Milk and dairy products contain significant amounts of nutrients that contribute to optimal health - nutrients like calcium, vitamin D, and high-quality protein. Fermented milk products or fermented dairy products are dairy foods that have been fermented with certain bacteria. Yogurt is a fermented dairy product containing millions of beneficial bacteria. In this study, the invesgitagtors will look at the effect of milk (a non-fermented dairy product) and yogurt (a fermented dairy product) supplementation on bone health and the amount of fat and muscle mass in Canadian young adults over a 24-month period. While dairy products contain significant amounts of nutrients, the scientific community does not know the impact of long-term supplementation of fermented (i.e., yogurt) or non-fermented (i.e., milk) dairy food on bone health and the amount of fat and muscle mass in young adults. To fill this knowledge gap, the investigators will recruit participants with low calcium intake and assign them to three different groups: 1) milk (intervention) group; 2) yogurt (intervention) group; and 3) control group. The investigators will ask the participants in the milk group to drink 1.5 servings (375 mL) of milk per day for 24 months. Participants in the yogurt group will consume 2 servings (350 g) of yogurt per day for 24 months. Those in the control group will continue their usual diets. Using a randomized controlled trial design, the investigators will measure bone health parameters, hormonal indices related to bone metabolism, body composition (e.g., muscle mass, fat mass), and the number and composition of bacteria living in the gastrointestinal (GI) tract. The hypothesis is that supplementation with yogurt will have more positive effects on bone health indices, particularly femoral neck BMD as the primary outcome, than milk in Canadian adults aged 19-30 years. The secondary hypothesis is that supplementation with yogurt, as a fermented milk product, will have a more beneficial effect than milk on body composition measures. The data will provide valuable information for developing targeted health initiatives and marketing strategies regarding the benefits of fermented and non-fermented dairy product consumption.

The overarching goal of this project is to determine the role of milk and yogurt supplementation on bone health and body composition in Canadian adults aged 19 to 30 years. Both the prevalence of obesity and osteoporosis among Canadians reflect a public health concern. According to data from 2018, 27% of Canadians aged 18 and older were classified as obese, and 36% were classified as overweight. Data from 2016 revealed a diagnosis of osteoporosis for 12% of Canadians. Consumption of milk and milk products play a role in bone homeostasis over the life course but most of the research has focused on children or older adults. Dairy product intake is associated with lower body weight or body fat. However, Canadian cross-sectional data shows a decline in the consumption of dairy products among all ages from 2004 to 2015. The overall impact of dairy consumption trends is reflected in the prevalence of calcium inadequacy among Canadians. Previous studies suggest that dairy products may positively influence bone homeostasis and body composition through various mechanisms involving key nutrients and the contribution of probiotics. Young adults are in a transitional period and thus at a critical point for developing healthy lifestyle habits that support optimal body composition and maintenance of peak bone mineral density. Further, as fermented milk products contain many beneficial nutrients, determining the specific role probiotics play is difficult to define. The research will build on previous studies with a specific focus on addressing current knowledge gaps on the health impacts of young adults and the comparison between milk and yogurt.

The specific objectives of the research are:

1. To examine the effects of milk and yogurt supplementation on bone mineral density (BMD), bone mineral content (BMC), bone structure, and bone geometry of Canadian adults aged 19-30 years.
2. To examine the effects of milk and yogurt supplementation on hormonal indices (parathyroid hormone, Insulin-like growth factor 1, 25-hydroxyvitamin D) related to bone metabolism in Canadian adults aged 19 to 30.
3. To examine the effects of milk and yogurt supplementation on biochemical indices of bone turnover (Procollagen type 1 N-propeptide, Osteocalcin, Bone alkaline phosphatase, N-terminal telopeptide of type I collagen, C-terminal telopeptide of type 1 collagen) in Canadian adults aged 19-30.
4. To examine the effects of milk and fermented milk product supplementation on body composition (bone-free lean tissue mass, total body fat mass, abdominal fat mass, percent total body fat) of Canadian adults aged 19 to 30.
5. To examine the effects of milk and fermented milk product supplementation on gut microbiota of Canadian adults aged 19 to 30

Inclusion Criteria:

• 19-30 years old
• Dietary calcium intake below 1000mg/ day
• living in the Saskatoon area (Saskatchewan, Canada)

Exclusion Criteria:

• Calcium intake from both food and supplement above the estimated average requirement (EAR) for adults aged 19-30 years (>800 mg/day)
• Total dairy intake of more than 1 serving per day
• Body mass index greater than to 30 kg/m2
• Medical history of metabolic bone, liver, endocrine, connective tissue, and respiratory diseases, thyroid disorders, or cancer
• Diagnosed cases with secondary osteoporosis due to hypoparathyroidism
• Hormonal disorders or disturbances
• Taking medications known to influence bone mass and density (e.g., steroids, diuretics, heparin, and cancer drugs)
• Cow's milk allergy
• Pregnant or lactating women, or those planning to conceive during the duration of the trial