A very low energy diet (VLEDs) has a very low total daily energy intake target. On this diet, people are guided to consume 2500–4000kJ per day. VLEDs lead to rapid weight loss which is why it is recommended that they only be used under medical supervision by a doctor and/or dietitian.
For more info see this: https://theconversation.com/health-check-whats-the-best-diet-for-weight-loss-21557.