Zippy Sources of Recommendations

Last updated: August 21, 2026

Overview

This page explains the general scientific and methodological basis for the formulas, targets, and scores that Zippy calculates for you — including your BMI, recommended water intake, recommended daily steps, calorie and macronutrient targets, suggested fasting plan, and in-app scores such as the Fat Burning Score and Protein Score.

These calculations are built on established, publicly available research and widely used clinical formulas, adapted into simplified, general-purpose rules. They are estimates intended for healthy adults and are not personalized medical advice. See ourTerms of Use for our full health disclaimer, and consult a physician before beginning any fasting or dietary program.

Note: individual educational articles within the App cite their own sources at the end of each article. This page does not repeat those article-specific citations — it covers only the sources behind the App's built-in calculators and scores.

Body Mass Index (BMI) and BMI Category

Zippy calculates BMI using the standard formula: weight (kg) divided by height (m) squared. Your BMI is then classified into a category (underweight, normal, overweight, obesity) using the World Health Organization's standard BMI classification thresholds (below 18.5, 18.5–24.9, 25–29.9, and 30 and above).

  • World Health Organization. Obesity: Preventing and Managing the Global Epidemic. WHO Technical Report Series 894, 2000.
  • World Health Organization. BMI Classification. Global Database on Body Mass Index.

BMI is a general population-level screening tool. It does not account for body composition, muscle mass, or individual variation, and Zippy presents it for general informational purposes only.

Recommended Daily Water Intake

Your recommended water intake is estimated from your body weight (roughly 33 ml per kg of body weight as a baseline), adjusted upward for higher activity levels and slightly downward for adults over 55. This approach reflects commonly cited general adequate-intake guidance for fluids, scaled to body weight and activity.

  • European Food Safety Authority (EFSA) Panel on Dietetic Products, Nutrition, and Allergies. Scientific Opinion on Dietary Reference Values for Water. EFSA Journal, 2010.
  • Institute of Medicine (US) Panel on Dietary Reference Intakes for Electrolytes and Water. Dietary Reference Intakes for Water, Potassium, Sodium, Chloride, and Sulfate. National Academies Press, 2005.

Actual fluid needs vary with climate, individual physiology, and medical conditions; this figure is a general estimate, not a prescription.

Recommended Daily Steps

Your recommended step count starts from a general baseline (around 7,000 steps/day) and is adjusted for your activity level, your goal, your age, and your BMI. This baseline reflects research associating step counts in the roughly 7,000–10,000/day range with meaningfully lower mortality risk compared with much lower step counts, rather than the informal "10,000 steps" figure, which did not originate from clinical research.

  • Saint-Maurice PF, Troiano RP, Bassett DR Jr, et al. "Association of Daily Step Count and Step Intensity With Mortality Among US Adults." JAMA. 2020;323(12):1151–1160.
  • Paluch AE, Bajpai S, Bassett DR, et al. "Daily Steps and All-Cause Mortality: A Meta-Analysis of 15 International Cohorts." The Lancet Public Health. 2022;7(3):e219–e228.
  • World Health Organization. WHO Guidelines on Physical Activity and Sedentary Behaviour. 2020.

Calorie Needs (TDEE), Weight Change Pace, and Target Date

Zippy estimates your basal metabolic rate (BMR) using the Mifflin-St Jeor equation, then multiplies it by an activity factor to estimate your Total Daily Energy Expenditure (TDEE) — the calories needed to maintain your current weight. This is one of the most widely validated resting-energy-expenditure equations in current use.

  • Mifflin 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.
  • Frankenfield D, Roth-Yousey L, Compher C. "Comparison of Predictive Equations for Resting Metabolic Rate in Healthy Nonobese and Obese Adults." Journal of the American Dietetic Association. 2005;105(5):775–789.

To set a calorie target for weight loss or gain, Zippy uses the standard energy-equivalence estimate that roughly 7,700 kcal corresponds to 1 kg of body fat, and paces changes at a generally recommended rate (approximately 0.5 kg/week for weight loss, capped at 1% of body weight per week, with more conservative pacing for other goals), and enforces minimum safe daily calorie floors.

  • Centers for Disease Control and Prevention (CDC). Losing Weight. Guidance on losing 0.45–0.9 kg (1–2 lb) per week as a safe, sustainable rate.
  • Hall KD, Sacks G, Chandramohan D, et al. "Quantification of the Effect of Energy Imbalance on Bodyweight." The Lancet. 2011;378(9793):826–837 (basis for dynamic energy-balance modeling, referenced alongside the classic 3,500 kcal/lb ≈ 7,700 kcal/kg estimate used here as a simplified static approximation).

Macronutrient Targets (Protein, Fat, Carbohydrates)

Protein targets are set relative to body weight and are increased during a weight-loss phase to help preserve lean muscle mass, consistent with sports-nutrition and clinical body-composition research. Fat targets are set at a minimum of roughly 25% of total calories or 0.8 g/kg body weight, whichever is higher, to support hormonal and general health. Remaining calories are allocated to carbohydrates.

