1.b. Very Low-Calorie Diets

Four RCTs compared VLCDs to LCDs (436-439). The VLCDs provided about 400 to 500 kcal/day, whereas the LCDs provided approximately 1,000 to 1,500 kcal/day. During the active phase, VLCDs were given exclusively for 12 to 16 weeks and then were followed by LCDs for a total duration ranging from 24 weeks to 5 years. The participants in these trials were primarily women who were extremely obese. 

VLCDs either alone or, usually, combined with behavioral therapy, promoted weight loss of approximately 13 to 23 kg (28.7 to 50.7 lb) during the active phase of the VLCD intervention, compared to 9 to 13 kg (19.8 to 28.7 lb) with LCDs. In three of the four studies, VLCDs resulted in 4 to 12 kg (8.8 to 26.5 lb) greater weight loss than the LCDs at the end of the active phase (436-438). Over the medium term of 6 to 12 months, weight loss on the VLCDs ranged from 1.1 kg (2.4 lb) to as much as 10.4 kg (22.9 lb) greater than weight loss on LCDs. One study did not show a particular advantage of VLCD over LCD either during the active phase or at 24 weeks (439). After 1 year, there was no long-term advantage of VLCDs over LCDs (436, 437).