Potential Cardiometabolic Health Benefits of Full-Fat Dairy: The Evidence Base

Since their inception in 1980, the Dietary Guidelines for Americans have promoted low- or fat-free dairy foods. Removing fat from dairy does not reduce putatively beneficial nutrients per serving, including calcium, vitamin D, and potassium. Additionally, links between saturated fat and dietary cholesterol intakes with cardiovascular disease risk have helped to sustain the view that low-fat dairy foods should be recommended. Emerging evidence shows that the consumption of full-fat dairy foods has a neutral or inverse association with adverse cardiometabolic health outcomes, including atherosclerotic cardiovascular disease, type 2 diabetes, and associated risk factors. Thus, although low-fat dairy is a practical, practice-based recommendation, its superiority compared with full-fat dairy is not obviously supported by results from recent prospective cohort studies or intervention trials. To evaluate the emerging science on full-fat dairy, a group of nutrition experts convened to summarize and discuss the scientific evidence regarding the health effects of consuming full-fat dairy foods. Future studies should focus on full-fat dairy foods (milk, yogurt, and cheese) in the context of recommended dietary patterns and consider meal composition and metabolic phenotype in assessing the relation between full-fat dairy consumption and cardiometabolic health.

Dairy Foods and Dairy Fats: New Perspectives on Pathways Implicated in Cardiometabolic Health

Low-fat and nonfat dairy products have been promoted as part of a healthy dietary pattern by both US dietary guidelines and professional organizations for several decades. The basis for this recommendation stems in part from the putative negative cardiometabolic effects associated with saturated fat consumption. However, as nutrition research has shifted from a single nutrient to a whole-food/dietary pattern approach, the role of dairy foods and dairy fat in the diet-disease relationship is being reexamined. Most observational and experimental evidence does not support a detrimental relationship between full-fat dairy intake and cardiometabolic health, including risks of cardiovascular disease and type 2 diabetes. Indeed, an expanded understanding of the dairy food matrix and the bioactive properties of dairy fats and other constituents suggests a neutral or potentially beneficial role in cardiometabolic health. To consider how consuming dairy foods, including full-fat dairy, is associated with cardiometabolic health, this review provides an innovative perspective on mechanisms that link dairy consumption to 3 main biological systems at the core of metabolic health, the gastrointestinal, hepatic, and vascular systems.

Cumulative average dietary pattern scores in young adulthood and risk of incident type 2 diabetes: the CARDIA study

AIMS/HYPOTHESIS

The evidence for the role of contemporary dietary patterns, trends and predominant aspects of energy intake in a typical American diet and in type 2 diabetes risk is limited. Therefore, we examined the association between dietary pattern scores created to reflect the 2015 Dietary Guidelines for Americans (DGA) Scientific Report, a Palaeolithic (Palaeo) diet, a diet high in 'empty calories', and the A Priori Diet Quality Score (APDQS) (cohort reference) and type 2 diabetes risk over time.

METHODS

We carried out a prospective analysis of 4719 young adult black and white men and women from the Coronary Artery Risk Development in Young Adults (CARDIA) study with repeated dietary histories collected at study years 0, 7 and 20. Using multivariable Cox proportional hazards regression models, we examined the association between time-dependent cumulative average dietary pattern scores and incident type 2 diabetes.

RESULTS

During the 30 year follow-up period, 680 (14.4%) incident cases of type 2 diabetes occurred. There was no association between the 2015 DGA, Palaeo or empty calorie scores and type 2 diabetes risk in the overall population. Participants in the fourth quartile of the APDQS, reflecting a more healthful dietary pattern, had a 45% lower risk of type 2 diabetes compared with those in the lowest quartile (HR 0.55 [95% CI 0.41, 0.74]). In stratified analyses there was an inverse association for the 2015 DGA in non-smokers per SD (HR 0.86 [95% CI 0.74, 0.99]) and an inverse association for the empty calorie score in white women (HR 0.76 [95% CI 0.60, 0.96]) as well as in a subgroup analysis of the Palaeo index of participants who maintained a high score over 20 years (per SD, HR 0.59 [95% CI 0.39, 0.88]).

CONCLUSIONS/INTERPRETATION

Higher levels of the APDQS, which largely aligns with the 2015 DGA, were strongly inversely associated with 30 year type 2 diabetes risk in the CARDIA cohort; the results from the other patterns were nuanced and need to be considered in the context of the study and potential biases.

