Intermittent Fasting

What it is

A family of eating patterns that interleave longer-than-usual fasting windows with feeding. The most common variants:

• Time-restricted eating (TRE): all calories in a 6–10 hour daily window.
• Alternate-day fasting (ADF): alternate fed and very-low-calorie days.
• 5:2: five normal days plus two ~500 kcal days per week.
• Prolonged fasting: 24–72 hours or longer, sometimes supervised.

Why it’s of interest

Caloric restriction extends lifespan in many model organisms. Fasting protocols are easier to adhere to than continuous calorie restriction and share some mechanisms (raised autophagy, AMPK activation, mTORC1 suppression, lower IGF-1).

Human evidence

• TRE often produces weight loss similar to continuous calorie restriction when calories are matched.
• Cardiometabolic improvements (insulin sensitivity, blood pressure, triglycerides) are reported but inconsistent independent of weight loss.
• Some recent observational data have raised concerns about 8-hour TRE and cardiovascular mortality — not yet replicated in RCTs.
• No human lifespan data.

Safety

Reasonable in healthy adults. Caution in:

• pregnancy, breastfeeding;
• type-1 diabetes and insulin-treated type-2 diabetes (hypoglycaemia risk);
• history of disordered eating;
• low body mass or frailty in older adults (risk of sarcopenia, falls).

Related entries

See also: Caloric restriction, Time-restricted eating, Deregulated nutrient-sensing.