Intermittent Fasting and Time Restricted Eating – updated

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Note: This article was written on August 17, 2025 and was updated on April 20, 2026.

Introduction

People have heard about the benefits of intermittent fasting and time-restricted eating; however, the duration and timing of fasting are important considerations. Intermittent fasting refers to specific times for ‘eating’ and ‘not eating’ (fasting) on a set schedule. There are two main types, which are (1) partial fasting or alternate-day fasting, and (2) time-restricted feeding (TRF).

Practitioner’s Preface

In the last 10 years of my almost 18 years of being in private clinical practice in British Columbia, Alberta, and Ontario, I have come across many people who have tried intermittent fasting as a way to lose weight. Almost all of these individuals chose their eating and fasting times based on something they heard about online, rather than around times that our body has evolved to eat and not eat. A recent meta-analysis published this January and outlined below seems to have settled the matter regarding the most effective time to fast, in terms of decreasing body weight, waist circumference, fasting insulin and systolic blood pressure.

Two Main Types of Intermittent Fasting

Partial Fasting or Alternate Day Fasting is a type of intermittent fasting where fasting days are set to a specific number of days out of the week and may include one day out of seven, or ‘alternate day fasting’ — where the usual amount of food is consumed every other day.

Time-Restricted Eating (TRE), also called time-restricted feeding (TRF), is a type of intermittent fasting where eating occurs during a specific period each day, and ‘not eating’ (fasting) occurs the remainder of the time.

The “5:2 diet” is a type of time-restricted eating that has people eating 25% of their normal caloric intake on two non-consecutive days per week (i.e., ~400-500 calories per day for women and ~500-600 calories for men), and consuming normal intake on the other five days. Since the focus is on restricted caloric intake and not intermittent eating, it has not been elaborated on in this article.

A common TRE schedule is 16:8, and is where all eating occurs during 8 hours, and the remaining 16 hours per day is a period of fasting. This is often done by people skipping breakfast and eating from midday until ~8 PM.

Periods of Fasting of 24 hours or more

Except as required for specific clinical or religious reasons, I do not recommend that people engage in periods of fasting of 24 hours or more based on the effect of fasting on lean body mass (muscle). For this, I refer to the work of medical doctor Dr. Stephen Phinney, MD, PhD, and Registered Dietitian Dr. Jeff Volek, RD, PhD.

Phinney and Volek have documented that, in periods of prolonged fasting (1-42 days), nitrogen loss, which is a marker of protein loss, begins on day 1 and reaches a maximum on day 3, then gradually declines[1].

“Net protein breakdown begins within the first day of fasting, reaches its maximum rate within 2-3 days – typically a pound of lean tissue lost per day.[1]”

While the human body has fat stores that can easily sustain us during extended periods where we don’t eat, the body does not have reserve protein stores to sustain us over long periods of fasting. All the protein in the body — whether as muscle, red blood cells, antibodies, or neurotransmitters is functional, so “whenever the body loses protein, it loses some of its functional reserve[1].“

Time Restricted Eating

Time-restricted eating (TRE), also called time-restricted feeding (TRF), is, for most people, the easiest form of intermittent fasting to do because the period of not eating only occurs for part of the day.

An early pilot study from 2019 in adults with metabolic syndrome which includes high blood pressure, elevated blood sugar, excess fat around the abdomen, and abnormal cholesterol levels found that limiting eating to only 10 hours per day (i.e. a 10 hour “eating window”) promoted weight loss, reduced abdominal fat, and led to more stable blood sugar and insulin levels in those taking standard medication to lower cholesterol and blood pressure [2].

The researchers from the Salk Institute, including circadian biologist Dr. Satchidananda Panda, concluded that the 10-hour time-restricted eating schedule supported an individual’s circadian rhythms, which results in health benefits evidenced by previous and subsequent mouse studies published by the Salk team[3].

Circadian rhythms are the regular 24-hour cycles of biological processes that affect nearly every cell in the body.

“Eating and drinking everything (except water) within a consistent 10-hour window allows your body to rest and restore for 14 hours at night. Your body can also anticipate when you will eat, so it can prepare to optimize metabolism.[3]”

A follow-up study from the researchers at Salk Institute that was published in 2024, found that people who ate within a consistent eight-to-ten-hour window each day for three months saw improvements in several markers of blood sugar and metabolic function, compared to those who received standard treatment [4].

