How Long Should I Be On An 800 Calorie Diet?

A rapid weight loss diet, like an 800-per day fasting approach, can be highly effective for individual goals. This eating pattern kickstarts metabolic health and can be instrumental in reversing prediabetes, tackling obesity and managing type 2 diabetes or metabolic syndrome.

However, there are some misconceptions about how long this eating pattern should be followed for, and ‘how long can I stay on an 800 calorie diet?’ is one of our most asked questions. This article will be delving into answering this common query, and exploring the options for after you’ve completed the 800 calorie phase so you can keep up your hard-earned results.

How does an 800 calorie diet work?

The majority of the time, your body runs on energy that is created when it burns glucose found in carbohydrates. This energy is used to fuel everyday activities and essential bodily processes. When you consistently consume more energy than your body needs, the excess is often stored as fat. The result of consuming more calories than your body uses is the leading cause of weight gain.¹

An 800 calorie per day diet approach creates a significant energy deficit, which forces the body to ‘flip the metabolic switch’ to burning fat stores for energy, instead of the glucose commonly found in carbohydrates. This switch can lead to rapid weight loss and, paired with a Mediterranean-style diet, it can also transform your insulin sensitivity and even reverse type 2 diabetes.

The DiRECT trial, for example, found that 46% of participants who were placed on an 800 calorie diet achieved type 2 diabetes remission at one year, compared with 4% receiving usual treatment for type 2 diabetes. These results demonstrate the potential impact of weight loss in as little time as a matter of weeks.

This said, although you reduce your intake of calories, you should still prioritise getting in the same amount of nutrients your body needs to optimally function.

What to eat during the initial 800-calorie phase

Reducing your calorie intake means making every meal count. When thinking about an 800 calorie diet, you should not just be wondering ‘how long can I stay on an 800 calorie diet?’ but you should also be focusing on what to eat during this time.

Continue to aim for your daily recommended intake of 60g of protein, 30g of fibre and plenty of healthy fats and non-starchy vegetables to stay properly nourished. A Mediterranean-style diet is naturally high in these nutrients, while being low in carbohydrates and ultra-processed, calorific foods, making it ideal for an 800 calorie diet.

The Fast 800 approach combines an 800 calorie daily fast with a low-carb, Mediterranean-style diet. Our Programme’s recipes use foods like leafy greens, lean meats, oily fish, full-fat dairy, nuts and seeds, and extra virgin olive oil to keep you properly satisfied and nourished during this time.

Nutritionist-developed plans like The Fast 800 are key during this phase to ensure you don’t accidentally become malnourished. Our Programme includes helpful meal plans with balanced macronutrients, delicious fasting-friendly recipes, automated shopping lists and on-hand support to make your journey easy and enjoyable. Head here to learn more, or keep reading to delve into your question of ‘how long can I stay on an 800 calorie diet?’

How long can I stay on an 800 calorie diet?

If you’re wondering ‘how long can I stay on an 800 calorie diet?’ then it’s time to set the record straight. An 800 calorie diet should be followed until:

1. For up to 12 weeks maximum, or;
2. Until you reach your goal weight or healthy BMI, whichever comes first.

Within this 12 week period, you’re likely to achieve dramatic results that then plateau after this initial phase. The DIAMOND study illustrates the power of that initial phase, with participants seeing an average of 9.5kg weight lost in just 8 weeks on an 800-calorie, low-carb, Mediterranean-style diet.

If this has answered your question ‘how long can I stay on an 800 calorie diet?’, then it’s time to find out what to do after completing your 12 weeks.

The next steps after the 12 weeks

While we limit how long you can stay on an 800 calorie diet to a maximum of 12 weeks, that doesn’t mean it has to be the end of your journey, or the limit of your results. Think of the 12 week 800 calorie phase as a launchpad towards your full potential.

After your 800 calorie phase, we recommend you move onto either Time Restricted Eating, which you can learn about here, or the 5:2™ diet, which involves consuming 800 calories just two days a week and a balanced diet with sensible portions on the other five days. This is best for those who still feel they have weight to lose after completing the initial phase.

Alternatively, if you simply want to maintain your hard-earned results, our Way of Life plan is designed to help you maintain muscle mass and lock in long-term results. As the name suggests, this particular lifestyle can be followed for life.

How do I know if an 800 calorie diet is right for me?

While rapid weight loss through fasting can be highly effective for addressing weight management and insulin resistance, it isn’t necessarily the right approach for everyone.

We do not recommend 800 calorie per day plans if you are under 18 years old, have a history of disordered eating, are a Type 1 diabetic, if you’re pregnant or breastfeeding, have certain underlying health conditions, or take certain medications.

To learn more about whether 800 calorie per day diets may not be right for you, head here, and ensure you talk to your usual general practitioner or health professional before starting any major lifestyle change.

The bottom line

If we’ve answered your query ‘how long can I stay on an 800 calorie diet?’ and you feel it may be the right approach for you to achieve your health goals, then sign up for your 7-day free trial of The Fast 800 Programme here.

There, you’ll find guided support to help you lose weight and keep it off, including tailored meal plans, fasting-friendly recipes, automated shopping lists and on-hand support from our team of health experts. Plus, the Programme’s Behaviour Change course, mindfulness resources and guided exercise videos are also there to support healthy habits and muscle maintenance.

Maintaining a healthy weight can reduce, or even prevent, the risk of chronic illnesses such as cardiovascular disease or type 2 diabetes.^{2 3} This is in addition to a multitude of other health benefits that go beyond simply the physical benefits, like improvements in sleep quality and mental health.^{4 5} So, get started on your journey towards better health with The Fast 800 today.