No single VLCD is definitively “the best” because the most effective program depends on your health goals, medical history, and how much support you need to keep the weight off afterward. What the research does show is that all major VLCD programs produce similar short-term results (roughly 4% to 13% more weight loss than standard counseling over 3 to 6 months) but diverge sharply in long-term maintenance, cost, and medical oversight. The real difference isn’t the meal replacement formula. It’s what happens after the active dieting phase ends.
What Counts as a VLCD
A very low-calorie diet provides 800 calories per day or fewer. Most programs land between 500 and 800 calories daily, with the calories coming primarily from protein (0.8 to 1.5 grams per kilogram of your ideal body weight) and small amounts of fat and carbohydrates. Carbs are typically kept under 50 grams a day, sometimes as low as 30 grams, which is low enough to push your body into ketosis, where it burns stored fat for fuel instead of glucose.
These diets almost always rely on commercial meal replacements (shakes, soups, bars) rather than regular food, because hitting the right protein targets on so few calories with whole foods is extremely difficult. The high protein ratio isn’t arbitrary. At 0.8 grams of protein per kilogram of body weight per day, your body can maintain near-maximal stimulation of muscle protein synthesis, which helps preserve lean mass while you’re losing fat. Below that threshold, muscle loss accelerates.
How the Major Programs Compare
The three most studied commercial VLCD programs are HMR (Health Management Resources), Medifast, and Optifast. A systematic review published in the Annals of Internal Medicine compared them head to head against standard dietary counseling, and the results were telling.
HMR showed the strongest numbers: 13.2% greater weight loss than counseling at 6 months. The program uses meal replacements plus fruits and vegetables, with structured coaching and a heavy emphasis on physical activity. It consistently outperformed the other two in clinical trials, though those trials were rated as having a high risk of bias, meaning the results should be interpreted with some caution.
Optifast, probably the most recognized name in medically supervised VLCDs, produced 4.2% to 9.2% greater weight loss than counseling at 4 to 5 months. It’s typically administered through hospital-based clinics with physician oversight, regular blood work, and group support sessions. The stronger medical infrastructure is a genuine advantage for people with obesity-related health conditions. However, the one trial that followed participants beyond 12 months found no statistically significant difference between Optifast and counseling.
Medifast achieved 5.6% greater weight loss than counseling at 4 months, but the difference was no longer statistically significant by 9 months. Medifast (now called Optavia in its coaching model) is the most consumer-accessible of the three, with products available without a prescription and support delivered through peer coaches rather than medical professionals.
The Long-Term Problem
This is where every VLCD struggles, and it’s the most important factor in choosing one. A follow-up study tracking VLCD participants for two years found that average weight regain was 69% of the weight lost. Out of 103 participants, only 13 kept off more than 90% of their lost weight. Ninety people regained more than 10% of it.
That pattern held across the commercial programs too. The Annals of Internal Medicine review noted that substantial short-term weight losses from VLCDs were consistently “attenuated after 6 months,” with differences between VLCD groups and counseling groups shrinking or disappearing entirely at the 9- to 12-month mark. The active restriction phase works. The transition back to regular eating is where most people lose their progress.
This means the best VLCD isn’t necessarily the one that drops weight fastest. It’s the one with the strongest transition and maintenance plan. Programs that include structured refeeding phases, where calories are gradually increased over weeks or months, and ongoing behavioral coaching tend to produce better long-term outcomes than programs that simply hand you meal replacements and send you on your way.
VLCDs for Type 2 Diabetes Remission
One area where VLCDs have shown genuinely impressive results is reversing type 2 diabetes. The UK’s National Health Service launched a large-scale “soups and shakes” program specifically for this purpose, using a total diet replacement approach of roughly 800 calories per day for 12 weeks, followed by a structured food reintroduction phase.
Early real-world data from the NHS program, published in The Lancet Diabetes & Endocrinology, found that 27% of participants with follow-up data achieved diabetes remission, with an average weight loss of 13.4% (about 14.8 kg, or roughly 33 pounds) at 12 months. That’s a meaningful result outside the controlled conditions of a clinical trial. If diabetes remission is your primary goal, a VLCD structured around this model, with a clear reintroduction protocol and medical monitoring, has the strongest evidence behind it.
Side Effects to Expect
Common side effects during the active phase include fatigue, headaches, dizziness, constipation, and hair thinning. Most of these resolve within the first two weeks as your body adapts to ketosis.
The more serious concern is gallstones. Rapid weight loss changes how your gallbladder processes bile, and reviews of VLCD studies have found that 10% to 25% of participants develop gallstones, with about one-third of those becoming symptomatic. A large matched cohort study found the risk of gallstones requiring hospital care was about three times higher with a VLCD than with a standard low-calorie diet (1,200 to 1,500 calories). The absolute risk is still relatively low, around 152 per 10,000 person-years, but it’s real enough to factor into your decision.
What Medical Monitoring Looks Like
Any VLCD under 800 calories per day should involve medical supervision. At UCLA’s weight management program, a typical monitoring schedule includes weekly physician visits for the first two weeks, then roughly twice-monthly visits with a physician or dietitian. Blood draws happen more frequently at the start and then settle to about every four weeks. Heart rhythm monitoring (EKG) and body composition testing occur at the initial visit, around week 9, and every two to three months after that.
This level of oversight matters because extreme calorie restriction can shift electrolyte levels in ways that affect heart rhythm, kidney function, and blood pressure. Programs that skip this monitoring, or that sell you meal replacements without requiring it, carry more risk. The calorie level is the same whether you’re on Optifast through a hospital clinic or ordering shakes online, but the safety infrastructure around it is not.
Choosing the Right Program for You
If you have a BMI over 30 and significant health conditions like type 2 diabetes, sleep apnea, or joint problems that would improve with rapid weight loss, a medically supervised program like Optifast or HMR through a hospital-based clinic gives you the strongest safety net. The medical monitoring catches problems early, and the structured transition phases help with long-term maintenance.
If you’re primarily looking for weight loss without complex medical issues, and you want something more affordable and accessible, Medifast/Optavia is easier to start but comes with weaker long-term data and less built-in medical oversight. You’d need to arrange your own blood work and physician check-ins.
Regardless of which program you choose, the evidence points to three features that separate successful VLCD experiences from unsuccessful ones: adequate protein intake (at least 0.8 grams per kilogram of your ideal body weight daily) to protect muscle mass, a structured multi-week refeeding phase rather than an abrupt return to normal eating, and some form of ongoing behavioral support that continues well beyond the active weight loss period. The shake you drink matters far less than what happens in the months after you stop drinking it.