Very Low Calorie Diet – All You Need to Know!

Introduction

In my post Diet Plan for Weight Loss – It’s going to be a journey, I had described various options for treatment of obesity. As highlighted there, the core principle of any obesity treatment is that it must shift the balance between energy intake and energy expenditure – treating obesity requires creating a state of negative energy balance, therefore a reduction in energy intake is the primary factor that needs to be addressed in a dietary intervention designed to promote weight loss. In the above post, under dietary interventions for the management of obesity, I had discussed various calorie reduction strategies including reduced-calorie diets, low-calorie diets (LCD) and very-low-calorie diets (VLCD). In the above referred to post, I had discussed reduced-calorie diets in details; here, in this post, I shall be discussing the other two diets plans viz. low-calorie diets and very-low-calorie diets. The use of very-low-calorie diets to induce rapid weight loss, in contrast to many other weight loss products in the market, is backed by decades of medical research, and very-low-calorie diets have been in clinical use for almost 40 years. 

A women shopping for vegetables in a food store. Consumption of fruits and vegetables are very useful in formulation of very low calorie diets.
Source: UConn Rudd Center for Food Policy & Obesity

Low-Calorie Diet 

Also known as low-energy diets (LEDs). A low-calorie diet is usually > 800 kcal/d and typically ranges from 1200 to 1600 kcal/d. A low-calorie diet can be planned based on normal foods, choosing ‘low-calorie foods’ and limiting portion sizes or meal replacements, often soups or shakes, containing a known amount of energy and macronutrient content can be used to add structure to the diet. Keeping in view the restricted nature of the diet, while planning the diet, make sure that it provides all the essential nutrients. These diets are usually meant for short-term use, often to give a ‘jump-start’ to a weight loss program. Selection of low-calorie foods plays an important role while planning low-calorie diets and I will briefly discuss these here. 

What are low-calorie foods and high-calorie foods

Calorie density is the number of calories or ‘energy’ in a particular weight of food and is generally presented as the number of calories in a gram (kcal/g). Foods with a lower calorie density provide fewer calories per gram than foods with a higher calorie density. Therefore, for the same number of calories, a person can consume a larger portion of food lower in calorie density than a food higher in calorie density; this promotes adherence to the low-calorie diet by helping to control the drive to eat. Evidence suggests that foods with a low-calorie density can help people maintain weight.

The calorie density of foods is influenced by the composition of foods. Water lowers the calorie density of foods because it has a calorie density of 0 kcal/g and contributes weight but not the calories to foods. Fibre also has a relatively low calorie density (1.5 to 2.5 kcal/g) and helps lower calorie density in food. On the opposite end of the calorie density spectrum, fat (9 kcal/g) is the most calorie-dense component of food, providing more than twice as many calories per gram as carbohydrates or proteins (4 kcal/g). In general, foods with a lower calorie density tend to be foods with either a high-water content, lots of fibre or little fat. Examples of low-calorie foods include soups and stews, foods like pasta and rice that absorb water during cooking, foods that are naturally high in water (and also fibre), such as fruits and vegetables, and fibre-rich foods like whole-grains. Adding fibre- and water-rich foods, such as vegetables, to dishes with high-calorie-density, lowers the calorie density of these foods. High-calorie-density foods tend to include foods that are high in fats and/or sugars. Examples of high-calorie-density foods include – fast food, sugar-sweetened beverages and fruit juices, confectionery and bakery products.

Thus, while people may consume about the same amount (weight) of food each day, it may differ drastically in terms of the number of calories. So, it is feasible to consume fewer calories while at the same time achieving a greater degree of hunger control, by eating low-calorie foods. In brief, by choosing the low-calorie foods, you get to eat a lot more food for the same number of calories. To watch your portion sizes, as to produce the required calorie deficit, portion-controlled diets are the best way to eat; the same has been discussed in my post Diet Plan for Weight Loss, referred to above.

Very-Low-Calorie Diets

Also known as very-low-energy diets (VLEDs). Very-low-calorie diets are a weight loss strategy that utilises severe and controlled energy restriction to induce rapid weight loss. Very-low-calorie diets involve restricting energy intake to < 800 kcal/d. Thus, very-low-calorie diets are the most intensive dietary intervention for obesity and the single most effective intervention. Very-low-calorie diets achieve greater initial weight loss compared with other approaches, with reported weight losses of 9-26 kg over 4-20 weeks. However, as with the other weight loss interventions, all of the initial weight loss is not maintained beyond the very-low-calorie diet intervention.

