Your body just isn’t expecting you to be eating when it’s dark outside. Our species may have only discovered how to use fire about a quarter million years ago. We just weren’t built for 24-hour diners.

Due to this circadian pattern in glucose tolerance, a low-glycemic food at night can cause a higher blood sugar spike than a high-glycemic food eaten in the morning. We’re so metabolically crippled at night: researchers found that eating a bowl of All Bran at 8pm caused as high a blood sugar spike as eating Rice Krispies at 8am. High-glycemic foods at night would seem to represent the worst of both worlds. So, if you’re going to eat refined grains and sugary junk, it might be less detrimental in the morning.

The drop in glucose tolerance over the day could therefore help explain the weight-loss benefits of front-loading calories towards the beginning of the day. Even just an earlier versus later lunch may make a difference. People randomized to eat a large lunch at 4:30pm suffered a 46 percent greater blood sugar response compared to an identical meal eaten just a few hours earlier at 1pm. And a meal at 7am can cause 37 percent lower blood sugars than an identical meal at 1pm. Now there doesn’t seem to be any difference between a meal at 8pm and the same meal at midnight—they both seem to be too late. But eating that late, at midnight, or even 11pm can so disrupt your circadian rhythm that it can mess up your metabolism the next morning––resulting in significantly higher blood sugars after breakfast, compared to eating the same supper at 6pm the evening before.

So, consuming more calories in the morning relative to the evening may actually have a triple benefit: more weight loss, better blood sugar control, and lower heart disease risk. So, if you’re going to skip any meal, whether practicing intermittent fasting or time-restricted feeding (where you try to fit all your food into a certain daily time window), it would be safer and more effective perhaps to skip dinner rather than breakfast.

"So, in the morning, our muscles are especially sensitive to insulin, rapidly pulling blood sugar out of our bloodstream to build up glycogen reserves. At night, though, our muscles become relatively insulin resistant. Our muscles resist the signal to take in extra blood sugar. So, does that mean you get a higher blood sugar and insulin spike in the evening compared to eating the exact same meal in the morning? Yes. In that 100-calorie difference study, for example, blood sugars rose twice as high after the 8pm meal compared to same meal in the morning. So, shifting the bulk of our calorie intake towards the morning would appear to have a dual benefit — more weight loss, and better blood sugar control."