Dairy Product Consumption in the Prevention of Metabolic Syndrome: A Systematic Review and Meta-Analysis of Prospective Cohort Studies

Investigation of bias due to selective inclusion of study effect estimates in meta-analyses of nutrition research

We aimed to explore, in a sample of systematic reviews (SRs) with meta-analyses of the association between food/diet and health-related outcomes, whether systematic reviewers selectively included study effect estimates in meta-analyses when multiple effect estimates were available. We randomly selected SRs of food/diet and health-related outcomes published between January 2018 and June 2019. We selected the first presented meta-analysis in each review (index meta-analysis), and extracted from study reports all study effect estimates that were eligible for inclusion in the meta-analysis. We calculated the Potential Bias Index (PBI) to quantify and test for evidence of selective inclusion. The PBI ranges from 0 to 1; values above or below 0.5 suggest selective inclusion of effect estimates more or less favourable to the intervention, respectively. We also compared the index meta-analytic estimate to the median of a randomly constructed distribution of meta-analytic estimates (i.e., the estimate expected when there is no selective inclusion). Thirty-nine SRs with 312 studies were included. The estimated PBI was 0.49 (95% CI 0.42-0.55), suggesting that the selection of study effect estimates from those reported was consistent with a process of random selection. In addition, the index meta-analytic effect estimates were similar, on average, to what we would expect to see in meta-analyses generated when there was no selective inclusion. Despite this, we recommend that systematic reviewers report the methods used to select effect estimates to include in meta-analyses, which can help readers understand the risk of selective inclusion bias in the SRs.

A review of dairy food intake for improving health among black adults in the US

The adult life stage encompasses a range of new experiences, opportunities, and responsibilities that impact health and well-being. During this life stage, health disparities continue to increase for Black Americans, with Black adults having a disproportionate burden of obesity, chronic diseases, comorbidities, and worse treatment outcomes compared to their White peers. While many of the underlying factors for these disparities can be linked to longstanding sociopolitical factors such as systemic racism, food insecurity, and poor access to healthcare, there are also several modifiable risk factors that are known to significantly impact health outcomes, such as improving diet quality, increasing physical activity, and not smoking. Of all the modifiable risk factors known to impact health, improving dietary habits is the factor most consistently associated with better outcomes for body weight and chronic disease. Of the major food groups recommended by the 2020-2025 Dietary Guidelines for Americans (DGA) for achieving healthier dietary patterns, dairy foods have a nutrient profile which matches most closely to what Black Americans are inadequately consuming (e.g., vitamin A, vitamin D, calcium, magnesium). However, Black adults tend to consume less than half the recommended daily servings of dairy foods, in part, due to issues with lactose intolerance, making higher intake of dairy foods an ideal target for improving diet quality and health in this population. This review examines the current body of evidence exploring the links between dairy intake, obesity, cardiometabolic disease risk, chronic kidney disease, and the most common types of cancer, with a special focus on health and disparities among Black adults. Overall, the evidence from most systematic reviews and/or meta-analyses published in the last decade on dairy intake and health outcomes has been conducted on White populations and largely excluded research on Black populations. The findings from this extensive body of research indicate that when teamed with an energy-restricted diet, meeting or exceeding the DGA recommended 3 daily servings of dairy foods is associated with better body weight and composition outcomes and lower rates of most common chronic diseases than lower intake (<2 servings per day). In addition to the number of daily servings consumed, the specific types (e.g., milk, yogurt, cheese) and subtypes (e.g., low-fat, fermented, fortified) consumed have also been shown to play major roles in how these foods impact health. For example, higher intake of fermented dairy foods (e.g., yogurt) and vitamin D fortified dairy products appear to have the most protective effects for reducing chronic disease risk. Along with lactose-free milk and cheese, yogurt is also generally low in lactose, making it an excellent option for individuals with lactose intolerance, who are trying to meet the DGA recommendations for dairy food intake.

Variation observed in consensus judgments between pairs of reviewers when assessing the risk of bias due to missing evidence in a sample of published meta-analyses of nutrition research

OBJECTIVES

To evaluate the risk of bias due to missing evidence in a sample of published meta-analyses of nutrition research using the Risk Of Bias due to Missing Evidence (ROB-ME) tool and determine inter-rater agreement in assessments.

STUDY DESIGN AND SETTING

We assembled a random sample of 42 meta-analyses of nutrition research. Eight assessors were randomly assigned to one of four pairs. Each pair assessed 21 randomly assigned meta-analyses, and each meta-analysis was assessed by two pairs. We calculated raw percentage agreement and chance corrected agreement using Gwet's Agreement Coefficient (AC) in consensus judgments between pairs.

RESULTS

Across the eight signaling questions in the ROB-ME tool, raw percentage agreement ranged from 52% to 100%, and Gwet's AC ranged from 0.39 to 0.76. For the risk-of-bias judgment, the raw percentage agreement was 76% (95% confidence interval 60% to 92%) and Gwet's AC was 0.47 (95% confidence interval 0.14 to 0.80). In seven (17%) meta-analyses, either one or both pairs judged the risk of bias due to missing evidence as "low risk".

CONCLUSION

Our findings indicated substantial variation in assessments in consensus judgments between pairs for the signaling questions and overall risk-of-bias judgments. More tutorials and training are needed to help researchers apply the ROB-ME tool more consistently.

