Fasting Window Calculator

What the research actually says about fasting

Patterson 2017's review¹Annual Review of Nutrition · 2017Patterson RE, Sears DD — Metabolic Effects of Intermittent Fasting established the early framework: time-restricted eating produces weight loss comparable to continuous calorie restriction. The TREAT trial (Lowe 2020)²JAMA Internal Medicine · 2020Lowe DA et al. — Effects of Time-Restricted Eating on Weight Loss and Other Metabolic Parameters in Women and Men With Overweight and Obesity (TREAT) found 16:8 produced no greater weight loss than three-meal eating, with greater lean-mass loss in the TRE group.

Liu 2022 (NEJM)³New England Journal of Medicine · 2022Liu D et al. — Calorie restriction with or without time-restricted eating in weight loss ran a year-long RCT comparing TRE + calorie restriction to calorie restriction alone — equivalent outcomes. No bonus from window timing per se.

Sutton 2018⁴Cell Metabolism · 2018Sutton EF et al. — Early Time-Restricted Feeding Improves Insulin Sensitivity, Blood Pressure, and Oxidative Stress Even without Weight Loss showed early-window TRE (eating 7am–3pm) improved insulin sensitivity, blood pressure, and oxidative stress in prediabetic men without weight loss — suggesting circadian alignment may matter independent of calories.

When fasting works

• Adults who naturally eat 2–3 meals/day already
• People who don't enjoy breakfast and end up overeating later when forced
• Adults with stable cortisol, good sleep, and moderate stress
• Prediabetics looking for an insulin-sensitivity nudge (especially early-window)
• Adults who find structure easier than calorie counting

When fasting backfires

• Women with cycle disruption or perimenopausal hormonal turbulence
• Adults with high training volumes who need fueling around workouts
• People with disordered-eating histories (the structural rule reinforces restrictive thinking)
• Adults already in chronic high stress (fasting amplifies cortisol)
• Sleep-deprived adults (fasting + sleep deficit compounds appetite dysregulation)

Why early-window beats late-window

Garaulet 2013⁵International Journal of Obesity · 2013Garaulet M et al. — Timing of food intake predicts weight loss effectiveness showed late lunch eaters lost 25% less weight on identical-calorie diets. Eating earlier in the day aligns with circadian glucose disposal (better insulin sensitivity in morning vs evening for most adults). The “eat from 7am to 3pm” version of 16:8 is generally a better choice than “eat from 12pm to 8pm” for metabolic markers.