Very Low-Calorie Diets (VLCDs): What You Need to Know
Jul 18, 2025 • 9 min read
Published on July 18, 2025 | Update on July 18, 2025
July 18, 2025
MS, Registered Dietitian, Former President of CT Academy of Nutrition & Dietetics
Table of Contents
Balancing a busy career, family life, and social commitments can make healthy eating feel nearly impossible. If you’ve considered very low-calorie diets (VLCDs) for rapid weight loss, you’re not alone. Many people turn to VLCD diet plans when other strategies fail or when their weight becomes a health concern.
At first glance, the results appear promising, with the average weight loss on VLCDs ranging from 3 to 5 pounds per week (2.27 kg). This seems especially impressive to those who live with obesity (BMI ≥30) and want to lose a significant amount of weight. However, as with any medical intervention, there’s more to it than just dropping pounds: VLCDs come with specific benefits and critical safety considerations.
Before making hasty decisions based on impressive-sounding numbers, it is worth examining what very low-calorie diets are, how to plan for them, and when it is best to avoid these diet plans.
A very low-calorie diet is defined as a dietary regimen providing 800 calories or fewer per day, significantly less than most people’s daily energy needs. This differs from standard low-calorie diets, which typically recommend 1000 to 1500 calories per day. Very low-calorie diet plans are formulated to be nutritionally complete and are administered under the supervision of a medical professional.
As a result, VLCD diet plans create large calorie deficits, forcing the body to use stored fat for energy. This can result in rapid weight loss—but that reduced intake also places stress on your body and requires close monitoring.
VLCDs have evolved significantly since the 1970s. Back then, poorly formulated “liquid protein” very low-calorie diets were linked to over 60 deaths as a result of fluid and electrolyte deficiencies as well as poor medical oversight. Today, thanks to nutrition science and medical support, VLCDs are much safer and more effective.
However, it is always advisable to consult a healthcare professional to determine the best plan for you.
As with many dietary patterns, very low-calorie diet plans can be approached in different ways. There are two general types of VLCDs commonly used today:
This approach relies on meal replacement products, bars. These diets are regulated for safety and nutritional adequacy in many countries, such as Canada and Europe.
When on a PSMF, the goal is to lose fat but maintain lean muscle tissue. As such, the dietary intake emphasizes high protein intake (70-100 grams per day) while reducing carbs (0-80 grams) and fat (15 grams)—an approach supported by research.
This VLCD focuses on high-protein, low-calorie foods, healthy fats, and vitamins and minerals to balance your nutritional intake while using calorie counting to ensure you hit your macros.
Due to its restrictive nature, many people view very low-calorie diets as simply another fad or crash diet. There are, however, two crucial differences: medical supervision and nutritional completeness.
Based on current scientific research, medically supervised VLCDs involve regulated meal replacements that are considered nutritionally complete meals. In this case, you are consuming a low-calorie diet that provides all the essential nutrients.
In contrast, fad diets like the ABC diet are low in calories but often lack a sturdy scientific basis. They are also often nutritionally unbalanced and riskier due to their lack of monitoring by healthcare professionals.
Given the aforementioned information, many people pause and ask themselves: Is a VLCD the right way to go? Let’s take a closer look at who might benefit from a VLCD.
Typically, very low-calorie diet plans are recommended for adults with a BMI ≥30 (obesity) who also deal with certain health conditions exacerbated by this weight, such as:
Very low-calorie diets may be recommended for weight loss before a surgery (e.g., before bariatric or joint replacement surgery) or for people who have failed multiple conventional or less restrictive diet attempts.
Even if you meet the criteria, it’s still essential to consult your physician before starting a low-calorie diet or any other drastic dietary regimen.
While very low-calorie diets can benefit some people for short-term success, they are not suitable for everyone. If any of the following contraindications apply to you, you should avoid a VLCD:
Before starting a VLCD diet plan, you should go through a comprehensive medical evaluation, including:
These assessments are useful not only when creating an effective diet plan but also offer a solid framework for a safe and tailored attempt at the VLCD.
When it comes to short-term success, research consistently shows that very low-calorie diets produce significant weight loss, typically 14-20 kg (31-44 lbs) in 11-14 weeks.
Beyond weight loss, very low-calorie diet plans can improve several medical conditions:
Some people even experience benefits to their mental health, such as improvements in depression scores, as very low-calorie diets help reset their eating habits.
Most drastic dietary changes come with a series of side effects, especially in the beginning. However, the significantly low calorie intake on VLCDs opens the door for further potential risks. This makes regular check-ins with your physician essential, especially if you experience any of the following symptoms.
During the initial two to four weeks of a very low-calorie diet, it’s common for people to notice certain side effects, such as:
Some people even report initial nausea or bad breath. Women might struggle with temporary hair thinning and menstrual irregularities. The good news? Most of these symptoms are short-lived as your body eventually adjusts.
Apart from short-term side effects, VLCDs can also lead to serious medical issues:
As with any new diet, the potential challenges aren’t just physical but can also be psychological. Adopting a strict diet can lead to social isolation, as you may feel unable to participate in food-related gatherings.
Additionally, mood changes such as irritability may occur if nutrient needs are not met, and there is an increased risk of binge-eating when you return to normal eating. These potential pitfalls make mental support equally as important as routine physical checks.
Despite the strong initial success on a VLCD, significant weight regain is common. Studies show that 25-30% of the initial weight loss is regained within a year, with even more unwanted weight gain accumulating over time.
So, what is the key to long-term success? Besides establishing a healthy relationship with food, you’ll typically see more long-lasting success when you build sustainable habits. This means lifestyle changes must be realistic and achievable on a daily basis, and there needs to be access to ongoing support when transitioning off a VLCD.
A properly executed VLCD is more like a tool, not a quick fix. As a result, proper medical supervision is needed to make a very low-calorie diet as safe as possible.
A trained doctor or dietitian can help monitor your progress and catch any potential health issues early on. This professional guidance makes a VLCD effective and reduces the risk of complications.
A qualified healthcare provider will protect both your physical and mental health and closely monitor you on your VLCD. Here are some of the oversight they can provide:
Before settling on a healthcare provider, make sure they are qualified in obesity medicine or nutrition and that your chosen program is transparent and evidence-based. Legitimate medical weight loss programs differ from commercial schemes in that they prioritize your safety and tailor the diet to your specific needs.
Apart from the medical professionals themselves, you should also consider the framework of your VLCD. Here are some key facts to keep in mind:
Very low-calorie diets can lead to rapid and significant weight loss when medically supervised. However, like any intervention, they require proper implementation and realistic expectations. VLCDs are not suitable for everyone and carry real risks, especially for people with a history of eating disorders or pre-existing medical conditions such as heart disease.
The decision to go on a very low-calorie diet should always be made with the guidance of qualified healthcare providers who can ensure both safety and effectiveness. If you want your VLCD to work, you have to go through a comprehensive medical evaluation first, ensure ongoing supervision, and make a structured transition to long-term lifestyle changes.
Most importantly, you should never attempt VLCD diet plans without professional medical oversight. To sustain weight loss, you need to develop appropriate post-VLCD habits and receive the right support for the best long-term outcome.
This article is intended for general informational purposes only and does not address individual circumstances. It is not a substitute for professional advice or help and should not be relied on to make decisions of any kind. Any action you take upon the information presented in this article is strictly at your own risk and responsibility!