A meta-analysis of six randomized controlled trials (RCTs), titled The Evolution of Very-Low-Calorie Diets: An Update and Meta-analysis, published in the journal of ‘Obesity’ in Aug 2006, compared weight-loss outcomes of very-low-calorie diets and low-calorie diets. The study found that although very-low-calorie diets produce significantly greater weight loss in the short-term (4 months), there was no difference in weight loss between the diets in long-term follow-up (> 1 year). The National Institutes of Health (US), National Task Force on the Prevention and Treatment of Obesity in 1991, concluded that very-low-calorie diet long term was no better than any other form of weight loss method despite initial weight losses of 20 kg over 12 to 16 weeks. Subsequent research has not provided any data to overturn the 1995 conclusion of National Institute of Health.

However, despite this very-low-calorie diets have their advantages. In addition to the benefits of weight loss which are common to most methods of weight reduction, one significant advantage of a very-low-calorie diet is the motivating effect of rapid weight loss commonly seen in patients while on a very-low-calorie diet, which can improve adherence to the weight loss efforts in the long-term. Another characteristic feature of a very-low-calorie diet is the development of mild ketosis; which normally develops by the third day of the patient being on a very-low-calorie diet. Ketosis suppresses the drive to eat, thereby improving adherence to the diet. While following a very-low-calorie diet, physical activity should be encouraged to minimise loss of lean body mass, and the potential amelioration of bone loss, especially in the elderly. In my post Health Benefits of Exercise: a grossly underutilised therapy, I have discussed the benefits of exercise and in my post Exercise Prescription for Optimum Health Benefits, I have discussed the guidelines for exercise prescription.

What is ketosis?

 Ketosis is a metabolic state characterised by elevated levels of ketone bodies in the blood or urine. Ketones sometimes referred to as “ketone bodies”, are water-soluble compounds (meaning that they dissolve in water) that are produced as “by-products” when the body burns fats for energy. Ketones are an efficient source of energy for many organs, particularly the brain. The human body uses the three macro-nutrients in the food, carbohydrates, fat and proteins to provide energy. Under normal healthy conditions, when an individual is on a balanced diet and is well fed, carbohydrates act as the main source of energy; though, fats are also a significant source of energy. Even though proteins are not usually used for energy, however, if the body’s energy requirements are not being met by carbohydrates and fats, the body breaks down proteins to provide energy. 

As under normal conditions, carbohydrates serve as the main fuel for energy and only small amount of fat is metabolised to supply energy, ketones are present in the blood in only small quantities. However, during states of starvation/fasting or when an individual is on very-low-calorie diets, the body uses fats as the primary source of fuel. This shift in fuel utilization is thought to be a survival mechanism that we have retained through our evolution and is a protective mechanism to maintain energy balance. During starvation/fasting liver burns stored fat for energy; when the individual is on a low-carbohydrate, high-fat diet (known as a ketogenic diet), the liver burns large quantities of dietary fat for energy. As a result, ketone production in the body increases; the metabolic state characterised by elevated levels of ketone bodies in the blood is known as ketosis. When the ketosis is induced by dietary modification, it is known as nutritional ketosis. Suppression of the drive to eat associated with ketosis, resulting in a spontaneous decrease in energy intake, is thought to be the key factor in enabling adherence to low-calorie diets, leading to weight loss.

There are broadly two types of diets that induce ketosis: very-low-calorie diets and ketogenic diets, commonly known as keto diets. Although both keto diets and VLCDs induce ketosis, keto diets can result in several-fold higher circulating levels of ketones compared to the VLCDs, as ketogenic diets limit carbohydrate intake to a much larger extent than very-low-calorie diets. However, ketogenic diets are nutritionally imbalanced and defy all principles of healthy eating. Also, eating such a restrictive diet, irrespective of the diet plan is difficult to sustain in the long-term. Besides, keto diets have numerous associated health risks; the most serious of these is the increased risk of cardiovascular diseases as a result of ensuing lipemia (prolonged and increased levels of triglycerides and triglyceride-rich lipoprotein levels after a meal) due to the high amounts of fat in the diet. Given the same, the ketogenic diet is not recommended. I will discuss ketogenic diets in a subsequent post.

Formulation of very-low-calorie diets

Such restriction of caloric intake cannot be achieved by restricting the usual diets since a daily food intake of 1200 to 1500 kcal is necessary for the body to obtain its requirement of various micronutrients such as vitamins and minerals. The only way to maintain nutrition, while reducing energy intake to 800 kcals or less is by substituting meals with commercially available meal replacement formulations, which may be used as the sole source of nutrition during the weight loss program.

