Time-Restricted Eating: Why You Should Try It

By Cambria Glosz, MS, RD
www.prohealth.com
January 17, 2020

time-restricted eating, a form of intermittent fasting, has many health benefits

In a world where we have constant access to refrigerators full of snacks, late-night drive-throughs, and services like Postmates delivering takeout to our doors at all hours, our bodies have never had as much food readily available as we do today. Rather than eating three meals per day, people are now consuming food or caloric drinks constantly - one study found that some people eat over ten times on any given day [1].

It's well known that overeating both calories and processed foods is a major contributor to the global obesity epidemic. But, acknowledging that calories and quality matter, what's more important: what we eat, how much we eat, or when we eat? Time-restricted eating is becoming increasingly popular as a method to lose weight, reduce chronic diseases and inflammation, and increase longevity. Let's dive into the research on how the time-restricted method works, and why you should consider eating this way.

What is time-restricted eating?

Time-restricted eating (TRE) is a form of intermittent fasting that limits the number of hours per day that you are consuming calories. While the number of hours does vary study by study, a typical TRE diet may include an eating window of 8 hours with a 16-hour fast, whereas a more extreme version could be 6 hours of eating with 18 hours of fasting. At the bare minimum, to qualify as TRE, eating should be restricted to ten hours per day, rather than the 15 hours of consumption that is the standard of the average American [2].

A most typical and sustainable version of TRE is the 16:8 version. In this case, for instance, you could have your dinner meal ending by 6 P.M. (no dessert or nightcaps!), then not breaking your fast until 10 A.M. the following morning.

While the definitions vary (purists will say no ingestion of any calories during fasting is allowed), most people allow coffee or tea during the fasting period, ideally drank black. If you need your coffee a bit milder, you can get away with about 1 teaspoon of fat (like cream or coconut oil) added to the coffee without significantly breaking your fast. Similarly, adding a scoop of pure collagen powder to your coffee may help curb your appetite and will likely keep you in ketosis. That said, the addition of these calories, whether from collagen or coconut oil, will reduce some of the benefits of fasting, like autophagy. (Keep reading for more details about autophagy.)

Black coffee can help during the fasting period of time-restricted eating

Whether or not you crave caffeine, make sure to up your water intake during your fasting window -- dehydration plus fasting can equal hangry pretty quickly. And, as you'll see, you may be better off skipping dinner rather than breakfast, which is what a more recently studied sub-type of fasting, called 'early-TRE', follows.

How does time-restricted eating work?

Let's dive into the research - how exactly does this process work? It all goes back to how our ancestors lived -- all the way back to the hunter-gatherer days. As you can imagine, over 10,000 years ago, our Paleo-before-Paleo-was-trendy ancestors did not have constant access to food. They often went days without eating or ate minimal amounts of gathered food, then they would feast for a period of time after a good hunting day.

These restricted windows of eating led to our ancestors being leaner and more muscular than us, without any of our modern-day diseases, like diabetes and heart disease [3]. And it's not just because they didn't have access to Fritos and fast food (although that definitely helps); there are true metabolic reasons as to how this style of eating benefits overall health. When we fast, the body is able to utilize different energy sources than its typical diet of glucose. Instead of using glucose when fasting, it switches to using ketone bodies for fuel, which has been linked to improved metabolism and reduced disease risk [4].

Even without making changes to nutrient quality or diet composition, adjusting to a time-restricted eating schedule that more follows our natural 24-hour circadian rhythms can lead to a reduction in chronic disease and healthier aging. Our circadian rhythms, which used to follow the cycles of the sun and moon, are now constantly disrupted by artificial light at all hours of the day [5].

Disruption of our natural circadian rhythm can lead to chronic disease and increased aging

This disruption of our body's internal clocks, combined with eating erratically around the 24-hour cycle, leads to compromised health by promoting energy storage and not allowing adequate time for our bodies to 'clean house' overnight, also known as autophagy [6]. Autophagy, which means 'self-eating', refers to the way our bodies recycle damaged cells and toxic compounds to make room for new, functional cells. When autophagy is disrupted or reduced, the aging process accelerates and diseases develop more rapidly [7].

Although there are some supplements that can increase autophagy, time-restricted eating or intermittent fasting is a simple way to achieve it [8]. (We also undergo autophagy during sleep and exercise, so make sure to get plenty of those, too!)

While time-restricted eating is the only form of fasting that doesn't require caloric restriction, many people who practice it do unintentionally reduce their food consumption during their eating window. The important thing to note is that the benefits of TRE remain the same whether calories are restricted or not [9].

What are the benefits of time-restricted eating?

Research on caloric restriction and fasting has been studied for decades with rodents, however, human studies are still catching up. Although many of the human studies are small, the results are promising for the benefits of intermittent fasting.

Here are five such benefits:

(1) Weight loss

With almost 40% of the world's adults classifying as obese, weight loss solutions are on the top of many people's minds. Despite the hundreds of complicated or expensive weight loss programs on the market, perhaps the easiest way to lose weight (for free!) is simply by shortening the window in which you consume your food each day.

One 12-week study found that restricting caloric intake to 10 hours per day in 19 patients with metabolic syndrome led to a reduction in both body weight and waist circumference [10]. Other studies have limited the eating window to 8 hours, which led to a 2.6% reduction in body weight over 12 weeks [11], and a decrease in fat mass over 8 weeks [12].

