New Study: Time-Restricted Eating, Weight Loss & Metabolic Health

Not a year goes by that some new diet or “magical” food promises to make weight loss effortless and faster than ever.

Several diets have jumped to the forefront recently, including keto, carnivore, intermittent fasting, and time-restricted feeding.

While these diets usually do help individuals lose weight (in the short term), diet gurus also attribute numerous other benefits to following their prescribed diet (yet hardly any of these stated benefits are backed by any considerable amount of human data).

Recently, a systematic review and meta-analysis was published titled “Beneficial Effects of Time-Restricted Eating on Metabolic Diseases.”[1]

Let’s take a look at this most recent “study of studies” and see what the researchers have to say regarding time-restricted feeding.

What Is Time-Restricted Eating?

The name pretty much says it all.

Time-restricted eating is a pattern of eating in which an individual restricts their food intake to only a certain span of time each day.

This is similar in effect to intermittent fasting where an individual fasts for a majority of the day (14-16 hours) and eats all of their calories for the day in their “feasting” window (8-10 hours).

The difference between time-restricted eating and intermittent fasting is that time-restricted eating entails consuming all calories within a consistent 8-12 hour span each day. 

Additionally, intermittent fasting usually involves calorie restriction while time-restricted feeding does not. Individuals following time-restricted feeding are allowed to eat as much as they want during the eating window. 

Lastly, time-restricted eating aligns the eating and fasting cycles to the body’s innate 24-hour circadian rhythm.[2]

The reason for this is that the timing of eating is essential to synchronize the peripheral circadian clock to the central clock.[1]

By reducing the duration of the eating window, researchers believe it can help reduce desynchronization between the central and peripheral clocks and improve previously impaired metabolic pathways.[1]

In case you weren’t aware, the body’s circadian system is composed of many cellular clocks found in all cells throughout the body. These clocks mastermind the regulation of gene expression that coordinates metabolic activities needed to support bodily functions. 

The “master” clock of the circadian system is a tiny region of the brain located within the hypothalamus called the suprachiasmatic nucleus, or SCN.

The suprachiasmatic nucleus, in turn, coordinates the body's peripheral clocks, such as those found in the pancreas, liver, muscles, and fat.[3]

As a result, the master clock drives the rhythms of activity and rest that dictate the body’s eating and fasting cycles.[4]

Together, the suprachiasmatic nucleus and peripheral clocks found in the cells of the major organs of the body comprise the core clock components. 

Research indicates that ~15% of all the genes in the human genome display daily fluctuations in their activity based on circadian rhythm. Many of these genes also happen to affect carbohydrate, lipid, and cholesterol metabolism.[5]

Both animal and human studies have noted that time-restricted eating may[6,7]:

• Facilitate weight loss
• Reduce fat mass,
• Improve heart function
• Enhance aerobic capacity

What’s really intriguing is that researchers have noted these improvements without altering diet quality or quantity.

For the most part though, these various trials are small in both population size and duration. No prospective large-scale studies have been conducted on the benefits of time-restricted eating.

This brings us to the most recent meta-analysis...

The Study

The authors set forth a list of inclusion criteria to help them identify suitable studies for consideration into the systematic review and meta-analysis.

Those criteria were:

• Adults aged 20 years or older
• Trials had to include a daily fasting period of 12–20 hours
• Include some sort of control group or crossover design to see the effects of not fasting
• Studies had to track data on one of the following metrics:
• Body weight
• Blood pressure, 
• Hypertension, insulin, 
• Blood glucose, 
• Total cholesterol, 
• Triglycerides, 
• LDL cholesterol
• HDL cholesterol

Additionally, for the purposes of this review, researchers categorized time-restricted feeding as fasting for 12–20 hours since most people typically eat 3 times a day over a 12 hour period.[1]

Beginning with a pool of 1500+ studies and then applying the inclusion criteria, researchers ended up with 19 studies that sought to address their topic of interest. 

