What is Intermittent Fasting?

Intermittent fasting is a fast is where you limit your calorie intake for a chosen period of time. Intermittent fasting is alternating between times of regular food intake and set periods of eating nothing.

What makes intermittent fasting popular is that it is flexible and becomes more of a way of eating than a traditional diet plan. Intermittent fasting, including the 5:2, doesn’t focus on eliminating certain food groups or ingredients. Rather it focuses on the time and duration of a non-eating period.

The potential health benefits of intermittent fasting are vast including weight loss, improved insulin levels and reduced risk of chronic health conditions such as heart disease.

What is the 5:2 Method?

The 5:2 method, also known as “The Fast Diet”, involves eating regularly for five days of the week and then on the other two days, you limit your calories to approximately 500 (2,090 kilojoules) for women and 600 calories (2,510 kilojoules) for men. The idea is that on fasting days, you’re consuming 25% of your regular intake.

Made popular by Dr Michael Mosley, the diet plan isn’t technically a true fast as instead of a designated non-feeding period, you’re simply restricting your calorie intake. The 500 calories can be eaten in one single meal, or broken up into several snacks throughout the day. To be truly successful, you do need to create a meal plan for the low-calorie days to ensure you’re not overeating.

More recently Dr Mosely has updated the diet to increase the calorie restriction to 800 calories and adhering to a Mediterranean diet every day citing health benefits can be still seen without restricting the calories so severely.

This has been backed up with several studies showing promising weight loss results and remission from type 2 diabetes with the calorie intake at approximately 800 calories on the fasting days. In addition, the Mediterranean diet is perhaps one of the most studied diets, particularly around cardiovascular health.

An appeal of the 5:2 diet is that calorie restriction only occurs on two days a week and you can eat normally on the other days. Many find this limits the feeling of deprivation that’s often experienced with dieting and the flexibility allows them to incorporate it easily into their lifestyles.

How to do the 5:2 Diet

The 5:2 method involves consuming 25% of your normal calorie intake on the two “fast” days and eat as you usually would on the other five days of the week.

The general guide is to reduce your calories to 500 (2,090 kilojoules) for women and 600 calories (2,510 kilojoules) for men. However, you can alter this to better reflect your individual calorie consumption or increase it to Dr Michael Mosley’s revised limit of 800 calories.

For example, if you eat 2,000 calories per day, you would limit your calories to 500 on the fast days.

If you usually eat 1,700 calories, you’d reduce your intake to 425 calories on the fasting days.

The 5:2 diet offers the flexibility for you to choose when you wish to fast within the week. You can choose to eat fewer calories on consecutive days or you can split them up. For example, you may choose to fast on Wednesday and Fridays or on Monday and Tuesdays after a big weekend of eating.

How you structure your meals and the timing within the fasting days is also up to you. You may choose to eat one meal or consume three small meals throughout the day. Some of the common ways to structure your meals are:

  • Eating a small breakfast, a late lunch and a light dinner
  • Eating brunch and dinner
  • Eating a small breakfast and a later lunch
  • Eating one single meal (breakfast, lunch or dinner)

There is no right or wrong way to structure your meals. The overarching idea is to make the diet work for you. The key is to limit the number of calories on your fasting days.

A Sample Day of a 5:2 Fast

7:00 am – Wake and drink 500 mL of water with lemon

8:00 am – Scrambled eggs with steamed greens

Noon – Vegetable soup

7:00 pm – A small portion of steamed fish with veggies

Foods to eat on fasting days

Making a diet plan or purchasing a 5:2 diet recipe book is advised to help you adhere to calorie restriction on your fasting days and to extend your diet beyond raw veggie sticks.

  • Steamed or roast veggies
  • Hard-boiled eggs
  • Greek yoghurt with blueberries
  • Baked apple
  • Miso soup
  • Grilled fish
  • Vegetable soup
  • Baked beans
  • Zucchini fritters

Tips for Starting your 5:2 Diet

To help you start your first 5:2 diet and successfully incorporate it into your lifestyle, try these tips:

Before you start:

  • Choose the days you wish to fast
  • Define your health goal and measure to collect a baseline
  • Plan your meals/snacks ahead to ensure they fit into your calorie restriction
  • If you are overwhelmed or concerned about fasting, speak to a health professional or engage a coach to help you navigate the process

During your fast days:

  • Focus on nutrient-dense whole food meals that fit into your calorie
  • Avoid and limit processed or junk foods
  • Keep hydrated by drinking water and herbal tea throughout your fast
  • Exercise before you consume a meal or snack
  • Practice slow and mindful eating when consuming meals

Eating on regular days

Just because you limit your calorie intake on two days, it doesn’t mean you can eat anything you want and as much as you want on the other five days. It is recommended you are still mindful of your portions and the type of food so you don’t overeat or consume unhealthy foods outside of your fast.

