Research basis

Every default, formula, threshold and coaching guideline in Almanac is listed here with its source and how the app uses it. The code lives in lib/science (calculations) and lib/safety (limits).

How to read the confidence column

High: taken directly from a peer-reviewed paper or an official guideline, and both the citation and the specific figure were checked against PubMed, the full text or the issuing body's own page (October 2026).
Medium: from a recognised source, but the specific figure was not re-read in the primary document during this pass, or it is being applied a little outside the population it was derived from.
Convention: widely used in practice, not established by a study. Treated as a starting point only.
Policy: a deliberately cautious product decision. Not a research finding. These need clinical review before launch (see COMPLIANCE.md).

Nothing here is medical advice, and no citation should be read as the authors endorsing this app.

1. Energy expenditure

What	Value in the app	Source	Confidence
Resting energy, adults	Mifflin-St Jeor: `10 x kg + 6.25 x cm - 5 x age + 5` (men), `- 161` (women)	Mifflin et al. 1990 [1]. A systematic review found it the most reliable of the common equations in non-obese and obese adults [2].	High
Resting energy, sex not given	Midpoint constant (`- 78`)	Our own handling. No equation exists for this case.	Convention
Resting energy when body fat is known	`370 + 21.6 x fat-free mass (kg)`	Cunningham 1991 [35], a synthesis of body-composition studies; the equation explains 65-90% of the variation in resting expenditure. It is the equation commonly called "Katch-McArdle". Only as accurate as the body-fat figure entered, so it is used only when the user supplies one.	High
Resting energy, ages 13-17	Schofield: `17.686 x kg + 658.2` (boys), `13.384 x kg + 692.6` (girls)	Schofield 1985 [3], as tabulated by FAO/WHO/UNU 2004 [4]. Used because Mifflin-St Jeor was developed in adults aged 19-78.	High
Physical activity level (PAL)	1.40 / 1.55 / 1.75 / 1.90 / 2.00 for the five activity choices	Chosen inside the FAO/WHO/UNU lifestyle bands: sedentary or light 1.40-1.69, active 1.70-1.99, vigorous 2.00-2.40 [4]. Doubly-labelled-water data agree: average adult PAL is 1.7-1.8 and sustainable lifestyles range from about 1.1-1.2 to 2.0-2.5 [36]; about 1.2 is the level of non-ambulant people [37]. The widely copied 1.2 / 1.375 / 1.55 / 1.725 / 1.9 set has no primary source we could find and its "sedentary" value matches bed- or chair-bound people, so it was replaced. The band edges are from the sources; the exact value picked within each band is ours.	High for the bands, Convention for the point values
Self-reported activity runs high	Onboarding says "between two, pick the lower one"	Lichtman et al. 1992 [38]: people who believed they could not lose weight under-reported intake by 47% and over-reported activity by 51% on average. A small study in a specific group, so it supports the caution rather than a correction factor.	Medium
Energy in a kg of weight change	7,700 kcal/kg (3,500 kcal/lb)	Hall 2008 [5] shows the rule fits people with higher body fat and overstates the deficit needed for leaner people. Used as an approximation and described as one.	Medium

How it is used. Onboarding computes resting energy, multiplies by the activity level for a first estimate of daily expenditure (TDEE), and converts the chosen weekly rate into a daily calorie adjustment. Because the multiplier is the weakest link, it is replaced by the adaptive estimate below as soon as there is enough data.

Adaptive TDEE

expenditure = average intake - (weight slope in kg/day x 7,700)

This is energy balance, the same principle used by adaptive trackers such as MacroFactor. The specific rules are ours:

Rule	Value	Basis	Confidence
Minimum data	14-day span, 10 logged days, 6 weigh-ins, in a 28-day window	Daily weight varies by a kilogram or more from water and gut content; shorter windows mostly measure noise.	Convention
Ignore days under 600 kcal	Treated as incomplete logging	Half-logged days would make expenditure look far too low.	Convention
Bound to within 30% of the formula	Hard clamp	Under-reporting of intake is well documented [38]; this stops one poorly logged month producing an unsafe target.	Policy
Use a weekly average, not single weigh-ins	7-day moving average and a 4-week regression	Body weight follows a weekly rhythm, higher after weekends and lower by Friday [39], on top of day-to-day water shifts.	High
Blend with the formula	35% / 60% / 85% weight on observed data by confidence, scaled by logging coverage	Our own shrinkage.	Convention

The coach is told the confidence level and must say so when it is low.

