Why the scale jumps around, and what to watch instead
Gaining a kilo overnight isn't fat. Water, salt, carbs and food in your gut all move the number. Here's how to read your weight properly.
You ate well all week, then weighed yourself and you’re up 1.2 kg. It’s enough to make anyone throw the scales out. Before you do, here’s what that number is actually measuring.
The scale weighs everything
Your scale doesn’t know the difference between fat, muscle, water, the food in your gut or last night’s salty takeaway. Over a few days, fat changes slowly. Everything else changes fast.
To gain 1 kg of fat overnight you’d need to eat roughly 7,700 calories more than you burned. It almost never happens. Water and food do it easily.
The usual suspects
Carbohydrate. Your muscles and liver store carbs as glycogen, and glycogen is stored with water: roughly three grams of water for every gram. A big pasta night or a weekend off your diet can add a kilo or more of water and glycogen. This is also why low carb diets show a fast drop in the first week.
Salt. A salty meal makes your body hold more water for a day or two, until it rebalances.
Food and drink in transit. A big meal, lots of fibre or a late dinner all weigh something until they’re digested.
Training. A hard session, especially legs or something new, causes muscle soreness and short term fluid retention as you recover.
The menstrual cycle. Many women retain extra fluid in the days before a period, often enough to hide a couple of weeks of fat loss.
Stress and poor sleep. Both can nudge water retention up.
How to weigh yourself so it’s useful
- Same time, same conditions. First thing in the morning, after the toilet, before food or drink, in the same clothing (or none).
- Weigh often. Daily or most days. More data points means individual weird days matter less.
- Average them. Look at your average across the week, or a trend line, not the single number.
- Compare like with like. This week’s average against last week’s. For women, comparing the same point in your cycle month to month can help.
When to actually adjust
Give any plan two to three weeks before changing it. If your weekly average has moved roughly as planned, you’re on track, whatever Tuesday said. If it has truly stalled for three weeks, then adjust: about 100 to 150 calories less, or more daily steps. See how fast should you lose weight.
Use more than one measure
The scale is one tool. A tape measure around your waist, progress photos in the same light every few weeks, and whether your lifts are going up all tell you things the scale can’t. If your weight is flat but your waist is shrinking and your strength is climbing, things are going well.
How Logpulse shows it
The Progress tab plots every weigh in as a trend against the rate you planned, so one heavy morning stands out as a blip rather than a disaster. Logging your weight is as easy as saying “weighed 84.6” along with the rest of your day.
This is general information drawn from published research, not personal medical or dietary advice. If you have a health condition, are pregnant, or have a history of disordered eating, speak to your GP or an Accredited Practising Dietitian first. For support with eating concerns, the Butterfly Foundation helpline is 1800 33 4673.
Sources
- Olsson KE, Saltin B. Variation in total body water with muscle glycogen changes in man. Acta Physiologica Scandinavica. 1970;80(1):11 to 18.
- Hall KD, Sacks G, Chandramohan D, et al. Quantification of the effect of energy imbalance on bodyweight. The Lancet. 2011;378(9793):826 to 837.
- 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.