups according to the tertiles of protein intake:medium intake group,higher intake group and highest intake group.The 0 g group for each food source was set as the reference group.If the percentage of participants with 0g protein intake from each food source was less than20%of the total participants,dietary protein intake was categorized into four groups according to the quartiles of protein intake:lowest intake group,medium intake group,higher intake group and highest intake group.The lowest level intake group was set as the reference group.Depressive symptoms were assessed by a nine-item Patient Health Questionnaire(PHQ-9).Depressive symptoms were identified when the PHQ-9 score?10.In this study,Student's t-test and chi-square test were conducted to compare the differences in basic characteristics of the two groups with different depression states.Logistic regression models were used to estimate the associations of total protein intake(g/kg/d)and protein intake from different food sources with the risk of depressive symptoms.Ten-fold cross validation was conducted to test the stability of the model.We conducted stratified analyses by age(<45 years old,45 to 64 years old and?65 years old),annual household income(<$20 000 and?$20 000),gender(male and female),and BMI(<18.5 kg/m~2,18.5 to<25 kg/m~2,25 to<30 kg/m~2,and?30 kg/m~2)to assess the association between total protein intake and depressive symptoms.Restricted cubic spline model was used to explore the dose-response relationship between protein intake and the risk of depressive symptoms.Furthermore,our study assessed the association between total protein intake and the risk of depressive symptoms based on Recommended Dietary Allowance(RDA).Considering the existence of missing data,logistic regression imputation was used to estimate and replace the missing values of variables;then this data was used to reassess association between total protein intake and the risk of depressive symptoms.Results:A total of 17 845 individuals aged 18 or older were included in this study.There were 1,629(9.21%)participants with depressive symptoms.Total protein intake was inversely associated with the risk of depressive symptoms.Compared with the lowest intake group of total protein,the full-adjusted odd ratio(OR)with 95%confidence interval(CI)of depressive symptoms for the highest intake group was 0.34(0.17-0.68).The results showed that the area under the(ROC)curve of the logistic regression model was 0.7409.And the area under the(ROC)curve after the ten-fold cross validation was0.7183,the accuracy of the cross validation model was 93.78%.For dietary protein sources,moderate intake protein from milk(OR=0.43,95%CI:0.26-0.70)was found to be inversely associated with the risk of depressive symptoms in full-adjusted model.For protein from red meat,poultry,fish,legumes and grain products,there were a significant association with depressive symptoms in unadjusted model and age-and gender-adjusted model,but the associations were not significant in full-adjusted model.In the dose-response analysis,nonlinear inverse associations of total protein intake and protein intake from milk and milk products with the risk depressive symptoms were observed;the shapes of the associations of total protein intake and protein intake from milk and milk products with the risk of depressive symptoms were approximately L-shaped and U-shaped,respectively.The results of analysis by classifying protein intake according to RDA indicated that compared with inadequate intake,adequate protein intake was negatively associated with the risk of depressive symptoms in model II(OR:0.57;95%CI:0.37-0.87).The negative association between dietary protein intake and the risk of depressive symptoms remaind significant after replacing missing values with estimated values calculated using logistic regression imputation;compared with the lowest intake group,medium intake group(OR=0.74,95%CI:0.58-0.95),higher intake group(OR=0.55,95%CI:0.39-0.78)and highest intake group of total protein(OR=0.46,95%CI:0.31-0.68)were both associated with a reduced risk of depressive symptoms in model II.Conclusions:The present study demonstrated that total protein intake and protein intake from milk and milk products might reduce the risk of depressive symptoms in US adults.The shape of the associations of total protein intake and protein intake from milk and milk products with the risk of depressive symptoms was approximatively L-shaped and U-shaped,respectively.