Right now, more than 2 in 3 adults in the US are considered to be overweight or obese - a statistic that's mirrored throughout some of the richest countries in the world, with 67 percent of men and 57 percent of women in the UK considered to be overweight or obese, and 63 percent of Australian adults in the same boat.

And while mysterious forces could be at play in some of that weight-gain, for the most part, our increasingly sedentary lifestyles and terrible eating habits are getting the better of us, and a new study has found that our love of late dinners and midnight snacks isn't helping. We simply haven't evolved to digest them properly.

Researchers from the Salk Institute for Biological Studies in the UK recruited 150 volunteers to record everything they ate and drank - including the time of day - on a special phone app over a three-week period. Rather than sticking to the 'three meals a day' regime of decades past, more than half the volunteers were found to stretch their meals across a period of more than 15 hours every day, with a huge chunk of the total eating done after 6pm.

According to the paper published in Cell Metabolism, on average, the volunteers consumed less than 25 percent of their total daily calories before midday, and then really ramped things up after 6pm each night, consuming more than 35 percent of their calories at night. 

Which makes sense, because for many of us, getting to work on time is the priority, not careful breakfast preparation, and getting home from work by 6pm would be a luxury. We're also staying up later than ever before, which means more hours available for second dinners and 10pm desserts. 

"Our ancestors spent some calories trying to get calories, now we don't do that anymore. If you want a chicken sandwich, you just go and pick it up," one of the researchers, Shubhroz Gill, told Brian Handwerk at Smithsonian Magazine. "But the main point for our paper is that not only are we consuming excess calories, we are consuming them later in the day. We don't have a way to measure this, but it's almost certain that our ancestors weren't staying up until 1am and consuming a lot of calories."

While the 'three meals a day' rule has in recent times been replaced with 'just eat when you're hungry', the benefit of a more rigid eating routine is that it can be coordinated to match the peaks and troughs that our metabolism goes through each day. As Handwerk explains, these metabolic shifts have been with us throughout human evolution, and while they used to be governed by natural light and our circadian rhythms, electricity has changed everything.

"We are not supposed to be consuming food at night, that's how our bodies have evolved, but now we are sort of forcing our bodies to have food when they aren't supposed to be," Gill told him, adding that our late-night eating habits create a "metabolic jet lag", which can mess with the internal body clocks responsible for actually doing something with all that energy.

The good news is it's actually pretty easy to adopt a healthier eating schedule, as Gill and his team discovered. After reviewing the terrible eating habits of their 150 volunteers, they asked them to use the same phone app from the last experiment to help them stick to more regimented eating hours. They were allowed to choose whatever hours they wanted, as long as they kept to an 8 to 11-hour 'eating window', and they had to be consistent about it over a 16-week period - including weekends.

The group ended up losing an average of 3.27 kg over the course of the experiment, which is interesting, because they weren't instructed to change anything about the actual contents or quantity of the diet. They were simply told to keep to the exact same meal times, day in, day out.

Gill said they actually managed to keep the weight off: "These people were extremely happy to do this longer on their own. After a year, the group returned and their weight loss, on average, remained about the same."

The researchers are reluctant to guess what could have contributed to the weight-loss, perhaps knowing that they were being studied, and being forced to be accountable for what they ate influenced the volunteers to choose healthier options. Maybe it was because the strict eating window made it impossible to indulge in midnight snacks, or perhaps it was because the volunteers were getting better sleep - something they reported throughout the second experiment - which has been proven to be beneficial to our weight.

Whatever's going on here, just remember that while the concept of a second dinner might seem really awesome, it's probably not worth it, so save that leftover pizza for breakfast. You'll thank us in the morning.