Time-Restricted Eating: The Benefits of Shorter Eating Windows and How to Practice It to Support Longevity
From Postmates and Uber Eats to 24/7 drive-throughs and freezers full of snacks ready to be microwaved, our modern society has more access to food than ever before. Unlike our long-ago ancestors, who consumed in excess only when they came across a bountiful hunting or gathering session, a typical American consumes food or calorie-containing beverages up to ten times on any given day.
We also tend to eat more at night, with over 35% of calorie intake occurring after 6 p.m.—a time that would have been a challenging feat up until just about 100 years ago, when the use of in-home electricity became commonplace. Although our modern-day technology is undoubtedly helpful in many situations, the ability to eat at any time and any place has set us back in our health.
We are now heavier and more metabolically dysfunctional than ever—and one reason might be our preference for around-the-clock eating. This knowledge has led many health researchers to advocate for time-restricted eating or intermittent fasting—let’s take a closer look at the science behind this eating style and how to practice it.
Time-Restricted Eating 101
Time-restricted eating typically involves forgoing food and caloric beverages for 14 to 16 hours per day, shortening the eating window to 8 to 10 hours. However, the exact eating style and timing can vary widely.
Another term for time-restricted eating is intermittent fasting, which may include an eating window of 8 hours with a 16-hour fast (sometimes referred to simply as “16:8”). In contrast, a more extreme version could be a 4- to 6-hour eating period followed by 18-20 hours of fasting.
To reap the benefits of time-restricted eating, the feeding window should be restricted to ten hours per day or less, equating to 14 hours of fasting. For example, this would look like stopping eating by 6 p.m. and fasting until 8 a.m. the following morning. A slightly more strict 16:8 fast would only allow caloric food and drink for 8 hours per day, such as between 10 a.m. and 6 p.m.
How Does Time-Restricted Eating Work?
During a period of fasting, the body can utilize different energy sources than its typical preferred fuel of glucose. After about 12 hours of fasting, the body will start to use ketone bodies for energy, which have been linked to improved metabolism and reduced risk of metabolic disorders.
A time-restricted eating schedule that follows the rhythms of our internal 24-hour circadian clocks may lead to better health outcomes. This is because eating outside of our typical “feeding time”—like midnight snacking—can disrupt how we metabolize food, leading to increased energy storage and metabolic dysfunction.
Time-restricted feeding also allows adequate time for our bodies to undergo autophagy, our “housekeeping” process that recycles or removes damaged or toxic cells and cell parts to make room for new, functional cells. Without proper autophagy, these dysfunctional cells build up, contributing to accelerated aging and disease.
The Potential Health Benefits of Time-Restricted Eating
1. Anti-Aging and Longevity
Although research is limited, following a time-restricted eating plan may lead to longer lifespans, in part due to increased autophagy. A 2019 study found that overweight adults who ate in a time-restricted manner had a 22% increase in a gene associated with autophagy, and other research indicates that increased autophagic processes are linked to lifespan extension.
Intermittent fasting may also reduce oxidative stress—a buildup of inflammatory molecules called reactive oxygen species that accelerate aging. In a study of obese adults, restricting the feeding window to 6 hours or less led to significant reductions in oxidative stress markers.
Research in rats, worms, and fruit flies suggests that time-restricted feeding can extend lifespan. In a study from 2017, mice that fasted every other day experienced a lifespan extension of about 13%. While these results haven’t been replicated in humans yet—and every-other-day fasting is much more challenging for people than simple time-restricted eating—the available evidence so far is promising.
2. Metabolic Health
As fasting switches the body’s fuel source to be less reliant on glucose, this style of eating is linked to improved metabolic health, including lower blood glucose and improved insulin sensitivity. People with better metabolic function have significantly reduced risk of several chronic disorders, including those related to dysregulated blood sugar, blood pressure, and body fat.
One small study of adults with blood sugar dysfunction found that eating during an early 6-hour window (eating between 8 A.M. and 2 P.M.) significantly improved metabolic markers. These benefits included a 4 mg/dL decrease in average glucose levels, increased autophagy markers, and a beneficial alteration in cortisol patterns and circadian clock genes, all of which are related to anti-aging pathways.
3. Weight Loss
In some people, time-restricted eating leads to weight loss—even without reducing caloric intake. Fasting is thought to enhance the production of certain hormones, leading to increased metabolic rate and calories burned.
