16:8 Intermittent Fasting

Last Updated: September 28 2022

The 16:8 protocol is a type of intermittent fasting (known as time-restricted eating in the scientific literature) that involves abstaining from calories for 16 hours of the day, and then eating within an 8 hour window. The eating window can occur at any point in the day, but many people choose to eat between around 12 p.m. and 8 p.m.

16:8 Intermittent Fasting is most often used for

What is 16:8?

As a note, the scientific community tends to restrict the term “intermittent fasting” to diets that drastically restrict calories for 2-4 days of the week (such as eating around 500 calories every other day, or eating no calories for a day or two out of the week). For daily fasting of set durations, the term “time-restricted eating” is preferred. For the sake of this page, the terms will be used interchangeably. Although 16:8 is a fairly mild protocol when it comes to time-restricted eating/intermittent fasting, it could have differing effects based on age and sex, so working with a dietitian and/or physician to see how it could affect you may be prudent.

Time-restricted eating is often described as the ratio of hours spent abstaining from food and the hours where eating is permitted.

16:8 is a particular time-restricted eating protocol in which individuals abstain from any caloric intake for 16 hours, and then eat freely for 8 hours. Other popular schedules include 18:6, 20:4, and one-meal-a-day (OMAD).

Previously, these types of eating schedules fell under the category of “intermittent fasting”, but now that term generally refers to eating schedules that involve abstaining from or drastically lowering energy intake for more than 24 hours. Time-restricted eating can involve a caloric deficit[1] to lose weight, but doesn’t have to.[2]

16:8 is a type of time-restricted eating where you abstain from eating for sixteen hours, and then eat freely for the remaining eight. It can be combined with a caloric deficit for weight loss, but doesn’t have to be.

What are the benefits of 16:8?

Following a 16:8 time-restricted eating protocol seems to be a viable tool for reducing body weight and body fat, with and without caloric restriction. Some studies have found that 16:8 can preferentially reduce fat mass while sparing muscle, but further research is still required to confirm this.[3] At worst, this limited evidence suggests this protocol can be about as effective as standard dieting, and potentially psychologically easier for some people.

16:8 time-restricted eating can be psychologically easier than other types of dietary restriction. It may have some unique metabolic benefits, but those findings aren’t as clear.

Is 16:8 safe? Are there side effects?

Extended periods without food can be challenging for some, which may make adherence difficult, and some studies have reported some degree of nausea, dizziness, and hunger.[4] There aren’t many safety studies, but in one small trial, the authors didn’t find 16:8 to cause negative impacts on body image, uncontrolled eating, or symptoms of eating disorders.[5]

That being said, fasting can be contraindicated in some diseases such as type 1 diabetes, pregnancy, and preexisting eating disorders. For individuals with these or similar conditions, speaking with a well-informed physician is warranted.

Although no significant side effects have been reported in these studies, some individuals with medical conditions may want to exercise more caution.

What else is 16:8 Intermittent Fasting known as?
Note that 16:8 Intermittent Fasting is also known as:
  • Time-Restricted Feeding
  • Time-Restricted Eating
Dosage information

Simply allocate a 16-hour window in the day that you will abstain from calories completely. Many choose their window to be from around 8 p.m. to 12 p.m. the following day, but it’s just as possible to eat earlier in the day and stop eating earlier.

In fact, insulin sensitivity (and thus overall glycemic response to food) tends to be better in the morning, so having an early eating window may be preferable for some people, although many opt to eat later in the day because it’s more conducive with social eating.[11][8][12][13] Adherence to these protocols is typically easier for people who have familial support, and for some the practice becomes easier with time.[14]

Generally speaking, water, tea, seltzer, and coffee are considered permissible to eat during the fasting window. While other things such as chewing gum, exogenous ketones, MCT oil, supplements, apple cider vinegar, and artificial sweeteners are hotly debated, a good rule of thumb is that if the product has more than 5-10 kcal then it should be avoided until the fasting window ends.

It’s simple: don’t consume anything except for water, coffee, or tea for 16 continuous hours, and then eat freely for the remaining 8 hours.

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      1.^Matthew T Stratton, Grant M Tinsley, Michaela G Alesi, Garrett M Hester, Alex A Olmos, Paul R Serafini, Andrew S Modjeski, Gerald T Mangine, Kelsey King, Shelby N Savage, Austin T Webb, Trisha A VanDusseldorpFour Weeks of Time-Restricted Feeding Combined with Resistance Training Does Not Differentially Influence Measures of Body Composition, Muscle Performance, Resting Energy Expenditure, and Blood BiomarkersNutrients.(2020 Apr 17)
      2.^Grant M Tinsley, M Lane Moore, Austin J Graybeal, Antonio Paoli, Youngdeok Kim, Joaquin U Gonzales, John R Harry, Trisha A VanDusseldorp, Devin N Kennedy, Megan R CruzTime-restricted feeding plus resistance training in active females: a randomized trialAm J Clin Nutr.(2019 Sep 1)
      3.^Tatiana Moro, Grant Tinsley, Antonino Bianco, Giuseppe Marcolin, Quirico Francesco Pacelli, Giuseppe Battaglia, Antonio Palma, Paulo Gentil, Marco Neri, Antonio PaoliEffects of eight weeks of time-restricted feeding (16/8) on basal metabolism, maximal strength, body composition, inflammation, and cardiovascular risk factors in resistance-trained malesJ Transl Med.(2016 Oct 13)
      5.^Kelsey Gabel, Kristin K Hoddy, Krista A VaradySafety of 8-h time restricted feeding in adults with obesityAppl Physiol Nutr Metab.(2019 Jan)
      6.^Dylan A Lowe, Nancy Wu, Linnea Rohdin-Bibby, A Holliston Moore, Nisa Kelly, Yong En Liu, Errol Philip, Eric Vittinghoff, Steven B Heymsfield, Jeffrey E Olgin, John A Shepherd, Ethan J WeissEffects of Time-Restricted Eating on Weight Loss and Other Metabolic Parameters in Women and Men With Overweight and Obesity: The TREAT Randomized Clinical TrialJAMA Intern Med.(2020 Sep 28)