Calories and Clocks
Years ago in the beforetime, people just worried about total calories. It didn't make any difference whether you swallowed your calories in one big, python-like bolus or you foraged throughout the day like a field mouse. And it certainly didn't make any difference if you consumed those calories under the watchful eye of the sun or the sly gaze of the moon.
Now, however, the thinking is that you'd best stop eating when the sun peters out. Whether it's because of reduced nighttime activity, fluctuating diurnal/nocturnal hormone levels, or whether calories, like vampires, become more powerful in the nighttime and turn you into the un-slim instead of the un-dead doesn't matter. People just believe it to be true.
However, if you look at the studies, even though many of them were conducted in metabolic wards where eating is strictly controlled by evil laboratory overlords, the truth about nighttime eating isn't so clear.
- A 2007 study involving 12 obese women found that nighttime eating didn't affect weight loss. There weren't any significant changes in weight, fat percentage, or fat-free mass between daytime eaters, all-day eaters, and nighttime eaters.
- A 2012 study involving 78 fat police officers found that the cops who ate most of their carbs at dinner lost more weight and more inches off their waist.
- A third study of 74 overweight women, conducted in 2013, found that subjects who ate most of their daily calories at breakfast lost more weight and more inches off their waist than a group that ate most of their calories at dinner.
- Another 2013 study (stop me if this is getting tedious) involving normal-weight people found that avoiding calories between 7 PM and 6 AM led to around 239 fewer calories per day, which can add up to a lot over time.
- While these previous two studies might have had us believing that you should avoid eating at night, yet another study spoiled the research broth. This one involved 10 overweight women and lasted 105 days and used a crossover methodology where subjects would follow one style of eating for 6 weeks and then switch to another style for another 6 weeks.
During the first crossover, those who ate most of their calories at night lost more fat than those who ate most of their calories in the morning. However, during the second crossover, the morning eaters lost more fat than the evening eaters.
- But then again, a University of Pennsylvania School of Medicine study found that nighttime eating impairs metabolism.
- But hold the bus. An animal study conducted by researchers at Oregon Health & Science University found that monkeys that ate most of their calories at night were no more likely to gain weight than monkeys who rarely eat at night.
Where does that leave us? The natural response to this merry-go-round of research should be a dull throbbing behind the temples. Still, if you managed to machete your way through those studies, you can see that medical research (which extends beyond the studies mentioned) hasn't reached a consensus on the wisdom or folly of nighttime eating.
Additionally, there's a problem with practically all of the studies in that they focus on the biological instead of the psychological. Human types are prone to "hedonic hyperphagia," which is the drive to eat for pleasure when you're not in a calorie deficit. I guess this is like hedonic drinking, hedonic sex, or hedonic bowling. Anyhow, it's known in less scholarly circles as "the munchies," or eating for the eff of it.
When we're not doing stuff, when our bodies or minds aren't involved in some activity, when we're in a passive state, e.g., watching television, our thoughts turn to eating for the fun of it instead of eating for the fuel of it.
This nighttime calorie surplus, rather than any kind of metabolic fluctuations caused by the presence or absence of light, is likely the source of many waistline-associated problems.
While there's no clear-cut winner in the daytime eating vs. nighttime eating conflict, it looks like nighttime eating contributes an itty-bitty more to your waistline than daytime eating. Either way, it's not enough to break your diet-back.
However, if you're prone to hedonic hyperphagia, you should pick a 9 to 12-hour nighttime slot where you refrain from eating. This would only be for those interested in fat loss. (Those that have muscle gain as their priority should probably continue to eat regularly up to bedtime.)
Even with this nighttime dietary curfew, however, it would be a good idea to have a pre-bedtime dose of protein with few or zero carbs to help maintain muscle mass. I suggest low- or non-fat cottage cheese, Oikos Triple Zero yogurt, or a serving or two of low-carb protein powder.
- Keim NL et al. Weight loss is greater with consumption of large morning meals and fat-free mass is preserved with large evening meals in women on a controlled weight reduction program. J Nutr. 1997 Jan;127(1):75-82. PubMed.
- Sofer S et al. Greater weight loss and hormonal changes after 6 months diet with carbohydrates eaten mostly at dinner. Obesity (Silver Spring). 2011 Oct;19(10):2006-14. PubMed.
- Oregon Health & Science University. Scientists Dispel Late-Night Eating/Weight Gain Myth. Science Daily. 2 February 2006.
- University of Pennsylvania School of Medicine. Timing meals later at night can cause weight gain and impair fat metabolism: Findings provide first experimental evidence of prolonged delayed eating versus daytime eating, showing that delayed eating can also raise insulin, fasting glucose, cholesterol, and triglyceride levels. ScienceDaily. 2 June 2017.