Effect of Yakult Ingestion on Diet-induced Insulin Resistance in Humans

Inclusion Criteria: * Males and females * Aged 18-30 * Physically active (exercising at least 3 times per week for more than 30 min at a time) * Non-smoker * Free from cardiovascular or metabolic disease * Weight stable for at least 6 months * Normal body mass index (BMI: 18.5-24.9 kg/m2)\* * Compliant (i.e. understands and is willing, able and likely to comply with all study requirements) * Note: If BMI is \>24.9, but body fat % (as measured by bioelectrical impedance analysis) is below 21% in males and 31% in females, then the subject may still be recruited at the PI's discretion. Exclusion Criteria: * Using probiotic or prebiotic supplements within the previous 3 months * Vegetarians and vegans * Diagnosis of insulin resistance, pre-diabetes or full diabetes * Underweight (determined as BMI less than 18.5 kg/m2) * Overweight or obese (determined as BMI greater than 24.9 kg/m2) * Those on a calorie controlled diet or other dietary restrictions that would prevent them from consuming the probiotic treatment and high fat/high calorie diet. * Those who are unwilling to restrict their intake of fermented dairy products. * Those with known or suspected food intolerances, allergies or hypersensitivity * Women who are known to be pregnant or who are intending to become pregnant over the course of the study. * Participation in another clinical trial * Those who have donated blood within 3 months of the screening visit and participants for whom participation in this study would result in having donated more than 1500 ml of blood in the previous 12 months. * Participants who take any form of regular medication that is known to affect either the gut microbiota and/or insulin sensitivity or who have taken any antibiotics in the previous 3 months. * Participants who know they would not be available for all the lab visits during the 4-week study period.