Given that more than 1/3 of adults in the US [4], and more than 19% — or 1 in 5 adults in Canada have metabolic syndrome[5] which rises to ~40% in adults over the age of 65, the implication that simply changing the amount of time each day in which eating occurs can significantly improve markers or metabolic syndrome, is significant.

Erratic Eating Patterns in Adults

A landmark study from 2015 by circadian biologist Dr. Satchidananda Panda of Salk Institute had healthy, normal-weight adults who did not perform shift work track everything they ate each day for 21 days (3 weeks) by taking pictures of it using a smartphone app. The time-stamp on each photo enabled analyses of the time at which eating occurred.

In contrast to the popular belief that most people eat three meals per day within a 12-hour interval, this study found that eating patterns are much more erratic and differ between weekdays and weekends. The amount of time spent eating each day approached 15 hours per day for half the people in the study, and the only time they were not eating was when they were sleeping. In addition, less than 25% of calories were eaten before noon, and more than 35% of calories were eaten after 6 PM.

Supporting Time-Restricted Eating

It’s important to keep in mind that for some people, the idea of eating actual meals over a 10-hour period without eating snacks IS intermittent fasting when compared to the way that they usually eat.

For those accustomed to eating meals and snacks or grazing over 15 hours, the idea of eating meals with nothing between over 10 hours can seem daunting. Many are concerned they will be hungry, and others that their blood sugar will drop, making them feel lightheaded or dizzy. By ensuring that meals are made up of sufficient amounts of highly bioavailable protein and healthy fats, both of these concerns are easily addressed.

Implementing a 16:8 Time Restricted Eating Schedule

As mentioned above, a common time-restricted eating schedule is 16:8, where eating occurs during an 8-hour eating window, and the remaining 16 hours per day are fasting. Most people skip breakfast and begin eating from 11 AM or noon until ~7 or 8 PM. This is called a late time-restricted eating window (TREL). That, however, is not the only way to eat within a 16:8 window.

Some will eat breakfast at ~7 or 8 AM and finish eating at 3 or 4 PM (with one or no meals in between), and this is called an early time-restricted eating window (TREE).

Chrononutrition

Chrononutrition is a field of study that examines the complex relationship between when eating occurs relative to normal human circadian rhythms and metabolic health, and studies indicate that the timing of eating matters — both the timing of the first eating occasion, and how late the last meal occurs.

Studies have shown that glucose tolerance as well as insulin sensitivity are at their peak in the morning and decrease significantly later in the day. As a result, when meals are eaten late in the evening, when insulin production is at its lowest, there is an increase in blood glucose, insulin release, appetite, and the risk of obesity [8,9].

When We Eat Matters

In the 16-year prospective Health Professionals Follow-up Study, which had almost 27,000 middle-aged male subjects, men who skipped breakfast had a 27% higher risk of coronary heart disease found to be mediated by higher BMI, high blood pressure, diabetes, and high cholesterol [10]. In the same study, there was a 55% higher coronary heart disease risk in men who ate late at night [11].

Early or Late Time-Restricted Eating – Some Considerations

For adults who need to eat their dinner with other family members, they will often adopt a late time-restricted eating window (TREL). A drawback to this is that eating this late can delay sleep onset because one of the signals required for the body to release melatonin from the brain is a drop in core body temperature. Since digestion of food produces a lot of heat, late consumption of food delays the release of melatonin and, subsequently, delays sleep.

Updated Study – January 2026

A January 2026 meta-analysis of 113 trials published in BMJ Medicine this January found that early time-restricted eating (eTRE), who ate their last meal before 5:00 PM (1700), had the most beneficial effect of the other fasting approaches studied over eight weeks on;
  • decreasing body weight by 2.48 kg / 5.5 pounds
  • reducing waist circumference by 3.52 cm / 1.4 inches
  • lowering fasting insulin by 3.67 uIU/mL / 25.5 mmol/L
  • lowering systolic blood pressure by 6.16 mmHg
The human body’s metabolism follows a natural circadian rhythm, where insulin sensitivity is highest in the morning and lowest at night. By eating early, we are having our body process food when it is metabolically the strongest to keep from spiking insulin and resulting in more fat storage.

Clinical Application

While online influencers usually encourage people to skip breakfast and not eat anything before noon to maximize weight loss, this idea is not supported by the most recent meta-analysis of over 100 studies. Eating early, when insulin is the most sensitive, and stopping eating 4-5 hours before bedtime encourages the most weight and inches lost, as well as lowering insulin, which drives hunger and fat storage. For the last decade of my almost 18 years in private practice, this has been my recommendation based on circadian health, and current data support it.

