TRAVEL19 Jul 2026 · 12 min · Nuno Machado Lopes

Six timezones and four kilos: what travel actually does

NMNuno Machado LopesFounder · far too many flights

The weight you put on during a travel week is rarely the food. It is the clock.

Every hormonal rhythm you own is keyed to light. Move the light and you move the hormones.

Cortisol should peak shortly after you wake and fall through the day. Melatonin should do the opposite. Cross six timezones and both curves stay where they were for several days, which means you are producing a wake-up hormone at midnight and a sleep hormone at a meeting.

An airport at night — The measurable cost of travel starts before the first meal.

What the data usually shows

Resting heart rate up three to eight beats for four to six days.

Deep sleep down sharply on the first two nights, then partially recovering.

Water retention that reads as weight for most of the week.

The part that is actually fat

Some of it is. Appetite regulation degrades with poor sleep, and the environment offers convenience over quality. But if you weigh yourself the morning after landing and again nine days later, most people find the difference is far smaller than the first reading suggested.

The useful discipline is not eating perfectly on the road. It is refusing to draw conclusions from a scale reading taken inside a disrupted week.

WHAT THIS IS NOTThis is a pattern written for a general reader. It is not a reading of your results and it is not a diagnosis. If something here matches what you are seeing in your own data, that is a question for a doctor, not a conclusion.