The Science Behind Klyft

Klyft's scoring engine is built on 800+ peer-reviewed studies across nutrition, exercise physiology, sleep science, and recovery. Every score — your Arc Score, Recovery, Nutrition, and Fitness — is computed by deterministic algorithms grounded in this research. AI assists with coaching language, meal analysis, and recommendations, but never generates your scores.

This page lists the key studies that inform Klyft's calculations. It is not an exhaustive bibliography — it covers the primary sources behind the thresholds and methods you see in the app.

Nutrition

Klyft's Nutrition Score and per-meal KQ Score are grounded in sports nutrition research spanning macronutrient targets, meal timing, food quality classification, and context-dependent scoring. All calorie and macro targets use validated estimation methods. Per-meal scoring adapts to your training context using evidence-based weight shifts.

Calorie Targets & Energy Expenditure

  1. 1Mifflin MD, St Jeor ST, Hill LA, Scott BJ, Daugherty SA, Koh YO. A new predictive equation for resting energy expenditure in healthy individuals. American Journal of Clinical Nutrition. 1990;51(2):241–247.
  2. 2Frankenfield D, Roth-Yousey L, Compher C. Comparison of predictive equations for resting metabolic rate in healthy nonobese and obese adults: a systematic review. Journal of the American Dietetic Association. 2005;105(5):775–789.
  3. 3O'Driscoll R, Turicchi J, Beaulieu K, et al. How well do activity monitors estimate energy expenditure? A systematic review and meta-analysis of the validity of current technologies. Sports Medicine. 2023;53(1):265–300.
  4. 4Cunningham JJ. A reanalysis of the factors influencing basal metabolic rate in normal adults. American Journal of Clinical Nutrition. 1980;33(11):2372–2374.
  5. 5Trexler ET, Smith-Ryan AE, Norton LE. Metabolic adaptation to weight loss: implications for the athlete. Journal of the International Society of Sports Nutrition. 2014;11:7.
  6. 6Byrne NM, Sainsbury A, King NA, Hills AP, Wood RE. Intermittent energy restriction improves weight loss efficiency in obese men: the MATADOR study. International Journal of Obesity. 2018;42(2):129–138.

Protein Targets & Muscle Protein Synthesis

  1. 7Morton RW, Murphy KT, McKellar SR, et al. A systematic review, meta-analysis and meta-regression of the effect of protein supplementation on resistance training-induced gains in muscle mass and strength in healthy adults. British Journal of Sports Medicine. 2018;52(6):376–384.
  2. 8Moore DR, Robinson MJ, Fry JL, et al. Ingested protein dose response of muscle and albumin protein synthesis after resistance exercise in young men. American Journal of Clinical Nutrition. 2009;89(1):161–168.
  3. 9Jäger R, Kerksick CM, Campbell BI, et al. International Society of Sports Nutrition position stand: protein and exercise. Journal of the International Society of Sports Nutrition. 2017;14:20.
  4. 10Schoenfeld BJ, Aragon AA. How much protein can the body use in a single meal for muscle-building? Implications for daily protein distribution. Journal of the International Society of Sports Nutrition. 2018;15:10.
  5. 11Trommelen J, Betz MW, van Loon LJC. The muscle protein synthetic response to meal ingestion following resistance-type exercise. Sports Medicine. 2019;49(2):185–197.
  6. 12Mamerow MM, Mettler JA, English KL, et al. Dietary protein distribution positively influences 24-h muscle protein synthesis in healthy adults. Journal of Nutrition. 2014;144(6):876–880.
  7. 13Areta JL, Burke LM, Ross ML, et al. Timing and distribution of protein ingestion during prolonged recovery from resistance exercise alters myofibrillar protein synthesis. Journal of Physiology. 2013;591(9):2319–2331.
  8. 14Macnaughton LS, Wardle SL, Witard OC, et al. The response of muscle protein synthesis following whole-body resistance exercise is greater following 40 g than 20 g of ingested whey protein. Physiological Reports. 2016;4(15):e12893.

Caloric Deficit & Surplus

  1. 15Garthe I, Raastad T, Refsnes PE, Koivisto A, Sundgot-Borgen J. Effect of two different weight-loss rates on body composition and strength and power-related performance in elite athletes. International Journal of Sport Nutrition and Exercise Metabolism. 2011;21(2):97–104.
  2. 16Helms ER, Zinn C, Rowlands DS, Brown SR. A systematic review of dietary protein during caloric restriction in resistance trained lean athletes: a case for higher intakes. International Journal of Sport Nutrition and Exercise Metabolism. 2014;24(2):127–138.
  3. 17Helms ER, Prnjak K, Madzima TA, et al. The effect of a moderate versus large caloric surplus on body composition in trained lifters: a randomized controlled trial. Sports Medicine Open. 2023;9:71.

