The rates of child and adolescent overweight and obesity (OW/OB) remain a global public health concern. The seriousness of this health concern is, in part, because an obese phenotype beginning in childhood tends to remain stable into adulthood (1–3). While it is rare for children and adolescents to be diagnosed with cardiovascular disease or to exhibit multiple criteria of the metabolic syndrome, the presence of some cardiometabolic disease risk factors, as well as OW/OB, in childhood and adolescence track into adulthood and are early antecedents of future diseases (4, 5). In 2013, 27% of Canadian youth aged 3–19 years old had OW/OB (6). In 2007–2009, only 2% of Canadian youth 10–18 years had the metabolic syndrome, but 38% had at least one metabolic syndrome risk factor (7). Thus, interventions that aim to reduce OW/OB and cardiometabolic disease risk factors should begin early to improve child and adolescent health as well as to help prevent chronic cardiometabolic diseases in adulthood.

Currently, no single pediatric cardiometabolic risk assessment standard exists, but variables used to indicate risk often include one or more of glucose metabolism (fasting glucose, insulin, or insulin resistance, homeostatic model assessment of insulin resistance [HOMA-IR]), cholesterol (total cholesterol [TC]; high-density lipoproteins [HDL]), triglycerides (TG), and waist circumference (WC) (8–10). Global cardiometabolic risk is another framework used to discuss one's comprehensive cardiometabolic risk, which includes the presence of traditional risk factors of cardiovascular disease (e.g., hypertension and high cholesterol), the metabolic syndrome criteria (e.g., waist circumference, and triglycerides), and inflammatory cytokines and adipokines (e.g., tumor necrosis factor alpha [TNF-α], low adiponectin) (11, 12). Global cardiometabolic risk has been supported for use in children and adolescents in whom one or more of the components of the metabolic syndrome may be present without the overt syndrome, or without traditional cardiovascular disease risk factors (12), however, its use for youth is not yet widely accepted. Nonetheless, the measurement of several cardiometabolic markers, including and in addition to traditional risk factors, can improve our understanding of how lifestyle interventions improve overall cardiometabolic health in pediatric populations.

Lifestyle interventions that incorporate healthy dietary changes can improve cardiometabolic outcomes in youth (13). Dairy products are rich sources of macronutrients and micronutrients, including protein, calcium, and vitamin D, and have been important dietary components of successful weight management interventions in adults, in part, because they promote favorable body composition and musculoskeletal changes (14–17). However, the effect of dairy product consumption on cardiometabolic health is mixed. Meta-analyses demonstrate that dairy product consumption is inversely associated with risk of OW/OB in youth (18, 19), and a cross-sectional multi-center study reported that higher dairy consumption was inversely associated with an improved cardiovascular risk score in adolescent females (20). In contrast, a review of evidence from randomized control trials (RCTs) suggests that dairy product consumption has a neutral effect on cardiometabolic health outcomes, including blood lipids (21). In terms of inflammation, while one systematic review concluded that dairy product consumption has no adverse effects on inflammatory markers (22), a more recent review of clinical trials, primarily conducted in adults, across different weight statuses concluded that dairy product consumption has a predominantly anti-inflammatory effect, particularly in those with metabolic disorders (23). To date there is a paucity of controlled research studies in adolescents with OW/OB that specifically investigate dairy product consumption and cardiovascular disease risk markers.

Cardiorespiratory fitness and physical activity levels demonstrate beneficial relationships with cardiometabolic disease risk factors in youth (24, 25), and some exercise interventions have improved markers of cardiometabolic health in adolescents with OW/OB (26, 27). Given the mixed findings (i.e., overall benefit or neutral) between dairy consumption and indices of cardiometabolic health and the benefits of dairy (and its components) on growth and development, lifestyle modification interventions including dairy consumption and exercise, that assess cardiometabolic disease risk markers, particularly in youth with OW/OB, are warranted. Our group has recently demonstrated that dairy intake with exercise promoted fat loss in adolescent females with OW/OB (28). Other similar investigations that have assessed the combined effect of both dairy intake and structured exercise training on body composition have been conducted in adolescent males of normal weight (29), and in a mix of males and females of varying weight statuses (30). These investigations demonstrated no benefit of increased dairy consumption on body fat and did not examine markers of cardiometabolic health. As females generally consume fewer dairy products than males (31, 32), and because of the less well-characterized relationships between changes in dairy intake, adiposity and cardiometabolic disease risk factors in youth, the objective of this investigation was to determine the effect of increased dairy product intake, as part of a 12-week diet and exercise weight management intervention, on cardiometabolic disease risk variables, and to assess the relationship between changes in adiposity and these markers in adolescent females with OW/OB.