Final Thoughts…

For those who are used to eating or grazing over 15 hours, eating set meals over a 10-hour eating window, beginning at 7:00 AM and finishing at 5:00 PM, can be a very effective way to start. This allows for improvements in metabolic markers, fat loss as weight and inches lost, while still being able to eat meals with family members.

More Info?

I discuss the effect of light exposure and sleep with all of my clients taking Routine Health services because achieving optimal metabolic health necessitates it, and I build in periods of time-restricted eating into the Meal Plans I design. Learn about me and the Comprehensive Dietary Package that I offer to improve weight and metabolic health.

To your good health!

Joy

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Twitter: https://twitter.com/jyerdile
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References

  1. Virta Health, Phinney S., Volek J., To Fast or Not to Fast: What are the Risks of Fasting, December 5, 2017, https://www.virtahealth.com/blog/science-of-intermittent-fasting
  2. Wilkinson MJ, Manoogian EN, et al Ten-Hour Time-Restricted Eating Reduces Weight, Blood Pressure, and Atherogenic Lipids in Patients with Metabolic Syndrome, Cell Metabolism, Volume 31, Issue 1, 92 – 104.e5. [https://pubmed.ncbi.nlm.nih.gov/31813824/]
  3. Salk News, December 5, 2019, Clinical Study Finds Eating Within a 10-hour Window May Stave Off Diabetes, Heart Disease, https://www.salk.edu/news-release/clinical-study-finds-eating-within-10-hour-window-may-help-stave-off-diabetes-heart-disease/
  4. Manoogian ENC, Wilkinson MJ, et al. Time-Restricted Eating in Adults With Metabolic Syndrome: A Randomized Controlled Trial. Ann Intern Med.2024;177:1462-1470. [https://pubmed.ncbi.nlm.nih.gov/39348690/]
  5. Rao DP, Dai S, et al, (2014) Metabolic syndrome and chronic disease, CDIC, Vol. 34, No. 1.
  6. Gill, S., and Panda, S. (2015). A Smartphone App Reveals Erratic Diurnal Eating Patterns in Humans. [https://pmc.ncbi.nlm.nih.gov/articles/PMC4635036/]
  7. Raji OE, et al. Chrononutrition and Cardiometabolic Health: An Overview. [https://pubmed.ncbi.nlm.nih.gov/39064774/]
  8. Poggiogalle E, Jamshed H, Peterson CM. Circadian regulation of glucose, lipid, and energy metabolism in humans. [https://pubmed.ncbi.nlm.nih.gov/29195759/]
  9. Saad A, Man, CD et al, Diurnal Pattern to Insulin Secretion and Insulin Action.
  10. Cahill L.E., et al. Prospective Study of Breakfast Eating and Incident Coronary Heart Disease. [https://pubmed.ncbi.nlm.nih.gov/23877060/]
  11. Paoli A., et al. The Influence of Meal Frequency and Timing on Health in Humans. [https://pubmed.ncbi.nlm.nih.gov/30925707/]
  12. Witbracht M., et al. Female Breakfast Skippers Display a Disrupted Cortisol Rhythm. [https://pubmed.ncbi.nlm.nih.gov/25545767/]
  13. Kutsuma A., Nakajima K., Suwa K. Potential Association between Breakfast Skipping and Late-Night-Dinner Eating. [https://pubmed.ncbi.nlm.nih.gov/24982814/]
  14. Ha K., Song Y. Associations of Meal Timing and Frequency with Obesity and Metabolic Syndrome. [https://pubmed.ncbi.nlm.nih.gov/31614924/]
  15. Xiao Q., et al. Meal Timing and Obesity. interactions with macronutrient intake and chronotype. Int J Obes (Lond). 2019 Sep;43(9):1701-1711. doi: 10.1038/s41366-018-0284-x. Epub 2019 Jan 31. PMID: 30705391; PMCID: PMC6669101 [https://pubmed.ncbi.nlm.nih.gov/30705391/]
  16. Chen YE, Tsai HL, Tu YK, Chen LW. Effects of timing and eating duration of time-restricted eating on metabolic outcomes: systematic review and network meta-analysis. BMJ Med. 2026 Jan 21;5(1):e001071. doi: 10.1136/bmjmed-2024-001071. PMID: 41586347; PMCID: PMC12829361.
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