VLCD explained: Everything you should know about very low-calorie diets

If you're working with a doctor to shed those stubborn pounds, you might hear about a thing called a very low-calorie diet (or VLCD for short). It's a type of strict low-calorie diet that can be recommended for people who are classified as obese or severely obese, as well as people managing diabetes.

While very low-calorie diets can support short-term weight loss, there are important drawbacks to consider, too.

Along with being very restrictive, a VLCD programme might not deliver sustainable results that you can maintain over the long term.

To help you understand whether a very low-calorie diet is right for you, let's run you through what this low-calorie diet is all about, what kind of weight loss you can expect, and how this diet compares to a low-energy diet programme.

What is a VLCD?

Let's start with the question that's likely on the top of your mind: what is a very low-calorie diet?

In a nutshell, a VLCD programme is a clinically supervised weight loss plan that involves restricting the number of calories you consume for a specific period of time. Typically, it involves eating 800 calories or less as a way to speed up the weight loss process.

A VLCD might be recommended if you're classified as an obese or severely obese patient, or if you're navigating another condition (such as diabetes) at the same time.

This tool is often prescribed if you record a BMI (body mass index) over 30 or 40 and can offer rapid weight loss over a set period of time (usually programmes run for up to 12 weeks) [1].

During a very low-calorie diet, you'll be supervised by a doctor or GP who will set out what you can and can't have as part of your diet.

How do very low-calorie diets work?

Typically, a very low-calorie diet involves swapping regular food for low-calorie products like shakes, soups, bars, and other diet supplements. These products will provide all the essential vitamins and nutrients you need, while still being incredibly low in calories and helping you lower your energy intake.

The principles behind very low-calorie diets are simple: the less you eat, the more weight you're expected to lose.

Each kind of VLCD is slightly different in what kinds of foods and products you'll be able to consume.

Some require you to switch every meal out for a shake or bar, while other versions of this low-calorie diet still allow you to eat low-calorie food like vegetables.

Because VLCD programmes are considered to be quite restrictive, it's important to speak with your GP first to ensure you're managing your diet in a safe way.

Without medical supervision, you may not be providing your body with the right nutrients and essential fatty acids it needs throughout your weight loss journey.

However, with the right support in place, you can use these meal replacement products as a way to speed up your weight loss journey. This combination of meal replacement drinks and low-calorie diets has proven to be effective when researched.

What are the benefits of following very low-calorie diets?

Clearly, very low-calorie diets are a challenging and demanding way to achieve weight loss. So, why would someone consider reducing their calorie intake to such an extreme level?

For people who are navigating obesity and looking for a rapid weight loss solution, VLCDs can offer large initial weight loss in a short space of time. That's because a very low-calorie diet totally transforms your diet and replaces some (if not all) meals with protein-rich shakes and diet products.

Rather than worrying about portion size or your level of carbohydrate intake, very low-calorie diets take the guesswork out of mealtime.

This can make it easier and more convenient to stick to the low-calorie limits and see a greater initial weight loss in a short space of time.

Plus, it's a less invasive approach than other common weight-loss strategies. The most common alternative to the dietary management of obesity has been bariatric surgery, which constricts the stomach and how much food can be consumed [2].

In the UK, common types of weight loss surgery include lap band surgery, gastric bypass or banding, and gastric sleeve surgery [3]. All of these options use a keyhole procedure and a pouch or adjustable ring to lower a patient's food intake.

However, this kind of surgery can come with complications such as infection and is much more expensive than the calorie restriction used in a VLCD programme.

Is there any research on the effectiveness of VLCD?

One study compared obese women with PCOS who were on a VLCD to those who were on a moderate energy deficit diet [6].

The results? The women who were on the VLCD lost more weight than those who were on the moderate energy deficit diet.

They also saw improvements in body composition and other metabolic markers compared to those who were on a moderate energy deficit diet.

In another study, the metabolic effects of a VLCD were examined in obese women over 24 weeks [7].

The women were randomly assigned to either a VLCD (500 kcal/day) or a balanced-deficit diet (BDD, 1,200 kcal/day).

After 8 weeks, the women on the VLCD saw a 17% decrease in resting energy expenditure (REE), while the women on the BDD saw no change in REE.

Both groups lost weight and fat-free mass, but there were no significant differences in the changes in REE when adjusted for fat-free mass.

It's important to note that while VLCDs can lead to significant short-term weight loss, they are typically recommended for short periods and under close medical supervision because of potential health risks.

For long-term weight loss, a more balanced approach that combines moderate caloric restriction with lifestyle changes — such as increased physical activity and behavioural changes — is more effective and safer in the long run.

Expected rate of weight loss using the VLCD

In general terms, a VLCD is shown to be very effective in supporting rapid weight loss, at least in the short term.

But the key to success is to ensure you're working with a medical professional who is able to monitor your weight loss and ensure you're not jeopardising your health and well-being in the process.

While the results will differ from person to person, studies have shown that obese people following very low-calorie diets tend to see an average weight loss of 1.5-2.5 kilos per week (3.3-5.5 pounds) [2].

Some studies have shown that using a total food replacement programme can be more effective in driving faster weight loss, in comparison to a food-based VLCD programme [4].

What is a VLED?

Very low-calorie diet (VLCD) and very low-energy diet (VLED) are interchangeable terms and refer to diets with less than 800 calories per day.

A very low-energy diet is the same as a very low-calorie diet and both usually require the replacement of all meals with shakes or bars (supplemented with some dietary fibre and a bit of olive oil to keep the gallbladder contracting and lower the risk of gallstones).

When undertaking VLEDs and VLCDs, you must be medically supervised as there is a risk of potentially serious side effects and not all patients are suitable due to pre-existing health issues.

Often VLEDs and VLCDs involve a low carb and high protein intake to induce ketosis in order to promote using fat stores as energy (instead of sugars and glucose). This is usually continued for 12 weeks to achieve rapid weight loss.

What are the downsides of a VLCD?

Following a very low-calorie diet (VLCD) can come with a set of challenges. From hunger pains to the question of whether weight regain is inevitable, there are a few downsides to consider before chatting to your GP about this kind of programme.

Some of the key things to consider about a VLCD include:

• Side effects like headaches, weakness, fatigue, nausea, vomiting, and low blood sugar can be common in the first 4-16 weeks [5].
• Medical supervision is needed to ensure you're meeting weekly weight losses and meeting the nutritional status your body needs to thrive.
• If you're losing weight quickly, you're likely to lose fat-free mass, including muscle tissue, especially if you're not consuming enough protein to meet your body's needs.
• A lack of fibre can lead to constipation, while sudden changes to your diet may cause a range of other digestive issues.
• Weight regain can be common, especially if long-term weight maintenance strategies aren't put in place to support long-term healthy eating habits.

What's the alternative?

Another option is the low-calorie diet, where you consume 1,000-1,500 calories per day, which is substantially more than a VLCD. This diet involves replacing 1 or 2 meals with shakes or bars and can be used after a VLED or VLCD to slowly transition back to meals with whole foods.

The bottom line is, you don't have to follow a VLCD in order to lose weight and body fat. If you need a hand kickstarting your health and weight loss journey, we can help.

Juniper's Weight Reset Programme is designed to motivate and guide you on a long-term weight loss journey. It combines weight loss medications (Wegovy or Mounjaro) with the tools you need for lasting change. 

Once in the programme, you’ll also gain access to a members-only app to help track your progress, unlock exclusive health education, and get informed support when you need it.

Image credit: Mike Jones