Baseline descriptive characteristics of the participants in RDa and LDa are shown in Table 1. There were significant increases in height (RDa: 0.4 ± 0.5; LDa: 0.5 ± 0.9 cm) and decreases in waist circumference (RDa: −1.4 ± 4.7; LDa: −2.2 ± 4.7 cm) in both groups over the intervention (main effects for time, p < 0.05). There were no changes in body mass (RDa: 0.1 ± 3.4; LDa: −0.5 ± 3.4 kg) or BMI (RDa: −0.1 ± 1.2; LDa: −0.3 ± 1.2 kg/m²; main effects for time, p > 0.05). There was a significant decrease in %BF in both groups (RDa: −1.7 ± 1.6; LDa: −1.2 ± 1.1 %; main effect for time, p < 0.001). FM decreased to a greater extent in RDa (−1.4 ± 2.2 kg) compared to LDa (−1.1 ± 2.0 kg) over the intervention (interaction, p = 0.04).

Dietary variables are shown in Table 2. There were no significant changes in energy or fat intake in both groups (main effect for time p > 0.05). Carbohydrate intake decreased over the intervention in both groups (main effect of time, p = 0.04). Dietary protein, calcium and vitamin D intake, and daily dairy servings increased to a greater extent in RDa compared to LDa (interactions p < 0.001).

Cardiometabolic variables are shown in Table 3. There were no significant changes over time or differences over time between groups for TG, TC, HDL, TC/HDL ratio, LDL, glucose, insulin, HOMA-IR, adiponectin, and TNF-α (main effects of time and interactions, p > 0.05). Leptin decreased over the 12-week intervention in both groups (main effect of time, p = 0.02). There were main effects of group for insulin and HOMA-IR (p = 0.04 and p = 0.03, respectively), reflecting higher values for RDa compared to LDa at both time points (Table 3).

Because we observed no interactions between group and time for the cardiometabolic variables, we collapsed the intervention groups to assess the global relationship between changes in adiposity, using change in %BF, and change in individual cardiometabolic variables. There were moderate correlations between change in adiposity and changes in some cardiometabolic variables. Specifically, change in %BF correlated with change in HDL (r = −0.40), TC/HDL ratio (r = 0.42), LDL (r = 0.36), and TNF-α (r = 0.35) (Table 4). Controlling for dairy intake did not further change or strengthen these relationships indicating that dairy intake had no influence on the relationships between change in adiposity and change in cardiometabolic variables.

The key finding from this secondary analysis is that a higher dairy intake (4 servings/day), consisting of mixed dairy products ranging in fat content, in combination with exercise and dietary counseling, did not affect (adversely or beneficially) cardiometabolic variables in adolescent girls with OW/OB. Despite no effect, this finding extends our previously published results from this intervention study highlighting significant improvements in body composition and markers of bone metabolism with increased dairy consumption (28, 33). Additionally, our previous observation that both RDa and LDa decreased fat mass following the 12-week lifestyle intervention corroborates our finding from the present study that leptin decreased in both groups. We also found favorable associations between changes in adiposity and changes in HDL, TC/HDL ratio, LDL, and TNF-α. While these relationships were not influenced by changes in dairy product consumption, correlations suggest that, through our lifestyle modification intervention (with or without increased dairy intake), reductions in adiposity were favorably associated with changes in some variables that contribute to increased cardiometabolic disease risk.

Our study provides novel data regarding the effect of increased dairy product intake, as part of a lifestyle modification program involving structured exercise training and dietary counseling, on cardiometabolic disease risk markers in adolescent females with OW/OB. Although, we noted that some participants in our study had elevated risk factors, most of them did not present with the metabolic syndrome, according to the International Diabetes Federation consensus definition of metabolic syndrome for children and adolescents (10). This may be a reason for the lack of observed change or group differences in cardiometabolic variables with the intervention. Indeed, while 89% of our participants surpassed even the adult female cut-off for WC (80 cm) and 41% had low age-specific HDL (<1.03 mmol/L ≤ 15 years; <1.29 mmol/L ≥ 16 years), only 15% had TG over cut-offs (≥ 1.7 mmol/L), and none surpassed fasting glucose cut-offs (≥ 5.6 mmol/L) (10). Many of the positive effects of dairy on cardiometabolic disease risk outcomes, and relationships therein are found in those with OW/OB who also have several pre-existing risk factors or diagnosed metabolic disorders (23, 36). Thus, our participants may have been relatively “too healthy” to see significant changes.