Dietary patterns derived by reduced rank regression are associated with lipid disorders among Korean adults: a cross-sectional analysis

BACKGROUND

Lipid disorders are a potent risk factor for cardiovascular diseases. Moreover, the intake of dietary fatty acids has been closely related to blood lipid levels. Therefore, this cross-sectional study examined the associations between dietary patterns related to fatty acid intake and lipid disorders in Korean adults.

METHODS

From the 2013-2019 Korea National Health and Nutrition Examination Surveys data, 8399 men and 11404 women (aged ≥ 19 years) were selected. Reduced rank regression was employed to identify dietary patterns from 26 food groups, aiming to explain the maximum variation in the intake of saturated fatty acids (SFA), polyunsaturated fatty acids (PUFA), omega-3 fatty acids, and the PUFA/SFA ratio. Associations of quintiles (Q) of dietary pattern scores with lipid disorders were examined using multiple logistic regression stratified by sex.

RESULTS

Three dietary patterns were identified: dietary pattern 1 showed positive factor loadings for vegetable oils, seasonings, legumes, nuts, and fish; dietary pattern 2 was high in consumption of red meat, bread and snacks, and milk and dairy products; and dietary pattern 3 was rich in fish and milk and dairy products. In men, dietary pattern 3 was inversely associated with elevated triglycerides (Q5 vs. Q1: odds ratio [OR] = 0.82, 95% confidence interval [CI] = 0.69-0.97, P-trend = 0.008). In women, dietary pattern 2 was positively associated with elevated total cholesterol (OR = 1.31, 95% CI = 1.12-1.52, P-trend < 0.001) but inversely associated with low HDL-cholesterol (OR = 0.70, 95% CI = 0.59-0.83, P-trend < 0.001).

CONCLUSION

In this study, dietary patterns explaining the intake of various types of fatty acids were differentially associated with lipid disorders in Korean adults. Dietary pattern characterized by higher intakes of red meat, bread and snacks and milk and dairy products were positively associated with elevated total cholesterol, whereas dietary pattern rich in fish consumption showed an inverse association with elevated triglycerides. These findings could be instrumental in developing dietary guidelines and strategies for preventing and managing lipid disorders in this population.

Dairy Intake and Risk of Cognitive Decline and Dementia: A Systematic Review and Dose-Response Meta-Analysis of Prospective Studies

Dairy intake may influence cognition through several molecular pathways. However, epidemiologic studies yield inconsistent results, and no dose-response meta-analysis has been conducted yet. Therefore, we performed a systematic review with a dose-response meta-analysis about the association between dairy intake and cognitive decline or incidence of dementia. We investigated prospective studies with a follow-up ≥6 mo on cognitive decline or dementia incidence in adults without known chronic conditions through a systematic search of Embase, Medline, Cochrane Library, Web of Science, and Google Scholar from inception to 11 July 2023. We evaluated the dose-response association using a random-effects model. We identified 15 eligible cohort studies with >300,000 participants and a median follow-up of 11.4 y. We observed a negative nonlinear association between cognitive decline/dementia incidence and dairy intake as assessed through the quantity of consumption, with the nadir at ∼150 g/d (risk ratio: 0.88; 95% confidence interval: 0.78, 0.99). Conversely, we found an almost linear negative association when we considered the frequency of consumption (risk ratio for linear trend: 0.84; 95% confidence interval: 0.77, 0.92 for 1 time/d increase of dairy products). Stratified analysis by dairy products showed different shapes of the association with linear inverse relationship for milk intake, whereas possibly nonlinear for cheese. The inverse association was limited to Asian populations characterized by generally lower intake of dairy products, compared with the null association reported by European studies. In conclusion, our study suggests a nonlinear inverse association between dairy intake and cognitive decline or dementia, also depending on dairy types and population characteristics, although the heterogeneity was still high in overall and several subgroup analyses. Additional studies should be performed on this topic, including a wider range of intake and types of dairy products, to confirm a potential preventing role of dairy intake on cognitive decline and identify ideal intake doses. This review was registered at PROSPERO as CRD42020192395.

Associations between dairy consumption and the physical function in Japanese community-dwelling older adults: The Shimane CoHRE study

OBJECTIVES

We investigated sex differences in the associations between dairy consumption and the physical function among community-dwelling older adults.

METHODS

Six hundred and fifty-six older adults (75.6 ± 6.4 years old) participated in this study. Dairy consumption (5-item Likert score) and the physical function (gait speed, handgrip strength, and skeletal muscle mass) were measured. The linear and quadratic associations between dairy consumption and the physical function measures were examined by a multiple linear regression analysis adjusted for covariates.

RESULTS

Among women, an increased dairy consumption was significantly linearly associated with greater hand-grip strength and faster gait speed (both p<0.05) after adjusting for covariates. Among men, dairy consumption was not associated with the physical function measures. Dairy consumption was not associated with the muscle mass in either sex.

CONCLUSIONS

Increased dairy consumption was associated with a superior physical function in older women.

Higher milk consumption is associated with a lower risk of diabetes mellitus: A case-control study

BACKGROUND & AIMS

Studies have determined that people with genetically defined lactase non-persistence have lower dairy intake that may lead to an increase risk of various non-communicable diseases. Furthermore, lactase non-persistence itself has been associated with insulin resistance. However, data on lactase non-persistence status and dairy intake in developing countries are sparse. We therefore aimed to define 1) the prevalence of lactase non-persistence among individuals with diabetes and non-diabetes in Thai population and 2) the links between lactase non-persistence, milk consumption, and risk of diabetes mellitus.

