How Fast Should You Lose Weight? I Simulated 3 Speeds

How fast should you lose weight? I ran the same 10 kg loss at three speeds (half a percent, one percent or two percent of body weight a week) through a published model of human metabolism to see how long each takes (23, 12 or 6 weeks), what you'd have to eat to stay on track (the 2% lane ends near 490 calories, about 2,000 kJ, a day), and how much of the loss is fat, lean tissue and water. Then I checked what randomised trials found about regain, muscle and gallstones. ▶ Watch next: Calorie Deficit but Slow Weight Loss? I Simulated 12 Weeks    • Calorie Deficit but Slow Weight Loss? I Si...   The simulation was coded for this video in Python. Assumptions are shown on screen and listed below. ⚠️ General information only, not medical or nutrition advice. Talk to your GP or an Accredited Practising Dietitian before making big changes, especially if you have a health condition, are pregnant, or have a history of disordered eating. Very-low-calorie diets should only be done with medical supervision. CHAPTERS 0:00 Intro: three speeds, same 10 kg 0:51 The setup: three speed lanes 1:58 Time: 23 vs 12 vs 6 weeks 2:26 What each speed makes you eat 3:32 Why the deficit has to keep growing 4:18 Same scale number, different loss 5:09 The trial: does fast loss come back? 6:26 The catch: muscle 7:20 Why leaner people should go slower 8:16 Fast loss and gallstones 9:03 So which speed? 9:40 Watch next SOURCES • Model: Hall KD et al. (2011), "Quantification of the effect of energy imbalance on bodyweight", The Lancet: https://pmc.ncbi.nlm.nih.gov/articles/PMC3... ; web appendix with the model equations: https://www.niddk.nih.gov/-/media/Files/BW... ; NIH Body Weight Planner: https://www.niddk.nih.gov/bwp • Melbourne trial: Purcell K et al. (2014), "The effect of rate of weight loss on long-term weight management: a randomised controlled trial", Lancet Diabetes & Endocrinology (200 randomised; 81% vs 50% reached ≥12.5% loss; 70.5% vs 71.2% of lost weight regained by week 144 among completers): https://pubmed.ncbi.nlm.nih.gov/25459211/ (doi:10.1016/S2213-8587(14)70200-1) • Trial registration for the Melbourne trial (3 Optifast shakes a day, dietitian review every 2 weeks): https://www.anzctr.org.au/Trial/Registrati... • Dutch trial: Vink RG et al. (2016), "The effect of rate of weight loss on long-term weight regain in adults with overweight and obesity", Obesity (−8.2 vs −9.0 kg; regain 4.2 vs 4.5 kg; fat-free mass loss 1.3% vs 8.8%): https://pubmed.ncbi.nlm.nih.gov/26813524/ (doi:10.1002/oby.21346) • American study: Nackers LM et al. (2010), "The association between rate of initial weight loss and long-term success in obesity treatment", Int J Behav Med: https://pmc.ncbi.nlm.nih.gov/articles/PMC3... • Norwegian athletes: Garthe I et al. (2011), "Effect of two different weight-loss rates on body composition and strength and power-related performance in elite athletes", IJSNEM (24 athletes; LBM +2.1% slow vs −0.2% fast): https://pubmed.ncbi.nlm.nih.gov/21558571/ (doi:10.1123/ijsnem.21.2.97) • Rate guidance for lean, resistance-trained people (~0.5-1% a week): Helms ER et al. (2014), JISSN: https://pmc.ncbi.nlm.nih.gov/articles/PMC4... • Gallstones and rapid weight loss; 5-10% over 6 months as a starting goal: NIDDK, "Dieting & Gallstones": https://www.niddk.nih.gov/health-informati... SIMULATION ASSUMPTIONS • Example person (same as EP01): male, 35, 178 cm, 95 kg, sedentary (PAL 1.5); starting fat ~26.4 kg (Jackson et al. equations); resting rate from Mifflin-St Jeor. Starting maintenance ~2,840 kcal/day (~11,900 kJ). • Three lanes: lose 0.5%, 1% or 2% of starting weight per week (compounding) until 10 kg is lost. Each simulated week, the code searches (bisection) for the constant daily intake that lands body weight exactly on the lane at the end of that week, like someone adjusting after a weigh-in. Intake is not allowed to rise above maintenance and there is no change in exercise. • Model: simplified Hall et al. (2011): energy densities of fat and lean tissue, Forbes fat/lean partitioning, glycogen with bound water, thermic effect of food and adaptive thermogenesis, 50% carbohydrate diet. In this model the fat/lean split depends on body fat, not on speed, so it cannot show the extra lean loss seen in some fast-diet trials; the video covers that with trial data. • Lean share of tissue lost (Forbes rule): 95 kg man ~28%; 60 kg woman (165 cm, 28 y) ~40%; lean athlete with 8 kg of fat ~57%. The simulation is an illustration, not a prediction for you, and results depend on these assumptions. Narration uses a synthetic (text-to-speech) voice. All charts and music are original. #weightloss #fatloss #caloriedeficit