What is Ketosis?

Like all new things, getting started on a new diet can be challenging. The Optifast® VLCD™ Program, however, is easier to follow after the first few days due to a metabolic reaction that occurs in your body, called ‘ketosis’. Very low calorie diets are designed to bring on a mild form of ketosis, which means your body shifts from using primarily carbohydrates to fats as an energy source. Ketones are by-products that are created when your body has to switch to fats as an energy source. It means your store of glycogen or carbohydrates has been depleted.

One of the consequences of ketosis is a decrease in appetite, which helps make it easier to follow a VLCD program.

Watch the "3 day challenge" video by dietitian Joanne Turner for more information on managing ketosis during the Optifast® VLCD™ Program.

Is ketosis harmful?

A very low calorie diet like the Optifast® VLCD™ Program intentionally causes mild ketosis. At this level, ketosis facilitates safe weight loss and keeps important body processes working properly while getting so few calories. Whilst your body and brain usually use carbohydrates as their main energy source, during ketosis, the body burns fat and ketones are produced which supply the brain with energy. Excess ketones that your body does not use are excreted via urine and breath (thus the incidence of bad breath in some cases). Ketosis also causes you to shed excessive amounts of sodium, potassium and water, which in turn can cause dehydration, fatigue, headaches and constipation. However, your body can adjust to these changes in your electrolyte levels.

With the Optifast® VLCD™ Program, you can rest assured that your body is receiving all essential macro and micronutrients to stay healthy and adequately nourished. As the Optifast® VLCD™ Program causes only mild ketosis, it is a very safe approach to weight loss. Before your body transitions into ketosis, you will most likely feel hungry. The hunger usually only lasts for about 3 days as your body is transitioning into ketosis. Once in a ketotic state, the ketones generated will curb hunger in most people. So being on a very low calorie diet, fuelled by fat loss and accompanied by reduced appetite, will all help in achieving your weight loss goals.

Your body will take a few days to adjust to the switch from using carbohydrates to fats as an energy source and once ketosis has set in, these symptoms should generally cease.  Should they continue please speak to your Health Care Professional.

Once ketosis has occurred on the Optifast® VLCD™ Program, symptoms usually pass by days 3-6. This is followed by an increase in energy and reduction in appetite which, through this Intensive Phase, is likely to result in consistent and successful weight loss. It's also important to know that these are typical symptoms - and you should try to stick to the program and pass through the 3 day challenge. Of course, if you are concerned about your symptoms or if they persist, speak to your doctor, dietitian or pharmacist before adjusting or choosing to stop the Optifast® VLCD™ Program.

Hang in there for a few days, and you will be reaping the rewards of your dedication in no time at all! If you are ready to take the first step to successful weight loss, join the Optifast® VLCD™ Program today.

How will I know if my body is in ketosis?

To determine if your body is undergoing ketosis (i.e. using fats as a major energy source), you can ask your Health Care Professional to measure the level of ketones in your body via a simple test. However, it is not essential to test for ketosis.

Ketosis is most likely to occur when you begin the Optifast® VLCD™ Intensive Phase (3 Optifast® VLCD products per day). When consuming 3 Optifast® VLCD™ products per day- (along with the 2 or more cups of low starch vegetables, 2 litres of water, and 1 teaspoon of oil) you will consume an amount of carbohydrates for your body to begin Ketosis.

The Intensive Phase of the Optifast® VLCD™ Program is the only phase that ensures minimal intake of carbohydrate to kick-start the ketosis process. Although the hunger from ketosis is a little uncomfortable to begin with (normally lasts around 3 days), the advantage of ketosis is that once the initial hunger subsides, ketosis causes a reduction in appetite and this can help manage your caloric intake through the Intensive weight loss Phase of the Program. For more information, watch the 



Optifast® VLCD™ has produced a range of videos to introduce you to the Program and help you on your weight management journey.

Click thumbnail to watch Dietitian Jo Turner introduce the Optifast® Program.

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Optifast®  Soups offer a hot savoury option to the Optifast® VLCD™ range, and are available in two tasty flavours: Mixed Vegetable or Chicken.

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Optifast® VLCD™ is a food for special medical purposes and must be used under the supervision of a health care professional.              © 2012 Nestlé Health Science.