METHODS

We conducted a case-control study from participants of the National Health Examination Survey. DNA was isolated from the blood for LCT -13910C>T (rs4988235) polymorphism and processed using the Bio-rad c1000 touch thermal cycler and MALDI-TOF Mass Spectrometry MassARRAY Typer v4.0 (Agena Bioscience, San Diego, CA, USA) at the Center for Medical Genomics, Faculty of Medicine Ramathibodi Hospital. Cases were participants with previously diagnosed diabetes mellitus or fasting plasma glucose ≥126 mg/dL (n = 1,756) vs. the controls (n = 2,380).

RESULTS

We included 4,136 participants, 62% female, and 98.8% were > 30 years old. Homozygous CC genotype (i.e., lactase non-persistence) was noted in 98.6% and only 1.4% carried heterozygous CT. Most (76%) consumed milk <1 portion/month. Participants with either CC or CT genotype had comparable milk consumption and the risk of diabetes mellitus. Males, older adults, and lower education had a lower chance of consuming milk at least one portion per month. Besides various baseline variables, we found that higher milk consumption was associated with a lower DM risk (P = .01).

CONCLUSION

The prevalence of lactase non-persistence in Thai population is very high. A significant difference in milk consumption frequency in relation to the lactase non-persistence status was not found. However, higher milk consumption is associated with a lower risk of diabetes mellitus.

Dairy intake in relation to metabolic health status in overweight and obese adolescents

There was a lack of evidence on the association between dairy intake and metabolic health status in overweight/obese adolescents. This study evaluated the association between dairy intake and metabolic health status in overweight/obese Iranian adolescents. Overweight/obese adolescents (n = 203; 101 boys and 102 girls) selected by a multistage cluster random sampling method have participated in this cross-sectional study. Dietary intake was assessed using a validated 147-item food frequency questionnaire. Anthropometric indices, blood pressure, fasting glucose, insulin, and lipid profile were measured. Participants were categorized to metabolically healthy obese (MHO) and metabolically unhealthy obese (MUO) according to International Diabetes Federation (IDF) criteria and a combination of IDF with Homeostasis Model Assessment Insulin Resistance (HOMA-IR) criteria. The frequency of MUO based on IDF, and IDF/HOMA-IR definitions was 38.9% and 33.0%, respectively. In fully-adjusted model, participants in the highest tertile of dairy intake had 61% lower odds of MUO based on IDF criteria (OR = 0.39, 95% CI 0.15-0.99). Higher dairy intake was associated with a non-significant lower risk of MUO according to IDF/HOMA-IR definition in the maximally-adjusted model (OR = 0.44, 95% CI 0.17-1.16). Stratifies analysis by sex and body mass index revealed that the association was stronger in girls and overweight subjects. Furthermore, higher intake of low-fat dairy was related to a reduced likelihood of MUO, while higher intake of high-fat dairy was related to increased odds of MUO. This community-based cross-sectional study revealed that higher intake of dairy was associated with a significant lower odd of MUO among Iranian adolescents, especially in girls and overweight subjects.

Multilevel Understanding of the Impact of Individual- and School-Level Determinants on Lipid Profiles in Adolescents: The Cross-Level Interaction of Food Environment and Body Mass Index

Adolescents with comparable personal risk factors may have different lipid profiles because of the school’s context. Lipid determinants in adolescents should be considered using a multilevel perspective. This multilevel study investigated the effects of individual-level and school-level factors on lipid profiles in adolescents and evaluated the cross-level influence of lipid determinants. A representative adolescent cohort (n = 2727) was randomly selected from 36 schools in three diverse economic areas in Taiwan and assessed for their personal dietary patterns, physical parameters, and lipid profiles. For individual-level factors, both low physical activity and high body mass index (BMI) were associated with elevated triglyceride (TG), low-density lipoprotein cholesterol (LDL-C), and total cholesterol (TC) levels, and a sugar-sweetened beverage intake of >500 mL/day was associated with increases of 5.97 and 6.12 mg/dL in LDL-C and TC levels, respectively, compared with abstinence. Regarding school-level factors, students in schools with ≥2 health promotion programs per year had a 5.27 mg/dL lower level of LDL-C than those in schools with 0−1 program, and students in schools with ≥46 food outlets within 600 m of the school had 6.90 and 13.3 mg/dL higher levels of TG and TC, respectively, than those in schools with <46 food outlets. School context modified the individual-level positive correlation between BMI and TG level (the p-value for the random-slope effect was 0.003). In conclusion, individual-level and school-level factors exert a multilevel effect on adolescent lipid profiles. The food environment near the school has a stronger cross-level impact on individual TG levels in adolescents with a high BMI than in those with a normal BMI.

Healthy dietary patterns and metabolic dysfunction-associated fatty liver disease in less-developed ethnic minority regions: a large cross-sectional study

BACKGROUND

Little is known about the associations between healthy dietary patterns and metabolic dysfunction-associated fatty liver disease (MAFLD) in less-developed ethnic minority regions (LEMRs), where the prevalence of MAFLD is increasing rapidly and dietary habits are quite different from those in developed countries. Moreover, a significant subset of MAFLD individuals in LEMRs are nonobese, but the efficacy of dietary patterns on MAFLD individuals with different obese statuses is also unclear. We aimed to test the associations of two wildly recommended a priori dietary patterns-Alternate Mediterranean diet (AMED) and Dietary Approaches to Stop Hypertension (DASH)-with the risk of MAFLD in the total population, and further in nonobese and obese individuals.