Diet Quality and Cardiovascular Disease Risk in Postmenopausal Women With Type 2 Diabetes Mellitus: The Women's Health Initiative

Background

Dietary patterns are associated with cardiovascular disease (CVD) risk in the general population, but diet–CVD association in populations with diabetes mellitus is limited. Our objective was to examine the association between diet quality and CVD risk in a population with type 2 diabetes mellitus.

Methods and Results

We analyzed prospective data from 5809 women with prevalent type 2 diabetes mellitus at baseline from the Women's Health Initiative. Diet quality was defined using alternate Mediterranean, Dietary Approach to Stop Hypertension, Paleolithic, and American Diabetes Association dietary pattern scores calculated from a validated food frequency questionnaire. Multivariable Cox's proportional hazard regression was used to analyze the risk of incident CVD. During mean 12.4 years of follow‐up, 1454 (25%) incident CVD cases were documented. Women with higher alternate Mediterranean, Dietary Approach to Stop Hypertension, and American Diabetes Association dietary pattern scores had a lower risk of CVD compared with women with lower scores (Q5 v Q1) (hazard ratio [HR]_aMed 0.77, 95% CI 0.65–0.93; HR_DASH 0.69, 95% CI 0.58–0.83; HR_ADA 0.71, 95% CI 0.59–0.86). No association was observed between the Paleolithic score and CVD risk.

Conclusions

Dietary patterns that emphasize higher intake of fruits, vegetables, whole grains, nuts/seeds, legumes, a high unsaturated:saturated fat ratio, and lower intake of red and processed meats, added sugars, and sodium are associated with lower CVD risk in postmenopausal women with type 2 diabetes mellitus.

Cumulative intake of artificially sweetened and sugar-sweetened beverages and risk of incident type 2 diabetes in young adults: the Coronary Artery Risk Development In Young Adults (CARDIA) Study

BACKGROUND

Epidemiological evidence has demonstrated a positive association between artificially sweetened beverage (ASB) and sugar-sweetened beverage (SSB) consumption and type 2 diabetes (T2D) risk. However, research informing this topic in young adults is limited.

OBJECTIVE

This study examined the association between ASB, SSB, and total sweetened beverage (TSB; combined ASB and SSB) consumption and T2D risk in young adults.

METHODS

A prospective analysis of 4719 Black and White men and women aged 18-30 y at baseline was conducted from the Coronary Artery Risk Development in Young Adults (CARDIA) study. Each participant's beverage intake was assessed using the CARDIA Diet History at baseline and at study Years 7 and 20. Multivariable Cox proportional hazards regression models were used to examine cumulative average ASB, SSB, and TSB intakes and risk of T2D.

RESULTS

During the 30-y follow-up period, 680 participants developed T2D. ASB consumption was associated with a 12% greater risk of T2D per serving/day (HR 1.12, 95% CI 1.04-1.20) in a model adjusted for lifestyle factors, diet quality, and dieting behavior. Further adjustments for baseline BMI (HR 1.07, 95% CI 0.99-1.14) and weight change during follow-up (HR 1.04, 95% CI 0.97-1.12) attenuated the association. SSB and TSB consumption as continuous variables per 1 serving/day of intake were associated with 6% and 5% increased risks of T2D, respectively (HRSSB 1.06, 95% CI 1.01-1.10; HRTSB 1.05, 95% CI 1.01-1.09), in the model accounting for lifestyle factors, dieting behavior, baseline BMI, and weight change. Results were consistent when the exposures were modeled in categories of consumption and quintiles.

CONCLUSIONS

In young adults, long-term ASB, SSB, and TSB consumption were associated with increased risks of T2D. However, the estimates for ASB were attenuated when accounting for weight changes.

The Association of Serum Carotenoids, Tocopherols, and Ascorbic Acid With Rapid Kidney Function Decline: The Coronary Artery Risk Development in Young Adults (CARDIA) Study

OBJECTIVE

Nutritional intervention targeting dietary intake modification is a major component of treatment for chronic kidney disease; however, little is known about the relationship between dietary intake and kidney function decline in individuals with preserved kidney function.

