Very low calorie and energy diet


This blog provides free information about VLCD before bariatric surgery, not intended as a medical consult. Please seek appropriate advice from an accredited practising dietician with specialised interest in bariatric surgery, for an individual assessment, personalised advice, individual tailored management and diet plan.



The aims of a VLCD pre-operatively is to:

Reduce the size of the fatty liver

The visceral adipose tissue and enlarged fatty liver makes laparoscopic surgery more difficult and potentially hazardous for any major bariatric and upper GI surgery. The ability to retract the liver up and laparoscopic visualization of the oesophagus and stomach is restricted. Often there is lack of operating space in the abdomen and hence the bariatric procedure may be slightly compromised.

VLCD in the pre-operative period helps patients lose the visceral fat and reduce the size of the fatty liver, making surgery safer, facilitates the technical aspects of the surgery and often leads to a better surgical outcome.


Reduce pre-operative body weight and the risk of surgery

The benefit of weight loss apart from the reduction in fatty liver size and improving the ease of surgery, is also to reduce the peri-operative risks.

Weight loss reduces the metabolic, pro-inflammatory and pro-thrombotic risk factors, all of which are associated with visceral obesity and metabolic syndrome. Weight loss reduces snoring, improves breathing and may improve the respiratory mechanics during surgery.

The risk of surgery is obviously increased in the obese population, especially in relation to respiratory and thrombotic complications. Hence any reduction in body weight pre-operatively is extremely beneficial.


Improve obesity related co-morbidities

The average weight loss with strict adherence to an intensive VLCD program is about 5kg in the 2 or 3 weeks leading up to surgery.

The use of VLCD and successful weight loss has also been shown to result in improvements with insulin sensitivity, better blood sugar and blood pressure control, as well as reducing high triglycerides and sleep apnoea.




Daily energy requirements

For an average sized adult living in our Western society, the recommended daily energy intake is 8 700 kilo joules (2 078 Calories). This value obviously depends on age, gender (less Calories intake for women), occupation (the level of physical activity), body physiology (basal metabolic rate) and various other factors.

The aim of these total meal replacement or the intensive VLCD program, is to restrict daily energy intake to 3 300 kJ (800 Calories) a day. These meal replacements also provides the macro-nutritients, the recommended daily intake of vitamins, trace minerals and essential fatty acids that are necessary for normal body function and to preserve lean body mass.

VLCD are low in carbohydrates. When such low calorie meals are being consumed, energy source will have to come from body fat stores instead of carbohydrate, leading to the body breakdown of fat stores, inducing a form of mild ketosis during the catabolic state. Ketosis also helps to suppress appetite and this effect usually kicks in 3 days into the VLCD program.

Excess ketones are excreted via urine and breath, resulting in an unusual odour.

Ketosis may be associated with a loss of sodium, potassium and water, which in turn can cause dehydration, fatigue, headaches and constipation. Patients on diuretic medications or those with cardiac or renal disease should be cautious.



Intensive VLCD program (pre-op)

VLCD products are not prescription medication. They are over the counter products that can be bought at the chemist.

The intensive VLCD program is recommended for at least 2 weeks before bariatric surgery.

The VLCD comes in a variety of products such as soups, shakes, bars or desserts.

  • It is recommended to have 3 VLCD preparations a day.
  • 1.5 to 2 litres of water a day is recommended.
  • 2 or 3 serves of steamed vegetables is recommended.
  • 1 or 2 slice of fruit is allowed.
  • Non-calorie beverages may be drunk.



VLCD program (post op)

During the post-operative period especially in the first 2 weeks, patients are only able to consume fluids. It is essential that commercial products (VLCD) adequately replace the necessary daily macronutrients (protein), vitamins and minerals during the transition phase before the patient returns to solid meals (which is usually 4 to 6 weeks after bariatric surgery).

During the post operative phase VLCD are consumed in conjunction with fluids or puree/soft foods rather than a strict meal replacement unlike the pre-op phase.



Cautions with VLCD

Patients with certain medical conditions especially hypertension and diabetes need to monitor their blood pressure and blood sugar levels closely.

During this time of fluid and electrolyte loss and calorie restriction, medication dosages for these medical conditions may need to be reduced. Diuretic medications may need to be ceased. Oral medications for diabetes and insulin doses may need to be halved.

The side effects of VLCD are mostly related to the rapid weight loss and ketosis rather than the product itself. Amongst the listed side effects of VLCD are sensitivity to cold, halitosis (bad breath), headache, hair loss, irritability, postural hypotension, fatigue, muscle cramps and menstrual disturbances.

In the first 3 to 5 days of commencing VLCD program there may be transient side effects such as fatigue, hunger, lack of concentration, nausea and headaches. Usually mild ketosis occurs and most of these symptoms will pass by day 4 to 6.



Protein intake

For an average person the daily protein requirement is about 1g per kg ideal body weight, which is about 50 to 60g a day. One serve of protein is equivalent to 65-100g meat, 2 eggs or 130g fish. Obviously no meals except steamed vegetables is consumed during the pre-operative phase.

Hence the VLCD are formulated to provide the necessary and adequate protein to preserve lean body mass when consumed 3 times a day.

Similarly during the early post operative phase the protein intake is insufficient from oral fluids or puree. Again protein intake will need to be in the form of liquid, in the form of VLCD preparations.



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