2. Protein and macronutrients

What	Value in the app	Source	Confidence
Protein, adults who lift	1.6 g/kg/day; range shown 1.6-2.2	Morton et al. 2018 [6]: 49 trials, 1,863 participants. The break point was 1.62 g/kg/day with a 95% confidence interval of 1.03 to 2.20, which is where the 2.2 upper figure comes from. The authors note the break-point model was not itself statistically significant (p = 0.079), so 1.6 is best read as "about here", not a sharp threshold.	High
Protein, adults who lift, in a deficit	2.0 g/kg/day	Hector and Phillips 2018 [40]: 1.6-2.4 g/kg/day during weight loss. Longland et al. 2016 [41], a randomised trial: 2.4 g/kg beat 1.2 g/kg for lean mass and fat loss during a large deficit with hard training. Helms et al. 2014 [7]: 2.3-3.1 g/kg of lean mass. 2.0 is the middle of the 1.6-2.4 range.	High
Protein, adults who do not lift	1.2 g/kg/day (1.6 in a deficit)	Phillips, Chevalier and Leidy 2016 [42]: "at least 1.2 to 1.6 g/(kg·day)" is a better target than the 0.8 RDA for health in adults. Inside the 10-35% AMDR [9].	High
Protein, teens	1.4 g/kg/day if lifting, otherwise 1.0; never over 30% of calories	Lower end of the ISSN range [8] and the 10-30% AMDR for ages 4-18 [9]. The adult trials in [6] did not include adolescents.	Medium
Protein reference weight	Bodyweight capped at the weight giving BMI 30	Protein needs follow lean mass, so g/kg of total weight overshoots at higher weights. The cap itself is a practical convention.	Convention
Fat	30% of calories (25% for adults in a deficit)	AMDR: 20-35% adults, 25-35% ages 4-18 [9].	High
Carbohydrate	The remainder	AMDR 45-65% [9] is checked, not forced.	High
Fiber	14 g per 1,000 kcal	Dietary Reference Intakes [9], adopted by the Dietary Guidelines for Americans 2020-2025 [10].	High

3. Rate of weight change

What	Value in the app	Source	Confidence
Fat loss, adults	Default 0.5%, maximum 1.0% of bodyweight per week	Helms et al. 2014 [7]: 0.5-1%/week to retain muscle. Garthe et al. 2011 [11]: athletes losing about 0.7%/week gained lean mass while those losing about 1.4%/week did not.	High
Muscle gain	Default 0.25%, maximum 0.5% per week	Iraki et al. 2019 [12]: 0.25-0.5%/week for novice and intermediate lifters.	High
Warning on measured loss	Shown when the weight trend exceeds the maximum above	Same sources.	High

4. Resistance training

What	Value in the app	Source	Confidence
Weekly volume target	10-20 hard sets per muscle group	Lower bound: graded dose-response, with 10+ weekly sets producing more growth than fewer [13]; the 2026 ACSM position stand (137 systematic reviews) reports hypertrophy enhanced at 10 or more sets per week [14]. Upper bound: 12-20 sets performed as well as more than 20 for most muscles in trained men [15], and returns diminish as volume rises [16].	High
Counting indirect work	A set counts 1 for its primary muscles and 0.5 for secondary ones	Pelland et al. 2026 [16]: the "fractional" method fitted the data best.	High
What counts as a hard set	Not a warm-up, and 4 or fewer reps in reserve (RPE 6+)	RPE = 10 - RIR scale [17]. Training to failure is not required for growth [18]. The cut-off at 4 RIR is our choice.	Medium
Frequency	Each muscle group at least twice a week	Schoenfeld et al. 2016 [19]. The 2026 meta-regression [16] finds frequency matters clearly for strength and little for size once volume is equal, so the app treats this as a soft suggestion.	Medium
Progressive overload	Before the first set of an exercise, the logger shows an "aim for today": keep the load and add a rep until every set reaches the top of the rep range, then add roughly 5% (never more than 10%) and restart at the bottom. Default range 8-12 reps.	ACSM 2009 [20], quoted from the abstract: "it is recommended that 2-10% increase in load be applied when the individual can perform the current workload for one to two repetitions over the desired number", and for novices "loads correspond to a repetition range of an 8-12 repetition maximum". The app waits for the top of the range on every set rather than one to two reps over it, a slightly more cautious trigger; that choice, and the 5% midpoint, are ours. Implemented in `lib/science/progression.ts`.	High for the rule, Convention for the exact trigger
Estimated 1RM	Mean of Epley `w(1 + r/30)` and Brzycki `w x 36/(37 - r)`, from sets of 10 reps or fewer	The two formulas are from Epley 1985 (a coaching manual) and Brzycki 1993 (JOPERD 64:88-90); neither is indexed in PubMed and we did not retrieve them. The rep limit is from Reynolds et al. 2006 [43]: 1RM can be estimated accurately from multiple-rep sets, 5-rep sets predict best, and no more than 10 reps should be used with linear equations.	High for the rep limit, Medium for the formulas