DESIGN AND METHODS

In this prospective cohort study we examined the association of biomarkers of dietary intake with kidney function decline over a 5-year interval in 2,152 men and women with cystatin-C-based estimated glomerular filtration rate > 60 mL/minute/1.73 m² from the Coronary Artery Risk Development in Young Adults study. The biomarkers of interest included carotenoids, tocopherols, and ascorbic acid. Multivariable logistic regression was used to explore the relationship between serum concentrations of the sum of 4 carotenoids (α-carotene, β-carotene, β-cryptoxanthin, and lutein/zeaxanthin), lycopene, α-tocopherol, γ-tocopherol, and ascorbic acid and rapid kidney function decline, defined as .15% decline in cystatin-C-based estimated glomerular filtration rate over 5 years.

RESULTS

During the 5-year follow-up, 290 participants (13.5%) experienced rapid kidney function decline. Relative to individuals in the lowest quartile of serum carotenoids, those in the highest quartile had significantly lower odds of rapid kidney function decline in the fully adjusted model (odds ratio, 0.51; 95% confidence interval [CI], 0.32-0.80; P trend, .02). No association of levels of serum tocopherols, ascorbic acid, or lycopene with kidney function decline was found. There was no evidence that results differed for individuals with hypertension or diabetes.

CONCLUSIONS

These results demonstrate that higher serum carotenoid levels, reflective of a fruit- and vegetable-rich dietary pattern, inversely associate with rapid kidney function decline in early middle adulthood and provide insight into how diet might play a role in chronic kidney disease prevention.

Temporal metabolomic responses of cultured HepG2 liver cells to high fructose and high glucose exposures

High fructose consumption has been implicated with deleterious effects on human health, including hyperlipidemia elicited through de novo lipogenesis. However, more global effects of fructose on cellular metabolism have not been elucidated. In order to explore the metabolic impact of fructose-containing nutrients, we applied both GC-TOF and HILIC-QTOF mass spectrometry metabolomic strategies using extracts from cultured HepG2 cells exposed to fructose, glucose, or fructose + glucose. Cellular responses were analyzed in a time-dependent manner, incubated in media containing 5.5 mM glucose + 5.0 mM fructose in comparison to controls incubated in media containing either 5.5 mM glucose or 10.5 mM glucose. Mass spectrometry identified 156 unique known metabolites and a large number of unknown compounds, which revealed metabolite changes due to both utilization of fructose and high-carbohydrate loads independent of hexose structure. Fructose was shown to be partially converted to sorbitol, and generated higher levels of fructose-1-phosphate as a precursor for glycolytic intermediates. Differentially regulated ratios of 3-phosphoglycerate to serine pathway intermediates in high fructose media indicated a diversion of carbon backbones away from energy metabolism. Additionally, high fructose conditions changed levels of complex lipids toward phosphatidylethanolamines. Patterns of acylcarnitines in response to high hexose exposure (10.5 mM glucose or glucose/fructose combination) suggested a reduction in mitochondrial beta-oxidation.

Associations between dairy foods, diabetes, and metabolic health: potential mechanisms and future directions

Epidemiological evidence supports an inverse relationship between adequate intake of dairy foods and susceptibility to type 2 diabetes (T2D). The biological mechanisms responsible for this association remain to be established. This review provides a current perspective on proposed mechanisms that may underlie these effects, and highlights how randomized clinical trials can be applied to investigate these relationships. Results from epidemiological studies generally support that consumption of milk and dairy products is associated with a lower incidence of T2D or improvements in glucose homeostasis indices, and studies of animal and cell models support a positive effect of dairy-rich diets or components on metabolic and inflammation factors relevant to T2D and insulin resistance. Emerging evidence indicates that dairy components that alter mitochondrial function (e.g., leucine actions on silent information regulator transcript 1 (SIRT1)-associated pathways), promote gut microbial population shifts, or influence inflammation and cardiovascular function (e.g., Ca-regulated peptides calcitonin gene-related peptide [CGRP] or calcitonin) should be considered as possible mechanistic factors linking dairy intake with lower risk for T2D. The possibility that dairy-derived trans-palmitoleic acid (tC16:1) has metabolic bioactivities has also been proposed. Pre-clinical and clinical studies focusing specifically on these parameters are needed to validate hypotheses regarding the potential roles of dairy products and their components on the determinants of glucose tolerance, particularly insulin sensitivity, pancreatic endocrine function, and inflammation in individuals at-risk for T2D development. Such experiments would complement epidemiological studies and add to the evidence base for recommendations regarding consumption of dairy products and their individual components.