Ideally, diets should be about smarter choices and finding a balance. But we don’t always choose the best path. We try to cut corners and try more drastic ways, ‘just to get rid of those first kilos and get things on a roll.’ This one, however, is not for everyone. A very low calorie diet is not a lifestyle tweak, but a serious medical intervention. So if you just want to drop a dress size before a vacation, don’t try this.
A very low calorie diet (VLCD) is a strict program for rapid weight loss. It can be used before surgeries, or in particular situations when it’s medically important to lose weight as soon as possible. Calories are drastically restricted (800 or lower), and it should only be used under medical supervision.
Who Is a Very Low Calorie Diet Actually For?
Your doctor may suggest a very low calorie diet in scenarios like:
- Preparing for bariatric or other major surgery
- Severe obesity with immediate health risks
- Conditions that would dramatically improve with fast weight loss—like poorly managed type 2 diabetes, obstructive sleep apnea, hypertriglyceridemia, or symptomatic peripheral edema
Or for people who have genuinely tried multiple approaches and haven’t been able to lose weight.
If you’re reading this out of curiosity or looking for a shortcut, this isn’t your diet. But if you’re in one of the situations above, keep reading—because there’s a lot to understand before starting.
What Can You Actually Eat?
You have two options in a very low calorie diet:
Commercial meal replacements: Protein shakes, bars, and liquid formulas specifically designed for VLCDs. These have all the vitamins, minerals, electrolytes, and fatty acids your body needs, even at extreme calorie restriction. But you won’t eat regular food on top of them—they replace everything.
Whole food approach: Very lean proteins (chicken, fish, tofu), non-starchy vegetables, all in strict portions. High protein, low carb.
If you want to focus on proteins, you may also want to read: Is the Carnivore Diet Safe for Weight Loss?
Either way, the goal is to get maximum nutrition from as few calories as possible.
Important!
Being overweight doesn’t mean you’re nutritionally topped up—many people are deficient in key vitamins and minerals even before they start. And a very low calorie diet can make that much worse fast if you’re not careful. That’s why lab work before and during is essential.
How Much Weight Can You Lose on a VLCD?
According to studies, you can expect rapid weight loss right from the start, usually 1.5 to 2.5 kg a week. In time, results are significant, especially for people with type 2 diabetes. They can find that glycemic control and insulin sensitivity can really improve even before they reach their goal weight.
But here’s the catch: some of that weight is muscle, not just fat. More on that below.
The Risks of a Very Low Calorie Diet
What are the disadvantages of VLCD?
You will lose muscle mass. When your body is severely under-fueled, it breaks down muscle for energy. Decent protein intake and some exercise (if possible) can help with that.
Your metabolism will slow down. If you follow a VLCD for too long, your body will start to adapt and burn fewer calories. You’ll plateau and find it even harder to return to normal eating.
Gallstones. Rapid weight loss is a known trigger. Another reason to do this only in close collaboration with your doctor.
Nutritional deficiencies. Anemia, bone density loss over time, and electrolyte imbalances. All possible without proper monitoring.
Yo-yo effect. Return to previous habits without a proper transition plan, and the weight comes back, or you can even gain some extra.
The Non-Negotiable Part: Medical Supervision
This needs to be underlined until it’s clear how crucial it is.
A VLCD without a doctor is a bad idea. Not ‘probably fine if you’re careful’—a genuinely bad idea. You need baseline bloodwork, ongoing monitoring, and a professional who can adjust the plan as your body changes.
Think of the very low calorie diet as a tool, and like any powerful tool, it needs to be handled properly.
For a more balanced diet, take a look at the flexitarian diet.
Bottom Line
You can get remarkable results with a very low calorie diet in the right circumstances. For someone facing surgery, managing a serious metabolic condition, or dealing with obesity that hasn’t responded to anything else, it can be genuinely life-changing.
Proper supplementation and medical supervision are a must. Plus, extreme low calorie meals can come with quite a few side effects.
Dramatic? Yes. Effective? Also, yes—when used correctly, by the right people, with the right support.
FAQ
How much weight can you lose in a week on a VLCD?
Most people lose 1.5 to 2.5 kg per week during the initial phase of a very low calorie diet. Results vary based on starting weight, how strict calorie restriction is, and whether they also add light exercise. People with more body fat tend to lose more weight in the beginning (as it happens with most diets).
How long can you stay on a very low calorie diet?
Most medical guidelines recommend VLCDs for no longer than 12–16 weeks without a break, and only under medical supervision. Longer use means a significantly higher risk of muscle loss and metabolic adaptation. Some structured programs alternate periodic VLCDs with less restrictive phases.
Which VLCD diet is best?
There’s no universal “best”—it depends on your health status, lifestyle, and what your doctor decides. Commercially formulated meal replacement programs (like Optifast or Cambridge) are popular because they’re nutritionally complete and simple. Whole food VLCDs need more careful planning to hit nutritional targets.
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