October 10, 2022
Trying to maintain a healthy diet in our hectic world is not easy. Busy schedules make it difficult for many people to sit down for meals at regular intervals throughout the day. And the temptation to turn grab fast food or to graze on sugary treats and salty snacks can be hard to resist.
Many studies have shown that the timing of when we eat matters as much as how many calories we consume. Intermittent fasting has become a popular dieting approach that limits food consumption to certain intervals during the day, and there are many scientists who advise against eating after 8 p.m.
Eating later in the evening has been shown to lead to weight gain and certain chronic health diseases, including obesity and type 2 diabetes. But can ignoring your body's natural biorhythms by eating later in the evening actually make people sick? Many studies say yes.
Our internal clocks not only regulate our sleep schedules, but they also influence our appetites, hormone levels and blood pressure levels. Researchers have found that consuming most of our calories earlier in the day may be better for our health.
The latest study, from Brigham and Women's Hospital in Boston, suggests the optimum consumption window is a 10-hour interval from the time one wakes up.
"We wanted to test the mechanisms that may explain why late eating increases obesity risk," said J. L. Scheer, director of the hospital's medical chronobiology program. "Previous research by us and others had shown that late eating is associated with increased obesity risk, increased body fat, and impaired weight loss success. We wanted to understand why."
The scientists found that the time that we eat significantly affects our energy expenditures, appetites and body fat. Specifically, eating four hours later leads to significant differences in our hunger levels, the way we burn calories and the way our bodies store fat.
During the study, 16 overweight or obese participants followed a strictly regimented meal schedule that began early in the day. They later shifted to eating the same meals 4 hours later in the day. For instance, a participant may have eaten at 9 a.m., 1 p.m. and 5 p.m. on the early schedule and then at 1 p.m., 5 p.m. and 9 p.m. on the later schedule.
Eating later profoundly affected the hunger and appetite-regulating hormones, leptin and ghreline. Leptin levels, which signal that we are full, decreased when participants ate later. People also burned calories at a slower rate and created more fat tissue when they ate later.
This research adds to scientists' understanding of the health benefits of early time-restricted eating.
Some of the earliest studies on this practice were mice studies published in 2012. Mice that ate a high-fat diet within an 8-hour window were much healthier than those who ate the same diet throughout the day. The latter group was stricken with obesity, diabetes and liver disease within 3 months. But when the sick mice were given the same food over just 8 hours, their conditions improved.
Since then, human trials have shown that eating in a restricted time window, rather than grazing all day, can significantly improve blood pressure and oxidative stress markers.
Not only is eating within a smaller window each day important for optimal health, but research suggests that eating most of one's calories early in the day is, too. People who eat their largest meal at breakfast and then eat a gradually smaller lunch and dinner have better blood pressure, cholesterol and insulin sensitivity than people who eat their largest meal at dinner time.
A pair of studies published in 2018 and 2019 found that people who consumed all of their calories during a 6-hour window that began an hour or two after they woke up had improved triglycerides and blood pressure and more efficient cell repair.
Other studies have suggested that practicing time-restricted eating at later intervals, such as skipping breakfast and eating anything desired from noon to 8 p.m. does not offer the same health benefits.
Steve Hendrick, author of "The Oldest Cure in the World: Adventures in the Art and Science of Fasting," detailed the way our eating schedules impact the body's natural repair process in an article for Salon. When we eat closer to bedtime, our bodies do not have as much time to make repairs. That includes replacing damaged cellular parts that can lead to disease. Instead, they are consumed with digesting our meals and delivering nutrients where they are needed.
Research has shown the body usually doesn't start its repair work until about 6 hours after a person has stopped eating, Hendrick wrote. It's also a gradual process that doesn't go into overdrive for another 6 hours. So this means that a fasting interval of more than 12 hours is needed for the body to properly repair itself, but most of us are only fasting for about 9 to 10 hours a night.
While intermittent fasting and other types of time-restricted eating are generally considered safe, it is not the best option for everybody and data on the optimal timing and frequency of meals remains conflicting. Some studies suggest that eating smaller, more frequent meals throughout the day may more effectively reduce the risk of chronic diseases and encourage weight loss.
Scientists also emphasize that what we eat also continues to be important. A healthy, balanced diet is still needed when practicing time-restricted eating.