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What the number on the scale measures

The scale adds water, muscle, bone and fat into 1 number that moves through the day and the week. BMI and your waist show what the scale cannot.

KiloCare Team · · 4 min read · How we write and review

A glass of water and a closed notebook with a pencil on a bedside table in soft morning light.

What weight is made of

The scale weighs water, muscle, bone and fat together, so it cannot show which part changed.

  • India's dietary guidelines name the parts of the body as water, muscle, bone and fat.[1]
  • A 2011 WHO expert report says that, after allowing for height, men on average have more lean mass and more bone than women, and less fat.[2]
  • India's guidelines say that with age the body needs fewer calories and muscle decreases. Inactivity speeds up muscle loss, and being active helps keep muscle.[1]

Why it moves from day to day

Food, drink and stored water move your weight up and down through the day and the week, while your body fat can stay the same.

In a German study of 27 young adults, published in 2002, average weight was about 0.4 kg higher late at night than after waking. Their measured body fat did not change significantly.[3] The German authors linked the rise to food and drink.[3] The adults ate only small meals that day, so an ordinary day could differ.

In a study of about 1,400 adults in the UK, Denmark and Portugal who were keeping off weight they had lost, recruited in 2017 and 2018, morning weight swung by about 0.35% across the week.[4] Weight was usually highest on Monday and lowest on Friday. Because those adults had lost weight, the weekly pattern may differ for you.

Glycogen, the body's store of carbohydrate, is held with water, and a very low calorie diet draws on it in the first days.[5] What weight loss looks like over months explains what this means for the first weeks.

These steps are our suggestion. Each one makes a reading easier to compare with the last.

Weigh the same way each time
  1. Weigh in the morning, soon after you wake. The German authors advise morning measures.[3]
  2. Pass urine first. The European study asked people to weigh this way.[4]
  3. Weigh before you eat or drink. In the German study, the morning weight was taken after a night without food.[3]
  4. Wear light clothing, or none, as the European study asked.[4]
  5. Compare each reading with the same day of the week before, because weight follows a weekly pattern.[4]
A desk calendar with one column of ticks, the same day in each row, beside a pencil and a glass of water.

If your doctor has asked you to weigh yourself every day, keep doing that and tell them about a quick gain or swollen ankles.

If counting or weighing makes you anxious, or you often skip meals to control your weight, talk to a doctor.

BMI, and the Asian cutoffs

BMI compares your weight with your height, and India's guidelines set lower BMI cutoffs for Asians than WHO's general range.

BMI is your weight in kilograms divided by your height in metres, squared. India's guidelines say BMI estimates total body mass and correlates closely with body fat. It does not measure fat directly.[1] It cannot show where in the body the fat sits.

  • India's 2024 dietary guidelines from ICMR's National Institute of Nutrition (NIN) recommend a BMI of 18.5 to 23 for Asians. They set it below WHO's general range of 18.5 to 25, because Asians tend to carry more body fat than Europeans at the same BMI.[1]
  • For Asians, NIN calls a BMI over 23 overweight, and a BMI above 27.5 obesity.[1]

Your waist adds what BMI misses

People with the same BMI can carry different amounts of belly fat, and WHO advises measuring both the waist and BMI where possible.

WHO's 2011 report on the waist notes that people with the same BMI can carry different amounts of fat around the belly.[2]

  • The report's review found convincing evidence that a larger waist goes with a higher risk of disease. Most of that evidence came from people of European descent. The report advises measuring both the waist and BMI where possible.[2]
  • The same report records that an earlier WHO consultation advised using the waist alongside BMI for Asian populations, where possible.[2]
  • India's guidelines ask adults to keep both waist and body weight in range, and to check body weight periodically.[1]

The steps and India's waist figures are in how to measure your waist.

Weigh the same way, on the same day each week, and keep a note of it. Measure your waist the same way each time, and take both numbers to your doctor.

If you lose weight you were not trying to lose, see a doctor.

Medical disclaimer: This article is general information. It does not replace advice from your doctor about your own health.

Common questions

Food and drink through the day probably add to it. In a small German study of young adults, published in 2002, average weight was about 0.4 kg higher late at night than after waking, and measured body fat did not change significantly. The authors advise using morning measures.

India's 2024 dietary guidelines from ICMR-NIN recommend a BMI of 18.5 to 23 for Asians, because Asians tend to carry more body fat than Europeans at the same BMI. They call a BMI over 23 overweight and a BMI above 27.5 obesity.

India's dietary guidelines ask adults to check their body weight periodically. You may find it useful to compare the same day of each week, because in a European study weight tended to rise at the weekend and fall on weekdays. If your doctor has asked you to weigh yourself every day, keep doing that and tell them about a quick gain or swollen ankles.

Sources

  1. ICMR-NIN Expert Committee. Dietary Guidelines for Indians - 2024. Hyderabad: ICMR-National Institute of Nutrition; 2024. Available from: nin.res.inCited atp. 37p. 62, Guideline 9p. 62, Guideline 9pp. 62 to 63, Guideline 9pp. 63 to 64, Guideline 9p. 64, Guideline 9
  2. World Health Organization. Waist circumference and waist-hip ratio: report of a WHO expert consultation, Geneva, 8-11 December 2008. Geneva: World Health Organization; 2011. Available from: iris.who.intCited atp. 8, §3.1p. 1, Backgroundp. 19, §5.1p. 1, Background
  3. Dittmar M, Raschka C, Koch HJ. Effect of diurnal variation on body composition under consideration of selected chronobiological marker systems. Anthropol Rev. 2002;65:17-26. doi:10.18778/1898-6773.65.02. Available from: doi.orgCited atp. 21, Table 1p. 17, Abstractp. 17, Abstractp. 18, Methods
  4. Turicchi J, O'Driscoll R, Horgan G, Duarte C, Palmeira AL, Larsen SC, et al. Weekly, seasonal and holiday body weight fluctuation patterns among individuals engaged in a European multi-centre behavioural weight loss maintenance intervention. PLoS One. 2020;15(4):e0232152. doi:10.1371/journal.pone.0232152. PMID: 32353079. Available from: pmc.ncbi.nlm.nih.govCited atResults, weekly analysisMethodsMethodsResults, weekly analysis
  5. Kreitzman SN, Coxon AY, Szaz KF. Glycogen storage: illusions of easy weight loss, excessive weight regain, and distortions in estimates of body composition. Am J Clin Nutr. 1992;56(1 Suppl):292S-293S. doi:10.1093/ajcn/56.1.292S. PMID: 1615908. Available from: pubmed.ncbi.nlm.nih.govCited atAbstract