The research that may compel you to give up the bedtime snack
Posted March 28
Cows and horses graze constantly, with no apparent harm to their health. But the American habit of snacking from mid-morning until bedtime may be damaging our health, some researchers believe.
Our bodies are designed to have periods of starvation, and they lose an essential time of renewal when we snack constantly, Hara Estroff Marano wrote for Psychology Today. This doesn’t mean that we need to fast for months or even days; going for 12 hours without food seems to allow the body the time it needs to reprogram cells and revitalize our metabolism. Scientists call this a “fasting-mimicking diet” and say it can markedly improve brain function.
“Fasting triggers a host of innate cell-renewal mechanisms, and studies in multiple organisms show that this fasting physiology is tied to the circadian cycle, as is our nutrient-sensing apparatus,” Marano wrote.
“Whatever gains we’ve made with our full larders open 24/7 and artificial lighting, we’ve disrupted the activity/rest cycle our metabolism was built on over millions of years of evolution, and we’ve inadvertently kick-started many chronic diseases.”
The American Heart Association also sounded the alarm on late-night snacking in a scientific statement published Jan. 30. The group's review of research shows elevated rates of obesity, poor heart health, diabetes and inflammation among people who routinely eat within two hours of going to bed. Unfortunately, that's a lot of us; Americans' rates of eating slow down significantly only between 1 and 6 a.m.
"This study clearly demonstrated that adults in the United States eat around the clock," the Heart Association said.
Our constant snacking is a relatively new, developed over the past 100 years, food historian Andrew F. Smith said in The Wall Street Journal. Before artificial lighting, refrigeration and fast-food drive-thrus open past midnight, it wasn't such a struggle to go for 12 hours without eating. But with Americans sleeping less and eating more, the "fast" implied in "breakfast" is shorter than it's ever been.
On average, Americans are asleep for fewer than 7 hours a day, according to research by Gallup. Fifty-six percent of us snack three or more times a day, according to government data from 2010. In the 1970s, just 10 percent of us did.
As New York magazine cheekily put it: "Americans Pretty Much Only Stop Eating When They're Sleeping."
The reasons to consider a 12-hour fast, however, are nothing to laugh about.
Of mice and monkeys
In recent years, lengthy fasts or calorie restriction have been touted as a veritable cure for aging. Because mice and monkeys who are forced to fast live longer and look younger, some researchers believe those results will translate to humans. We'll know in a half-century or so if they're right — or at least, our descendants will.
Some people aren't willing to wait and have already embraced sustained low-calorie diets, not for weight loss, but for health. There's even an international Calorie Restriction Society.
Others are trying diets that involve fasting two days a week, or five days a month.
But many people are not willing to endure the deprivation that regular fasting requires. For them, just kicking the habit of eating after dinner may make a difference in their health, the Heart Association's report suggests.
The report, "Meal Timing and Frequency: Implications for Cardiovascular Disease Prevention," explains why not just what we eat, but when we eat, matters. It's all about our inner clocks that affect our metabolic processes.
We usually think of circadian rhythms in terms of how light exposure affects sleep. That "clock" is based in our brain, but our other organs also have their own clocks, and they respond to the timing and size of our food supply. We can reset these clocks by changing when we eat, the study's authors said. They also note that our bodies are better at processing certain types of foods at different times of the day.
"For example, later in the evening, it's harder for the body to process glucose, compared with earlier in the day," Marie-Pierre St-Onge, an associate professor of nutritional medicine at Columbia University in New York City, told Amy Norton of HealthDay News.
This could help explain why studies have found that mice fed continually are fatter and sicker than mice whose eating is confined to 9 or 12 hours, even if they consume the same amount of calories.
The Heart Association's report, published in the journal Circulation, said that more human study is necessary because most of the research done on the subject is observational and can't prove causation. Moreover, the studies represent a wide variety of eating times; for example, one study showed a decrease in inflammation specifically among women who stopped eating before 6 p.m.
The Heart Association found the findings compelling enough, however, to recommend that Americans be more mindful about when they eat. Its recommendations include eating more of our total calories earlier in the day to reduce the risk of heart disease and diabetes, and to employ "consistent overnight fast periods."
If you still can't resist
If all this isn't enough, there's another reason to forgo that bedtime snack: the health of your teeth.
Children, in particular, are at risk for tooth decay if they eat or drink products containing sugar right before bed, according to Col. Georgia Rogers, dental public health consultant to the surgeon general of the U.S. Army.
“Consuming snacks or drinks right before bedtime is the most dangerous because your saliva flow slows down when you go to sleep. The acids produced by the bacteria in your mouth aren’t washed away or neutralized. That’s why it’s critical to always brush with fluoride toothpaste before sleeping,” Rogers wrote in the Fort Campbell Courier.
There is one group of people who could benefit from a bedtime snack, according to nutritionist Toby Amidor, writing in U.S. News and World Report: people who haven't consumed enough calories already during the day.
But those people should treat it as a miniature meal and keep it under 200 calories and healthful, like a quarter of a mashed avocado on whole-wheat toast, Amidor wrote.
For people who don't like avocados, that could be yet another reason to stop eating long before bed.