Sodium, carbs and the two-pound overnight swing

You were on target all week. You had a curry on Saturday. Sunday morning the scale is up two pounds and the week feels wasted.

It is not. Two pounds of body fat represents roughly seven thousand calories of surplus, and no single restaurant meal delivers that. What moved overnight is water, and it moved for two entirely predictable reasons.

Reason one: sodium

Your body holds sodium and water at a fairly fixed ratio in the fluid outside your cells. Take in a large sodium load and, until your kidneys clear it, you retain water alongside it to keep that concentration stable. Roughly speaking, each extra gram of sodium retained brings a few hundred millilitres of water with it.

Restaurant food, takeaways, processed meals, bread, cheese and sauces are where sodium concentrates. Dietary guidance puts the recommended ceiling at around 2,300 mg a day for adults, and a single restaurant main can approach or exceed that on its own. Two or three grams above your normal intake is an easy way to gain a pound or more of water without a single surplus calorie.

It works in the other direction too, which is part of why week one drops so fast. Cutting out processed food and takeaways lowers your sodium intake sharply, and the water that was being held alongside it leaves within days. That was never fat either.

Reason two: carbohydrate refill

Carbohydrate is stored as glycogen in muscle and liver, and glycogen is stored wet — roughly three grams of water for every gram of glycogen. On a cut you run those stores partially depleted most of the time.

A large carbohydrate meal refills them. Several hundred grams of glycogen returning, with its associated water, is another pound or two on the scale by morning. This is the same mechanism as the dramatic first week of the program, running in reverse.

Put the two together and a curry with rice, naan and a beer can plausibly move the scale two pounds overnight while leaving you in a calorie deficit for the week. The scale is measuring what you weigh, which is not the same measurement as how much fat you are carrying.

“Two pounds of fat is seven thousand calories. Look at what you ate and ask whether that is even arithmetically possible.”

How long it takes to clear

Usually one to three days of ordinary eating and ordinary drinking. Your kidneys excrete the excess sodium, the water goes with it, and the trend line resumes where it left off.

The counterintuitive part is the water. Cutting fluid to lose water weight does the opposite of what you expect — hold your 3.5 litres, keep the sodium at its usual level rather than dropping to nothing, keep the steps up, and let the mechanism finish. There is nothing to fix here.

• Hold the water target. Restricting fluid does not accelerate anything
• Return to your normal sodium intake rather than cutting it to zero
• Keep the steps and the training as prescribed
• Weigh daily and expect the seven-day average, not any single morning, to tell you the truth
• Do not cut calories in response. You will be cutting in response to water

Why this is where week two ends

Week one drops fast, because that is the same fluid mechanism working in your favour. Week two is the first time the scale behaves like real fat loss — slow, uneven, punctuated by exactly these overnight jumps.

So people who did nothing wrong get a Sunday morning that reads as failure, and quit on a program that was working. That is the single most common exit point on any thirty-day plan, and it is caused by a measurement artefact rather than a result.

Your progress page plots both the daily dots and the seven-day average precisely so this is visible. A salty Saturday shows up as one dot well above the line, and the line barely notices. The plateau protocol only comes into play when the average itself is flat for four days or more with compliance holding — a single high morning is not a plateau, it is a Saturday.

The other swings worth knowing

Hard or unfamiliar training holds fluid in the muscles that repaired it, which is why the scale often rises the day after a heavy lower-body session. The menstrual cycle produces a predictable multi-pound swing for many people across the month. Travel, poor sleep and constipation each add their own noise.

None of these are fat, all of them are larger than a day's fat loss, and every one of them clears on its own. If a swing is genuinely persistent — weeks, not days — accompanied by swelling or breathlessness, that is a conversation with a clinician rather than an adjustment to your calorie target.