METHODS

We recruited 99,556 participants in the China Multi-Ethnic Cohort Study, an ongoing cohort study in less-developed southwest China. Using validated food frequency questionnaire, each participant was assigned an AMED score and a DASH score. MAFLD was ascertained as hepatic steatosis on ultrasound together with diabetes, overweight/obesity, or two other metabolic risk factors. We performed logistic regression with inverse probability of exposure weighting (IPEW) to examine associations between two dietary patterns and MAFLD, adjusting for potential confounders under the guidance of directed acyclic graphs. Further, analyses were stratified by body mass index.

RESULTS

We included 66,526 participants (age 49.5±11.0; 62.6% women), and the prevalence of MAFLD was 16.1%. Participants in the highest quintile of DASH score showed strong inverse associations with risks of MAFLD (OR = 0.85; 95% CI, 0.80-0.91; Ptrend < 0.001) compared with participants in the lowest quintile. The association between DASH and nonobese MAFLD (OR = 0.69; 95% CI, 0.61-0.78; Ptrend < 0.001) was stronger (I2 = 78.5 % ; Pheterogeneity = 0.001) than that with obese MAFLD (OR = 0.90; 95% CI, 0.83-0.98; Ptrend = 0.002). There was a null association between AMED and MAFLD risk.

CONCLUSIONS

In LEMRs, a DASH diet but not AMED was associated with MAFLD. The relationship appeared to be more pronounced in nonobese MAFLD individuals than in obese MAFLD individuals.

Higher Animal Protein Intake During the Second Trimester of Pregnancy Is Associated With Risk of GDM

Background and Aims: This study aimed to examine the associations between the total protein intake as well as types and sources of proteins with the gestational diabetes mellitus (GDM) risk. Method and Results: This was a prospective cohort study of the pregnant women in Malaysia. In this study, the total, animal, and plant protein intakes were assessed using a semi-quantitative food frequency questionnaire. Of the 452 women, 48 (10.62%) were diagnosed with GDM. From pre-pregnancy to second trimester, most of the women had 10-20% of energy intake from protein (88.9-90.3%) and ≥75% of recommended protein intake (74.6-86.5%). The women in the highest tertile (T3) of total animal protein intake [adjusted odds ratio (AOR) = 2.76, 95% CI = 1.27-6.04] and red meat protein (AOR = 2.69, 95% CI = 1.27-5.70), specifically in the second trimester, had significantly higher GDM risk compared with the women in the middle tertile of intake (T2). Interestingly, the women in the T3 of egg protein in the second trimester were significantly at lower GDM risk (AOR = 0.43, 95% CI = 0.18-0.91) compared with those in T2. Conclusion: The highest tertile of animal protein (≥42.15 g/day) intake, particularly red meat protein in the second trimester was positively associated with the GDM risk, whereas the highest tertile of egg protein was inversely associated with the GDM risk. Protein intake before or during early pregnancy was not associated with the GDM risk. These findings underscore the importance of sources and types of protein intake, particularly after the first trimester of pregnancy, in relation to GDM risk.

Total, low-fat, and full-fat dairy consumption and risk of metabolic syndrome among workers

BACKGROUND & AIM

Dairy products may play a beneficial role against metabolic syndrome; however, epidemiological evidence is scarce in Asian populations, who consume less dairy than Western populations. We prospectively investigated the association between dairy product intake, both overall and by fat content, and metabolic syndrome in a Japanese working population.

METHODS

Participants were 1014 workers (aged 19-68 years) without metabolic syndrome at baseline who completed a 3-year follow-up survey. Dietary intake was assessed using a validated self-administered diet history questionnaire. Metabolic syndrome was defined according to the Joint Interim Statement (JIS) criteria. Multiple logistic regression was used to estimate the odds ratio of metabolic syndrome according to tertile of total, low-fat, and full-fat dairy product intake with adjustment for covariates.

RESULTS

At the 3-year follow-up, 66 (6.5%) workers were newly identified as having metabolic syndrome. A trend towards decreased odds of developing metabolic syndrome was observed among those in the highest tertile of total and full-fat dairy product intake: multivariable-adjusted odds ratio for the highest versus lowest tertile was 0.54 (95% CI 0.26-1.12; P for trend = 0.094) for total dairy products and 0.50 (95% CI 0.24-1.05; P for trend = 0.038) for full-fat dairy products. Low-fat dairy intake was not associated with metabolic syndrome.

CONCLUSIONS

Our results suggest that higher intake of full-fat, but not low-fat, dairy products may be associated with a lower risk of metabolic syndrome among Japanese.

Dietary Animal to Plant Protein Ratio Is Associated with Risk Factors of Metabolic Syndrome in Participants of the AHS-2 Calibration Study

BACKGROUND

Few research studies have focused on the effects of dietary protein on metabolic syndrome and its components. Our objective was to determine the relationship between the type of dietary protein intake and animal to plant (AP) protein ratio with metabolic syndrome and its components.

METHODS

This population-based study had a cross sectional design and conducted on 518 participants of the Adventist Health Study 2 (AHS-2) Calibration Study. Two sets of three dietary 24-h recalls were obtained six months apart. Anthropometric measures and biochemical tests were performed in clinics. Regression calibration models were used to determine the association of type of dietary protein with metabolic syndrome and its components (raised triglyceride, raised blood pressure, reduced high-density lipoprotein cholesterol (HDL), raised fasting blood glucose and increased waist circumference).