A 2020 review looked at data from 27 intermittent fasting trials, finding that every one of the trials led to significant weight loss, with a range of 0.8% to 13.0% of weight loss from baseline.
Similarly, a 16-week study of overweight individuals found that reducing the eating window to 10 hours per day led to an average weight loss of 7.2 pounds, which was kept off for one year after the study ended. However, although it was not instructed to alter dietary intake, most people unintentionally reduced their calories by about 20%, which could have played a role in their weight loss.
4. Cardiovascular Health
Time-restricted eating may support heart health by improving markers related to inflammation, blood pressure, lipid levels, and oxidative stress—all of which are risk factors for cardiovascular conditions.
In a review of human trials of intermittent fasting, researchers concluded that all forms of time-restricted fasting led to reductions in blood pressure, insulin dysregulation, oxidative stress, cholesterol, and triglyceride levels.
5. May Support Cognitive Health
Research suggests that fasting may play a role in supporting brain health and cognition with age—possibly because fasting increases levels of brain-derived neurotrophic factor (BDNF), a protein that promotes neuron growth and survival and is linked to memory.
Fasting may also boost mitochondrial function in the hippocampus—the brain region most associated with learning and memory—and regulate the secretion of the neurotransmitters serotonin, noradrenaline, and dopamine. Plus, many neurodegenerative conditions have roots in inflammation, oxidative stress, and poor metabolic health—all of which have evidence of improvement from intermittent fasting.
Although we don’t have research on humans, fasting, and neurodegenerative conditions, some animal studies have shown promising results for how time-restricted eating improves age-related cognitive function.
How to Practice Time-Restricted Eating
While there are many different ways to go about intermittent fasting, there are four ways that tend to be the most popular:
- Time-restricted eating (TRE): The most common way to do intermittent fasting involves fasting every day for 14 hours or longer. A 16:8 fast (fasting for 16 hours and eating in an 8-hour window) is the most typical. There is a subset of this form called early-TRE, which shifts the eating window to the morning or early afternoon and fasting after 2 or 3 P.M.
- One Meal A Day (OMAD): Eating just one meal a day is a newer trend in the fasting world, in which people consume all of their recommended calories within one to two hours and fast the rest of the day and night.
- The 5:2 Diet: This form of fasting involves eating normally for five days of the week while restricting your intake to 500–600 calories on the remaining two days. However, this is more of a calorie restriction diet than solely time-restricted eating.
- Alternate Day Fasting (ADF): With this method, you would fast for a full 24 hours, then eat normally the next day, and continue alternating every day. Again, ADF restricts calories while regular TRE does not.
Should Women Intermittent Fast?
Recent research and anecdotal evidence have shown that women don’t reap as many benefits of fasting as men. This may be because females are highly sensitive to fasting, which alters hormone production and fertility as the body believes there aren’t enough calories to sustain a pregnancy—even if you aren’t trying to have a baby.
However, research from 2022 concluded that only testosterone was reduced in females from intermittent fasting—not estrogen. If you experience menstrual abnormalities from fasting, you may consider a modified approach to intermittent fasting, such as shorter fasting periods or fewer fasting days.
Time-Restricted Eating Safety and Side Effects
Time-restricted eating or intermittent fasting is generally considered a safe style of eating. However, fasting can be dangerous for certain groups of people, including:
- Children and teenagers
- People who are pregnant or breastfeeding
- People with metabolic disorders or those taking medications for blood sugar dysregulation because fasting can cause low blood sugar
- People with a history of disordered eating
- People taking certain medications
If you’re unsure whether to practice time-restricted eating, speak with your doctor or health care provider first.
The side effects of intermittent fasting can include headaches or lightheadedness, dehydration, irritability or mood swings, low energy, fatigue, constipation, and increased hunger or cravings. However, these side effects are generally mild and tend only to occur when you first begin a fasting protocol.
- Time-restricted eating typically involves fasting for 14 to 16 hours per day, limiting the eating window to 8 to 10 hours.
- The health benefits of time-restricted eating may include increased longevity, improved metabolic markers, weight loss, cardiovascular health, and cognitive function.
- There are several different styles of fasting, including early time-restricted eating, OMAD (one meal a day), 5:2 fasting, and alternate-day fasting.
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