If you've ever tried to lose weight, you've probably heard that crash dieting isn't the best way to go about it. Although you may lose lots of weight initially, you won't be able to keep the weight off and may even end up being heavier than you were before.
But our latest research suggests that this isn't always the case.
Most people are aware that being overweight is bad for their health, so it's not surprising that about half of the UK population is trying to lose weight at any given time.
But many people struggle to stick to traditional diets long enough to achieve results.
Some people opt for a quicker, more drastic solution: crash dieting. These diets, otherwise known as total diet replacement (TDR) programmes, involve drastically reducing calorie intake to between 800-1,200 calories per day. (The usual calorie intake for a woman is 2,000 calories, and for a man it's 2,500 calories.)
People on these diets consume nothing but specially formulated soups, shakes and bars for up to 12 weeks.
Although lots of retailers sell these TDR products, they are more effective when combined with support and encouragement from a dietitian or trained counsellor. This professional support helps dieters develop the skills to stick with the programme and keep the weight off once the programme is complete.
However, in the UK, GPs don't tend to refer people who are looking to lose weight to these programmes. This is because NICE, the agency that evaluates treatments for the NHS, doesn't recommend TDR programmes, perhaps because there wasn't enough evidence to support TDR when NICE published their guidance.
But recent studies suggest that it may be time for NICE to reevaluate the evidence.
Time to reevaluate crash diets
For our study, which is published in the BMJ, we recruited 278 obese patients. Half were randomly assigned to a 12-week TDR programme, while the other half were assigned to see the practice nurse for advice on how to lose weight ("usual care").
After one year, those assigned to receive the TDR programme lost an average of 11 kilograms, while those in the usual care group lost an average of 3kg.
Using a tool that helps GPs estimate a patient's risk of having a heart attack or stroke in the next ten years, the people in the TDR group had significantly reduced their risk score.
The TDR group also had significantly greater improvements in blood glucose control than the usual care group. Perhaps most important of all, participants in the TDR group reported bigger increases in quality of life than people in the usual care group.
More people in the TDR group reported side effects, but the number of more serious side effects was similar across groups. Side effects that were more common in the TDR group than in the usual care group included constipation, headache, fatigue and dizziness.
This new evidence suggests that TDR is a safe and effective way to lose a large amount of weight.
For now, though, TDR programmes are not available on the NHS. Those interested in losing weight using TDR have to pay for it themselves, which means that many people who could benefit from this treatment may be unable to access it.