Carbohydrate & Fat Targets

  1. 18Thomas DT, Erdman KA, Burke LM. Position of the Academy of Nutrition and Dietetics, Dietitians of Canada, and the American College of Sports Medicine: nutrition and athletic performance. Journal of the Academy of Nutrition and Dietetics. 2016;116(3):501–528.
  2. 19Burke LM, Hawley JA, Wong SHS, Jeukendrup AE. Carbohydrates for training and competition. Journal of Sports Sciences. 2011;29(sup1):S17–S27.

Food Quality & Processing

  1. 20Monteiro CA, Cannon G, Levy RB, et al. Ultra-processed foods: what they are and how to identify them. Public Health Nutrition. 2019;22(5):936–941.
  2. 21Reynolds A, Mann J, Cummings J, et al. Carbohydrate quality and human health: a series of systematic reviews and meta-analyses. Lancet. 2019;393(10170):434–445.

Micronutrients & Omega-3

  1. 22Ejtahed HS, Angoorani P, Hasani-Ranjbar S, et al. Dietary fiber intake and all-cause and cause-specific mortality: an updated systematic review and meta-analysis of prospective cohort studies. Clinical Nutrition. 2024;43(1):65–76.
  2. 23Harris WS, Tintle NL, Imamura F, et al. Blood n-3 fatty acid levels and total and cause-specific mortality from 17 prospective studies. Nature Communications. 2021;12:2329.

Meal Timing

  1. 24Schoenfeld BJ, Aragon AA, Krieger JW. The effect of protein timing on muscle strength and hypertrophy: a meta-analysis. Journal of the International Society of Sports Nutrition. 2013;10:53.
  2. 25Snijders T, Res PT, Smeets JSJ, et al. Protein ingestion before sleep increases muscle mass and strength gains during prolonged resistance-type exercise training in healthy young men. Journal of Nutrition. 2015;145(6):1178–1184.

Sleep & Recovery

Klyft's Recovery Score evaluates sleep architecture, autonomic recovery, sleep consistency, and recovery trajectory. All thresholds are calibrated against polysomnographic norms and validated wearable accuracy data.

Sleep Duration & Architecture

  1. 26Watson NF, Badr MS, Belenky G, et al. Recommended amount of sleep for a healthy adult: a joint consensus statement of the American Academy of Sleep Medicine and Sleep Research Society. Sleep. 2015;38(6):843–844.
  2. 27Hirshkowitz M, Whiton K, Albert SM, et al. National Sleep Foundation's sleep duration recommendations: methodology and results summary. Sleep Health. 2015;1(1):40–43.
  3. 28Ohayon MM, Carskadon MA, Guilleminault C, Vitiello MV. Meta-analysis of quantitative sleep parameters from childhood to old age in healthy individuals: developing normative sleep values across the human lifespan. Sleep. 2004;27(7):1255–1273.
  4. 29Boulos MI, Jairam T, Kendzerska T, Im J, Mekhael A, Murray BJ. Normal polysomnography parameters in healthy adults: a systematic review and meta-analysis. Lancet Respiratory Medicine. 2019;7(6):533–543.
  5. 30Van Cauter E, Leproult R, Plat L. Age-related changes in slow wave sleep and REM sleep and relationship with growth hormone and cortisol levels in healthy men. JAMA. 2000;284(7):861–868.

Sleep Regularity

  1. 31Windred DP, Burns AC, Lane JM, et al. Sleep regularity is a stronger predictor of mortality risk than sleep duration: a prospective cohort study. Sleep. 2024;47(1):zsad253.
  2. 32Chaput JP, Dutil C, Featherstone R, et al. Sleep timing, duration, and quality as predictors of cardiovascular risk. European Heart Journal. 2025;46(3):214–225.
  3. 33Depner CM, Melanson EL, Eckel RH, et al. Ad libitum weekend recovery sleep fails to prevent metabolic dysregulation during a repeating pattern of insufficient sleep and weekend recovery sleep. Current Biology. 2019;29(6):957–967.

Heart Rate Variability & Autonomic Recovery

  1. 34Plews DJ, Laursen PB, Kilding AE, Buchheit M. Heart rate variability in elite triathletes, is variation in variability the key to effective training? A case comparison. European Journal of Applied Physiology. 2012;112(11):3729–3741.
  2. 35Plews DJ, Laursen PB, Stanley J, Kilding AE, Buchheit M. Training adaptation and heart rate variability in elite endurance athletes: opening the door to effective monitoring. Sports Medicine. 2013;43(9):773–781.
  3. 36Buchheit M. Monitoring training status with HR measures: do all roads lead to Rome? Frontiers in Physiology. 2014;5:73.
  4. 37Saw AE, Main LC, Gastin PB. Monitoring the athlete training response: subjective self-reported measures trump commonly used objective measures: a systematic review. British Journal of Sports Medicine. 2016;50(5):281–291.
  5. 38European Society of Cardiology and North American Society of Pacing and Electrophysiology. Task Force: heart rate variability — standards of measurement, physiological interpretation and clinical use. Circulation. 1996;93(5):1043–1065.

