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Eating after 8pm makes you gain weight.

The clock does not add calories. What the clock does is change how much you eat and how well you sleep — and those are real effects with an ordinary explanation.

Verdict: Mostly falselate eatingnight eatingmeal timing

The claim, as people state it

“Eating after 8pm makes you gain weight.”

What is actually known

Body weight tracks the energy you take in against the energy you use, over weeks. A meal does not carry a different amount of energy at 21:00 than it did at 18:00; the food is identical and so is the arithmetic. Trials that hold daily calories constant and move them earlier or later in the day find, at most, small differences — nothing like the effect the folk rule implies.

What is real is that late eating and higher intake travel together. Evening is when people are tired, unsupervised, in front of a screen, and eating from a packet rather than a plate. Portion control is worst at the point of the day when attention is lowest. A rule that says "nothing after eight" works for the people it works for because it deletes that window, not because 20:00 is metabolically special.

There is also a sleep mechanism worth taking seriously. A large meal close to bedtime is associated with more reflux and more fragmented sleep for some people, and short sleep is in turn associated with higher next-day appetite. That chain is plausible and partly demonstrated, but it is a sleep story, not a calorie-storage story.

Why the myth persists

Because it works often enough to feel true. Someone who stops eating after eight usually stops eating a packet of something in front of the television, loses weight, and credits the clock rather than the packet. The rule also has the shape people want from diet advice: simple, absolute, and free.

The arithmetic

Potato chips carries 532 kcal per 100 g in the food database, so a 50 g handful of crisps is 266 kcal. That figure is a property of the food. It does not consult a clock.

Repeat that portion every evening and it is 1 862 kcal a week. At roughly 7 700 kcal per kilogram of body fat, an unmatched 266 kcal a day works out at about 12.6 kg a year — which is the actual mechanism people are noticing when they blame the hour.

kcal/min = MET × 3.5 × 75 kg ÷ 200 (ACSM)

Those minutes are computed at 75 kg using the ACSM equation above and the MET values behind every exercise page on this site. They do not change if you move the meal earlier, which is the whole point.

Every figure in this section was computed when this page loaded, from 5 237 food rows and 31 exercise rows already in this repository. Nothing in it is stored as prose.

The honest nuance

For shift workers the picture is genuinely less settled. Eating at 03:00 is not the same as eating at 20:00, because circadian rhythm affects glucose handling, and the research on night-shift eating is real, ongoing and not yet conclusive. If you work nights, treat the general "late eating is fine" answer as weakly supported for your situation.

If a cut-off time helps you, use it. There is nothing wrong with a rule that works by removing an eating opportunity — just be honest about why it works, because that tells you what to do when it stops working.

General information, not a diagnosis and not medical advice. Anything touching a condition you have, a medicine you take or a test result belongs with your own clinician, who has information no web page does.

Frequently asked questions

Source: USDA FoodData Central (SR Legacy) via the TempoLife food database; MET values from the 2011 Compendium of Physical Activities · checked 2026-09-02

Work it out for yourself

• Calories in an evening snack
• Your daily calorie needs
• Does eating late cause weight gain?

Other claims checked

All claims · Weekly research digest