Clear sources. Practical guidance.
Source methodology
Sources and Methodology
ProteinCalc combines calculator formulas, food composition databases, nutrition guidelines, and practical meal examples. This page explains which sources we trust most and how we turn them into reader-friendly guidance.
Last updated May 18, 2026
Understand the assumptions.
01 / Start with the source
Institutional Sources We Prefer
Institutional sources are the backbone of our methodology because they are stable, transparent, and easier for readers to verify. For food values, our preferred source is USDA FoodData Central. For nutrient reference values, we rely on the National Academies, NIH Office of Dietary Supplements, and NCBI Bookshelf.
For medication-adjacent topics such as GLP-1 use, we prefer FDA labels, DailyMed, PubMed-indexed studies, and clinician-facing institutional guidance before using general wellness articles.
02 / Evidence in everyday life
Trusted Sites as Supporting Resources
Trusted medical sites and professional organizations are useful when they explain how evidence applies to patients or everyday food choices. These may include Mayo Clinic, National Kidney Foundation, American Diabetes Association, Academy of Nutrition and Dietetics, American College of Sports Medicine, and similar bodies.
We treat these as supporting resources unless the page is quoting an official guideline, consensus statement, or patient standard from that organization.
03 / Understand the estimate
Calculator Methodology
Protein calculator ranges are based on body weight, activity, goal, and life stage. General targets start from Dietary Reference Intakes, then move higher for muscle gain, fat loss, athletic training, older adults, and other contexts where peer-reviewed sources support a higher intake range.
Calculator outputs are estimates. They are intended to start a nutrition decision, not finish it. Readers with kidney disease, diabetes medication changes, pregnancy, lactation, appetite loss, or complex medical histories should use clinician guidance.
Unit conversions
Baseline adult protein uses g/kg/day and g/lb/day conversions.
Training ranges
Muscle gain and athletic ranges lean on sports nutrition position stands and meta-analyses.
Food values
Food pages show per serving, per 100 g, calories, and protein density using representative USDA-based entries.
Practical portions
Meal plans use practical portions and should be adjusted to a reader's calculator target.
04 / Make room for uncertainty
How We Handle Source Conflicts
If sources disagree, we prefer the more recent, higher-quality, population-matched source. A sports nutrition target for trained lifters should not override kidney disease guidance, and a general nutrition article should not override a medication label or condition-specific clinical source.
Where evidence is not strong enough for precision, the page should use ranges, explain uncertainty, and avoid absolute language.
Explore the references
Institutional and trusted resources we use
- USDA FoodData Central - U.S. Department of Agriculture
- Nutrient Recommendations and Databases - NIH Office of Dietary Supplements
- Dietary Reference Intakes summary tables - National Academies Press
- Dietary Reference Intakes for Energy - NCBI Bookshelf
- PubMed biomedical literature database - National Library of Medicine
- DailyMed drug label database - FDA / National Library of Medicine
- Nutrition and healthy eating - Mayo Clinic
- Nutrition Hub - National Kidney Foundation
Medical disclaimer: ProteinCalc content is for educational purposes and does not diagnose, treat, or replace medical care. Use individualized guidance from a qualified clinician for medical conditions, medication changes, pregnancy, lactation, appetite loss, kidney disease, diabetes, or eating disorder history.