First things first, what is a crash diet?

While there’s no official medical definition of a crash diet, it’s a weight loss diet undertaken on an urgent, short-term basis to achieve very rapid, and significant, results. It may sound promising but crash diets can be more harmful than good and they definitely don’t encourage long-term habit change, meaning they rarely work. Sure, the weight may come off but the chances of putting that weight back on are pretty definite.

No diet plan is ever going to say it's a crash diet—marketing teams are far too clever for that, promoting it instead with vastly unrealistic promises and positive language. Other red flags to look out for are phrases such as ‘liquid diet’, ‘cleanse’, or ‘detox’ (our bodies don’t need help to get rid of a toxin, they’re armed with a liver and kidneys to do that for us!). 

Total diet replacement (TDR) is a nutritional tool to support weight loss that is often misunderstood to be a crash diet. While it does help the user lose a significant amount of weight quickly, TDR is different to most crash diets because it is an incredibly powerful, safe, method of achieving sustainable, long-term weight loss—and we’ve got the science to prove it.

So, what is TDR?

TDR is a form of low-calorie diet that delivers everything your body needs nutritionally while keeping daily calories to around 800. Often confused with meal replacements, TDR can be used in this function but it's important to note that meals labelled as ‘meal replacements’ are not nutritionally-complete—that is, they do not provide the level of nutrition your body needs to function healthily. TDR meals (labelled as ‘total diet replacement’ meals) on the other hand are subject to strict regulations to ensure they provide all the macro and micronutrients your body needs, which is why it's possible to live on TDR for an extended time without compromising your overall health and wellbeing. 

A low-calorie TDR helped people lose on average 6.6kg more weight

Churuangsuk et al., Diabetologia

TDR diets involve powdered meals—think porridges, soups, and shakes—that are typically around 200 calories in total. Four of these meals a day bring total daily calories to 800. Here at Habitual, our patients follow a TDR diet for 3 months before gradually reintroducing food over the following 3 months. It’s incredibly important to slowly transition back onto ‘real’ food after a period of TDR to help you safely maintain your weight loss, stay healthy, and rebuild your eating habits.

How does TDR work?

We’ll state the obvious first—living off 800 calories is of course going to help people lose weight. It’s a far cry from the recommended 2,500 and 2,000 calories for men and women, respectively.[1] So perhaps the question you’re really thinking is, ‘But surely I’ll be hungry?!’.

Well, that’s where the science comes in. One study determined that consuming food as liquid tricks the stomach into thinking it’s more full than it really is—blend your meal and you’ll feel fuller than if you ate it. In their research, scientists found that food and liquid separate in the stomach. If you drink water alongside your meal, the water would sit separately in your stomach and you would feel less full than if you had eaten something blended with the water. This is because the feeling of fullness is triggered by the size of your stomach. If water can be separated and extracted from your stomach quickly like if you drank water alongside your meal, your stomach would shrink in size more quickly—leaving you with a feeling of hunger.[2] Another concluded that losing weight through a combination of TDR and weekly support from a counsellor is more effective than attending a series of appointments with a nurse, highlighting the need for access to quality, regular support during weight loss journeys.[3]

One of the most surprising moments for people on TDR is when they realise that they don’t feel hungry. The first few days are certainly an adjustment period for your body and mind as they get used to living off fewer calories and the change in routine but after this, your body, incredibly, adapts. TDR also puts the body into a mild state of ketosis (not diabetic ketoacidosis!), which contributes to this feeling of fullness.

So, why do we think TDR is a crash diet?

