Emad Yuzbashian-Sharifabad | ALES Graduate Seminar

Event details: A graduate exam seminar is a presentation of the student’s final research project for their degree.

This is an ALES MSc Final Exam Seminar by Emad Yuzbashian-Sharifabad. This seminar is open to the general public to attend.

PhD with Dr. Catherine Chan

Thesis Topic: Dairy Product Consumption and Metabolic Health

Abstract: 

The increasing prevalence of overweight and obesity worldwide has raised the alarm for urgently needed preventative strategies to counter the trend of increased risk associated with these conditions, including type 2 diabetes (T2D) and metabolic-associated fatty liver disease (MASLD). Energy imbalance and suboptimal diets can induce these conditions. The contribution of dairy products remains debatable in this regard. Dairy products are quite heterogeneous regarding nutrient composition, physical state, and structure, and their effect on health will likely vary.

In this dissertation, I aim to unravel the effects of different types of dairy foods on obesity-associated metabolic outcomes. It covers a prospective cohort study, a meta-analysis of observational studies, a preclinical trial, and a scoping review. I hypothesize that the impact of dairy consumption on metabolic health varies significantly based on the type of dairy product, fermentation status, and food matrices, and they can attenuate the metabolic consequences of a Western-style diet.

To address the first objective, the association of dairy consumption patterns with the incidence of T2D among Alberta’s Tomorrow Project (ATP) participants was evaluated. The average follow-up time was 5.2 years. Detailed dietary intake information was assessed using a validated food-frequency questionnaire; health outcomes were collected using a self-report questionnaire. Principal component analysis (PCA) was used to extract the dairy consumption pattern. A mixed intake of low and whole-fat milk 36% decreased the risk of T2D in males. This effect was more pronounced in high-risk groups such as those with obesity.

The second objective was to document the association between total dairy intake, intake from specific dairy foods, and MASLD. A meta-analysis of 11 observational studies with 43,649 individuals. Pooled data indicated that high dairy product consumption was significantly inversely associated with MASLD risk. Milk and yogurt consumption were associated with a 14% and 12 lower risk of MASLD, respectively. However, no significant association was seen with cheese intake.

Objective 3 was conducted to elucidate the mechanism of action of low/non-fat dairy matrices on metabolism in a mouse model of obesity. Male C57BL/6 obese mice were fed an HFD and subsequently allocated into treatment groups receiving either fat-free milk, plain yogurt, or reduced fat (19%) cheddar cheese at 10% daily caloric intake for 8 weeks. Milk-treated mice showed high energy expenditure and lower weight gain due to the activation of brown adipose tissues through the SIRT1-PPARγ-PGC1α pathway, which includes increasing UCP1, one of the major thermogenic regulators. Milk consumption also markedly decreased hepatic steatosis, confirmed by a lower triglyceride content. The mechanism involved lipogenesis suppression and
enhancement of liver fat oxidation. Milk-fed mice showed improved glucose homeostasis, at least in part via ameliorating the insulin signaling pathway and suppressing gluconeogenic enzymes. While yogurt supplementation improved hepatic steatosis and insulin sensitivity, these beneficial effects were less potent than milk ones. Yogurt increased BAT activity and energy expenditure. Supplementation with cheese had a more neutral effect, with modest improvements in body weight. Changes in the activity of BAT and energy expenditure pathways were minimal after cheese feeding, and they had minimal to no effect on liver lipids. Gut microbiota analysis indicated increased beneficial bacteria such as Streptococcus in the yogurt and Anaerotignum in the milk groups. Serum and liver lipidomics demonstrated that milk and yogurt consumption significantly reduced diacylglycerides and increased levels of beneficial lipid species, indicating enhanced lipid metabolism and reduced hepatic lipotoxicity.

Objective 4 was a scoping review summarizing studies on the impact of dairy products on phosphatidylcholine (PC) and lysophosphatidylcholine (LPC) concentrations in humans and animals. Fifteen publications were included in this review. Generally, total phospholipids were stable, and specific PC and LPC species increased, especially those with dairy fatty acid biomarkers, including C15:0 and C17:0. In animal models, dairy consumption also resulted in increased excretion of fecal phospholipids and significant changes in the level of liver and serum PC and LPC species.

The combination of results from this research, along with a review of the current literature, supports my hypothesis that dairy products can mitigate the adverse effects of a Western diet on metabolic health with shared and unique mechanisms. Specifically, the positive effects of milk and yogurt in elevating thermogenesis, insulin sensitivity and lowering liver fat underscore the importance of such dairy products in dietary recommendations to prevent T2D and MASLD.