This study will investigate the effect of providing a daily ketogenic nutritional supplement in the evening for a prolonged time (4 weeks) to induce a mild ketogenic state during the night in healthy elderly (60-80 years), overweight/obese (BMI: 25-35 kg/m2) individuals with low physical activity, on 24h rhythmicity in energy metabolism as compared to a non-ketogenic, isocaloric control.

Inclusion Criteria:

• Aged 60-80 years
• Body mass index (BMI) 25-35 kg/m2
• Sedentary lifestyle (not more than 2 hours of structured physical activity per week in the past 3 months)
• Stable dietary habits (no weight loss or gain > 5 kg in the past 3 months)
• Healthy (as determined by dependent physician based on medical questionnaire)
• Regular sleeping habits (7-9h of daily sleep)

Exclusion Criteria:

• Type 2 diabetes
• Participants with active congestive heart failure and/or severe renal and or liver insufficiency
• Uncontrolled hypertension
• Alcohol consumption of >3 servings per day for men and >2 servings per day for women
• Unstable body weight (weight gain or loss > 5 kg in the last 3 months) or intention to lose weight
• Participants who are on an intermittent fasting diet
• Previous enrolment in a clinical study with an investigational product during the last 3 months or as judged by the investigator which would possibly hamper our study results
• Significant food allergies/intolerance (seriously hampering study meals or study product)
• Participants who do not want to be informed about unexpected medical findings
• Blood donation during or within 2 months prior to the study
• Disturbances in circadian rhythm determined with the follow criteria:
• Extreme early bird or extreme night person (score ≤30 or ≥70 on MEQ-SA questionnaire)
• Heavily varying sleep-wake rhythm
• Night shift work during last 3 months
• Travel across > 1 time zone in the last 3 months
• High daily caffeine intake > 400mg (more than 4 cups of coffee or energy drinks)