The aim of this research is to clarify the role of different dairy products including both full-fat and low-fat dairy in maintaining health in adults and children through its effects beyond their well-known contribution of healthy nutrients. The deleterious health consequences of obesity are recognized as a major financial burden to health care systems. Diets rich in fruits and vegetables and that also include dairy products have been suggested to play a role in the control of body weight and other aspects of health including the maintenance of healthy gut bacteria. In contrast, full-fat diets, especially those high in saturated fat, have been linked with negative health effects. Although dairy products represent an important source of saturated fat, it has been proposed that the combination of nutrients and complex food forms of the various dairy products may in fact counteract the negative effects of the fat. Thus, increased consumption of dairy products could very likely provide a partial dietary solution to improved body weight and metabolic health. Therefore, we are investigating the role of both full-fat and low-fat dairy products in their different physical forms (i.e. varying levels of fat that contribute to different textures) on appetite, food intake, control of blood sugar (glucose), body weight, cholesterol levels, and blood pressure in both children and adults. Existing dairy products (milk, cheese, and yogurt) ranging in fat content will be compared for their effects on satiety, food intake, glucose, insulin, satiety hormones, gut bacteria and other metabolic parameters linked to cardiometabolic health in normal weight children and adults, as well as in children and adults living with overweight and obesity.

The overall objective is to examine the long-term effects of full-fat dairy products on appetite and body weight control, diet quality, and metabolic health in adults living with obesity (18-55 y) and in children (8-16 y). This project also aims to identify some key mechanisms (i.e. gut peptides, gut microbiota) involved in the beneficial impact of dairy products on these outcomes. This study aims to evaluate the impact of a web-based nutrition intervention integrating full-fat or low-fat dairy products into the diets of families (at least one parent with BMI >30 kg/m2) under free-living conditions, on overall dairy consumption, body weight and composition, diet quality, eating and psychobehavioural traits and cardiometabolic outcomes, in normal weight/obese adults and children. This is a randomized, controlled, single-blind study consisting of three parallel groups. Families (n=25/group) will be randomized to either an intervention promoting either 1) low-fat or 2) full-fat dairy) or 3) control group (no intervention but same follow-up) over an 8-week period. The nutrition intervention aims to increase the quantity and variety of dairy products (i.e. low and full-fat milk, yogurt and cheese) in the diet. Evaluation periods for each family will be conducted before the study (week 0 in the lab), at the end (week 9 at home) and after 3 months (week 20 at home) after the intervention. Measurements include anthropometry, fasting lipid and glycemic profiles, diet quality, eating and psychobehavioral traits and food reward/appreciation/acceptance. The proposed research will provide timely data required to support recommendations to consume low and full-fat dairy products in individuals living with obesity, particularly during weight loss and maintenance. It will also provide the basis for family interventions that have the potential to positively impact diet quality and dairy consumption.

Inclusion Criteria:

Parent criteria are as follows:

• men and women between 18-55 years
• body mass index (BMI) between 30-40 kg/m2
• absence of pregnancy, breastfeeding or menopause (no menstruation)
• stable body weight (weight change <5 kg for three months prior to screening).

Family criteria are as follows:

• being a family composed of at least one parent (mother/father) and at least two children between 8 to 16 years old (families between 3 to 5 persons). Families with at least one obese parent (BMI between 30-40 kg/m2) will be recruited since children coming from these families are more at risk of developing obesity and may benefit more from dairy products
• all participants should have no allergies to dairy products or lactose intolerance and be in good general health.
• since we are recruiting adults with obesity and dairy products may positively impact several metabolic markers, those with hypertension or deteriorated blood glucose and lipid profiles and/or taking medications will also be considered.

This study will be single-blinded.