Bad Appetite

The social, psychological, and biological drivers of appetite.

Does Late-Night Snacking Make You Fat?

Cheese before bedtime could trigger nightmares—and weight gain.

Some of the most satisfying meals I have consumed in my life have taken place extremely late at night.

Yes, I admit that it can be hard to beat the artery-clogging joy of a home-cooked English breakfast, or the thrill of fancy canapés nibbled delicately over cocktails in the early evening.

But my food memory banks also positively overflow with happy times wolfing down builder's tea and toast with Marmite in the various kitchens of good friends after college bops and teenage house parties.

And can you honestly tell me that anything tastes better than salty fries with a generous sprinkling of mayonnaise and grated cheddar, devoured on the way home from a dodgy nightclub?

I thought not.

One problem, though: divine though these midnight snacks may taste, they're not necessarily so praiseworthy when it comes to your health.

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Obviously french fries aren't exactly a health food, whatever time of day you consume them.

But a recent study found that people who ate more calories after 8pm were significantly heavier, even when controlling for other possible influences on weight like sleep duration. And a number of studies have shown that obese people eat more meals in the evening or night than lean people do.

Part of the reason for these findings is probably that late-night snackers tend to pick high-calorie options, and people who eat a larger number of calories in the evening end up eating a larger number of calories over the whole day.

But recent animal research also suggests that some of the late-night eating effect may be independent of the type and amount of food consumed: Feeding mice on a high-fat diet at the <wrong> time of day (i.e. in the daytime, when they would normally be sleeping, adorably) made them gain 28% more body weight than fellow furries eating almost exactly the same amount of the same diet on their normal schedule.

(*In actuality the <wrong> time of day mice ate very slightly more food and moved around ever so slightly less than the <right> time of day mice, but the differences weren't statistically significant. 

Interestingly, a different study also found that messing with light levels and light-dark cycles in a mouse's house was enough to throw off his circadian rhythms and disrupt his cheese-munching routine.

So humans who want to establish a regime of regular eating may also find it advisable to buy blackout curtains, and to turn off light-emitting electronic devices when night starts to fall...)

Anyhow, while researchers try to figure out exactly why eating late might wreck havoc on one's figure (it could be something to do with dysregulation of important appetite- and weight-related hormones such as insulin and leptin), it's also worth reflecting on some other nasty consequences of late-night binges.

For example, have you ever indulged in a generously-proportioned kebab after a boozy evening out then spent the night dreaming crazy nightmares and tossing and turning in a pool of sweat?

This phenomenon (sometimes referred to by the attractive moniker, meat sweats) is probably the result of extremely high levels of diet-induced thermogenesis - the body's generation of heat after eating a meal, particularly one that involves alcohol and large amounts of protein.

The brutal truth is that our evolutionarily ancient bodies are probably not designed to eat during the night. And eating heavy meals right before sleeping is, at the very least, likely to cause digestive discomfort and a poor night's sleep.

(The disapproving headmistresses from the Enid Blyton boarding school stories in whose pages I was first introduced to the concept of the illicit "midnight feast" would doubtless agree...)

So, much though I would like to tell you otherwise, it's probably better for all of us if we do our best to forgo our favorite night-time morsels - especially the delicious energy-dense ones - and aim to consume the majority of our calories in the earlier part of the day instead.

Chips and cheese for breakfast, anyone?

Susan Carnell, Ph.D., is a research psychologist at Johns Hopkins University, where she studies what drives some people toward obesity.

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