There’s a common misconception that TDR is unacceptable, unsafe, and leads to rapid weight gain as a result of the speed of weight loss. But, scientific results are in fact showing the opposite. In one study, researchers found that the rate of weight loss doesn’t affect the speed of weight regain—if the weight is going to return, it will take the same amount of time regardless of how quickly it was lost in the first place.[4] Another was the first study to look into the effectiveness and safety of TDR in a large group of adults and found that participants on TDR lost an average of 11kg over the course of a year, while the group following routine care lost just 3kg.[3] The famous Diabetes Remission Clinical Trial (DiRECT) saw similar results, when participants lost an average of 10kg (and 24% of study participants lost 15kg+) over the course of a year involving a period of TDR, while a 2021 review of the best diet to lose weight if you have type 2 diabetes found that a low-calorie TDR helped people lose on average 6.6kg more weight.[5,6] At Habitual we can report that patients lose an average of 19kg by month 4. There’s no denying that TDR is a powerful method of weight loss and most importantly, it's safe. 

To protect against weight regain, behaviour change and gradual food reintroduction are essential. The latter is because the dramatic reduction of calories during TDR slows down your metabolism, meaning that eating food in the same way as before TDR would leave you susceptible to weight gain. But, the key to everything here is behaviour change. 

Losing weight through a combination of TDR and behavioural support is more effective than regular weight loss support

Astbury et al., BMJ

Every research paper we turn to is in agreement—TDR works best if used in conjunction with behaviour change. The leading DiRECT and DIADEM-I trials combined the two and so do we at Habitual.[5,7] The time on TDR is the perfect opportunity for a reset, giving your mind and body a break from thinking about food, cooking food, and planning what to eat. By using the time you free up to create new habits, learn about nutrition, grow your confidence, and start changing your relationship with food and exercise, you’ll be ready to build a brand new lifestyle for yourself when the TDR period finishes. The gradual reintroduction of food goes on to support this as you get into the habit of preparing and eating healthier dishes. It’s the behaviour change that keeps the incredible weight loss off once TDR finishes and having seen hundreds of patients go through it, we can confidently say that it works. 

Total diet replacement and type 2 diabetes

As we briefly mentioned earlier, the amount of weight that’s possible to lose as a result of TDR has been shown to reverse the disease process underlying type 2 diabetes, putting the condition into remission.[5] This is a life-changing discovery that could change the nature of type 2 diabetes care, improving patient health and saving the NHS vast amounts of money. Not only is TDR more successful in helping people lose weight than other treatments, its capacity to reverse type 2 diabetes reduces the number of people both needing medication and experiencing complications of the condition. In the UK, type 2 diabetes costs the NHS £10 billion a year largely because its complications like amputation, blindness, kidney failure, and stroke, cost a lot of money.[8]

Of course, not everyone with type 2 diabetes is overweight. Around 10% of people with type 2 diabetes are of a healthy weight. Following the astounding results from the DiRECT trial, the team are now exploring whether TDR can be used to reverse type 2 diabetes in people who don’t need (or shouldn’t!) to lose a substantial amount of weight. In the study, called ReTUNE, the team investigated whether people with type 2 diabetes who are of a healthy weight can enter remission following 2-week cycles of TDR. As they are of a healthy weight, 3 months of TDR wouldn’t be safe—they simply don’t need to use that much weight—but a short burst could be enough to reduce the amount of fat in the liver and pancreas (it’s this internal fat that affects natural blood sugar regulation). ReTUNE has only just finished but the early results look promising—from the first data collection, participants on the TDR programme lost weight and fat from their liver and pancreas, and two-thirds entered remission.[9]

Forget the fads

Quick fixes can be appealing when it comes to weight loss but it’s important to focus on your long-term health as well as your weight. The combination of methods such as TDR and behaviour change has now been repeatedly shown to support sustained weight loss and even reversal of conditions such as type 2 diabetes.

Related reading

TDR is so much more than a weight-loss method; it’s the first step to a better life. If you’d like to find out more about TDR and type 2 diabetes reversal, take a look at some of the following articles:

• A brief history of type 2 diabetes reversal
• ‍Is type 2 diabetes curable?‍
• What is total diet replacement and is it for me?‍
• Are low-calorie diet replacements safe?‍

Before starting a new weight loss plan, we always recommend speaking to your doctor or diabetes team first.