Careful management of the side-effects during the Intensive phase of the OPTIFAST® VLCD™ can greatly increase the success of the program as well as the patient’s compliance. It is important to note that some initial side-effects, especially during the first 3 days of the program, are normal and can be easily managed. Please see the list below for tips on how to manage the more common side-effects

3 Day Challenge

The first few days on the OPTIFAST® VLCD™ Program Intensive phase are commonly known as the 3 Day Challenge. As the body transitions into ketosis, your patient may experience some transient side effects such as; fatigue, hunger, lack of concentration, nausea, headaches. Typically, only mild ketosis occurs during the Intensive phase of the OPTIFAST® VLCD™ program and most symptoms pass by 4-6 days. Encourage your patients to stick to the program as prescribed and to avoid eating any extra food during this initial 3 days, otherwise they will just prolong the uncomfortable feeling. If your patient has quite an intensive type job, recommending starting the program on a weekend where they have more time to rest may assist them with managing their symptoms. Headaches can be managed by recommending some over the counter pain relief.


It is normal to feel hungry for the first few days of the program as the body transitions into ketosis. If possible, encourage your patient not to eat any extra food to compensate for the fatigue or hunger. However, if they are struggling then recommending to add in a small serve of lean protein each day may help manage their hunger feelings whilst they adjust to ketosis. It is very important that they avoid foods that contain carbohydrates, as this will stop ketosis from occurring. If hunger is a problem whilst on the Additional Allowances table OPTIFAST® VLCD™ Program, make sure fluid intake is adequate as we sometimes mistake hunger for thirst or recommend they distract themselves with another activity such as going for a walk or taking a bath. If all else fails use the foods listed in the, such as increasing the allowed quantity of vegetables, diet fluids, diet jelly or some sugar free lollies.


A complete meal replacement program is usually a dramatic change of intake for most people, and this can cause changes in bowel habits. In addition, if the recommended fluid and low starch vegetables are not consumed, a lack of Fiber (dietary bulk) and fluid can result in constipation. It’s important to know the difference between going less frequently and true constipation. It is normal to go less frequently when you are consuming less food, whereas true constipation is when the consistency is also affected. If your patient is experiencing constipation, recommend they consume more than the 2 cups of low starch vegetables per day, drink 2-3 Liters of fluid, and ensure they are exercising daily to help keep the bowels healthy and regular. If they still find they are constipated suggest a fibre supplement such as Nutrisource Fiber, or Metamucil. Nutrisource Fiber is sugar free, has no flavour and dissolves completely, so is ideal to add into the OPTIFAST® VLCD™ Shakes.


Diarrhea can be a temporary side effect of taking OPTIFAST® VLCD™ and should pass with time. If Diarrhea continues for more than a week you may need to investigate for further causes.


There could be several explanations to explain bloating or an increase in flatulence. Bloating/increase flatulence maybe caused by the change in diet. If there is more fibre in the new regimen due to increased intake of vegetables, this may result in the bloating. Some people find that they feel bloated because they are drinking a lot more fluid than usual. The bloating/increased flatulence is usually transient and resolves quickly so it is recommended to keep progressing with the program. Alternatively if your patient is lactose or fructose intolerant, the OPTIFAST® VLCD™ products may cause bloating as they contain both lactose and fructose. If the symptoms don’t improve within a week it may be worth doing some further investigation.


Estimated fluid requirements are 35-45mL/kg Adjusted IBW/day. For most patients greater than 80kg this will equate to approximately 2.5-3.0L/day. As 3 sachets of OPTIFAST® VLCD™ provides approximately 600mL per day, most patients on OPTIFAST® VLCD™ will require an additional 2L per day of fluid preferably water.

Nutritional Deficiencies / Supplementation


The OPTIFAST® VLCD™ Intensive phase (minimum of 3 OPTIFAST® VLCD™ products plus 2 cups of vegetables) is designed to meet the recommended dietary intake for most people. Therefore, additional supplementation is not necessary unless there has been a pre-existing nutritional deficiency diagnosed when starting the OPTIFAST® VLCD™ Program. If additional supplementation is desired, care would need to be taken to ensure that recommended safe levels of vitamins, minerals and trace elements are not exceeded.

Fish Oils

Fish oil supplementation is considered relatively safe and there is substantial research regarding the benefits of Omega-3, particularly in the area of cardiovascular health. The recommendation of 500mg per day for all adults would help reduce the risk of heart disease. The OPTIFAST® VLCD™ Shakes and Tomato Soup contain on average 60mg of Omega-3 (combined EPA/DHA) per serve. If additional fish oil supplementation is desired for health benefits, then this will be safe to include as part of the OPTIFAST® VLCD™ Program.


Rapid weight loss may induce the formation of gallstones. Fat intake is low with a VLCD, therefore the addition of fat (i.e. 1tsp vegetable oil per day) to the OPTIFAST® VLCD™ Program Intensive phase is recommended to stimulate the emptying of the gallbladder and prevent the formation of gallstones. Formation of gallstones can also be prevented with ursodeoxycholic acid in predisposed individuals.


Bad breath or halitosis can occur whilst using OPTIFAST® VLCD™. This is caused by ketosis and generally due to an increase in acetone levels. This is characteristic of ketogenic type diets and indicates compliance to the program. The halitosis will only last whilst they are following the Intensive phase of the OPTIFAST® VLCD™ Program. Recommending chewing on a low-calorie mint or sugar free chewing gum can help. Chewing fresh parsley can also be very effective.

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