The aim this study is to investigate the effects of time-restricted eating (TRE) on body composition, muscle function and markers of metabolic health of adults over 60 years old. This study will compare different variations of TRE - with and without an additional protein.

This study involves attending two study days at the University of Surrey for baseline and end-of-intervention measurement of body composition using a gold-standard dual energy x-ray absorptiometry (DEXA) scan; muscle function using hand grip strength and 30-second sit-to-stand tests; weight. A blood sample will be taken at each study visit to measure markers of lipid and glucose control, and insulin sensitivity.

Participants will be randomly allocated to one of four study groups:

• control group: maintain habitual dietary patterns
• TRE group: fast for 16 hours overnight, eat between 12-8pm
• TRE + Protein (AM): fast for 16 hours overnight, eat between 12-8pm; take a 30g plant-based protein supplement in the morning
• TRE + Protein (PM): fast for 16 hours overnight, eat between 12-8pm; take a 30g plant-based protein supplement in the afternoon Participants will be asked to follow the intervention according to their allocated group for 8 weeks.

Inclusion Criteria:

• Gender: male and female
• Age range: 60 years or older
• Fasting for 12 or less hours on a daily basis
• BMI range: 23-30 kg/m2
• Weight stability: no more than 3kg weight gain or loss in the past 3 months
• Regular eating pattern, i.e. 3 meals a day
• Able to prepare the protein supplement

Exclusion Criteria:

• Any of the following present (in line with exclusion criteria used in previous TRE research in older adults):

  • known renal impairment
  • heart attack or stroke in the past three months
  • continuous use of supplemental oxygen to manage a chronic pulmonary condition or heart failure
  • rheumatoid arthritis
  • Parkinson's disease
  • active treatment for cancer in the past year
  • insulin dependent diabetes mellitus

• taking medications that preclude fasting for 16 h

• actively trying or planning to lose weight

• history of an eating disorder

• outside of stated age or BMI range

• fasting for longer than 12 hours on a daily basis

• unable to prepare the protein supplement

• extreme morning/evening chronotype

• sleep disorders

• regular meal skipping

• history of difficulty having a blood sample taken

• Recent exposure to high-dose radiation

• Vigorous exercise on more than 3 occasions a week

Not required or applicable for this study protocol