Last updated 9 September 2026
Every calorie, macronutrient and micronutrient target you see in Zelos was set for you by your coach, a human personal trainer. Zelos does not generate targets on its own. This page lists the public data and published research behind the numbers the app and your coach work from, so you can check them yourself.
The nutrition figures for foods you search and log come from FoodData Central, the public food composition database published by the United States Department of Agriculture. Zelos carries the Foundation and Standard Reference foods with their full nutrient profiles, including 32 vitamins and minerals.
Calories for a food or a day are computed from its protein, carbohydrate and fat using the standard conversion factors of 4, 4 and 9 kilocalories per gram.
When a coach sets micronutrient targets, the form is pre-filled with the adult Dietary Reference Intakes published by the National Academies of Sciences, Engineering, and Medicine. These are the Recommended Dietary Allowance or Adequate Intake for an adult, in the units shown. The coach can raise or lower any of them for you, and only the ones they choose to track appear in the app.
Zelos offers coaches an optional estimate of a client's total daily energy expenditure to start from. Resting energy expenditure is estimated with the Mifflin St Jeor equation, which a systematic review found to be the most reliable of the common predictive equations in healthy adults. That figure is multiplied by a physical activity level between 1.2 (sedentary) and 1.9 (very active), the convention established by the FAO, WHO and UNU expert consultation on human energy requirements. Coaches may also enter a known figure from a metabolic assessment or a wearable device instead.
When a coach picks a fat loss or muscle gain phase, Zelos suggests a daily adjustment of minus 500 or plus 250 kilocalories against the estimated expenditure. Those are conventional starting points, not prescriptions; the research below explains why the true rate of change is slower than the old 3,500 kilocalories per pound rule implies, which is exactly why your coach reviews and adjusts the number rather than the app.
If you type a meal as a sentence instead of searching for each food, an AI model (Claude, made by Anthropic) estimates the items and portion sizes and matches each item to the USDA data above. This is an estimate and it can be wrong. Adjust the portions before logging, or search for the food directly to get an exact catalogue match. Only the text you typed is sent to the model; no health data, account details or Apple Health data go with it.
Heart rate zones in the Endure tab are set by your coach from a lactate threshold heart rate or a maximum heart rate they choose. Threshold based zones follow Joe Friel's scheme (zone ceilings at 85, 90, 95 and 100 percent of threshold); maximum based zones use the conventional 60, 70, 80 and 90 percent bands. When neither has been set, Zelos estimates a maximum from the highest heart rates seen in your synced sessions and marks those zones as estimated until your coach sets a value. Daily active and resting energy burn are read directly from Apple Health as your device reports them and are not recalculated by Zelos.
None of this is medical advice, diagnosis or treatment, and none of it replaces a doctor or a registered dietitian. The figures are approximate and are meant for general fitness use with a coach. Do not rely on them where precision matters medically, such as managing diabetes, an allergy, pregnancy or a clinical diet. The full statement is in our Terms.
If you believe a figure or a source here is wrong, email john@zelos.fitness and we will look into it.