Ketosis is a metabolic reaction that occurs in the body, when following the OPTIFAST® VLCD™ Program Intensive phase. This means the body shifts from using primarily carbohydrates to using fats as an energy source resulting in a reduction of body fat stores. Ketones are by-products that are created when the body has to switch to fats as an energy source. It means stores of glycogen or carbohydrates have been depleted. One of the consequences of ketosis is a decrease in appetite, which helps make following the OPTIFAST® VLCD™ Program Intensive phase much easier. As the Intensive phase causes only a mild ketosis; it is a very safe approach to weight loss.


Following the initial 3 Day challenge your patients will experience an increase in energy and reduction in appetite which, through the Intensive phase, will result in a consistent and successful weight loss. It is important to know that these are typical symptoms and that your patient should try to stick to the program as prescribed or otherwise they will simply pro-long these first few days of the OPTIFAST® VLCD™ Program.


Once the body is in ketosis, any excess ketones that the body does not use for energy are excreted via your urine and breath (thus the incidence of halitosis in some cases). This therefore allows the patient to measure the ketone levels in their urine with Ketone Reagent Strips or Ketostix. Ketostix can be purchased over the counter from a local pharmacy.


The amount of carbohydrate required to induce ketosis depends on a number of factors and can actually vary from day to day depending on activity levels and fluid intake. A diet containing 50-70g carbohydrate is generally considered low enough to produce ketosis but there is no absolute level that guarantees ketone production. The OPTIFAST® VLCD™ Program generally only produces a mild ketosis, therefore for some reason, some people find that Ketostix do not show ketones or the levels fluctuate. If your patients are losing weight steadily, then there is no need to be concerned. You can rely on the other symptoms of ketosis such as a reduction in appetite and the presence of halitosis as a guide instead.

Prior to the transition into ketosis, your patients will most likely feel hungry and may experience some side-effects such as


These side-effects should only last about 3 days and most symptoms usually pass by days 4-6. This is what is referred to as the 3 Day challenge.

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