The OPTIFAST Guide to Intermittent Fasting

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What is Intermittent Fasting?

Intermittent fasting is a type of eating plan that alternates between fasting and eating on a regular schedule. Research has shown that intermittent fasting is a way to help promote and maintain weight loss.

The most popular approaches to intermittent fasting include 5:2 fasting, alternate-day fasting and time-restricted fasting.

Intermittent fasting has been used as a weight loss strategy for decades and has become increasingly popular in recent years. Studies show that following an intermittent fasting long term may be as effective as a typical low-calorie diet, and a more sustainable approach to weight loss.

5:2 Fasting

A 5:2 fasting plan involves eating regularly five days a week and, on the other two days, limiting yourself to 800 calories per day. It’s one of the more frequently used plans, because it provides more flexibility to fit weight loss goals around a busy lifestyle, and you don’t have to restrict your calorie intake for too many days in a row.

5:2 fasting is easy to incorporate into your OPTIFAST weight loss programme too. On a fast day, you would consume four OPTIFAST products for a total of 800 calories, and on your feast days consume 1,200-1,500 calories.

Whether you choose alternate day fasting or a 5:2 plan, after three months, you can increase your intake to 1,400-1,800 calories, depending on your weight loss goals.

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16/8 Intermittent Fasting

16/8 fasting is sometimes also referred to as time-restricted fasting or 18/6 fasting. This is an eating pattern in which food intake is restricted to a time window of 8 hours or less, followed by a daily fast for the remaining 16 to 18 hours of the day. For example, this could involve eating meals only between 9am and 5pm, or 10am and 6pm, or 12pm and 6pm.

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Eat Stop Eat Intermittent Fasting

The Eat Stop Eat diet involves fasting for 24 hours twice a week. On this particular weight loss plan, you don’t have to change the foods that you eat, but fasts are much longer, which can be a challenge.

The diet plan encourages you to eat something every single day, for example by beginning your fast after dinner on a Friday and ending it with dinner on a Saturday.

The Eat Stop Eat diet should only be followed with medical guidance or support, due to the challenging length of the fasts.

Alternate Day Fasting

On an alternate day fasting plan, you cycle between fast and feast days in a continuous pattern. You eat a normal diet one day and either consume 4 OPTIFAST products or have one small meal (of between 600 and 800 calories) the following day.

Fast Days

On a fast day, you’ll replace all of your usual meals and snacks with four OPTIFAST products, making your daily caloric intake approximately 800 calories.

OPTIFAST products are scientifically designed and contain the essential vitamins and minerals your body needs, including protein and fibre that can help you to feel full and manage hunger.

Choose from Meal Replacement bars, shakes, soups and desserts in a range of tasty flavours – from chocolate bars to coffee shakes and a tempting dessert, there’s plenty of choice to make fast days easy.

Feast Days

On a feast day, you’ll eat conventional foods, but keep your calorie intake to around 1,200 per day for a woman, and 1,500 for a man. However, this will depend on your weight loss goals.

Check out our collection of low-calorie recipes for some mouth-watering feast day inspiration.

What are the Benefits of Intermittent Fasting?

Studies have shown that intermittent fasting offers several benefits beyond just weight loss, for example with blood sugar levels.

In contrast to other weight loss plans, intermittent fasting offers the flexibility to plan your ‘feasting days’ around your social life, work events or even holidays, fasting when it’s more convenient.

How to Stay on Track with Intermittent Fasting

There are times when we lose sight of our goals, but keep these tips in mind to stay on track:

  • Create a meal plan: Plan tasty meals to look forward to on your feast days, such as our Mexican bean burgers or skinny Singapore noodles
  • Fill up on protein and fibre: Keep your cupboards and fridge stocked with healthy, high-protein, fibre-filled ingredients and OPTIFAST products so you’ve got plenty of convenient options on hand that fit with your eating plan
  • Avoid snacking: Check out our advice on stopping snacking for good
  • Remember your goals: Turn to your support network and keep your long-term goals in mind when the going gets tough. You’ve got this

Is Intermittent Fasting Safe?

Intermittent fasting is safe for most people, but you should always check with your GP before starting a new diet plan to make sure it’s right for you.

Intermittent fasting can involve fasting for long periods, which isn’t advised for people who are pregnant or breastfeeding or for individuals with certain health conditions. With this in mind, you should always seek advice from a healthcare professional before trying intermittent fasting for the first time.

How Long Should I Do Intermittent Fasting For?

Intermittent fasting can be a long-term lifestyle change; you might want to continue with an intermittent fasting plan even after reaching your weight loss goal to help maintain your weight.

You could also follow an intermittent fasting diet plan for a shorter period, such as before a holiday, wedding or other special occasion.

How Long Does It Take for Intermittent Fasting to Work?

Everyone’s goals are different, which means everyone will notice the results of intermittent fasting at a different time. Most people often notice a difference in the way that they feel in the first couple of weeks of a weight loss plan, such as with the way their clothes fit or what the scales show.

If you’re unsure of what’s a realistic goal to aim for, speak to your GP who will take your individual circumstances and health needs into account.

What Can I Drink While Intermittent Fasting?

When you’re following an OPTIFAST Intermittent Fasting Plan, you can drink water, tea and coffee (preferably black or with just a splash of skimmed milk) or squash with no added sugar.

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Find out more about what you can drink while following an OPTIFAST diet plan:

What Can I Drink on an OPTIFAST Plan?


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Find out everything you need to know about what you can drink on an OPTIFAST weight loss plan.

2021-04-22 13:38:16By Health & Nutrition Expert


Rynders CA, Thomas EA, Zaman A, Pan Z, Catenacci VA, Melanson EL. Effectiveness of Intermittent Fasting and Time-Restricted Feeding Compared to Continuous Energy Restriction for Weight Loss. Nutrients. 2019 Oct 14;11(10):2442. doi: 10.3390/nu11102442. PMID: 31614992; PMCID: PMC6836017. Sutton et al., 2018, C Early

Time-Restricted Feeding Improves Insulin Sensitivity, Blood Pressure, and Oxidative Stress Even without Weight Loss in Men with Prediabetes ell Metabolism. Cell Metabolism. 27: 1212–


Health & Nutrition Expert

Health & Nutrition Expert

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