  • Jäger 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.
  • Phillips SM, Van Loon LJ. "Dietary Protein for Athletes: From Requirements to Optimum Adaptation." Journal of Sports Sciences. 2011;29(sup1):S29–S38.
  • Helms ER, Zinn C, Rowlands DS, Brown SR. "A Systematic Review of Dietary Protein During Caloric Restriction in Resistance Trained Lean Athletes." International Journal of Sport Nutrition and Exercise Metabolism. 2014;24(2):127–138.

Fasting Plan Recommendation

Zippy suggests a starter fasting schedule (from gentler options like 12:12 up to 16:8) based on your reported prior fasting experience, your goal, your activity level, your age, and any relevant health considerations you disclose, with more conservative recommendations for higher-risk profiles. The underlying time-restricted eating windows themselves (e.g., 12:12 through 20:4 and beyond) are drawn from established intermittent fasting research literature; the personalization logic that maps your profile to a starting point is our own general-purpose rule of thumb, not a clinical algorithm.

  • de Cabo R, Mattson MP. "Effects of Intermittent Fasting on Health, Aging, and Disease." New England Journal of Medicine. 2019;381(26):2541–2551.
  • Patterson RE, Sears DD. "Metabolic Effects of Intermittent Fasting." Annual Review of Nutrition. 2017;37:371–393.
  • Varady KA. "Intermittent Versus Daily Calorie Restriction: Which Diet Regimen Is More Effective for Weight Loss?" Obesity Reviews. 2011;12(7):e593–e601.
  • Harvie M, Howell A. "Potential Benefits and Harms of Intermittent Energy Restriction and Intermittent Fasting Amongst People with Obesity." Behavioral Sciences. 2017;7(1):4.

This recommendation is a general starting point, not a medical prescription — it does not account for conditions or medications you may not have disclosed, and should not be followed by anyone advised against fasting by a physician.

Fasting Stages and the Fat Burning Score

The App illustrates a fast's progression through general physiological stages (e.g., fuel processing, blood sugar settling, the "fat switch," ketosis, and deeper autophagy-associated renewal) at approximate elapsed-hour milestones, and combines this with your streak, activity, recent calorie balance, last-meal composition, hydration, and any voluntarily logged blood glucose/ketone readings into a single illustrative "Fat Burning Score." The stage timing and general metabolic shifts (glycogen depletion, the shift toward fat oxidation and ketone production, and increased autophagic activity during extended fasting) are grounded in fasting-physiology research, but the specific hour cutoffs and the scoring weights themselves are simplified, App-specific approximations for motivational and educational purposes, and vary meaningfully between individuals.

  • Anton SD, Moehl K, Donahoo WT, et al. "Flipping the Metabolic Switch: Understanding and Applying the Health Benefits of Fasting." Obesity. 2018;26(2):254–268.
  • Cahill GF Jr. "Fuel Metabolism in Starvation." Annual Review of Nutrition. 2006;26:1–22.
  • Mizushima N, Komatsu M. "Autophagy: Renovation of Cells and Tissues." Cell. 2011;147(4):728–741.
  • Bagherniya M, Butler AE, Barreto GE, Sahebkar A. "The Effect of Fasting or Calorie Restriction on Autophagy Induction: A Review of the Literature." Ageing Research Reviews. 2018;47:183–197.
  • Longo VD, Panda S. "Fasting, Circadian Rhythms, and Time-Restricted Feeding in Healthy Lifestyle." Cell Metabolism. 2016;23(6):1048–1059.

Protein Score

The Protein Score reflects how your protein intake so far in the day compares to what would be expected by that point (based on your planned meal schedule), rewards spreading protein intake across multiple meals rather than one large meal, and factors in your recent consistency. The evidence that distributing protein intake across meals (rather than concentrating it in one meal) more effectively supports muscle protein synthesis motivates the distribution component of this score.

  • Mamerow 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.
  • Areta 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.

Weight Progress and Target Date Charts

The weight-change chart and target date shown in your personal plan and nutrition plan are a direct projection from the calorie target and pacing described in the "Calorie Needs" section above — they illustrate the expected trajectory if your target calorie intake is followed consistently, not a guarantee of results. Actual results vary based on adherence, individual metabolism, water retention, hormonal factors, and other variables outside the App's model.

General Methodology Note

Zippy's calculators combine peer-reviewed research and internationally recognized clinical/public- health guidance (as cited above) with simplified rules to make the numbers actionable inside a consumer wellness app. They are not diagnostic tools, are not personalized by a healthcare professional, and do not replace individualized medical, dietetic, or fitness advice. If you have a pre-existing health condition, are pregnant or breastfeeding, are underweight, or are taking medication, consult your physician before relying on any target or score in the App.

Questions

If you have questions about how a specific number or score was calculated, contact us at support@tryzippy.app.