Introduction

Dietary intake during the adolescence has an important role in both the prevention and treatment of diseases. Also, dietary patterns and habits acquired during adolescence are also likely to persist throughout adulthood [1].

Although dietary intake assessment is challenging [2], and the majority of studies focus on the intake of individual nutrients, foods or food groups [3], dietary patterns have been widely used in nutritional epidemiology to examine the joint effects of multiple dietary components [4]. This approach identifies overall patterns of food intake and their apparent effects on disease risks, allowing us to examine potential synergistic or antagonistic effects between nutrients and/or foods [4].

While previous studies have looked into the role of family structure on dietary intake [5–7], few have evaluated the effect of number of siblings on adolescent dietary patterns [8–10]. One of these studies found that individuals with no siblings had a higher daily intakes of nutrients (except carbohydrate and added sugars) compared to individuals with siblings, suggesting that only-children may have a better diet quality [9]. Other studies found that having more than one sibling is associated with higher nutritional risk (according to nutrients intake based on Reference Nutrient Intake) [10], and that additional siblings may decrease the availability of food for each child [8].

Considering the scarce literature on this subject, the aim of the present study was to examine the association between number of siblings and dietary patterns in 18 year-old adolescents from a birth cohort in Southern Brazil.

Materials and methods

Results

Sample characteristics

Of the 5249 infants enrolled into the study at birth, 4563 were located. Of those, 127 refused to participate in the study and 330 were considered losses, totalizing 4106 interviewed at 18 years of age. Added to those known to have died, this represents an 81.3% follow-up rate. Of these, 4052 adolescents had complete data on dietary patterns. After excluding those with inaccurate reports of energy intake (<-2 and >+2 SD), following standard procedures [16], our final sample consisted of 3751 individuals.

There was no difference between the participants included in our analyses and those excluded in relation to the variables studied (number of total siblings, family income, maternal education, presence of the father, maternal skin colour, and maternal age at birth) (data not shown in Table).

Table 1 describes the characteristics of our sample. Most adolescents had the father living in the house when they were born (88.4%) and about one-third of them at the age of 15 had one sibling (31.3%). Regarding the mothers, the average education at birth was near 7 years (SD 3.5) and age at birth was 26 years (SD 6.4). In addition, median family income was 830 reais (interquartile range 420–1500).

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Table 1. Characteristics of sample according to the variables studied (n = 3 751).

The 1993 Pelotas Birth Cohort, Brazil.

https://doi.org/10.1371/journal.pone.0174087.t001

Dietary patterns

We identified four dietary patterns, which together explained 40% of the total variance in food group consumption. The first pattern, which we called protein and fast food, included fish, processed meat (canned tuna/sardine, salt-cured meat, bacon), hamburger, hot dogs, viscera (heart and liver), fried and roasted chicken, and pork meat. The second pattern, fruits and vegetables, included banana, orange and tangerine, tomato, other fruits, vegetables and legumes. The third one, common Brazilian, included coffee, black beans, white sugar, fat (butter and margarine), white rice, and white bread. Finally, the fourth pattern, called sweets, soft drinks, and dairy products, included chocolate powder, regular sodas, dairy products, sweets, candies and caramels, and ice cream. All food items showed positive loadings (Table 2).

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Table 2. Four components of dietary pattern of adolescents at 18 years of age (The 1993 Pelotas Birth Cohort, Brazil).

https://doi.org/10.1371/journal.pone.0174087.t002

Regression models

Crude and adjusted analyses evaluating the association between number of siblings and dietary pattern scores are presented in Table 3. S2 Fig also shows the crude analyses. Adjusted models showed that individuals with three or more siblings, compared to only-children, had higher adherence to the fruits and vegetables pattern (β = 0.21 z-scores, 95% CI 0.12; 0.29); the sweets, soft drinks, and dairy products pattern (β = 0.40 z-scores, 95% CI 0.30; 0.50); and the protein and fast food pattern (β = 0.10 z-scores, 95% CI 0.05; 0.15). There was no difference in consumption of the common Brazilian pattern according to number of siblings. There was some mild attenuation of effect sizes in the adjusted models, but the results were qualitatively similar to those from the unadjusted models.