5. Physical activity

What	Value in the app	Source	Confidence
Adults	150-300 min/week moderate or 75-150 min vigorous aerobic activity; muscle strengthening on 2 or more days a week	WHO 2020 guidelines [21], confirmed in the full text.	High
Ages 13-17	An average of 60 min/day moderate-to-vigorous activity; vigorous and muscle- and bone-strengthening activity on at least 3 days a week	WHO 2020 guidelines [21], both figures confirmed in the full text.	High
Calories burned	`MET x kg x hours`, MET values from the 2024 Adult Compendium	Herrmann et al. 2024 [22]; values and codes copied from pacompendium.com and listed in `lib/science/met.ts`.	High
Caveat on calories burned	Always labelled an estimate; never added back to the calorie budget; device calorie figures are not imported	METs are population averages and gross of resting energy. Adult METs fit teenagers less well; a Youth Compendium exists [23] and is not yet implemented. Wearables do no better: in a validation of seven wrist devices none estimated energy expenditure within 20% [44], and a systematic review of 158 studies found no brand accurate for energy expenditure [45].	High
Intensity by MET	Light under 3, moderate 3 to under 6, vigorous 6+	Standard WHO/ACSM bands [24].	High

6. Heart rate

What	Value in the app	Source	Confidence
Maximum heart rate	`208 - 0.7 x age`	Tanaka et al. 2001 [25], from 351 studies and a laboratory cross-validation. Individual error is commonly 10 beats or more.	High
Zones, % of maximum	Light 57-63, moderate 64-76, vigorous 77-95, near-maximal 96+	ACSM position stand, Garber et al. 2011 [24]. The stand itself is paywalled and was not re-read; the moderate and vigorous edges were confirmed in several independent papers that reproduce its table.	Medium
Zones, heart-rate reserve	Light 30-39, moderate 40-59, vigorous 60-89, near-maximal 90+	Same [24], confirmed only through secondary reproductions, some of which give slightly different vigorous upper edges (84 or 85). Used on the cardio form when the user has logged a resting heart rate in the last 14 days; otherwise the percent-of-maximum bands are used.	Medium
Where heart rate comes from	The app asks for resting and average heart rate and explains how to get them from a watch, band, chest strap or a manual pulse count	Wrist devices measure heart rate adequately in controlled tests (median error under 5% for most devices in cycling), with larger errors during walking, at higher BMI and on darker skin [44]; Apple Watch and Garmin were the most accurate brands in a systematic review [45].	High
Why resting heart rate is tracked	Shown as a trend in the check-in	Higher resting heart rate is associated with higher all-cause and cardiovascular mortality in a meta-analysis of 46 cohort studies (about 9% per 10 beats/min) [46]. This is an association in populations; the app shows the number and makes no health claim about an individual reading.	High

7. Sleep

What	Value in the app	Source	Confidence
Adults	At least 7 hours; target range 7-9	AASM and Sleep Research Society consensus [26]; National Sleep Foundation [27].	High
Ages 13-18	8-10 hours	AASM consensus statement for paediatric populations [28].	High

8. Hydration

What	Value in the app	Source	Confidence
Adults	3.0 L (men), 2.2 L (women) from drinks per day	Dietary Reference Intakes for Water [29]: Adequate Intake for total water 3.7 L and 2.7 L, of which about 81% comes from fluids.	High
Teens	2.7 L / 1.9 L (14-18), 1.95 L / 1.7 L (13)	Same DRI table: total water 3.3 / 2.3 L (ages 14-18) and 2.4 / 2.1 L (ages 9-13), confirmed in reproductions of the table. The 81% drinks share was measured in adults aged 19-30; applying it to teens is our assumption.	Medium
Framing	A reference point, not a requirement	The DRI report itself says needs vary widely with climate and activity and that thirst is an adequate guide for most healthy people.	High

