Research

Energy balance

Very low calorie diets (VLCDs) providing less than 800 kcal/day produce rapid, large weight losses (average 20 kg in 12 weeks) in moderately to severely obese adults, significantly outperforming conventional behavioral or pharmacological treatments.

If you have severe obesity, a medically supervised VLCD (under 800 calories/day) is the most effective non-surgical way to lose weight quickly, averaging 20kg in 3 months. It is not safe to do this alone; you need medical monitoring, high-quality protein, and supplements to prevent heart and muscle damage. The main challenge is keeping the weight off after you stop.

ModerateSupportsMEDIUM confidence
Very low calorie diets used to treat moderate and severe obesity produce average weight losses of 20 kg in 12 weeks... Treatment of over 10,000 persons has shown that very low calorie diets produce large weight losses, the size of which is directly proportional to the duration of treatment.
Thomas A. Wadden et al. · Annals of Internal Medicine · 1983

Why this rating

Based on a review of multiple observational and uncontrolled studies (n>10,000), but lacking randomized controlled trials (RCTs) comparing VLCD to other diets directly in this review.

Source

Very Low Calorie Diets: Their Efficacy, Safety, and Future

Thomas A. Wadden et al. · Annals of Internal Medicine · 1983

DOI 10.7326/0003-4819-99-5-675

narrative_review · n=10000Cited 264×
Read the paper
DOI resolved against Crossref · corpus check 2026-06-10

This is one finding among thousands. Every one is graded and traced to its source, so you can see what the evidence actually supports. Browse the research →