12:12 vs. 16:8 intermittent fasting — explained by SIMPLE

Written by Trey Reck

Medically reviewed by Josie Porter, RD

Published on May 18, 2023 | Updated on March 28, 2024

Which is better: 

Cats or dogs? Peanut butter or jelly? Ketchup or mustard?

We all love a good comparison question, and the world of intermittent fasting isn’t immune. Judging by online searches, the people of the internet are often eager to learn which intermittent fasting schedule comes out tops. 

Let’s put a couple of heavyweight fasting schedules into the ring and find out:

12:12 vs. 16:8. Which will be crowned Ultimate Intermittent Fasting Champion? 

(Spoiler alert: it’s going to depend on your goals.)

What is 16:8 intermittent fasting?

16:8 goes like this:

Eat all your meals during an 8-hour period. Fast for the remaining 16 hours. 

If you’re a newbie to intermittent fasting, you’re likely thinking, “Woah. 16 hours without so much as an apple? How is that even possible?!” 

Before you flip your laptop closed and banish all ideas of intermittent fasting from your mind, think about this: 

You’ll knock out a big chunk of those 16 hours overnight when you’re asleep. Then, hold off on breakfast, and you’re home free with a 16-hour fast in the bag.

If you love breakfast, though, no sweat. Start your fast with an early dinner and roll straight into overnight fasting that way.

What is 12:12 intermittent fasting?

If a 16-hour fast feels too hard to handle, maybe 12-hour intermittent fasting could ride to the rescue. With 12:12, your day gets split up like this:

Fast for 12 hours, leaving the other 12 hours to eat all your meals. 

A 12-hour fast will likely fit far more neatly into your life (though it still takes effort). Perhaps you quit eating after dinner at 8 PM, then break your fast with breakfast at 8 AM. It’s a much more easygoing approach, with only a few waking hours when you might feel hunger or cravings. 

This makes it an ideal intermittent fasting schedule for beginners. If you’re a beginner, you don’t have to start your intermittent fasting journey alone — we’re right here to help. Try our SIMPLE quiz to get up and running today! 

The difference between 16:8 and 12:12 intermittent fasting

Aside from the obvious difference (the length of the fast, ICYMI), there are a few ways these two fasting schedules differ. 

When — or if — you hit ketosis

You could hit ketosis — when your body starts burning your fat stores for fuel [1] — with both 16:8 and 12:12. 

But it’s not guaranteed either, and it’s more likely with 16:8.[2] Some people don’t get into ketosis on 12:12 simply because the fasts are shorter, although other factors can influence it too, like your age, how active you are, how much carbohydrate you eat, and so on. 

The calorie deficit 

There’s no need to count calories on intermittent fasting (one of its most winning features, in our eyes). The fasts cut your calories for you. The longer the fast, the greater calorie deficit (when you burn more calories than you eat) you’ll experience. 

Based on the average recommended calorie allowance (2,000 kcals for women; 2,500 kcals for men), it stacks up like this:

• 12:12: deficit of roughly 200 calories
• 16:8: deficit of roughly 300–400 calories 

Of course, this will vary depending on what you eat. To help you hit these numbers, check out what to eat during intermittent fasting and get some ideas on how to stay full, nourished, and energized while keeping your calories where you want them. 

The side effects

Intermittent fasting has some potential side effects — like increased hunger, ragey cravings, grumpy moods, and increased snaccidents — especially at the start of your fasting journey. 

These tend to increase with the length of the fast, so you’re likely to meet these guys more often and more intensely if you kick off with 16:8 compared to 12:12.

They should subside with time, but if you have any severe or consistent side effects, speak with your doctor.

Benefits of 12:12 and 16:8 intermittent fasting 

Here’s a brief rundown on how intermittent fasting can support your health. 

Weight loss

Weight loss is one of intermittent fasting’s best-known benefits.

Generally speaking, there’s more evidence to support 16:8’s efficacy for weight loss results for those living with overweight and obesity.[3] As we saw earlier, 16:8 creates a bigger calorie deficit. 

That said, 12:12 can lead to weight loss for those living with obesity, as this study discovered [2], and also helps you lay the groundwork for longer fasts. 

Improved blood glucose control 

Frequent fasting can improve the body’s ability to respond to insulin — a hormone that breaks down the carbohydrates we eat — which can help lower the risk of developing type 2 diabetes.[4] However, these benefits may be more likely for those who are overweight or have obesity. 

Increased cardiovascular health 

Studies have shown that intermittent fasting may help to reduce LDL cholesterol and triglycerides, two common risk factors for heart disease [5], though the researchers did state that these benefits may not be deemed clinically significant. 

But there is good evidence to suggest that intermittent fasting can significantly lower systolic blood pressure.[6] 

Anti-inflammatory effects

Intermittent fasting may enhance the body’s resistance to oxidative stress. This can help lower inflammation which can often lead to chronic diseases.[7,8]

Risks of 12:12 and 16:8 intermittent fasting 

Of course, there are a few risks with intermittent fasting. Let’s check them out. 

Dehydration

Fasting can result in dehydration, leading to headaches, fatigue, and that groggy feeling we know from hot days (or drunken nights).

Make sure to drink plenty of water or other low-calorie fluids during both your fast and eating window. Check out our guide on what you can drink while fasting to keep your drinking choices fresh and interesting.

