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Is 12 hours enough for intermittent fasting?

12-hour fasting is also known as overnight fasting. When practiced correctly, the health benefits are similar to other intermittent fasting methods.
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Summary

12-hour fasting means that you fast for 12 hours every day and eat within a 12-hour window. While the fasting time is set, there are different possibilities for arranging meals in your eating window. Research suggests that the benefits of 12-hour fasting are similar to longer fasting times, as long as you restrict the number of meals in the eating window.

Written by
Sarah Neidler, PhD
Freelance Science and Medical Writer

16/8 fasting is considered the beginner’s version of intermittent fasting. Many people don’t consider 12-hour fasting (also known as overnight fasting) as intermittent fasting–whether it is or not is debatable. 

If you want to learn more about different intermittent fasting methods, we recommend our in-depth article about the 8 different methods of intermittent fasting.

In our opinion, what matters are the health benefits. Don’t you agree?

Before answering this question, let’s have a closer look at how 12-hour fasting works.

Different ways to 12-hour fast

12-hour fasting means that you fast for 12 hours per day and have a 12-hour eating window. While the fasting time is set, there are different ways to arrange meals in your eating window.

1. Eating three meals–a good approach

3 plates with different kinds of foods.

With this approach, you eat three meals during your eating window: breakfast, lunch, and dinner. Does this sound familiar? This way of eating was considered normal until the food industry successfully convinced us a few decades ago that we have to eat at least every 2-3 hours.

Nowadays, many people eat 14 times per day or more: breakfast, second breakfast, some cookies with coffee, lunch, cookies with coffee after lunch, another coffee break with cake, a snack before dinner, dinner, multiple snacks after dinner before going to bed,...

You can see already that eating only three meals with no snacks in between is a completely different eating behavior. It also significantly affects hormonal levels and improves overall health.

The benefits of eating only three meals per day were nicely demonstrated in a very well-designed study with type 2 diabetes patients (3). 

34 participants were randomly divided into two groups:

  1. A 3-meal per day group: People in this group ate breakfast, lunch, and dinner within a ~12-hour eating window
  2. A 6-meal per day group: People in this group ate breakfast, lunch, dinner plus three snacks. 2 snacks between the main meals and one snack after dinner.

Both groups consumed the same food and the same number of calories. The only difference was the number of meals they ate.

After 12 weeks, participants in the 3-meal group, on average, lost 5.4 Kg, decreased their HbA1c (long-term blood sugar) by 1.2 %, and fasting blood sugar levels decreased by 55 mg/dl. At the same time, they significantly reduced their daily insulin dosage by 27 units.

In comparison, the 6-meal group gained 0.3 Kg. Fasting blood sugar decreased by 23 mg/dl, while the other parameters remained constant.

Incredible results, right? Preventing a condition is much easier than treating it. So, if you don’t have diabetes, these results suggest that you can dramatically decrease your diabetes risk by eating only three meals per day.

Whether 12-hour fasting counts as intermittent fasting is debatable and a matter of definition. However, the health benefits are clear.

If you want to learn more about the health benefits of intermittent fasting, we invite you to join our intermittent fasting community for women only

2. Eating two meals–maximum benefit

The last option is to eat only two meals within your 12-hour eating window. With most intermittent fasting methods, you only have one long fast per day. But with this option, you have two long fasts! You only raise your blood sugar and insulin levels two times per day, which is a very effective method to improve insulin sensitivity (4).

This approach is ideal for people who like to have breakfast and enjoy a social dinner with their family and friends but don’t care much about lunch. You can even use the lunch hour to go for a walk or do some exercise.

One concern is that a 12-hour fast is not long enough to induce autophagy–a recycling program that is responsible for many intermittent fasting benefits. There is very little research about the timing of autophagy, and it depends on many factors such as age, underlying conditions, physical activity, and what and how much you eat

In one study with moderately overweight participants, autophagy could be measured after 18 hours of fasting (5). However, that does not mean that autophagy cannot begin sooner. If you feel comfortable with 12-hour fasting, and it suits your lifestyle, you can occasionally fast longer to make sure that you stimulate autophagy.

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3. Eating many small meals and snacks–not recommended

Table full of food, on small plates.

Every time you eat, your blood sugar rises, and insulin is released. Insulin is a blood sugar-lowering hormone that brings your blood sugar back to normal levels (1). When you eat often, with only small breaks in between, blood sugar and insulin hardly have time to return to normal levels between meals. This kind of eating behavior leads to insulin resistance in the long term (2).

If you follow this eating pattern during your 12-hour eating window, you only have one fast per day, during which your blood sugar and insulin reach normal levels for several hours. That’s not much.

Fasting for 12 hours per day is slightly better than fasting for 8 or 10 hours, but it doesn’t make much of a difference.

Bottom line

12-hour fasting is a very beginner-friendly approach to intermittent fasting. While many people don’t consider it intermittent fasting, the benefits are comparable to longer fasts. 

It is the ideal solution for people who don’t feel comfortable with longer fasts or have to eat three meals per day to take their medications.

References:

1. Wolever TM, Miller JB. Sugars and blood glucose control. Am J Clin Nutr. Jul 1995;62(1 Suppl):212S-221S; discussion 221S-227S. doi:10.1093/ajcn/62.1.212S

2. Petersen MC, Shulman GI. Mechanisms of Insulin Action and Insulin Resistance. Physiol Rev. Oct 1 2018;98(4):2133-2223. doi:10.1152/physrev.00063.2017

3. Jakubowicz D, Landau Z, Tsameret S, et al. Reduction in Glycated Hemoglobin and Daily Insulin Dose Alongside Circadian Clock Upregulation in Patients With Type 2 Diabetes Consuming a Three-Meal Diet: A Randomized Clinical Trial. Diabetes Care. Dec 2019;42(12):2171-2180. doi:10.2337/dc19-1142

4. Paoli A, Tinsley G, Bianco A, Moro T. The Influence of Meal Frequency and Timing on Health in Humans: The Role of Fasting. Nutrients. Mar 28 2019;11(4)doi:10.3390/nu11040719

5. Jamshed H, Beyl RA, Della Manna DL, Yang ES, Ravussin E, Peterson CM. Early Time-Restricted Feeding Improves 24-Hour Glucose Levels and Affects Markers of the Circadian Clock, Aging, and Autophagy in Humans. Nutrients. May 30 2019;11(6)doi:10.3390/nu11061234

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