In total, the meta-analysis contained data on 475 participants (219 men, 256 women). 10 of the 21 studies were on healthy individuals while the remainder were on individuals with metabolic abnormalities.[1]

The Results

Major findings from the study noted by the authors were that time-restricted feeding helped[1]:

• Lose body weight in overweight and obese participants
• Reduce fat mass
• Decrease systolic blood pressure 
• Lower blood glucose concentration
• Improve lipid profiles and reduce triglyceride levels

Interestingly, time-restricted feeding did not lead to a statistically significant decrease in body weight In the healthy participants, but researchers did note improvements in fat mass reduction.[1]

Researchers also posit that time-restricted eating could be a more effective means for weight loss than conventional calorie restriction options.

One of the main reasons asserted by the authors is that time-restricted eating may be easier to maintain than conventional dieting approaches for a longer time because individuals do not need to reduce total food intake or to calculate total daily energy intake.

Takeaway

Time-restricted eating is a pattern of eating in which individuals eat during an 8-12hour daytime window and fast during the remaining 12 to 16 hours of the day/night.

Research to date shows that it may be an effective means for losing weight and maintaining it compared to traditional dieting.

Time-restricted eating also does not come with the intentional “restriction” mindset that accompanies other dieting modalities, which may make time-restricted eating feel less restrictive than other diets.

Is time-restricted eating a “miracle” for weight loss?

Not really.

At the end of the day, you still need to be in an energy deficit to lose weight. Limiting the hours you eat during the day ultimately helps individuals to curb their calorie consumption, which supports weight loss.

It’s true that there is a circadian component to metabolism and glucose oxidation and insulin sensitivity are higher during daylight hours compared to evening hours.

But, this doesn’t necessarily take into account an individual's physical activity.

If you’re mostly sedentary during the day, but crush a workout late at night, your insulin sensitivity and glucose oxidation will be higher at night compared to an individual who doesn’t train in the later hours of the day.

At the end of the day, time-restricted feeding can be a useful tool for weight loss, especially for those people who enjoy using a more intuitive approach to dieting and not relying on a food scale and phone app to track every morsel of food they eat.

Do you have to use time-restricted feeding to lose weight?

Not at all.

It’s a tool that can be used if the job calls for it.

References

1. Moon, S., Kang, J., Kim, S. H., Chung, H. S., Kim, Y. J., Yu, J. M., Cho, S. T., Oh, C., & Kim, T. (2020). Beneficial effects of time-restricted eating on metabolic diseases: A systemic review and meta-analysis. Nutrients, 12(5), 1267. https://doi.org/10.3390/nu12051267
2. Kessler, Katharina, and Olga Pivovarova-Ramich. Meal Timing, Aging, and Metabolic Health International Journal of Molecular Sciences 20, no. 8 (April 2019): 1911. doi:10.3390/ijms20081911.
3. Mohawk, Jennifer A., Carla B. Green, and Joseph S. Takahashi. Central and Peripheral Circadian Clocks in Mammals Annual Review of Neuroscience 35, no. 1 (July 2012): 445–62. doi:10.1146/annurev-neuro-060909-153128.
4. Vieira, Elaine, Thomas P. Burris, and Ivan Quesada. Clock genes, pancreatic function, and diabetes Trends in Molecular Medicine 20, no. 12 (December 2014): 685–93. doi:10.1016/j.molmed.2014.10.007. 
5. Duffield, G. E. DNA microarray analyses of circadian timing: the genomic basis of biological time J. Neuroendocrinol. 15, no. 10 (October 2003): 991–1002
6. Wilkinson, M.J.; Manoogian, E.N.; Zadourian, A.; Lo, H.; Fakhouri, S.; Shoghi, A.; Wang, X.; Fleischer, J.G.; Navlakha, S.; Panda, S. Ten-hour time-restricted eating reduces weight, blood pressure, and atherogenic lipids in patients with metabolic syndrome. Cell Metab. 2020, 31, 92–104.
7. Longo, Valter D., and Satchidananda Panda. Fasting, Circadian Rhythms, and Time-Restricted Feeding in Healthy Lifespan Cell Metabolism 23, no. 6 (June 2016): 1048–59. doi:10.1016/j.cmet.2016.06.001.