After all, it’s not 5 “cheat days”!

In Dr Michael Mosley’s revised 5:2 plan, he recommends following a Meditteranean style diet featuring ample of protein such as lean meats, fish, eggs, beans, legumes and tofu, healthy fat and plenty of non-starchy veggies.

Health Benefits of 5:2

Low-calorie intermittent fasting, like in the case of the 5:2 diet, has had several studies into its effects on various health markers, including weight loss. In fact, this method is one of the most widely studied.

Weight loss

Six out of eight human trials into the effects of modified fasting regimens, such as the 5:2, reported significant weight loss in those who fasted compared to the control group.

In two trials of approximately 100 women, it was the 5:2 intermittent-fasting regimen resulted in the same weight loss over a 6 month period as those participants who reduced their daily calorie intake by 25%.

When compared to the conventional method of daily energy restriction, participants following a 5:2 plan consuming 600-650 calories on fasting days lost twice as much body fat in this 2013 study.

A study into fasting for 5 days consuming 700-100 kcal/day every month for 3 months was also found to reduce overall body weight as well as trunk and total body fat.

Disease prevention

Intermittent fasting methods that reduce the calorie intake on 1 or more days each week have been found to result in increased levels of ketone bodies on the fasting days. Ketones not only provide fuel, but they also help to regulate the expression and activity of several proteins and molecules that are known to influence our overall health and aging.

Beyond weight loss, many of the studied benefits of intermittent fasting methods including the 5:2 diet reveal improvements in glucose regulation, blood pressure and heart rate. All of these health parameters will influence the occurrence of disease.

Studies also found intermittent fasting with calorie restriction just 1 day a week is an effective solution to lowering cardiovascular disease risk in overweight women.

Promise has been seen for intermittent fasting methods such as the 5:2 and calorie restriction in reducing fasting insulin levels and insulin resistance in people who are overweight or obese helping to reduce the risk of type 2 diabetes. It’s important to note, the researchers called for more studies to be undertaken and no suggestion was made that fasting was superior to overall calorie restriction.

Pros of the 5:2 Fasting Method

There are many potential pros of the 5:2 intermittent fasting method:

  • No foods are restricted or demonised
  • You can decide when to schedule your fasting days in the week
  • Can be easy to schedule around social commitments
  • May experience benefits such as weight loss and blood sugar regulation

Cons of the 5:2 Fasting Method

There are some potential cons of the 5:2 fasting method:

  • 5:2 doesn’t replace healthy nutritional basics
  • Need to plan and weigh out low-calorie meals/snacks on fasting days
  • May experience hunger pangs and other side effects
  • People can binge or overeat on non-fasting days

Side Effects and Risks of the 5:2

Intermittent fasting can result in some side effects, particularly if you haven’t fasted before. These are usually minor and generally subside quickly once your body is used to fasting. And remember, with the 5:2 plan you are able to eat on your fasting days, just not much.

Some of the most common side effects you may experience on the fasting days include:

  • Hunger
  • Tiredness
  • Headaches
  • Poor or reduced focus
  • Mood swings
  • Irritability
  • Nausea

5:2 is Not for Everybody

Intermittent fasting, in general, is not suitable for everybody. This includes the 5:2 diet and even the new modified plan of increasing your calorie intake to 800 cal on the fasting days.

If you’re trying to conceive, pregnant or breastfeeding, you shouldn’t fast. Fasting is not ideal for those who are under 18 years old, underweight or have battled an eating disorder.

If you have a medical issue such as anemia, hypoglycemia or type 1 diabetes, you should consult your general practitioner before trying the 5:2 fasting method.

The Bottom Line

The 5:2 diet is a great protocol for those who are trying intermittent fasting for the first time and offers an alternative to low-calorie diets for people wanting to achieve weight loss.

This protocol does require a little planning and organisation around what to eat on the fasting days and can take some time for the body to get used to this way of eating. Most commonly people do experience hunger pangs and a little lightheadedness in the initial few weeks of trying the intermittent fast.

If you are considering a fasting method, it is important to speak to your health practitioner before you commence particularly if you have an existing health issue or are concerned about your specific dietary needs.

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