Time-restricted eating can lead to weight loss

In a 16-week study of overweight individuals, a reduction in the eating window from 14 hours to 10 hours led to a 7.2-pound average reduction in body weight that was kept off for one year post-study. Although it was not instructed to alter dietary intake, most people did unintentionally reduce their calories by about 20%. In a note of how sustainable this eating pattern is, all the participants voluntarily decided to continue with their TRE pattern after the study finished [13].

(2) Blood sugar improvements

The damaging effects of high blood sugar on our bodies are well documented. Chronically high blood sugar can lead to type 2 diabetes, as well as a slew of other potential health problems, including heart disease, kidney failure, blindness, and nerve problems.

One small study of diabetic adults found that an early eating window of 8 A.M. to 2 P.M. led to a 4 mg/dl decrease in mean 24-hour glucose levels, compared to those eating from 8 A.M. to 8 P.M. Although this timing of meals may be harder to sustain, the benefits extended beyond blood sugar control. Those who ate within the early-TRE schedule had increased autophagy markers, increased ketones in the morning, and a beneficial alteration in patterns of cortisol and circadian clock genes, all of which are related to anti-aging [14].

In a controlled, crossover feeding study, prediabetic men who consumed their calories in a six hour period that ended before 3 P.M. had improved insulin sensitivity and pancreatic beta-cell responsiveness, both of which are markers of improved blood sugar control. However, fasting glucose levels were not significantly different between the early-TRE group and the group eating 12 hours per day, although glucose was only measured once in the morning, rather than continuously [15].

(3) Cardiovascular markers improved

In one of the same studies mentioned earlier, a ten hour eating window led to a reduction in both LDL and non-LDL cholesterol in 19 patients with metabolic syndrome [16]. In obese mice, intermittent fasting was linked to a reduction in serum LDL levels, even when eating a high-fat, high-sugar diet, compared to mice eating on a normal schedule [17].

Other markers of cardiovascular health include inflammatory proteins, such as C-reactive protein (CRP), homocysteine, and interleukin-6 (IL-6). In a study done during Ramadan, the religious month of Islam in which participants do not eat or drink from sunrise to sunset, blood markers of IL-6, CRP, and homocysteine all significantly decreased during the fasting month, although cholesterol levels did not [18].

Some studies show time-restricted eating can lower cholesterol

(4) Anti-aging and longevity

Caloric restriction and longevity have been studied more in animals than humans, as the shorter lifespans make for quicker research. In humans, biomarkers of aging tend to be studied more than actual lifespan. With caloric restriction, which differs from TRE in that calories are always reduced and in TRE they may or may not be, studies on worms, flies, and rodents all see increases in lifespan when calories are reduced by 10-40%.

In a 4-day crossover study done with 11 overweight adults, utilizing early-TRE and eating within a 6-hour window from 8 A.M. to 2 P.M. led to an increased morning-time expression of sirtuin (SIRT1), an enzyme that upregulates fat metabolism and extends lifespan by protecting against oxidative DNA damage and increasing telomere stability, and LC3A, a gene that promotes autophagy. Although the study was short, the changes in these longevity-related biomarkers are promising [19].

(5) Improved brain health

Since one of the main risk factors for neurodegenerative disorders like Alzheimer's and Parkinson's disease is advancing age, it would make sense that employing anti-aging defenses in the body and brain could help to prevent them. Research on fasting has found that there are a number of beneficial byproducts to the brain, such as an increase in brain-derived neurotrophic factor (BDNF), which promotes neural growth and survival during stress, as well as regulates synaptic plasticity -- a crucial component of maintaining memories [20].

Fasting also leads to an increase in ketone production, which ramps up once all of the stored glycogen from the liver is used; some research in rodents has indicated that ketones can protect against the neuronal degradation seen in Alzheimer's disease [21, 22]. This metabolic switching from glucose to ketones is highly unlikely to occur in people who eat the standard three-plus meals per day [23]. Fasting, as well as the production of ketones, may also be able to calm down excitatory neurons. This is beneficial, as over-excited neurons drive inflammation, damage themselves, and lead to the accumulation of tau proteins, a marker of Alzheimer's disease [24].

While trials on this topic in humans with neurodegenerative diseases have not been done, studies in rodents have found that intermittent fasting led to improved motor skills and cognitive function, as well as reduced oxidative damage [25].

How you can try time-restricted eating

Recent research has shown the most benefits if you practice early-TRE, which constricts the eating window to the morning and early afternoon and skips dinner. While it may seem easier to skip breakfast, one study found that those who practiced early-TRE and skipped dinner actually had reduced appetite and increased fullness throughout the day [26].

If six hours seems too small of a window, you could try an eight hour eating period, like from 7 A.M. to 3 P.M. This style of eating supports our natural circadian rhythms more than skipping breakfast and eating later in the night.

If you do decide to make your eating window later in the day and skip breakfast, caffeine can help to bridge the gap until lunchtime. As mentioned earlier, adding calories will break the fast, so keep your coffee black if you can, or just with a little bit of fat. Be sure to have plenty of water, as your hydration needs will remain the same.

Your Takeaways

Human studies have found the most benefit of time-restricted eating when the consumption window is earlier in the day, which leads to skipping dinner and a longer overnight fast.
Benefits found include modest weight loss, blood sugar improvements, increased anti-aging markers, ketone production, and improved brain health.
Even if you don't practice TRE to the full extent, fasting for 12 --14 hours out of the day can provide some of the benefits.

References:

By Cambria Glosz, MS, RD

Cambria Glosz, MS, RD is a Registered Dietitian and health writer with her Master's degree in Nutrition from Cal Poly in San Luis Obispo. She spends her spare time exploring San Diego and posting recipes on her food and nutrition blog, Veggies Then Wine.

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