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16:8 Intermittent Fasting

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.

Our evidence-based analysis on 16:8 intermittent fasting features 14 unique references to scientific papers.

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Summary of 16:8 Intermittent Fasting

Primary information, health benefits, side effects, usage, and other important details

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.

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How to Take

Recommended dosage, active amounts, other details

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.[6][7][8][9] Adherence to these protocols is typically easier for people who have familial support, and for some the practice becomes easier with time.[10]

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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Human Effect Matrix

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The Human Effect Matrix summarizes human studies to tell you what effects 16:8 Intermittent Fasting has on your body, how much evidence there is, and how strong these effects are.

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Grade Level of Evidence
Robust research conducted with repeated double-blind clinical trials
Multiple studies where at least two are double-blind and placebo controlled
Single double-blind study or multiple cohort studies
Uncontrolled or observational studies only
Level of Evidence
? The amount of high quality evidence. The more evidence, the more we can trust the results.
Outcome Magnitude of effect
? The direction and size of the supplement's impact on each outcome. Some supplements can have an increasing effect, others have a decreasing effect, and others have no effect.
Consistency of research results
? Scientific research does not always agree. HIGH or VERY HIGH means that most of the scientific research agrees.
Notes
grade-d Minor - See 2 studies
grade-d Minor Low See all 3 studies
TRE seems to be effective at reducing fasting blood glucose and glucose response after a meal, both with and without a caloric deficit.
grade-d Minor High See all 3 studies
TRE has been shown to reduce blood pressure compared to baseline and historical controls, but randomized controlled trials are required to draw any solid conclusions.
grade-d Minor High See all 4 studies
When paired with a caloric deficit, 16:8 TRE can reduce fat mass about as effectively as a standard diet.
grade-d Minor - See 2 studies
16:8 doesn't seem to lower fasting glucose under all circumstances, but one study found that a group that placed their eating window early in the day lowered it compared to baseline.
grade-d Minor - See study
grade-d Minor - See study
grade-d Minor - See study
grade-d Minor - See all 5 studies
One study reported that 16:8 plus a caloric deficit increased in HDL-C compared to a caloric deficit alone.
grade-d Minor - See study
grade-d Minor - See study
grade-d Minor Moderate See 2 studies
grade-d Minor - See study
Individuals may feel more full by employing 16:8 compared to a standard diet.
grade-d Minor Moderate See 2 studies
grade-d Minor Moderate See 2 studies
One study found that testosterone decreased in a group that did 16:8 plus a caloric deficit compared to a control diet, but these findings need to be supported by more research.
grade-d Minor Low See all 6 studies
Some studies have demonstrated a reduction in triglycerides due to TRE, but this effect is probably more due to weight loss than the TRE per se.
grade-d Minor - See study
grade-d Minor - See study
grade-d Minor Very High See all 3 studies
16:8 can be a viable weight loss strategy so long as it's paired with a caloric deficit.
grade-d - - See study
grade-d - - See study
16:8 doesn't seem to provoke body dysmorphia, but more research is required.
grade-d - - See study
grade-d - - See study
grade-d - High See all 3 studies
grade-d - - See study
grade-d - - See study
grade-d - - See study
grade-d - - See study
16:8 doesn't seem to provoke eating disorder symptoms, but more research is required.
grade-d - - See study
grade-d - - See study
grade-d - - See study
grade-d - - See study
grade-d - - See study
grade-d - - See study
grade-d - - See study
grade-d - See study
grade-d - - See study
grade-d - Very High See all 3 studies
grade-d - - See study
grade-d - - See study
grade-d - - See study
16:8 doesn't seem to produce irritability, but "hangry" folks may want to exercise some caution.
grade-d - Very High See all 5 studies
grade-d - Very High See all 4 studies
Lean body mass does not seem to be significantly affected by 16:8, with or without a caloric deficit.
grade-d - - See study
grade-d - - See study
Based on a single study, 16:8 didn't alter gut microbiome diversity or phyla proportions.
grade-d - - See study
grade-d - Very High See all 3 studies
16:8 seems to be conducive to the development of muscle mass during resistance training.
grade-d - Very High See 2 studies
grade-d - - See study
grade-d - - See study
grade-d - - See study
grade-d - - See study
grade-d - - See study
grade-d - Very High See all 3 studies
16:8 doesn't seem to change resting metabolic rate any more so than an ordinary diet.
grade-d - - See study
grade-d - Very High See 2 studies
grade-d - Very High See all 3 studies
grade-d - - See study
grade-d - - See study
grade-d - - See study
grade-d - - See study
grade-d - - See study
grade-d - Very High See all 5 studies
16:8 TRE alone does not seem to be sufficient to reduce cholesterol.
grade-d - - See study
grade-d - - See study
grade-d - Very High See 2 studies
grade-d - - See study
grade-d - - See study
grade-d - - See study
grade-d - - See study

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Things to Note

Is a Form Of

  • Diet

Primary Function:

Also Known As

Time-Restricted Feeding, Time-Restricted Eating

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Click here to see all 14 references.