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Why the Scale Jumps After a Salty or High-Carb Weekend

Weight2 min readOlsson & Saltin (1970); Visser et al. (2009)

A heavy weigh-in after a salty or carb-heavy couple of days is mostly water, not fat. It passes, and the weekly trend is what tells you about fat.

Key points
  • Stored carbohydrate holds roughly three grams of water for every gram, so refilling it after a big weekend shows on the scale.
  • Salt makes the body hold on to fluid: a week of high salt added about 1.2 litres in one study of healthy men.
  • Creatine and the days around a period can do the same, and none of it is fat.
  • Read the trend across weeks, not one morning's number.

Carbohydrate brings water with it

Your muscles and liver store carbohydrate as glycogen, and each gram of it is stored alongside roughly three grams of water. A weekend of pizza, pasta and pints tops those stores up, and the water comes with them. The same effect runs the other way at the start of a diet, which is why the first week can drop a couple of kilos that are nowhere near a couple of kilos of fat.

Salt holds water

Your body keeps the salt concentration of its fluids within tight limits, so when you eat more salt it holds on to more water to match. In one study, healthy men moved from a low-salt week to a high-salt week carried about 1.2 litres more fluid outside their cells on average, which weighs about 1.2 kg. It leaves again as your salt intake settles back down.

Other water that is not fat

Creatine draws water into muscle, typically a kilogram or two in the first week of a loading phase. Many women also hold more water in the days before a period and at its start. None of these is a failed week.

What the check-in looks for

The weekly check-in compares the last two days of your week with the days before them. It names salt when those two days averaged at least 6 g, the most the NHS recommends for an adult in a day, and ran well above the rest of your week. It names carbohydrate when those days ran at least 60 g a day higher and about a third above your usual.

See a GP if…
  • Your ankles, feet or legs stay swollen for more than a few days, or the swelling gets worse
  • You have swelling and a condition that affects your heart, kidneys or leg veins
  • One leg only is swollen, or it is painful, red or hot: ask for an urgent appointment or call 111
How Kriterion uses this

Kriterion's trend weight smooths water out of your weigh-ins for free, and Premium's weekly check-in tells you when salt, carbohydrate, creatine or your cycle is the likelier reason for a heavy morning.

References

  1. Olsson KE, Saltin B. Variation in total body water with muscle glycogen changes in man. Acta Physiologica Scandinavica, 1970;80(1):11-18.
  2. Kreitzman SN, Coxon AY, Szaz KF. Glycogen storage: illusions of easy weight loss, excessive weight regain, and distortions in estimates of body composition. The American Journal of Clinical Nutrition, 1992;56(1 Suppl):292S-293S.
  3. Visser FW, Krikken JA, Muntinga JH, Dierckx RA, Navis GJ. Rise in extracellular fluid volume during high sodium depends on BMI in healthy men. Obesity, 2009;17(9).
  4. White CP, Hitchcock CL, Vigna YM, Prior JC. Fluid retention over the menstrual cycle: 1-year data from the prospective ovulation cohort. Obstetrics and Gynecology International, 2011;2011:138451.
  5. Kreider RB, Kalman DS, Antonio J, et al. International Society of Sports Nutrition position stand: safety and efficacy of creatine supplementation in exercise, sport, and medicine. Journal of the International Society of Sports Nutrition, 2017;14:18.
  6. NHS. Salt: the facts. nhs.uk (adults should eat no more than 6g of salt a day).

Last reviewed 28 Sep 2026 · Next review due Sep 2029

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