RESULTS

The likelihood of metabolic syndrome was lower in those with higher total dietary protein and animal protein intake (p = 0.02).Total protein (β = 0.004, [95%CI: 0.002, 0.007]), animal protein intake (β = 0.004, [95%CI: 0.001, 0.007]) and AP protein intake ratio (β = 0.034, [95%CI: 0.021, 0.047]) were positively associated with waist circumference. Higher AP protein ratio was related to higher fasting blood glucose (β = 0.023, [95%CI: 0.005, 0.041]).

CONCLUSION

Our study suggests that considering a significant amount of plant protein as a part of total dietary protein has beneficial effects on cardiometabolic risk factors.

Methods used to select results to include in meta-analyses of nutrition research: a meta-research study

OBJECTIVES

To investigate how often review authors encounter multiple results from included studies that are eligible for inclusion in a particular meta-analysis, and how often methods to select results are specified.

METHODS

MEDLINE and Epistemonikos were searched (January 2018 - June 2019) to identify systematic reviews with meta-analysis of the association between food/diet and health-related outcomes. A random sample of these reviews was selected, and for the first presented ('index') meta-analysis, rules used to select effect estimates to include in this meta-analysis were extracted from the reviews and their protocols. All effect estimates from the primary studies that were eligible for inclusion in the index meta-analyses were extracted (e.g. when a study report presented effect estimates for blood pressure at 3 weeks and 6 weeks, both unadjusted and adjusted for covariates, and all were eligible for inclusion in a meta-analysis of the effect of red meat consumption on blood pressure, we extracted all estimates and classified the study as having "multiplicity of results").

RESULTS

Forty-two systematic reviews with 325 studies (104 randomized, 221 non-randomized) were included; 14 reviews had a protocol. In 29% of review protocols and 69% of reviews, authors specified at least one decision rule to select effect estimates when multiple were available. In 68% of studies included in the index meta-analyses, there was at least one type of multiplicity of results.

CONCLUSIONS

Authors of systematic reviews of nutrition studies should anticipate encountering multiplicity of results in the included primary studies. Specification of methods to handle multiplicity when designing reviews is therefore recommended.

Association between Milk Intake and Incident Stroke among Japanese Community Dwellers: The Iwate-KENCO Study

We aimed to evaluate the association between the milk consumption and incident stroke in a Japanese population, where milk consumption is lower than that of Western countries. In total, 14,121 participants (4253 men and 9868 women) aged 40–69 years, free from cardiovascular diseases (CVD) were prospectively followed for 10.7 years. Participants were categorized into four groups according to the milk intake frequency obtained from a brief-type self-administered diet questionnaire. The adjusted HRs of total stroke, ischemic stroke and haemorrhagic stroke associated with milk intake frequency were calculated using the Cox proportional hazards model. During the follow-up, 478 stroke cases were detected (208 men and 270 women). Compared to women with a milk intake of <2 cups/week, those with an intake of 7 to <12 cups/week had a significantly low risk of ischemic stroke in a model adjusting CVD risk factors; the HR (95% CI) was 0.53 (0.32–0.88). No significant associations were found in men. This study suggested that milk intake of 7 to <12 cups/week decreased the risk of ischemic stroke in Japanese women. Milk intake of about 1 to <2 cups/day may be effective in the primary prevention of ischemic stroke in a population with low milk intake.

Dairy protein intake is inversely related to development of non-alcoholic fatty liver disease

BACKGROUND & AIMS

Non-alcoholic fatty liver disease (NAFLD) is the most common chronic liver disease and is closely related to metabolic dysfunction, including insulin resistance, obesity, and metabolic syndrome. Dairy protein, rich in casein and whey protein, could help to reduce metabolic diseases. Therefore, we investigated the relationship between dairy protein intake and incident NAFLD.

METHODS

We analyzed data for 5171 adults aged 40-69 years from the Korean Genome and Epidemiology Study.(KoGES) Participants were separated as men, women aged ≥50 years, and women aged <50 years and then divided into tertiles based on dairy protein intake. NAFLD was defined as NAFLD liver fat score >-0.640. Scores were calculated as 1.18 × metabolic syndrome (Yes: 1, No: 0) + 0.45 × diabetes mellitus (Yes: 2, No: 0) + 0.15 × serum insulin +0.04 × AST - 0.94 × (AST/ALT) - 2.89. Cox proportional hazards spline curves were drawn to visualize dose-response relationships between dairy protein intake and incident NAFLD. Multiple Cox hazard regression analysis was conducted to examine associations between dairy protein intake and incident NAFLD.

RESULTS

The Cox proportional hazards spline curves revealed a negative linear relationship between dairy protein intake and incident NAFLD. The cumulative incidence of NAFLD significantly decreased with increasing tertiles of dairy protein intake in men and women aged ≥50 years. After adjusting for confounding factors, the hazard ratios and 95% confidence intervals for NAFLD in the middle and highest tertiles, compared to the lowest tertile, were 0.80 (0.67-0.96) and 0.71 (0.57-0.88) in men, 0.89 (0.72-1.09) and 0.72 (0.56-0.92) in women aged ≥50 years, and 1.01 (0.80-1.27) and 0.91 (0.67-1.24) in women aged <50 years, respectively.

CONCLUSIONS

We found that higher dairy protein intake was significantly and inversely associated with the risk of incident NAFLD in men and women aged ≥50 years. Consumption of milk and other dairy products could help prevent the development of NAFLD.