9. Safety limits

What	Value in the app	Source	Confidence
Minimum age	13	US COPPA threshold; see `COMPLIANCE.md`.	n/a
No deficit when underweight (adults)	BMI under 18.5	WHO adult underweight cut-off.	High
Adult calorie floor	1,200 kcal (women), 1,500 kcal (men or unspecified)	The 2013 AHA/ACC/TOS obesity guideline [47] describes prescribing "1200 to 1500 kcal/d for women and 1500 to 1800 kcal/d for men" in comprehensive lifestyle programmes. The app uses the bottom of each range as a floor it will not go below. Note the guideline's context: supervised programmes for adults with overweight or obesity. For lean or very active people these floors are too low to be a target, which is why the 25% deficit cap usually binds first.	High for the figures, Policy for using them as a floor
Largest deficit, adults	25% of estimated expenditure	Our limit.	Policy
Teen approach overall	Focus on habits, sleep, activity and strength, not weight	AAP clinical report, Golden et al. 2016 [30]: "The focus should be on a healthy lifestyle rather than on weight." A five-year cohort study found adolescents who dieted were at higher risk of later disordered eating and of weight gain [48]. The AAP 2023 obesity guideline [31] places treatment of adolescent obesity in supervised, family-based care.	High
Teen fat loss allowed at all	Yes, with the limits below	Product decision by the app owner. Not an AAP recommendation.	Policy
Teen maximum loss rate	0.5% of bodyweight per week; default 0.25%	Half the adult figures.	Policy
Teen largest deficit	15% of estimated expenditure	Our limit.	Policy
Teen calorie floor	The higher of estimated resting needs and 1,600 kcal (girls) or 1,800 kcal (boys or unspecified)	Our limit.	Policy
Teen BMI-for-age bands	Under the 25th percentile: no deficit. 25th to 85th: default rate only. 85th and above: up to the teen maximum.	Percentiles computed from the CDC 2000 growth reference (LMS method) [32]. The 85th percentile is the CDC overweight threshold; the 25th is our own cautious line.	Policy
Disordered-eating signals	Supportive message and resources replace optimisation; deficit targets are withdrawn	Approach follows [30]. Helplines listed in the app were checked against the US Office on Women's Health 2026 materials and the organisations' own sites [33].	Medium

10. Product principles with evidence behind them

Principle	Source	Confidence
Logging speed and consistency matter more than precision	Burke et al. 2011 [34], a systematic review: more consistent self-monitoring of diet, activity and weight was associated with more weight loss.	High
Smoothed weight trend, never single weigh-ins	Follows from day-to-day variability; standard practice.	Convention

References

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How this file was checked (October 2026)

Every numbered reference was looked up in PubMed (or on the issuing body's own site) to confirm authors, journal, year and identifier.
Figures marked High were read in the abstract or full text: the Morton break point and interval, the WHO activity recommendations, the AHA/ACC/TOS calorie ranges, the Schofield equations and PAL bands (FAO), the Cunningham equation, the protein ranges in [40] to [42], the wearable findings in [44] and [45], the rep limit in [43], the resting heart-rate meta-analysis, the adult water intakes, and every MET value against the Compendium's site.
Changes made as a result: the activity multipliers were replaced (and the top tier later lowered from 2.20 to 2.00, the bottom of the vigorous band, because that level is self-selected), and the rep limit for 1RM estimates was lowered from 12 to 10.
lib/science/science.test.ts includes a simulation of four weeks of noisy, partly missing food and weight logs for someone whose true expenditure is 500 kcal below the formula's guess; the adaptive estimate lands within 250 kcal of the truth.

Still not verified, and labelled as such above

The ACSM heart-rate zone edges, confirmed only through other papers that reproduce the position stand's table.
The Epley and Brzycki source publications, which are not in PubMed.
Reference [48]'s specific findings: the citation was confirmed, the abstract's results section was not retrieved, and the one-line summary above is from memory of the paper.
Reference [39]'s detail beyond its title.
The Dietary Guidelines' own wording for fibre (14 g per 1,000 kcal); the figure was confirmed in secondary sources that attribute it to the DRI.
Any claim about nutrient timing, meal frequency or supplements. The app makes no recommendations on these.