Time Restricted Feeding In Clinical Practice
A potential new approach to weight loss and metabolic disease management - Dr Julia Shrosbree - Endocrinologist.
Time restricted feeding or TRF (such as 16 hours of fasting and 8 hours of eating) presents a potential new strategy to approach weight loss and metabolic disease management beyond the traditional model of energy intake (amount and type of food) and expenditure (exercise and thermogenesis).
Recent studies in humans suggest that the median duration of eating is approximately 14.5 h per day with over 50% spreading their daily caloric intake over 15 hours or longer.
TRF vs Intermittent Fasting
TRF is often bundled into the same category of 'intermittent fasting' but there are some important distinctions. Intermittent fasting such as fasting for 2 days and then consuming normal calories on 5 days (the 5:2) is thought to result in weight and metabolic benefits due to energy restriction. In contrast, the benefits of TRF appear to be independent of caloric restriction, suggesting an important interplay with the circadian clock.
For instance, rodents fed a high fat diet ad libitum were compared to rodents allowed to consume the same number of calories within a restricted time interval of 8–10 h (TRF mice). TRF mice were protected from diet-induced obesity and had increased energy expenditure and fat oxidation.
In animal studies, TRF:
- Reduces body weight, insulin levels, blood pressure and hepatic fat
- Prevents hyperlipidaemia
- Slows tumor growth
- improves inflammatory markers and glycaemic control
- Increases lifespan
Emerging data in human studies suggests TRF:
- Decreases body weight, blood pressure and inflammation
- Improves insulin sensitivity and lipid profiles
In addition, participants using TRF report subjective improvements in sleep satisfaction, less hunger at bedtime, and increased energy levels.
Mechanisms of the metabolic benefits of TRF
TRF triggers a key physiological process referred to as metabolic switching. Increasing the fasting window beyond 12 hours when glycogen stores in hepatocytes are depleted, triggers a metabolic switch between glucose oxidation to accelerated adipose tissue lipolysis reflected by increased plasma free fatty acids and glycerol. In addition, TRF may influence metabolism by altering the gut microbiome to one that is less obesogenic.
Does timing matter?
Several recently published human studies indicate that early TRF (TRF at the start of the day - e.g. 10am to 6pm) may be associated with additional metabolic benefits over TRF later in the day. This approach is based on aligning TRF with hormonal circadian rhythms in which β-cell responsiveness, peripheral insulin sensitivity and clearance, and the thermic effect of food are highest in the morning. However, further randomised controlled trials that look at different TRF windows are awaited.
Potential risks of TRF and/or Intermittent Fasting
Potential disadvantages of TRF include adverse effects such as nausea, diarrhea, constipation, fatigue and dizziness.
Fasting may be dangerous and it is not recommended for pregnant and breastfeeding women, people with (or at risk of) eating disorders, or those with a BMI under 18.5 kg/m2.
It should be used cautiously in patients with diabetes on medications associated with a risk of hypoglycaemia such as insulin or sulfonylureas as doses may need to be adjusted to avoid hypoglycaemia. In addition, patients on SGLT-2 inhibitors are at risk of euglycemic DKA in the setting of fasting and reduced carbohydrate intake. The exact window of safe TRF in these patients is not known.
Dr Shrosbree is a specialist Endocrinologist who is committed to ensuring her patients receive evidence-based, personalised and professional care. She has a particular interest in osteoporosis and calcium disorders, obesity/weight management, thyroid disorders, type 2 diabetes, gestational diabetes, menopause, PCOS. She also has experience in managing the endocrinopathies associated with eating disorders such as anorexia nervosa.