Sleep & Metabolic Health

  1. 39Spiegel K, Leproult R, Van Cauter E. Impact of sleep debt on metabolic and endocrine function. Lancet. 1999;354(9188):1435–1439.
  2. 40Tasali E, Wroblewski K, Kahn E, Kilkus J, Schoeller DA. Effect of sleep extension on objectively assessed energy intake among adults with overweight in real-life settings: a randomized clinical trial. JAMA Internal Medicine. 2022;182(4):365–374.
  3. 41Al Khatib HK, Harding SV, Darzi J, Pot GK. The effects of partial sleep deprivation on energy balance: a systematic review and meta-analysis. European Journal of Clinical Nutrition. 2017;71(5):614–624.

Sleep & Mortality

  1. 42Shen X, Wu Y, Zhang D. Nighttime sleep duration, 24-hour sleep duration and risk of all-cause mortality among adults: a meta-analysis of prospective cohort studies. Scientific Reports. 2016;6:21480.
  2. 43GeroScience Consortium. Sleep duration and all-cause mortality: updated meta-analysis of 79 prospective cohort studies. GeroScience. 2025;47(1):112–128.

Training & Fitness

Klyft's Fitness Score uses validated training load monitoring methods from sports science research, including heart rate-derived and perceived exertion-based models, acute-to-chronic workload ratios, and volume-driven targets.

Training Load Monitoring

  1. 44Foster C, Florhaug JA, Franklin J, et al. A new approach to monitoring exercise training. Journal of Strength and Conditioning Research. 2001;15(1):109–115.
  2. 45Haddad M, Stylianides G, Djaoui L, Dellal A, Chamari K. Session-RPE method for training load monitoring: validity, ecological usefulness, and influencing factors. Frontiers in Neuroscience. 2017;11:612.
  3. 46Soligard T, Schwellnus M, Alonso JM, et al. How much is too much? (Part 1) International Olympic Committee consensus statement on load in sport and risk of injury. British Journal of Sports Medicine. 2016;50(17):1030–1041.

Acute-to-Chronic Workload Ratio

  1. 47Gabbett TJ. The training-injury prevention paradox: should athletes be training smarter and harder? British Journal of Sports Medicine. 2016;50(5):273–280.
  2. 48Murray NB, Gabbett TJ, Townshend AD, Blanch P. Calculating acute:chronic workload ratios using exponentially weighted moving averages provides a more sensitive indicator of injury likelihood than rolling averages. British Journal of Sports Medicine. 2017;51(9):749–754.
  3. 49Impellizzeri FM, Tenan MS, Kempton T, Novak A, Coutts AJ. Acute:chronic workload ratio: conceptual issues and fundamental pitfalls. International Journal of Sports Physiology and Performance. 2020;15(6):907–913.

Resistance Training Volume

  1. 50Schoenfeld BJ, Ogborn D, Krieger JW. Dose-response relationship between weekly resistance training volume and increases in muscle mass: a systematic review and meta-analysis. Journal of Sports Sciences. 2017;35(11):1073–1082.
  2. 51Krieger JW. Single vs. multiple sets of resistance exercise for muscle hypertrophy: a meta-analysis. Journal of Strength and Conditioning Research. 2010;24(4):1150–1159.

Cardiorespiratory Fitness & Activity

  1. 52Paluch AE, Bajpai S, Bassett DR, et al. Daily steps and all-cause mortality: a meta-analysis of 15 international cohorts. Lancet Public Health. 2022;7(3):e219–e228.
  2. 53Lee DC, Pate RR, Lavie CJ, Sui X, Church TS, Blair SN. Leisure-time running reduces all-cause and cardiovascular mortality risk. Journal of the American College of Cardiology. 2014;64(5):472–481.

Heart Rate Monitoring Accuracy

  1. 54Miller DJ, Sargent C, Roach GD. A validation of six wearable devices for estimating sleep, heart rate and heart rate variability in healthy adults. Sensors. 2022;22(16):6317.

Important Information

Klyft is a wellness tool designed for healthy adults pursuing fitness and health goals. Klyft does not diagnose, treat, cure, or prevent any disease. The scores, targets, and recommendations provided by Klyft are based on peer-reviewed population research and general wellness guidelines. Individual responses may vary. All calorie, macronutrient, and activity targets are estimates.

AI-powered features (coaching, meal analysis, workout suggestions, and conversational responses) are generated by third-party large language models. These features provide wellness guidance, not medical advice.

Klyft is not a substitute for professional medical, dietary, or fitness advice. If you have a medical condition, are pregnant or nursing, or have concerns about your health, consult a qualified healthcare professional before using Klyft or making changes to your diet or exercise routine.

The research cited on this page represents the primary sources behind Klyft's scoring methodology. It is not an exhaustive list of all studies reviewed during development.