Recent Progress in Metabolic Syndrome Research and Therapeutics

Metabolic syndrome (MetS) is a well-defined yet difficult-to-manage disease entity. Both the precipitous rise in its incidence due to contemporary lifestyles and the growing heterogeneity among affected populations present unprecedented challenges. Moreover, the predisposed risk for developing severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection in populations with MetS, and the viral impacts on host metabolic parameters, underscores the need to investigate this mechanism thoroughly. Recent investigations of metabolomics and proteomics have revealed not only differentially expressed substances in MetS, but also the consequences of diet consumption and physical activity on energy metabolism. These variations in metabolites, as well as protein products, also influence a wide spectrum of host characteristics, from cellular behavior to phenotype. Research on the dysregulation of gut microbiota and the resultant inflammatory status has also contributed to our understanding of the underlying pathogenic mechanisms. As for state-of-the-art therapies, advancing depictions of the bio-molecular landscape of MetS have emerged and now play a key role in individualized precision medicine. Fecal microbiota transplantation, aiming to restore the host's homeostasis, and targeting of the bile acid signaling pathway are two approaches to combatting MetS. Comprehensive molecular inquiries about MetS by omics measures are mandatory to facilitate the development of novel therapeutic modalities.

Dairy Consumption and Risk of Metabolic Syndrome: Results from Korean Population and Meta-Analysis

Dairy consumption has been associated with decreased risk of metabolic syndrome (MetS) in previous studies, but the association may be different according to each type of dairy products and its subgroups. Thus, we conducted an updated meta-analysis of observational studies to examine the association between various dairy products and risk of MetS. The PubMed and Web of Science databases were searched for eligible studies published up to February 2021. In addition, we included unpublished results from Korea National Health and Nutrition Examination Survey, 2013-2018, including 23,319 Korean adults and the elderly. A total of 35 studies (12 cohort studies and 25 cross-sectional studies) with 398,877 subjects were included in the meta-analysis. The pooled relative risks (RR) of MetS for the highest versus lowest categories of dairy consumption was 0.80 [95% confidence interval (CI): 0.72-0.88]. For the type of dairy products, there were also significant inverse associations with milk (RR: 0.83; 95% CI: 0.78-0.89) and yogurt consumption (RR: 0.89; 95% CI: 0.83-0.95). For cheese consumption, however, no significant association was found (RR: 0.98; 95% CI: 0.86-1.11). Our findings suggest that milk and yogurt consumption is inversely associated with the risk of MetS, but not cheese consumption.

Effect of low-fat dairy products fortified with 1500IU nano encapsulated vitamin D3 on cardiometabolic indicators in adults with abdominal obesity: a total blinded randomized controlled trial

BACKGROUND & AIMS

Vitamin D deficiency is widespread worldwide. In this study, we aimed to evaluate the effect of a nano encapsulated form of vitamin D used for fortifying low-fat dairy products (milk and yogurt) on anthropometric indices, glycemic status, and lipid profile in subjects with abdominal obesity.

METHODS

In a totally (quadruple) blinded, randomized, and parallel-controlled trial, 306 individuals with abdominal obesity were randomly allocated to one of four groups: fortified low-fat yogurt (FY, 1500 IU nano encapsulated vitamin D₃ per 150 g/d), non-fortified low-fat yogurt (nFY), fortified low-fat milk (FM, 1500 IU nano encapsulated vitamin D₃ per 200 g/d), non-fortified low-fat milk (nFM), for 10 weeks (nFM and nFY, were considered as the control groups). Anthropometric and biochemical parameters were measured at baseline and after a ten-week trial in Mashhad, Iran.

RESULTS

After the ten-week intervention, we found a significant increase in serum concentration of 25(OH)D in both the FM and FY groups compared to the respective control groups (19.10 ± 5.69 ng/mL and 20.88 ± 5.76 ng/mL respectively, p < .001). We observed a significant reduction in weight to hip ratio (p = .04) and a significant improvement in triglyceride (p < .001) and HDL-C (p = .01) only in FM group compared to nFM group. Also, we found a significant reduction in fasting serum insulin (p < .001), and a significant improvement of HOMA-IR (p < .001) and QUICKI (p < .001) in both intervention groups compared to their placebos.

CONCLUSIONS

An intake of fortified dairy products containing nano-encapsulated vitamin D₃ was associated with an improvement in some measures of anthropometric indices, glucose homeostasis, and lipid profiles, particularly in individuals receiving fortified milk. Hence, along with other benefits, fortification of dairy products with vitamin D may be an effective approach to improve some cardiometabolic indicators, such as insulin resistance.

TRIAL REGISTRATION NUMBER

IRCT20101130005280N27.

Associations of dairy intake with risk of incident metabolic syndrome in children and adolescents: Tehran Lipid and Glucose Study

AIMS

This cohort study examined the association of total and individual dairy products with the risk of incident MetS and its components in children and adolescents.

METHODS

We prospectively assessed 531 participants aged 6-18 years without the MetS at baseline during an average 6.6-year follow-up period. Dairy consumption was estimated with a valid and reliable food frequency questionnaire. The MetS was defined according to the Cook criteria. The multivariable regression model was used to calculate the odds ratio (OR) for incident MetS associated with the consumption of dairy products.

RESULTS

The incidence of MetS was 9.8% after an average 6.6-year follow-up. After adjusting for potential confounders, OR (95% confidence interval) for incident MetS was 0.48 (0.23-1.00) for total dairy, 0.44 (0.21-0.92) for low-fat dairy, 0.46 (0.22-0.98) for low-fat milk, and 0.45 (0.21-0.97) for low-fat yogurt when comparing participants in the highest versus lowest tertile. A moderate intake of regular cheese was associated with decreased risk of MetS (OR = 0.43, 95% CI: 0.19-0.97). Replacing one serving/day of total dairy with nuts was associated with a lower (OR: 0.63, 95% CI: 0.42-0.95), whereas replacement by red and processed meat was associated with higher (OR: 1.55, 95%CI: 1.21-1.97) MetS risk. No significant association was found between high-fat dairy and MetS risk.