Very-low-calorie diets are usually consumed in the form of liquid meal replacements and are most commonly prepared commercially. These are available in the form of bars, soups, and desserts. However, despite their reduced total energy levels, VLCDs are designed to provide optimum intakes of vitamins, minerals, trace elements and fatty acids. More importantly, very-low-calorie diets are designed to conserve lean body mass, as they provide 0.8 to 1.5 g of high-quality protein per kilogram body weight. It is important to add a small quantity (7-10 g) of fat daily to the diet to stimulate gallbladder contraction and thus reduce the risk of gallstone formation.Tea and coffee (without any sugar) and diet drinks are allowed. Milk, other than small quantities in tea or coffee should be avoided. At least 2 litres of water (including calorie-free fluids) daily is advised.

Type of very-low-calorie diet regimens

There are two types of very-low-calorie diet regimens – complete or partial. In the complete VLCD regimen, all three meals are replaced with the replacement meal formulations. Besides, patients are allowed to have some non-starchy vegetables which provide fibre and induce satiety. In the partial VLCD regimen, only two meals (typically breakfast and lunch) daily are replaced with a meal replacement formulation. For the dinner, the patient has one serving of lean protein (which can be any type of meat, red or white, fish or seafood, egg or dairy or soybean-based such as tofu) and non-starchy vegetables.

The choice of complete or partial very-low-calorie diet depends on the target weight and the individual’s ability to tolerate the VLCD. However, in practice compliance to complete very-low-calorie diets is poor; most individuals tend to prefer partial VLCD as it gives them the pleasure of looking forward to a meal each evening, potentially improving compliance.

Indications for very-low-calorie diets

Very-low-calorie diets can be used as part of comprehensive weight-loss interventions and have been used in combination with physical activity, behavioural therapy and/or pharmacotherapy. These are commonly used in the following conditions:

  • In cases of Class I and II obesity, where supervised lifestyle interventions (comprising of reduced-calorie diets or low-calorie diets combined with a program to increase regular physical activity) has failed to produce sufficient weight loss or weight regain is experienced.
  • In cases of Class I and II obesity associated with obesity-related complications such as type 2 diabetes or obstructive sleep apnoea, which are likely to improve with weight loss, very-low-calorie diets can be considered as an initial option.
  • In all cases of class III obesity, even when no obesity-related complications have been detected, VLCDs should be used as an initial option, along with other lifestyle interventions.
  • When rapid weight loss is required (e.g. before bariatric surgery or general surgery which is conditional on weight loss of a certain degree).

Contraindications of very-low-calorie diets

Although these products are widely available in pharmacies and online, without prescription, these products are recommended to be used under medical supervision. These are contradicted for use in the following conditions:

  • In people with an increased nutritional requirement such as pregnant women, lactating mothers and children and adolescents below 18 years of age.
  • In patients with severe psychological disturbances, alcoholism or drug dependence.
  • In patients who have had a major cardiovascular event such as myocardial infarction or stroke within the past three months.
  • In patients suffering from porphyria (a group of diseases in which substances called porphyrins build up, negatively affecting the skin or nervous system).
  • The VLCDs should be used with caution in patients suffering from Type 1 diabetes, gallbladder and kidney stones, and gout and in individuals over the age of 65 years. However, in case the benefits of rapid weight loss are likely to outweigh the potential risks for people in the above-mentioned conditions, VLCDs should be used with caution under expert medical supervision.

Recommended duration of very-low-calorie diets

Very-low-calorie diets are often recommended for 03 months. If effective in achieving adequate weight loss, the meal replacements can be gradually reduced and regular foods progressively reintroduced over a period of about 08 weeks. However, depending on the person’s weight at baselines and the target weight, the VLCDs can be continued for 6 to 12 months under careful medical supervision.

Monitoring of very-low-calorie diets

As highlighted above, while on a very-low-calorie diet, the patient must be kept under regular medical supervision. Before starting a VLCD, baseline blood tests should be taken and thereafter monitored periodically. In case any abnormalities develop, consider discontinuing the very-low-calorie diet.

Complications associated with very-low-calorie diets

Some common side effects of very-low-calorie diets include constipation, headache, fatigue, dizziness, dry mouth and skin, hair loss, altered menstrual function and asymptomatic gallstones.

Conclusion

Very-low-calorie diets are the most intensive dietary intervention for obesity and the single most effective intervention; very-low-calorie diets achieve greater initial weight loss compared with other approaches. Unlike many other weight loss products in the market, VLCDs are backed by medical research and are in clinical use since last almost 40 years. However, as with the other weight loss interventions, all of the initial weight loss is not maintained beyond the very-low-calorie diet intervention. 

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