Many studies assessing the effect of dairy on blood lipids, and/or inflammatory markers have been carried out in adult populations, and are summarized in narrative and systematic reviews, which have suggested that dairy product intake has neutral to beneficial effects (21–23, 37, 38). The most recent of these reviews included 27 RCTs in adults without severe inflammatory disorders and concluded that dairy product and/or dairy protein consumption had no adverse effects and possibly beneficial effects on low-grade systemic inflammation; a finding that was most commonly observed in adults with OW/OB (37). None of these reviews specifically assessed these relationships in youth with/without exercise.

A few RCTs have assessed increased dairy intake on markers of cardiometabolic health in pediatric (i.e., 5–18 years) populations with OW/OB (39–42). St-Onge et al. (40) implemented 16 weeks of healthy diet counseling supplemented with either high-milk (944 ml/d) or low-milk (236 ml/d) consumption in children (mean age 9.4 ± 0.8 years) with OW and found no beneficial changes in blood lipids, fasting glucose, or insulin in the high-milk group relative to the low-milk group. A longer 3 year RCT in younger children (mean age 5.6 ± 0.5 years) with OB by Kelishadi et al. (39) compared changes in cardiovascular disease risk factors in three groups: those consuming a dairy-rich diet (>800 mg ca/day) plus healthy lifestyle counseling, those on a calorie-restricted diet plus healthy lifestyle counseling, and those given only the healthy lifestyle counseling. Following the initial 6 months, TG, HDL fasting insulin and HOMA-IR were improved in all groups, but this improvement was maintained at 1 year only in the group consuming a dairy-rich diet. After 3 years, these markers of cardiometabolic health appeared similar across the 3 groups. Thus, like our study, these studies (39, 40) report little to no benefit of increased dairy intake on cardiometabolic variables. Although, the participants in our study differed substantially in age and maturation from those in St-Onge et al. (40) and Kelishadi et al. (39), all participants were of pediatric age, and were undergoing substantial growth, development and maturation, and thus dairy-related improvements in markers of cardiometabolic disease risk may have been masked by these concurrent physiological changes. Interestingly, St-Onge et al. (40) found that 16 weeks of high-milk consumption improved insulin area under the curve following an oral glucose tolerance test to a greater extent than low-milk consumption. Measuring cardiometabolic variables in a challenged, postprandial state, may be more informative from a disease risk standpoint than measuring under static, fasting conditions (43). Indeed, postprandial measures of glucose and TG in adults show stronger associations with cardiovascular events relative to fasting measures (44, 45), and this may be the case in youth too. Thus, to assess whether dairy product consumption improves cardiometabolic health it may also be important for future studies in adolescents with OW/OB to assess these cardiometabolic outcomes in a postprandial or challenged state.

Several intervention studies have included structured exercise training and assessed cardiometabolic outcomes in adolescents with OW/OB, and some have combined nutritional counseling (without a focus on dairy) with supervised exercise training (27). Two 4-month RCTs involving combined exercise training and nutritional education have reported improvements in fasting glucose (46), HOMA-IR and markers of inflammation (47) in adolescents with OW/OB. In addition, a 1 year family-based weight management program consisting of exercise, nutritional education, and behavior modification improved body composition, TC, fasting insulin and HOMA-IR relative to a control group in youth with OB (48). Despite the similar study designs reflecting our LDa group, there were several differences between these studies compared to ours that could account for the different results including a longer study duration and higher initial body fat levels. Also, it is important to note that our main intervention was not designed with cardiometabolic disease risk factors as the primary endpoint, and thus, we may have been underpowered. Future studies should be undertaken with adequate power to specifically detect changes in cardiometabolic disease risk factors with and without dairy in adolescent females and males undergoing lifestyle modification for obesity management.

Although, our study was conducted in the context of energy balance producing weight maintenance, weight loss in youth is associated with improvements in some cardiometabolic outcomes (49). To this effect, there are also lifestyle interventions in youth that have focused on weight loss and have improved cardiometabolic disease risk factors (50, 51). For example, a 12-week diet and exercise intervention induced weight and fat loss, and improved blood lipids, fasting insulin and HOMA-IR in children (range: 6–11 years) with obesity (50). In adult populations, our previous research in premenopausal females with OW/OB undergoing a 4-month diet and exercise intervention also demonstrated significant beneficial changes in cardiometabolic variables (i.e., blood lipids, inflammation) with weight and fat loss (14). Dairy intake in this study did not affect these results. Thus, weight loss (with fat loss) may be an important driver for change in cardiometabolic disease risk factors, and dairy product intake, in lifestyle modification programs, adds no further benefit. In the present investigation, the lack of improvement in indices of cardiometabolic health may be related to the lack of overall weight loss, despite improvements in adiposity in both groups. This notion is corroborated by previous research in youth with OB (52, 53) and could be further explored in the context of weight loss and dairy consumption.

