Long before there was the Atkins, the Dukan or the Paleo, there was one diet favoured by anyone looking to lose weight fast: the liquid diet.

The 20th century had its fill of them: the cabbage soup diet (which promised a sulphurous detox and fewer than 100 calories per bowl), the apple cider vinegar diet (when sipped before every meal, it nixed your appetite and stripped your tooth enamel)... even the milk diet, whereby followers downed four pints of semi-skimmed a day.

But then in 1988, chat show host Oprah Winfrey announced she had lost 67 pounds by drinking a particular ‘meal-replacement’ shake and celebrated by dragging a wagon full of that much fat across her studio set.

Now, ultra-low calorie soups and shakes have been pulled out of the diet archives and are being touted as an effective way to rapidly lose weight and even reverse type 2 diabetes, which studies show can increase the severity of a bout of coronavirus.

Research has emerged that shows that half of type 2 diabetics placed on a 12-week, 800-calorie diet were in remission a year later.

The rapid weight loss from liquid diets can have a powerful psychological effect on slimmers, says Kim Pearson, a London-based nutritionist. "Rapid weight loss is 100 per cent good for motivation," she says. She recommends meal replacement products, which deliver between 800 and 1,000 calories a day, and can lead to weight loss of around six kilos a month.

Among her patients is Martina Coogan, 49, who shed 53kg using meal replacement products over two years. She turned to Pearson for support after her cousin, just six weeks her senior, died from a heart attack. "Kim saved my life – literally," she says.

Pearson believes that a few months away from solid food can be effective because it helps to ‘reset’ behaviour patterns and stop clients constantly thinking about eating. "It’s kind of like food rehab," she says.

Debbie Kersey, 58, who lost 15kg using such shakes, recommended by her doctor as a treatment for her type 2 diabetes, agrees. "It stops you thinking about mealtimes," she says.

In one popular low-calorie diet plan, followers have up to two shakes a day and one light meal

Kersey has been dieting since she was 14, but says that only using the low-calorie shakes could prevent cravings for unhealthy food. She is not the only one – bizarrely, very-low calorie liquid diets can leave followers feeling less hungry than they would if they steadily cut down on portion sizes.

There is not yet solid evidence as to why that might be the case, but Prof Francesco Rubino, a consultant bariatric surgeon at London Bridge Hospital, has a theory: very-low calorie diets – as few as 800 calories per day – whether in soups, shakes or whole food, have a similar effect on the body as a gastric bypass. He explains that bariatric surgery is not just effective by reducing the size of the stomach, it also disrupts the body’s attempts to make you regain the weight by increasing hunger and decreasing fullness. This happens because the part of your gut responsible for creating these signals is bypassed surgically: it is no longer stimulated, and so stops telling your brain that you are hungry.

With very-low calorie liquid diets, Rubino believes the same thing is happening: the gut is not being constantly stimulated by food passing through, and in its resting state does not create feelings of hunger.

"It can happen either with surgery, or a diet that is so low in food intake that it brings that level of gut exposure to stimulus as close as possible to zero," he says.

However, he advises a note of caution, given there are not yet any studies into the potential long-term effects of these diets.

Dr Michael Mosley, the BBC broadcaster and creator of the 5:2 Diet, believes there might be another mechanism at work that explains how liquid diets reduce hunger: ketosis, or when the body uses fat, not sugar, for fuel. He thinks we have evolved to feel less hungry when this is happening: in times of food shortage, it would have been ‘fatal’ for ancient humans to be "too distracted by hunger", he says.

Dr Mosley himself sells an 800 calorie-a-day diet plan, where followers have up to two shakes a day and one light meal. He says that eating this way for eight to 10 weeks can be markedly effective for controlling diabetes – and much more so than conventional steady dieting.

This is because rapid dieting encourages the body to first use stores of fat in the liver and pancreas – crucial for type 2 diabetes patients where excess fat around the pancreas prevents it from working properly and producing insulin.

"Most of these patients have 30 to 35 per cent liver fat – they’re like foie gras geese," he says. "But in a few weeks [of rapid dieting], it drains out and reduced to 3 per cent."

He points to a 2018 study, which compared the effects of a meal replacement programme of around 800 calories a day to those using traditional NHS weight-loss programmes. Those who followed the low-calorie diet were 10.7kg lighter a year later, three times more than in the other group. They also managed much better reductions in their risk of diabetes, heart disease and stroke.

However, these diets need to be followed with caution. They are most suitable for those who have a lot to lose already, and would be a no-go for anyone with a history of eating disorders. Different brands of soups and shakes on the market also differ widely in the nutrition they provide. One with high levels of carbohydrates and low fat and protein might be a disaster for your metabolism, says Pearson.

"With a low-calorie, low-protein diet, you eat salad and fruit and don’t have enough protein, so the body will lose muscle," she says. Since muscle uses more energy at rest than other tissues in the body, this could mean that your metabolism will slow down and you will "put weight back on so fast". Instead, look for something with adequate protein and fats, as well as vitamins and minerals.

There may also be some short-term side effects, which could be frustrating, like headaches and constipation. Dr Mosley recommends that drinking plenty of water may help with these effects.

Then there is the great big elephant in the room: what happens when the 12-week programme is over and you have to go back to eating normal, solid food?

This stage has tripped up Kersey time and again. Over lockdown, she has put back 6kg from her initial 15kg weight loss. "It’s the maintaining that’s the hard bit," she says.

It seems clear that soups and shakes can be effective in the short term for rapid weight loss and treating diabetes. But the effects this might have on their body in the years to come are still unclear, says Rubino. "We simply don’t know what will happen over the long term."

IMPORTANT: Please consult a doctor before making any changes to your diet.

The Daily Telegraph

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