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Mass and energy balance Educational / worked examples

How Do Mass and Energy Balance Calculations Work?

These worked examples keep energy units separate from mass units, show every arithmetic step, and label static estimates clearly so students can practice conservation principles without mistaking simplified calculations for personalized predictions.

Evidence reviewed July 15, 2026 | Educational information, not medical advice

What should you remember?

The most important points connect this page's main entity with the relevant energy-balance mechanisms and practical decisions, while separating population estimates from individual measurements, identifying important limitations, and avoiding conclusions or individualized prescriptions that the cited evidence cannot reasonably support for every reader.

  • Define boundary, interval, and units first.
  • Show the storage term explicitly.
  • Label static estimates and measurement limits.

What makes a valid worked balance example?

A valid worked balance example defines the system boundary, time interval, units, inputs, outputs, storage term, assumptions, and rounding. It also distinguishes a static calorie-to-weight equivalent from an observed body-composition change and avoids combining kilograms with kilocalories in one arithmetic expression.

Each example below is educational. The static 3,500 kcal/lb and 7,700 kcal/kg conversions are reference approximations, while the mass-flow examples describe matter and the glycogen example describes a transient storage pool.

Where can you practice more problems?

Use the downloadable worksheet for additional human-metabolism practice problems with solutions, then use the Excel tracker to enter daily intake, expenditure, body weight, water, sodium, and macronutrients. Neither resource diagnoses metabolism or prescribes a calorie target.

The worksheet progresses from unit identification to multi-step interpretation and includes a separate answer key.

Which worked examples show the calculation clearly?

Example 1

Daily surplus to weekly energy storage

Intake is 2,500 kcal/day and expenditure is 2,000 kcal/day for seven days.

(2,500 - 2,000) x 7 = +3,500 kcal

Result: +3,500 kcal, a static energy equivalent of about +1.0 lb; actual tissue and scale change can differ.

Example 2

Daily deficit over 30 days

A planned deficit is 500 kcal/day for 30 days.

500 x 30 = 15,000 kcal; 15,000 / 3,500 = 4.29 lb

Result: A static 4.29 lb energy equivalent, not a guaranteed 30-day fat loss.

Example 3

Convert a weekly deficit to kilograms

A weekly deficit totals 7,700 kcal.

7,700 / 7,700 ≈ 1.0 kg

Result: Approximately 1 kg by a common static reference; dynamic physiology changes the realized result.

Example 4

Triglyceride oxidation products

Model the fate of 1 kg of oxidized triglyceride using the published 84%/16% product split.

1.00 x 0.84 = 0.84 kg CO2; 1.00 x 0.16 = 0.16 kg H2O

Result: About 0.84 kg of the triglyceride mass in CO2 and 0.16 kg in metabolic water; inhaled oxygen adds mass to total products.

Example 5

Glycogen-associated water

A simplified model stores 300 g more glycogen, with about 2.7 g water per gram.

300 g glycogen + (300 x 2.7) g water = 1,110 g

Result: About 1.11 kg of combined glycogen and associated water, illustrating a scale change that is not equivalent to fat gain.

Example 6

Whole-body mass ledger

Measured mass input is 3.4 kg and measured mass output is 3.7 kg over one day.

3.4 - 3.7 = -0.3 kg

Result: A -0.3 kg measured net mass balance for the listed streams; omitted streams and measurement error limit interpretation.

Which free learning resources can you download?

PDF Download practice problems with solutions for mass-energy balance Twenty human-metabolism practice problems, reference equations, and a complete answer key. XLSX Download the calorie and mass-balance tracker Formula-driven daily tracking, weekly summaries, weight trend, macros, sodium, and water.

Which sources and methods support this guide?

The guide uses primary studies, systematic reviews, government resources, or peer-reviewed journal articles to support its formulas and EAV claims, with each numbered citation linking to the underlying evidence so readers can inspect the population, method, limitations, and meaning of the reported value.

  1. Body Weight Regulation - Energy BalanceNCBI Bookshelf / Endotext
  2. When somebody loses weight, where does the fat go?The BMJ
  3. Dynamic Mathematical Model of Body Weight Change in AdultsNIDDK

What should you explore next?

Continue with the related calculator or guide that explains the next variable in the same energy-balance pathway, using the descriptive link text to identify the exact scientific relationship, calculation, and practical limitation covered on the destination page before you leave the current topic.

Mass and energy balance How Do Mass and Energy Balance Explain Weight Loss? Mass and energy balance How Do You Calculate Energy Balance? Mass and energy balance How Can You Track Calorie and Body-Mass Balance in Excel?
Return to the calorie-to-pounds calculator

What do readers ask about this topic?

These concise answers address the most common interpretation and application questions for this topic, while preserving the distinction between an educational population estimate and individualized medical, nutritional, or metabolic advice, and directing readers back to the page's stated evidence, assumptions, and limitations when necessary.

No. They apply conservation principles to human metabolism and weight change. They do not cover reactors, process streams, industrial unit operations, or engineering design.
No. They are educational calculations. Individual energy needs, health conditions, medications, growth, pregnancy, and clinical risks require appropriate professional guidance.