Could checking your watch instead of nutritional labels be the answer to losing weight, improving sleep, increasing energy and warding off chronic health conditions? That’s been the promise of a diet strategy called time-restricted feeding or TRF, and now there’s science behind it. It’s a twist on fasting—you limit your eating to a set number of hours each day so that you are “fasting” during the other hours. And that period of fasting is longer than the amount of time most people tend to “fast” naturally each day—shortly before they go to bed and while they are sleeping.

This doesn’t mean you will have carte blanche to binge during eating hours. What and how much you eat still matter, certainly for overall health reasons. TRF isn’t meant to overcompensate for eating processed foods, for instance. Think of it as a beneficial addition to a healthy lifestyle or a simple, and quite clever, way to start a healthy lifestyle, says Adena Zadourian, clinical research coordinator at  University of California San Diego, department of medicine-cardiology. In fact, even if all you do is change when you eat, you may still see benefits—that’s because of your body’s reaction to a longer time span without nutrients.

How TRF Works

Consuming food triggers the body’s metabolism-digestion to start, Zadourian explains. When people are always eating, the body is constantly in digestion mode. But the digestive system was never meant to be “on” all the time. When you stop eating for a fairly long period each day—referred to as “intermittent fasting”—neuroendocrine hormones aren’t signaled, so the metabolism-digestion mechanism isn’t initiated. This gives the body a chance to rest from all the work it was previously doing to process food.

Practicing TRF is simple: Limit your eating to within a specific span of hours each day. Courtney M. Peterson, PhD, assistant professor in the department of nutrition sciences at  University of Alabama at Birmingham, recommends “early TRF,” or limiting eating to early in the day (with dinner by midafternoon) or to the middle of the day (with dinner by early evening). Such forms of TRF are based on the body’s circadian system, the internal clock that influences everything from your sleep-wake cycle to eating habits to the release of hormones.

Work, play, family obligations—these can also influence when we eat or sleep, but they aren’t always aligned with the body’s natural timing for those activities, explains Zadourian, who is working on a three-year study of 150 firefighters to see whether TRF can improve their well-being. The theory is that intermittent fasting helps reset the body’s clock to its natural rhythms.

There are many health benefits to the concept. Because your body is spending less time and energy digesting food, fasting gives the body more time to recycle damaged and worn-out tissues and to reduce a form of molecular damage called oxidative stress—in other words, time to rest, repair and rejuvenate, says Peterson. Her studies found that early TRF improves insulin sensitivity (the body’s ability to process blood sugar), blood pressure, oxidative stress, hunger levels and fat-burning. Other research has found that it cuts diabetes risk (inflammation and oxidative stress directly increase blood sugar) and cardiovascular disease (caused by damaged blood vessels). Fasting also slows down the rate at which cells grow and divide, which reduces the risk for cancer. Studies done in the lab and with people have linked TRF with the prevention of digestive disorders, high cholesterol, liver disease and obesity.

And what about weight loss? In the first human study of early TRF, or eTRF, Peterson and her colleagues found that a daily 18-hour fast (yes, that means eating during a mere six hours a day, from 8 am to 2 pm) helped to keep appetite levels on an even keel throughout the day and to rev up fat-burning during the night. There were no hunger spikes that encourage unwanted eating and make it harder to stick to a weight loss diet. TRF also can boost metabolic flexibility, the body’s ability to switch between burning fats and carbs, which is helpful for weight loss.

5 Tips for Trying TRF

Many people tend to eat at various times during a much larger chunk of the day—often about 12 to 14 hours, from breakfast at 7 am to an after-dinner snack at 9 pm. There’s no doubt that cutting your daily chow time by a third or more can be a challenge. These pointers from Peterson and Zadourian can help you stick with the plan…

Start slowly. Ease into a time-restricted diet to give your body time to adapt. Start by restricting eating to a 10-to-11-hour daily window. If you typically eat breakfast at 7 am, you’ll have to shut off the kitchen lights by 5 pm or 6 pm. After two weeks, start shortening your eating period, scaling down to nine and then eight hours a day. (If you want to take the plunge and try a six-hour limit, you can, says Peterson, but she thinks that most of the benefits of TRF can be had with an eight-hour or nine-hour eating period.)

Find your own TRF “sweet spot.” There are variations on the TRF diet. For instance, during your daily fasting period, Peterson OKs consuming anything that has no calories—water, plain tea or coffee (but no cream, milk, sugar or honey…you get the idea) or sugarless gum. Zadourian, on the other hand, advises only water during the fasting times and suggests sipping hot water as a substitute for coffee or tea in the morning before you start eating.

Another difference concerns taking planned days off from the routine. Lab studies involving mice suggest that people will get nearly the same benefits in blood sugar control and cardiovascular health if they practice TRF only five days per week, says Peterson. This way, you can still enjoy going out to restaurants with others who aren’t on TRF or entertaining in the evening at home. She generally advises that people experiment—after trying different eating periods for a while, pick the time frame that you can comfortably sustain for four to six days a week.

However, Zadourian suggests staying as consistent as possible with the eating time window and, rather than planning to take days off, thinking of off-days as things that happen on occasion (and are nothing to worry about).

Reframe your thinking. If you want to stick with TRF, ban the idea of “falling off the wagon”—failing—from your mind. This is because it’s bound to take trial and error to figure out how many hours you can go without eating each day without being unhappy.

Stock up on the right fuel. Adapting to the no-eating period could make you physically uncomfortable beyond just hunger—for example, study participants have cited increased thirst and headaches. Staying hydrated is key, so be sure to drink plenty of water, especially during your daily fasting period. What foods best work to prepare you for the daily fast? Scientists still are unsure, yet plenty of research shows that the super trio of healthful fats, fiber and protein can keep you fuller longer. Check out 8 Forever Foods Every Healthy Kitchen Needs for more ideas.

Track your experience. Using a journal to log what and when you eat is a great way to measure your progress, reinforce good habits and stay motivated. Keep a written journal or consider participating in a study that gives you access to the free smartphone app MyCircadianClock developed by Satchin Panda Lab at the Salk Institute. You’ll be able to track your eating, sleeping, exercise and other activities and help scientists learn more about how circadian rhythms affect health.

The bottom line: While more research is needed (both Peterson and Zadourian have studies in the works to prove the concept), reducing your eating hours may help your waistline and your overall health. Bonus: Fasting can remind us what it’s actually like to feel satiated and to recognize real hunger cues as opposed to false ones—both crucial for a more mindful approach to eating.

For more fast ways to get in shape for summer, please see the following stories…

9 New Ways to Lose the Last 10 Pounds

7 Smart Ways to Control Nighttime Eating

The Secret to a Truly Sculpted, Sleek Body

Can the Love Hormone Help You Lose Weight?


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