CONCLUSIONS

Higher consumption of dairy products, particularly low-fat milk and yogurt, was associated with reduced risk of incident MetS, suggesting the capability of low-fat dairy products in the primary prevention of MetS in children and adolescents.

Effect of Yogurt Consumption on Metabolic Syndrome Risk Factors: a Narrative Review

PURPOSE OF REVIEW

Metabolic syndrome (MetS) comprises risk factors such as obesity, hypertriglyceridemia, hypertension, and hyperglycemia. Here we described the outcome of various yogurt consumption, either conventional, low-fat, high-fat, Greek, or enriched with nutrients or probiotics: (1) on the parameters of MetS risk factors and (2) on the mechanisms of action of the MetS risk factors.

RECENT FINDING

The majority (25 studies) of clinical trials and meta-analyses of clinical trials reported a beneficial effect of yogurt consumption in the prevention of MetS risk. Yogurt components, such as calcium, vitamin D, proteins, and probiotics, were associated with the multiple beneficial effects on the prevention of MetS. In general, yogurt consumption may be promoted within healthy dietary patterns to prevent MetS. More studies are needed to determine what type of yogurt has the greatest benefits for specific MetS risk factor prevention.

Milk consumption and multiple health outcomes: umbrella review of systematic reviews and meta-analyses in humans

In order to recapitulate the best available evidence of milk consumption and multiple health-related outcomes, we performed an umbrella review of meta-analyses and systematic reviews in humans. Totally, 41 meta-analyses with 45 unique health outcomes were included. Milk consumption was more often related to benefits than harm to a sequence of health-related outcomes. Dose–response analyses indicated that an increment of 200 ml (approximately 1 cup) milk intake per day was associated with a lower risk of cardiovascular disease, stroke, hypertension, colorectal cancer, metabolic syndrome, obesity and osteoporosis. Beneficial associations were also found for type 2 diabetes mellitus and Alzheimer's disease. Conversely, milk intake might be associated with higher risk of prostate cancer, Parkinson’s disease, acne and Fe-deficiency anaemia in infancy. Potential allergy or lactose intolerance need for caution. Milk consumption does more good than harm for human health in this umbrella review. Our results support milk consumption as part of a healthy diet. More well-designed randomized controlled trials are warranted.

Goat's Milk Intake Prevents Obesity, Hepatic Steatosis and Insulin Resistance in Mice Fed A High-Fat Diet by Reducing Inflammatory Markers and Increasing Energy Expenditure and Mitochondrial Content in Skeletal Muscle

Goat's milk is a rich source of bioactive compounds (peptides, conjugated linoleic acid, short chain fatty acids, monounsaturated and polyunsaturated fatty acids, polyphenols such as phytoestrogens and minerals among others) that exert important health benefits. However, goat's milk composition depends on the type of food provided to the animal and thus, the abundance of bioactive compounds in milk depends on the dietary sources of the goat feed. The metabolic impact of goat milk rich in bioactive compounds during metabolic challenges such as a high-fat (HF) diet has not been explored. Thus, we evaluated the effect of milk from goats fed a conventional diet, a conventional diet supplemented with 30% Acacia farnesiana (AF) pods or grazing on metabolic alterations in mice fed a HF diet. Interestingly, the incorporation of goat's milk in the diet decreased body weight and body fat mass, improved glucose tolerance, prevented adipose tissue hypertrophy and hepatic steatosis in mice fed a HF diet. These effects were associated with an increase in energy expenditure, augmented oxidative fibers in skeletal muscle, and reduced inflammatory markers. Consequently, goat's milk can be considered a non-pharmacologic strategy to improve the metabolic alterations induced by a HF diet. Using the body surface area normalization method gave a conversion equivalent daily human intake dose of 1.4 to 2.8 glasses (250 mL per glass/day) of fresh goat milk for an adult of 60 kg, which can be used as reference for future clinical studies.

Fermented dairy foods rich in probiotics and cardiometabolic risk factors: a narrative review from prospective cohort studies

Probiotic foods, including fermented dairy (FD) products such as yogurt and cheese, naturally contain live microorganisms, but the relationship between the consumption of probiotic foods and health is unclear. The aim of the present narrative review is to integrate the available information on the relationship between the most studied FD products, which are yogurt and cheese, and cardiometabolic risk factors obtained from meta-analysis, systematic reviews of prospective cohort studies (PCSs) and PCSs published up to 2 November 2019. Additionally, the effects identified by randomized controlled trials of less-studied FD products, such as kefir and kimchi, on cardiometabolic risk factors are provided. PCSs have shown that the consumption of cheese, despite its high saturated fat content, is not associated with expected hypercholesterolemia and an increased cardiovascular risk. PCSs have revealed that the total consumption of FD appears to be associated with a lower risk of developing stroke and cardiovascular disease. The consumption of yogurt seems to be associated with a lower risk of developing type 2 diabetes. There is a lack of sufficient evidence of a protective relationship between FD or cheese consumption and metabolic syndrome. Moreover, the association of FD, cheese and yogurt with hypertension needs further evidence. In conclusion, the intake of fermented foods containing probiotics, particularly yogurt and cheese (of an undetermined type), opens up new opportunities for the management of cardiometabolic risk factors.