In our study, participants in both groups were counseled to eat a healthy diet, and while both groups improved body composition, the high dairy group saw greater reductions in fat mass (28). While this reduction did not translate to significant improvements in markers of cardiometabolic risk, our correlations suggest that a reduction in adiposity was favorably associated with changes in some cardiometabolic variables, specifically HDL, TC/HDL ratio, LDL, and TNF-α. Similarly, Lira at al. (54) conducted a 1-year single-arm exercise, nutrition, and psychological intervention study that induced weight and fat loss but showed no significant improvements in inflammation in adolescents with OB. The authors also observed significant positive correlations between visceral fat (measured by ultrasonography) and inflammatory markers (54). Therefore, in both our study and the study by Lira et al. (54), adiposity was positively associated with inflammation during a lifestyle intervention where adiposity improved over time (i.e., fat mass and %BF decreased) without significant improvements in inflammation. Of note, in our study, this association was found in the absence of weight loss (but with significant fat loss) and independent of dairy consumption.

Throughout puberty, the trajectories of most cardiometabolic disease risk factors (e.g., TG, HDL, LDL, insulin, HOMA-IR) are curvilinear (8, 55). Changes in these variables during this time may make it more difficult to identify significant improvements in these variables (56). Indeed, in accordance with the patterns of pubertal change for these cardiometabolic disease risk factors, the International Diabetes Federation cardiometabolic risk cut-offs are age-specific, grouping together 10 to 15-year-olds and 16- to 18-year-olds (10). As such, observations of “no change” in cardiometabolic variables in our study may not actually be due to a lack of a response to the intervention, per-se, but rather to the variability in the physiological levels of these factors and the natural progression of these pubertal changes (56). For example, because younger adolescents, aged 10–13 years, undergo a period of transient insulin resistance indicated by an increasing HOMA-IR (55), the absence of change in fasting insulin and HOMA-IR over our intervention, could indicate a positive adaptation. While we only recruited participants who were menarcheal, our participants' ages spanned 10–19 years (by the end of the intervention), and there can be up to 5 years of variability in biological maturation at a single chronological age, especially during times of peak pubertal change (at ~11–13 years old in females) (57). Indeed the participant heterogeneity across the cardiometabolic variables was large, and we did not have a reliable measure of maturation [e.g., Tanner staging or years from menarche (57)] to ensure that sexual and somatic maturation was similar between groups. Thus, the ability of our intervention to significantly improve markers of cardiometabolic disease risk may have been masked by different trajectories of pubertal development and the variability therein. Nonetheless, intensive multicomponent interventions that work to improve healthy lifestyle habits remain the recommendation for adolescents with OB (58) and are effective at reducing adiposity and some cardiometabolic outcomes (13, 59). As such, it is important to continue to design intervention studies with the purpose of improving body composition (specifically decreasing body fat) and decreasing cardiometabolic disease risk within the context of lifestyle modification and weight management in this population that can account for the inherent variability during the adolescent period.

In summary, our study demonstrated that, compared to a low dairy diet, the addition of a variety of dairy foods (4 servings/day) to a diet and exercise, lifestyle modification program for weight management did not differentially change markers of cardiometabolic disease in adolescent females with OW/OB. Favorable associations were found between changes in adiposity and changes in cardiometabolic disease risk factors, but these were not altered after controlling for changes in dairy consumption. Our previous findings from this intervention demonstrate the positive effect of dairy consumption on musculoskeletal health, body composition and nutrient intake (28, 33); and, while the current findings demonstrate no additional benefit (or harm) of dairy on indices of cardiometabolic health, we assert that dairy foods should still be included as part of a healthy diet for adolescent girls with OW/OB during this critical time of growth and development. Future research designed to primarily assess the effect of increased dairy product consumption on cardiometabolic disease risk factors in this population is warranted.

The raw data supporting the findings of this study are available from the corresponding author, Andrea R. Josse, upon reasonable request.

The studies involving human participants were reviewed and approved by Brock University's Biosciences Research Ethics Board (BREB 14-284). Written informed consent to participate in this study was also provided by the participants' legal guardian/next of kin.

PK, BF, and AJ: study design conceptualization. LS, EB-T, NK, MC, PK, BF, and AJ: data analysis, interpretation, and drafting and revising manuscript. All authors approved of the final version of this manuscript.

AJ, BF, and PK report grants for this research from Dairy Farmers of Canada, US National Dairy Council (Dairy Management Inc.), non-financial support from Danone and Parmalat during the conduct of the study; AJ reports personal fees from Dairy Farmers of Canada Grant Review Board outside the submitted work. LS and EB-T report some salary support from the US National Dairy Council grant. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.