A women running

800 Calorie
Intermittent Fasting Plan

Our Intermittent Fasting plan is designed to help you to lose weight and maintain weight loss. It offers the flexibility to switch between periods of fasting and eating, without restricting your caloric intake for days in a row.

Shop 4 Weeks 5:2 Plan Now
Intermittent Fasting Plan

How does it work?

Depending on your lifestyle and week schedule, there are two plans to choose from:


Alternate Day Fasting Plan - Staggers fast and feast days one after the other.

On fast days: Enjoy four Optifast meal replacements as your sole food consumption of the day.

On feast days: Eat conventional meals. Check out recipes, tips & tricks.

Total calories intake per feast day: 1,200 for women and 1,500 for men, depending on your weight loss goal.


5:2 Plan - Alternates five feast days with two fast days.

On fast days: Enjoy four Optifast meal replacements as your sole food consumption of the day.

On feast days: Eat conventional meals. Check out recipes, tips & tricks.

Total calories intake per feast day: 1,200 for women and 1,500 for men, depending on your weight loss goal.


Depending on your weight loss goals, after three months of either plan, you can increase the calories you consume on feast days usually 1,400 to 1,700. or move into our Maintenance plan.

Intermittent Fasting Plan Bundles

OPTIFAST offers a range of bundles to suit 3 weeks and 4 weeks supply on the Intermittent Fasting Plan.

OPTIFAST Support Hub

Check out our blog for more recipes, workouts and tips.
Intermittent Fasting - FAQs

In order to lose weight, we need to take in less energy in the form of calories than we burn off. By taking in around 800 - 850 calories each day, most people will achieve a significant energy deficit which helps to promote weight loss. The OPTIFAST diet replacement approach provides fewer calories whilst still providing all the micronutrients you need than some other approaches to weight loss, and is usually followed for a shorter period of time.


During the programme, the number of calories you take in reduces significantly compared to your usual diet. For this reason, it can be normal to experience some tiredness, headaches, nausea, or light-headedness. This tends to settle down as your body adjusts to the programme. However, if you experience severe or persistent symptoms, always make sure you seek medical advice.


We recommend you spend around 3 months on this plan. After this time has passed you can continue with the Maintenance plan.

Everyone is different when it comes to weight loss. How much and how quickly you lose weight depends on many things, including how much you weigh, how active you are, and how many calories you are taking in each day. On our intermittent fasting diet plan, weight loss is expected to be more gradual than with our continuous six week plan because overall you will be taking in more calories each week. Your rate of weight loss should increase the more days you follow intermittent fasting diet plan.

If your new diet contains a very different amount of fibre compared to what you are used to, it is possible to experience some digestive changes such as a change in bowel habit, bloating, or flatulence. As you adjust to your new plan this should settle down. If you experience persistent, severe or worrying symptoms, we advise you to seek advice from your GP.

When using the intermittent fasting plan Optifast provides all the nutrition you require, and there should be no need to take additional supplements. If you have a diagnosed deficiency or take prescribed vitamin or mineral supplements, we recommend you speak to your GP to decide if you need to continue these.

Optifast days on the intermittent programme will provide you with approximately 850 calories each day. This low calorie intake is to support you to lose weight. By taking four products from the Optifast® range each day, you will also receive all the vitamins and minerals you require.

Optifast® products are high in protein. On the fasting days, your protein intake will be between 70 and 81g of protein per day, depending on the combination of products you choose.


Yes, including tea and coffee is fine, but during phase one remember not to have them with milk, sugar or syrups which will provide additional calories.


Alcohol is not recommended as it can place extra strain on your liver and kidneys. Alcohol also has a diuretic effect and contains extra calories which could slow down your weight loss. Try to choose calorie-free drinks instead, such as tea (without milk), or soda water with a spritz of lemon or lime.