Disordered eating 

Intermittent fasting, while flexible, still includes aspects that can feel like rules. For some people, that can trigger disordered eating behaviors, like binging or restricting.[9,10] 

If this happens, and/or you feel that fasting is having a negative impact on your thoughts and feelings, then it’s likely that intermittent fasting is not the kindest or safest way for you to lose weight. Stop and speak to your healthcare provider for support in finding a method that suits your needs. 

Weight gain

Sometimes fasting can kick your hunger and cravings into overdrive. Perhaps you exercised more than usual, didn’t sleep well [11], or your stressors increased — things like this can push your appetite cues out of whack (even if you’re not fasting).

When that happens, it’s hard to make wise food choices. The chocolate (or chips or wine … ) will call to you, and it’s tough to resist.

Having a meal plan and some health-promoting, tasty meals / snacks prepped and ready to go will make it easier to grab what you need rather than what your sleep-deprived, stressed-out, exercise-weary cravings are clamoring for. 

Are 12:12 and 16:8 intermittent fasting safe?

For most people, both 12:12 and 16:8 intermittent fasting are safe. 

But not for everybody. This includes people who:

• are under the age of 18, or 80 years old or more
• have a Body Mass Index (BMI) < 18.5
• take prescription medications 
• have (or are at risk of having) an eating disorder, or have a history of one
• have a medical condition
• are extremely active
• are pregnant, breastfeeding, or trying to conceive

If any of these apply to you, don’t try 12:12 or 16:8 (or anything in between!) intermittent fasting unless you have your doctor’s permission. 

Pros and cons of the 12:12 and the 16:8 intermittent fasting method 

How to get started with 12:12 or 16:8 intermittent fasting

If you’re eager to get started on your intermittent fasting journey, here are four steps to help: 

1. Choose your fasting schedule

In the battle of 12-hour fasting vs. 16-hour fasting, which one has won your heart? 

Once you’ve got that locked down — and before you move on to step two — take our SIMPLE quiz and get set up with the smart tools to help you manage your fasting schedule. We’ve got reminders to make sure you remember to fast, eat, and drink, plus a food journal to log your meals and insights aplenty to help you lean into the change process.  

2. Decide your fasting hours

Are you going to eat earlier and finish earlier (science suggests this is the way to go for optimum results [12]), or do you prefer a later eating time? 

It’s totally your call. Play around with some options to see what fits you best.  

3. Write a meal plan

It doesn’t have to be super fancy or long. Even a few days will help. 

If you’re 16:8-ing, get a head start with our 16:8 intermittent fasting 7-day meal plan, and if you’re 12:12-ing, check out our intermittent fasting meal planning how-to guide.

4. Keep your mind occupied 

At first, your belly — and how loudly it’s growling — may be all you can think about. But you can get through it. 

Do something nice for your brain to help distract from these sensations. Listen to music, do some meditation (if you enjoy it), phone a friend, do a puzzle, make, paint, or knit something. (We don’t recommend baking at this juncture unless you have a masochistic streak.)

Being mentally engaged with an activity is a powerful way to keep hunger from derailing your fast.[13] 

5 pro tips on how to choose the right intermittent fasting schedule for you

Here are the five best tips we can give you on choosing the right intermittent fasting schedule for you.

1. Experiment 

Dip your toe in the water and see how regular fasting feels. You won’t know till you try!

2. Start small 

Try 12:12 to start off with. If that works well and you’re eager to go bigger, expand your fasting practice to 14:10. Let your intermittent fasting schedule grow with you. 

3. Fasting has to fit your life

Choose a fasting schedule that works for your lifestyle rather than contorting your lifestyle to fit fasting. 

If life is non-stop busy, and you need plenty of energy to power through but don’t have much time to eat, a longer eating window gives you more options. 12:12, 14:10, or 16:8 intermittent fasting could be perfect.  

If life is relaxed and breezy — and you’ve ample time for meal prep — a shorter eating window could work great. Perhaps 18:6 or 20:4 could be your ideal intermittent fasting routine. 

4. Give yourself time

It may well feel all kinds of weird to start with. Perhaps your hunger is off the charts, you accidentally break your fast now and then, and you’re more snappish for a while. 

Let yourself settle in. Let your body and mind adapt. It’ll get easier. 

If it doesn’t, try a different schedule. It’s all part and parcel of the learning process. 

5. Stay flexible 

Our bodies are always changing, so we gotta stay tuned in. 

The intermittent fasting schedule that’s right for you now may not be ideal if you change your job. Or your fitness regime. Or while you’re moving house. 

Stay flexible and adjust your fasting times to suit your needs as they evolve. 

6. Some intermittent fasting schedules are best left alone

A bonus tip from the SIMPLE team: 

When choosing the right intermittent fasting schedule for you, choose a time-restricted eating (TRE) option like 12:12, 14:10, 16:8, or 18:6 intermittent fasting. TRE intermittent fasting schedules are kinder to your body, safe, and plenty effective. 

If you have your doctor’s approval, the 5:2 diet and alternate day fasting could be options … but always take a hard pass on fasting schedules like Eat Stop Eat, water fasting, dry fasting, and OMAD. They carry more risks without bringing any more benefits. 

Written by Trey Reck

Medically reviewed by Josie Porter, RD

Published on | Updated on March 28, 2024