What schedule can you follow for intermittent fasting?

Intermittent fasting (IF) involves switching between periods of fasting and periods of eating as usual.

Depending on your IF schedule, “fasting” may mean eating nothing or just a few hundred calories.

Some popular IF schedules include 14/10, 16/8, 5:2, and alternate-day fasting. We’ll look at these below. 

If you’re interested in trying IF, pick the schedule that’s easiest for you and fits your lifestyle best.

But IF isn’t for everyone, so we also describe the risks to consider before you get started.

Intermittent fasting schedules to follow

Below, we take a close look at some of the most popular IF schedules and give specific examples. 

14/10 intermittent fasting schedule

The 14/10 version of IF involves fasting for 14 hours and eating as normal for the next 10 hours.

So, let’s say you choose to eat between 10 a.m. and 8 p.m. This means you’d fast from 8 p.m. until 10 a.m. the next day.

16/8 intermittent fasting schedule

The 16/8 IF schedule is just like the 14/10 one, but you fast for 2 hours longer. This means that your eating window is 2 hours shorter.

The 5:2 diet schedule

The 5:2 approach to fasting is often called the 5:2 diet.

On 2 days a week, you have only very small amounts of calories, often between 500 and 800. On the other 5 days, you eat as usual.

Generally, people space out their 2 days of fasting. So, if you follow a 5:2 schedule, your week might look like this:

Alternate-day fasting schedule

Alternate-day fasting involves eating as usual one day, fasting the next day, and so on.

Some people consume 0 calories when they fast, but others have a few hundred calories on their fasting days.

How long does intermittent fasting take to work?

The time it takes to see results may depend on your IF schedule, the results you’re aiming for, and your body’s response. You might notice some changes in just a couple of weeks.

One review of research found that in most cases, participants lost at least 5% of their starting body weight in studies that had lasted 8–26 weeks.

In October 2022, ZOE ran The Big IF Study. More than 37,500 people completed our 2-week IF trial. They used the 14/10 schedule. 

After just 2 weeks, participants reported, on average, an 18% increase in energy and a 9% improvement in mood.

In terms of gut health, around 64% said they had reduced symptoms of bloating.

What to eat during intermittent fasting

Below, we look at what breaks a fast and what’s best to have during your eating windows.

What can you eat and drink when fasting?

Technically, consuming anything with calories counts as breaking a fast. 

But not all forms of IF are so strict. If you’re following the 5:2 plan or the low-calorie version of alternate-day fasting, you can consume a few hundred calories on your fasting days.

What should you eat when you’re not fasting?

According to the “rules” of IF, you can eat whatever you want when you’re not fasting.

Plus, good sources of fiber and lean protein can help you feel fuller for longer.

Try to regularly include these in your diet:

• a wide variety of vegetables

• fruits

• whole grains

• nuts and seeds

• legumes, like lentils, beans, and chickpeas

• fish or poultry, if you eat meat

It’s best to limit ultra-processed foods and drinks. These have high levels of unhealthy fats, salt, and refined sugars. And they offer you few valuable nutrients.

Research has linked diets high in these foods with an increased risk of weight gain, heart disease, and cancer.

Plus, ZOE’s research has found that eating lots of ultra-processed foods is associated with increased levels of “bad” bacteria in your gut.

Also, your body breaks down refined carbs quickly, which can lead to a sharp rise in blood sugar for many people.

Sharp rises can lead to dips, and ZOE’s research shows that these dips can make you feel hungrier and less energetic.

You can learn how our personalized nutrition program can help you manage your blood sugar responses and eat for your best health by taking our free quiz.

Potential health benefits

From weight loss to gut health, IF may offer a number of health benefits.

• Weight loss: There’s good evidence that IF is as effective as standard calorie-restricted diets for short-term weight loss.

• Heart health: Research shows that IF can improve a number of risk factors for heart disease.

• Hunger: Early data from ZOE’s Big IF Study suggests that IF could be linked to a small reduction in hunger, but we have more work to do.

• Type 2 diabetes: Some studies suggest that IF may help improve insulin sensitivity and insulin levels even if it doesn’t lead to weight loss.

• Gut health: IF may increase the diversity of your gut bacteria and give your gut lining more of a chance to repair itself.  

If you want to learn more about what research says about IF, there’s a ZOE Science & Nutrition podcast on the topic.

Risks and other downsides

IF is not without downsides, and the risk is greater for some people:

• IF can be hard to stick to: Like any restricted eating program, IF may be hard to sustain in the long term. 

• IF may cause headaches: The initial results of ZOE’s Big IF Study saw an increase in headaches after 2 weeks on the 14/10 schedule.

• IF could lead to disordered eating: Many people can do IF without harming their relationship to food. However, some research has linked IF to symptoms of eating disorders.

Specific considerations for females

Scientists are exploring how IF might affect different areas of health. Here’s where the research currently stands in two areas:

• Hormone levels: Animal studies have suggested that IF could lower levels of “female” hormones, like estrogen. A review of studies involving females found that while IF did not affect estrogen levels in general, it may lead to a reduced availability of hormones in those with obesity.

• Bone health: Older females are more likely to have osteoporosis than older males. While traditional calorie-restricted diets may reduce bone density, a 2019 review suggests that IF doesn’t negatively affect your bone minerals in the same way. Still, most of these studies were small, so we need more research to confirm the findings.

Is intermittent fasting right for you?

If you’re looking to lose weight, TRE might help. This type of IF involves eating only during a certain period every day.

Overall, though, we need more research into the long-term effects of IF. And it’s certainly not for everyone.

Until you've spoken with a doctor, you should avoid IF if you:

• are pregnant or breastfeeding

• have a history of an eating disorder

• have diabetes

• take medication that you need to have with food

Summary

There are different types of IF. One type is TRE, and some examples of this are the 14/10 and 16/8 eating schedules. Following a TRE schedule means fasting for a given period every day.  

Other examples of IF schedules are 5:2 or alternate-day fasting. This means eating either no calories or a small amount on certain days every week.

IF may also have other benefits, involving your heart, gut, and brain health, though we need much more research before we draw firm conclusions. 

Some people shouldn’t try IF before they speak with a doctor. This includes people who are pregnant, have diabetes, or have a risk of disordered eating.