What is the 5:2 diet and what are the guidelines?

The 5:2 diet, also known as The Fast Diet involves restricting your calorie consumption to 25% of your energy (calorie) needs on two non-consecutive “fasting” days, and eating normally the other five days of the week. On fasting days, total calorie consumption works out to be about 500 calories for women and 600 calories for men. You can choose whichever two days of the week you prefer to fast, as long as there is at least one non-fasting day in between. On non-fasting days, you eat normally and don’t have to think about restricting calories.

The notion of this style of eating is that you’re consuming less calories and therefore, you will lose weight. This diet is considered more of an eating pattern than a diet. There are no requirements about which foods to eat, but rather when you should eat them. The most common way people plan their week is to fast on Mondays and Thursdays, with two or three small meals, then eat normally for the rest of the week.

It’s important to emphasise that eating “normally” does not mean you can eat literally anything. If you binge on junk food, then you probably won’t lose any weight, and may even gain weight.

You should eat the same amount of food as if you hadn’t been fasting at all.

Is this diet sustainable?

Firstly, it should be noted that there is no magic to weight loss, nor a quick fix. Changing eating habits should occur gradually, especially if you have existing poor eating behaviours. A successful weight-loss program looks at many aspects including nutrition, exercise, hormone balance, stress management and proper sleep hygiene. It also requires support and a complete lifestyle change and the sad truth is that fad diets will not change the relationship people have with food.

While the 5:2 diet may suit some people, I believe it’s an unbalanced and unhealthy approach to eating, alternating fasting with feasting. It’s the ultimate all-or-nothing cycle of hungry days and (potentially) high-calorie days. It’s been clinically proven that extreme dieting triggers over-eating, and may cause mood swings and fluctuations in energy levels.

Some may consider the 5:2 diet more sustainable than other forms of fasting or fad dieting in the fact that you are not necessarily depriving yourself of your favourite foods. This is usually one of the largest barriers to success, eliminating or being deprived of your favourite foods. However, it does not teach healthy eating behaviours, and for that reason it should be considered unsustainable over the long-term.

If you are someone who is struggling with your weight and have tried many different approaches with little success, you will benefit from the advice of your GP, Dietitian or Nutritionist, who can investigate the reasons for your challenges you are facing and put together an individually tailored program that is suited to your lifestyle so you can achieve long-term weight loss success.

What are the pros and cons of the 5:2 diet?


Intermittent fasting certainly has its benefits to certain population groups. It has shown to reduce blood glucose, triglyceride and LDL cholesterol levels, which are all associated with a reduced risk of type 2 diabetes and cardiovascular disease. It may also reduce the risk of developing age-related conditions such as cancer and Alzheimer’s disease.


The diet does not teach healthy eating habits or behaviours as it allows you to eat whatever you want five days of the week. The diet principles also place consumers at risk of malnutrition and nutrient deficiencies (especially on fasting days). Although the diet states you can eat whatever you like on five days of the week, it doesn’t provide participants a guide towards the variety of foods required for optimal nutrition i.e. vegetables, fruit, grains, dairy or dairy alternatives and protein sources such as lean meats, eggs and nuts. Finally, this diet can be potentially dangerous and should not be recommended for:

  • Women trying to conceive or have issues with infertility
  • Women who are pregnant or breastfeeding
  • Children or teenagers
  • People taking certain medications
  • People with type 1 diabetes
  • People who are underweight, malnourished or have known nutrient deficiencies, or
  • People who have a history of eating disorders.

How can people do the 5:2 diet safely?

Before deciding to do this diet, it is best that you are well informed and educated by a Dietitian, who can provide you proper insight and protocols on how to follow this diet, properly and safely.

There are some general practices that people follow when doing the 5:2 diet. Some people function best by starting the day with a small breakfast, while others find it best to start eating as late as possible. Gage which ever suits you best and experiment with the below two meal patterns:

  1. Three small meals: Usually breakfast, lunch and dinner.
  2. Two slightly larger meals: Lunch and dinner, only.

Due to the limited daily calorie intake on fasting days, be sure to use your calorie budget wisely, choosing from a variety of foods and food groups to minimise your risk of malnutrition and nutrient deficiencies. Focus on nutritious, high-fibre, high-protein, low GI foods that will make you feel full without consuming too many calories.