NutriCalc Pro, an Open Source Metabolism and Nutrient Needs Calculator

Online nutrition calculators tend to share three recurring flaws. They rely on a single equation without saying which one, they mix general population and athletic recommendations without separating levels of evidence, and they list supplements most of which have never shown an effect in humans. NutriCalc Pro was built to address those three points.

What the tool calculates

Results are organised in six tabs.

• Energy. Basal metabolic rate from five selectable equations, additive total daily energy expenditure, target intake by goal, body mass index and fat free mass.
• Macronutrients. Protein expressed per kilogram of body weight, carbohydrate scaled to training load, fat treated as a floor, fibre and fluid intake.
• Micronutrients. Twenty nine nutrients with dietary reference value, tolerable upper intake level and contextual prioritisation.
• Sport. Energy availability, carbohydrate during exercise, nutrient timing around the session and supplements with a high level of evidence.
• Gut microbiota. Foundations that apply to nearly everyone, plus advice triggered by the declared context.
• Sources. About thirty primary references one click away, with the explicit limitations of the tool.

Using NutriCalc Pro

The tool works directly below, with no sign up and no data transmission. Every calculation runs in your own browser. The switch in the top right corner toggles between French and English, and between light and dark theme.

If the frame does not load, open the tool in a new tab: jetpod.github.io/nutricalc

How energy expenditure is estimated

Basal metabolic rate can be estimated with five equations, selectable according to the profile. Mifflin-St Jeor remains the default for non athletic adults. Cunningham is more relevant when fat free mass is known, which is often the case in trained athletes. Schofield and Roza-Shizgal complete the range, with Harris-Benedict kept for historical comparison.

Daily expenditure is not derived from a single global multiplier. The tool adds a baseline physical activity level taken from FAO and WHO work, the occupational load, then the energy cost of training computed from the metabolic equivalents of the declared sport, weekly volume and session duration. This additive construction limits the classic overestimation produced by calculators that apply an athletic factor to the whole day. The resulting values stay consistent with the ranges retained by the SACN.

Macronutrients and training load

Protein is expressed per kilogram of body weight, following the ISSN position stand on protein and exercise, with an increase during energy deficit phases in order to preserve lean mass. Carbohydrate follows training load according to the ranges retained in the joint ACSM, Academy of Nutrition and Dietitians of Canada position stand and in recent syntheses on carbohydrate and performance. Fat is treated as a floor not to be crossed rather than a free adjustment variable.

For prolonged exercise, the tool displays an hourly carbohydrate range during effort and a reminder on distribution around the session, consistent with the ISSN position stand on nutrient timing.

Micronutrients, prioritised by context

Population reference values come from the ANSES 2021 opinion and from the EFSA dietary reference values. Tolerable upper intake levels come from the EFSA 2024 summary report, so each nutrient is shown with both a target and the ceiling above which intake becomes a risk.

The main contribution lies in prioritisation. Rather than listing twenty nine nutrients on the same scale, the tool surfaces those that deserve attention in the declared profile. A vegan diet raises vitamin B12, iron, zinc, iodine and omega 3 fatty acids, consistent with Rogerson’s review on vegan diets in athletes. Intense endurance training raises iron, using the framework proposed by Sim and colleagues. Low energy availability triggers an explicit flag pointing to the 2023 IOC consensus statement on relative energy deficiency in sport.

Supplements, high level of evidence only

This is the most restrictive editorial choice in the tool. Of the thirty or so substances commonly presented as ergogenic, only five are displayed. They are the ones that the International Olympic Committee consensus statement on dietary supplements in athletes and the ISSN review on supplements and sports nutrition classify as supported by converging human data.

Substance	Documented benefit	Level of evidence
Creatine monohydrate	Repeated high intensity efforts, strength, lean mass	Meta-analyses
Caffeine	Endurance, alertness, perceived exertion	Meta-analyses
Beta-alanine	Efforts of 1 to 4 minutes, intramuscular buffering	Meta-analyses
Dietary nitrate	Running economy, submaximal endurance	Randomised controlled trials
Sodium bicarbonate	Anaerobic efforts with marked acidosis	Randomised controlled trials

Everything else was removed, including very popular products such as citrulline, glycerol and ashwagandha. That absence is not a final verdict: it means available human data are not yet sufficient to recommend those substances in a tool designed to be used without supervision.

Gut microbiota, advice triggered by context

The sixth tab separates foundations, which apply to nearly everyone, from contextual advice triggered by the declared situation.

On the foundations side, the fibre reference intake retained by EFSA is 25 grams per day in adults. Plant diversity is treated separately from fibre quantity: in the American Gut Project, participants eating more than thirty plant types per week showed higher microbial diversity than those eating ten or fewer. Fermented foods are supported by a ten week randomised trial in which six daily servings increased microbial diversity and lowered nineteen inflammatory markers.

On the contextual side, eleven rules can fire. Prolonged exercise surfaces the threshold identified by Costa and colleagues, beyond two hours at 60 per cent of maximal oxygen uptake, together with the gut training protocol described by the Gatorade Sports Science Institute, where tolerance to 60 to 90 grams of carbohydrate per hour is acquired over six to ten weeks. Exercise induced gastrointestinal symptoms point to the trial by Lis and colleagues, in which a seven day low FODMAP diet improved symptoms in eleven of sixteen athletes. Antibiotic therapy surfaces the data of Szajewska and Kolodziej on Saccharomyces boulardii, with antibiotic associated diarrhoea falling from 17.4 to 8.2 per cent in adults. Pregnancy, conversely, triggers a caution pointing to ANSES guidance on listeriosis rather than to fermented food data.

Open and reusable code

The full source code is published on GitHub under the MIT licence. It is a static application with no dependency, no database and no data collection: equations, reference tables and prioritisation rules can be read file by file. Anyone who wants to verify a calculation, correct a value or adapt the tool to another national reference framework is free to do so. The scientific references cited remain the property of their authors.

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French version of this article: NutriCalc Pro, le calculateur ouvert de métabolisme et de besoins nutritionnels

Dr Jean-Etienne PODIK, public health physician
NutriCellScience