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Table 3. Crude and adjusted analyses of association between number of siblings and dietary patterns (in z-score) (The 1993 Pelotas Birth Cohort, Brazil).

https://doi.org/10.1371/journal.pone.0174087.t003

Additional analyses were performed to assess the association between number of siblings and energy intake. In the adjusted analysis, adolescents with three or more siblings showed an increase of 666.7 Kcal (95% CI 454.5; 878.9) in energy intake compared to those who had no siblings (data not shown).

Discussion

Our findings showed the number of siblings was positively associated with higher adherence to each dietary pattern except the common Brazilian pattern. Corroborating the results of the present study, a British study reported no association between number of siblings (older or younger) and ‘traditional’ diet (based on meat, potatoes and vegetables) at age 7 years. In addition, the authors found that ‘health-conscious’ dietary component (vegetarian style foods, rice, pasta, salad and fruit) was positively associated with the number of older siblings the child had, whereas the ‘junk’ diet component (high-fat and sugar content, processed and convenience foods) was positively associated with the total number of siblings (older or younger) [17]. Similarly, a study carried out in Spain found that having more than one sibling was related to higher nutritional risk [10]. Such finding may be associated with less attention being given to food or individuals in families with a larger number of children [18].

Two previous studies have found that a higher number of siblings was associated with lower average daily intake of total protein, animal protein, calcium, vitamins, and fat; but a higher consumption of carbohydrate and added sugar [9, 19]. The finding that individuals with siblings had a lower intake of all nutrients except carbohydrate and added sugar indicates that they have diets that rely on cheaper nutrients as sources of energy rather than more expensive diets including proteins and fats [19]. One possible explanation is that the greater number of siblings means that the family has less income to spend per family member [20].

Our results showed that a greater number of siblings was associated with a more diverse diet. This finding may be reflecting the nutritional transition occurring in lower and middle income countries [21, 22]. Study including children from eight European countries reported that those from lower socioeconomic status (SES) have higher risk of unhealthy eating [23]. Also, recent review with studies from low and middle-income countries (the majority of them were conducted in Brazil) including adults showed that higher SES was associated with a healthier dietary pattern [24]. Since we observed adherence to varied patterns among individuals with siblings, it may suggest that these adolescents are in the middle of a nutritional transition (i.e. going from a dietary pattern typical from low-income countries, where higher SES is positively associated to unhealthier patterns, to a dietary pattern typical from high-income countries, where higher SES is positively associated to healthier patterns) [25].

A greater dietary variety may predict better nutrient adequacy and health outcomes [26, 27]. Also, it is important to note that dietary variety, food group intakes, and nutrient adequacy are all strongly correlated with energy intake [27].

Some methodological considerations should be highlighted. Due to loss of follow-up, potential selection biases might exist, however we compared the sample participants with the original participants assessed at the baseline and observed no difference in relation to the variables included in our analysis (data not shown). The 12-month recall period for the FFQ may be considered a limitation of our study, since it may generate recall bias. While we adjusted our regression models for a number of potential confounding factors, we cannot exclude the possibility that residual confounding explains the associations we have described. It is also important to emphasize that adherence to a dietary pattern does not, necessarily, exclude the adherence to other patterns, and the dietary patterns we identified may be not generalizable to other populations [28]. Finally, we used the information on the number of siblings at 15-year-old follow-up because we did not have this information at 18 year-old follow-up. Moreover, we do not have the information whether the siblings live together with the adolescent enrolled in the cohort.

Some strengths of this study are its high follow-up rate and its longitudinal design. Also, the four independent dietary components identified in our study explained 40% of the variation in adolescent food group consumption. In other studies which used PCA to analyze dietary patterns, the variance ranged from 15% to 31% [6, 15, 29].

In conclusion, our results showed that the number of siblings is associated with the dietary patterns in later adolescence, even after adjustment for potential confounders. Having siblings is associated to higher adherence to the protein and fast food pattern; the fruits and vegetables pattern; and the sweets, soft drinks, and dairy products pattern, which characterize a diversified diet.

Supporting information

Acknowledgments

All colleagues and workers who contributed to the study included since its 1^st year. This article is based on data from the study "Pelotas Birth Cohort, 1993" conducted by Postgraduate Program in Epidemiology at Universidade Federal de Pelotas with the collaboration of the Brazilian Public Health Association (ABRASCO) and the Brazilian National Research Council (CNPq). From 2004 to 2013, the Wellcome Trust supported the 1993 birth cohort study. The European Union, National Support Program for Centers of Excellence (PRONEX), and the Brazilian Ministry of Health supported previous phases of the study.