Why the scale lies: water, salt and whooshes
Your weight can jump by a kilogram or more overnight, and almost none of it is fat. To gain a kilogram of fat you'd need to eat around 7,700 kcal more than you burn. What moves the scale from day to day is water and food, and it can hide real fat loss for a week or more.
What moves the scale
Carbohydrate and water
Your body stores carbohydrate in your muscles and liver as glycogen, and each gram is stored with around three grams of water. A full store can hold a kilogram or two of water. That's why the first week of cutting back, and especially of cutting carbs, shows a big drop, and why a pasta or pizza night shows up on the scale the next morning.
Salt
Your body holds on to extra water to balance out extra salt. A salty takeaway or a curry can add noticeable weight by the next morning, and it goes again within a couple of days of eating normally.
Food still being digested
A day's food and drink can weigh a couple of kilograms, and some of it is still on its way through. Heavy, high fibre or watery foods weigh more than their calories suggest, so a big salad can move the scale more than a chocolate bar.
Hormones
Many people retain water in the days before a period, which can hide a week or two of fat loss until it passes. Comparing the same point in each cycle gives a fairer picture.
Exercise, stress and sleep
Starting a new workout or training hard makes your muscles hold extra water while they repair, which can mask fat loss for a week or two. Stress and poor sleep can play a part too.
Whooshes: when the scale catches up
Many people find their weight sits still for a week or two and then drops suddenly overnight, often called a whoosh. It isn't well studied, but it fits everything above: fat loss carried on underneath, and water balance shifting hid it for a while. The lesson is the same either way. A flat week in a real deficit isn't a failed week, so keep going rather than cutting harder.
How to weigh yourself
- Same time, same conditions: first thing in the morning, after the loo and before eating or drinking, in the same clothes or none.
- Same scale, on a hard floor. Carpet and moving the scale both change the reading.
- Weigh daily and compare weekly averages. Daily weigh-ins averaged over the week give the clearest picture, and people who weigh daily tend to lose more. If daily numbers get to you, weighing once a week at the same time works too.
Compare this week's average with last week's, never one morning with another. A day-to-day change tells you about water; a week-to-week change tells you about fat.
Other ways to see progress
The scale isn't the only measure. A tape measure round your waist at the same spot once a week, how your clothes fit, and photos taken in the same light all move more steadily than your weight. If they're improving while the scale is flat, you're still on track.
When it's a real stall
If your weekly average hasn't moved for three or four weeks (or a full cycle, if you have periods), it's probably real. Before cutting further, check three things:
- Your counting. Weigh everything for a week and look out for the calories that slip through. Portions tend to creep up over time.
- Your maintenance. It falls as you lose weight, so recalculate it from your recent weeks.
- Your weekends. Look at the week totals rather than the weekdays. Two big days can cancel out five good ones.
If all three check out, take another 100 to 200 kcal a day off your target, or add some daily walking, and give it another three weeks.
Questions
Why did I gain weight overnight?
Almost always water and food still being digested, often after a salty or carb-heavy meal. Gaining a kilogram of fat takes around 7,700 kcal more than you burn, which is far more than one big meal.
How often should I weigh myself?
Daily weighing with a weekly average gives the clearest picture, as long as the daily figures do not get to you. Weighing once a week at the same time also works.
How long does water weight take to go?
Water from a salty or carb-heavy day usually goes within two or three days of eating normally again.
Why have I stopped losing weight?
If the weekly average has not moved for three or four weeks, check your counting, then recalculate your maintenance calories, as they fall as you lose weight.
Sources
- Kreitzman SN, Coxon AY, Szaz KF. Glycogen storage: illusions of easy weight loss, excessive weight regain, and distortions in estimates of body composition. American Journal of Clinical Nutrition, 1992; 56(1 Suppl): 292S–293S.
- Fernández-Elías VE, Ortega JF, Nelson RK, Mora-Rodriguez R. Relationship between muscle water and glycogen recovery after prolonged exercise in the heat in humans. European Journal of Applied Physiology, 2015; 115(9): 1919–1926.
- Steinberg DM, Bennett GG, Askew S, Tate DF. Weighing every day matters: daily weighing improves weight loss and adoption of weight control behaviors. Journal of the Academy of Nutrition and Dietetics, 2015; 115(4): 511–518.
- Hall KD, Sacks G, Chandramohan D, et al. Quantification of the effect of energy imbalance on bodyweight. The Lancet, 2011; 378(9793): 826–837.
This guide is general information, not medical advice. If you have a health condition, are pregnant, or have a history of disordered eating, talk to your GP or a registered dietitian before changing how you eat.