People around the world show remarkable similarity in their daily eating habits: meals start off healthy in the morning, but get progressively worse throughout the day – until by nightfall we're deep into junk food territory. Just take a look at these images from mobile startup Massive Health . Focus on the dots over North America in the upper left, which indicate the healthiness (green) or unhealthiness (red) of people's meals at different times of day.

At 10 a.m. Eastern, North America is covered in green as people dig into healthy breakfasts. But by 10 p.m., red and orange splotches dominate most of the continent. And at 1 a.m., there's hardly any green to be seen. Similar trends appear according to local time in Europe, Asia, and elsewhere. View an interactive version showing the whole day here .

The data was culled from Massive Health's iPhone app, Eatery . Users record, rate, and track the healthiness of their meals over time. The images reflect ratings on about 500,000 meals from users in 50 countries, collected over 5 months.

The data doesn't explain why we eat worse the later it gets – it just tells us that we do. But there's something profound about such a consistent, worldwide pattern. In an email to The Salt, Massive Health founder Aza Raskin says:

In terms of why, we can only make educated guesses. There is a 1.7 percent overall decrease in healthiness of what's eaten for every hour of the day that passes after breakfast. That's as true in Tokyo as it is in San Francisco as it is in São Paulo. It teaches us about something fundamental about the way people make decisions about food—and decisions in general.

Part of the problem could be a lack of healthy food options in the late evening and wee hours, which we wrote about in December. Or, as some research suggests , it could be that we use up our reserves of willpower throughout the day, until we eventually succumb to the temptation of late-night snacking.

And just what are we doing awake – not to mention hungry – at that hour, anyway? As NPR's Allison Aubrey reported just last week, staying out later on the weekends and sleeping in (a.k.a. "social jetlag") may also be linked to weight gain.

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