Association between dairy product intake and hypertriglyceridemia in Korean adults

BACKGROUND/OBJECTIVES

Hypertriglyceridemia may be a more important predictor of cardiovascular disease in Asian population consuming carbohydrate-rich foods than in Western populations. Dairy products are known to play a beneficial role in obesity, dyslipidemia, and metabolic syndrome, but the results vary depending on gender and obesity. In this study, we investigated the associations between dairy product intake and hypertriglyceridemia in Korean adults.

SUBJECTS/METHODS

The participants were selected from the Korea National Health and Nutrition Examination Survey 2007–2012 (KNHANES IV and V). A total of 22,836 participants aged 19–64 years were included in the analysis. A food frequency questionnaire used to determine the frequency of consumption of products (milk and yogurt). Multivariable logistic regression was used to assess the associations between dairy product intake and hypertriglyceridemia.

RESULTS

A significantly decreased risk of hypertriglyceridemia was detected in the highest dairy product intake frequency group (≥ 1 time/day) (odd ratio [OR] = 0.79; 95% confidence interval [CI] 0.64–0.97, P for trend = 0.022) compared to that for the lowest dairy product intake frequency group. Among obese participants, the group with the highest intakes of milk (in men, OR = 0.64; 95% CI: 0.46–0.91, P for trend = 0.036) and yogurt (in women; OR = 0.53; 95% CI: 0.29–0.94, P for trend = 0.019) showed inverse associations with hypertriglyceridemia. No associations were detected in normal weight participants.

CONCLUSION

The association between dairy product intake and hypertriglyceridemia differed by gender and obesity status. Further prospective studies are needed to confirm these associations.

The association between milk consumption and the metabolic syndrome: a cross-sectional study of the residents of Suzhou, China and a meta-analysis

The association between milk consumption and the metabolic syndrome remains inconclusive, and data from Chinese populations are scarce. We conducted a cross-sectional study to investigate the association between milk consumption and the metabolic syndrome and its components among the residents of Suzhou Industrial Park, Suzhou, China. A total of 5149 participants were included in the final analysis. A logistic regression model was applied to estimate the OR and 95 % CI for the prevalence of the metabolic syndrome and its components according to milk consumption. In addition, the results of our study were further meta-analysed with other published observational studies to quantify the association between the highest v. lowest categories of milk consumption and the metabolic syndrome and its components. There was no significant difference in the odds of having the metabolic syndrome between milk consumers and non-milk consumers (OR 0·86, 95 % CI 0·73, 1·01). However, milk consumers had lower odds of having elevated waist circumference (OR 0·78, 95 % CI 0·67, 0·92), elevated TAG (OR 0·83, 95 % CI 0·70, 0·99) and elevated blood pressure (OR 0·85, 95 % CI 0·73, 0·99). When the results were pooled together with other published studies, higher milk consumption was inversely associated with the risk of the metabolic syndrome (relative risk 0·80, 95 % CI 0·72, 0·88) and its components (except elevated fasting blood glucose); however, these results should be treated with caution as high heterogeneity was observed. In summary, the currently available evidence from observational studies suggests that higher milk consumption may be inversely associated with the metabolic syndrome.

Introduction and Executive Summary of the Supplement, Role of Milk and Dairy Products in Health and Prevention of Noncommunicable Chronic Diseases: A Series of Systematic Reviews

Milk and dairy products contain multiple nutrients and contribute significantly to meet the nutritional requirements for protein, calcium, magnesium, phosphorus, potassium, zinc, selenium, vitamin A, riboflavin, vitamin B-12, and pantothenic acid. However, consumption of dairy is decreasing and moving away from the advised level in many countries and the potential benefits of milk and dairy products for health have come under question. This, in spite that numerous studies report health benefits associated with dairy consumption. The present supplement aims to assess and summarize scientific evidence regarding the impact of dairy intake on health and all-cause mortality, and on the prevention of diverse chronic diseases, mainly from meta-analyses of observational studies and randomized controlled trials (RCTs). There seem to positive associations between moderate maternal milk intake during pregnancy and infant birth weight, length and bone mineral content during childhood. Moreover, consumption of dairy products in older subjects may reduce the risk of frailty and decrease the risk for sarcopenia. The highest consumption of dairy products did not show a clear association with total osteoporotic fracture and hip fracture risk; however, a diminished risk of vertebral fracture was found. Analysis of the differences between high and low dairy consumption and for dose-response found no association between dairy product consumption and risk of all-cause mortality. Total and low-fat dairy consumption is associated with a reduced risk of developing metabolic syndrome and current evidence supports that consumption of dairy does not adversely affect the risk of cardiovascular outcomes and may even have a subtle protective effect. Moreover, evidence has been provided of an inverse association between the consumption of dairy products and ischemic heart disease and myocardial infarction. Also, the evidence suggests that dairy consumption, particularly low-fat dairy and yogurt is associated with a lower risk of type 2 diabetes. Likewise, moderate compared with medium consumption of dairy is associated lower risk for colorectal and bladder cancer and has no association with prostate cancer. Finally, consumption of milk or dairy products did not show a proinflammatory effect on healthy subjects, overweight/obese individuals, or individuals with other metabolic abnormalities, and fortification of dairy products with phytosterols and ω-3 fatty acids seems to be a good approach to improve cardiometabolic risk biomarkers. In conclusion, the systematic reviews and meta-analyses of the present supplement support adequate milk consumption at various stages of life and in the prevention/control of various noncommunicable chronic diseases.