16:8 intermittent fasting: what the research currently shows

16:8 (also called time-restricted eating, TRE) means eating within an 8-hour window each day and fasting the other 16. A typical pattern is no food before midday, last meal by 8 pm. It's the most studied form of intermittent fasting in human trials.

What the trials report#

A growing number of RCTs in the last decade have compared 16:8 to ad-libitum eating with no time constraint, and to matched calorie-restriction without time constraint.

Weight. Most 8- to 12-week trials show modest weight loss with TRE, in the range of 1–3% of body weight. Head-to-head trials versus standard calorie restriction (e.g. Lowe et al. 2020 JAMA Internal Medicine; Liu et al. 2022 NEJM) find similar weight loss when calories are matched, suggesting most of the effect is from eating less, not from the timing per se.

Glucose and insulin. TRE generally improves fasting insulin and HOMA-IR in trials lasting 8+ weeks. Effects are larger in people with insulin resistance or obesity than in healthy lean adults.

Lipids and blood pressure. Several trials report modest improvements in triglycerides and systolic blood pressure. Effects are not consistently distinguished from those of matched-calorie controls.

Lean mass. A point of debate. The NEJM 2022 trial of TRE in adults with obesity found similar lean-mass loss to standard calorie restriction. Sutton et al. (2018) in a smaller, well-controlled trial in prediabetic men reported good preservation when protein intake was high.

Where the evidence is thinner#

• Long-term outcomes. Most trials are under 6 months. There is no long-term outcome data (hard endpoints like cardiovascular events, mortality) for TRE in healthy people.
• Specific window timing. Earlier eating windows (e.g. 7 am–3 pm) appear better than later windows (e.g. 12 pm–8 pm) for insulin sensitivity in some trials. Practical adherence usually pushes people toward later windows.
• Effect in women. Some trials report differential effects on hormonal markers in women, though the data are mixed. See the linked piece on fasting and women's hormones.

Practical version#

The most reliable version of 16:8 in practice:

• Pick an 8-hour window that aligns with the rest of your life.
• Keep protein intake adequate during the window (≥1.2 g/kg body weight per day for most adults).
• Be more careful in the first 2 weeks: hunger adapts but takes time.
• Hydration matters; coffee, tea, and water are universally counted as "outside the window" by trial protocols.

Who should be cautious#

Pregnant or breastfeeding women, people with a history of disordered eating, people with type 1 diabetes, and anyone on glucose-lowering medication should not adopt TRE without clinical input. The pattern was tested largely in middle-aged adults with overweight or metabolic markers slightly out of range; it isn't validated as a universal optimiser.

The honest summary: 16:8 is a reasonable behavioural tool for moderate weight management. The exotic claims for it (large metabolic transformations, dramatic longevity effects) are not yet supported by human evidence at the level of clinical guidelines.