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Cycles & seasons · 3 min read
The seasonal weight wave almost everyone rides
Average body weight follows an annual curve: a winter peak around the holidays, a slow spring fall, a late-summer low. The wave is smaller than people believe, stickier than they expect, and easy to misread on a single weigh-in.
Weight has a season
Put a few thousand people on connected scales and average the readings, and a shape appears: weight climbs through November and December, peaks in the days after Christmas, falls through spring, and bottoms out in late summer or early autumn. A three-country study of daily scale data (Helander et al., NEJM 2016) found the same wave in the United States, Germany and Japan — each country's peaks timed to its own feast calendar. The wave is not a personal failing. It is what populations do.
Smaller than you think
When researchers actually weighed US adults through the holiday season (Yanovski et al., NEJM 2000), the average gain was 0.37 kg — a fraction of the 2–3 kg of Christmas folklore. What the average cannot tell you: your number. The spread was wide, and people already carrying more weight tended to gain more. But across the cohort, the measured wave was a few hundred grams — real, and far smaller than the story everyone tells about it.
Small, but sticky
The problem is not the height of the peak. It is the retrace. In the scale data, about half the holiday gain disappeared within weeks — likely water and glycogen draining after richer food. The other half hung around until summer. In the Yanovski cohort, weight a year on was up about 0.6 kg, with the holiday weeks accounting for more than half of it. A wave that never fully retraces is a ratchet: +0.4, −0.2, repeated for a decade, leaves a residue of kilograms.
One weigh-in cannot see it
Daily weight swings from water, glycogen, salt and meal timing run 1–2 kg — larger than the entire seasonal wave. A single January weigh-in therefore says almost nothing about the season; it is weather. A 7-day rolling average is the smallest unit that can show the wave at all, and the fair comparison is December against last December, not December against your July low. The scale also cannot tell you composition: the fast-draining part of the peak was largely water, not fat.
Ride it, don't fight it
The practical read: in December, the win is a smaller peak, not a loss — restriction during the highest-pressure eating weeks of the year rarely sticks. In late winter, the curve turns down on its own; a deficit started in February works with the season. And if you set a summer target from a January number, you have quietly included the wave in your maths. Subtract it first. One caveat: if regular weighing feeds anxiety or a history of disordered eating, skip the scale and judge the season by how clothes fit instead.
How to ride the wave
Adherence collapses exactly when weight climbs. Weigh anyway — a number you see beats one you avoid.
Judge December by the 7-day average, against last December — not against your July low.
The winter goal is a smaller peak, not a loss. A 0.5 kg peak leaves spring far less to undo than 1.5 kg.
The population curve turns down in late winter anyway. A deficit started then works with the season, not against it.
Quick answers
Is winter weight gain real or a myth?
The wave is real: daily scale data from the US, Germany and Japan all show a peak in the days after the big winter holidays. The size is the myth. Measured average gain is around 0.4 kg, not the 2–3 kg of folklore — though individuals vary widely, and heavier people tend to gain more.
How long does holiday weight take to come off?
In connected-scale data, about half the post-Christmas gain was gone within a few weeks — likely water and glycogen. The other half persisted into spring and, for many, until summer. That sticky half is why the seasonal wave matters: repeated yearly, a few hundred retained grams compound into visible long-term gain.
Should I try to lose weight in December?
Usually no. Aiming to hold — a smaller peak rather than a loss — is more realistic during the year's highest-pressure eating weeks, and restriction then tends not to stick. The efficient move is to cap the peak, keep weighing, then start a deliberate deficit in late winter when the curve turns down anyway.
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