In January 2018, the plan featured in an episode of Channel 4's How To Lose Weight Well and was described by the show's Dr host Xand van Tulleken as 'punishing'.
'This is one of the most dreaded diets on the market,' he said. 'Not least because of it's daily 600-calorie limit.'
What is the Copenhagen Diet?The Copenhagen Diet, also known as the Royal Danish Hospital Diet, is a 13-day plan that claims to result in weight loss of up to 22 lbs.
A strict short-term diet, calories are severely restricted and meals consist of high-protein and low-fat foods.
Height, weight, age and lifestyle aside, a man typically needs around 2,500 daily calories to maintain his weight, according to the NHS. The figure sits around 2,000 for women.
Vitamin supplements are to be taken in place of missing nutrients and alcohol, cooking with oil and foods that don't feature on the Copenhagen Diet list are all banned.
Those deciding to give it a go must also drink at least two litres of water per day.
Concerning side effects that must be reported to a doctor include muscle cramps, dizziness and confusion.
If the Copenhagen Diet is successfully completed, individuals can repeat the process again after a two-year break. Those who decided to quit are advised not to try it again for six months.
How does the Copenhagen Diet work?While helping those who follow it drop a significant amount of weight in under two weeks, the Copenhagen Diet also alleges to speed up metabolism in the long term.
Although there are a few variations of the plan, an example of the first day is as follows:
Breakfast - coffee with a single cube of sugar
Lunch - 400g of cooked spinach served with two hard boiled eggs and a tomato
Dinner - 200g steak with a green salad, lemon juice and oil dressing
A slice of plain toast is added on the second day and lunch becomes 250g ham with one cup of low-fat yoghurt. Dinner is 200g of roast beef with the same accompaniment as the first day.
The plan continues in a similar fashion for the remainder of the 13 days, although meals do vary slightly. A different dinner, for example, may be a 250g bowl of assorted from with one boiled egg and carrot shavings.
Does the Copenhagen Diet work?While the plan may result in rapid weight loss due to the cutting of calories, Alix Woods - a nutritionist at Quest Nutra Pharma - would not recommend following the Copenhagen Diet.
'It is an unhealthy diet due to its very restricted calorie and nutrient allowance. It lacks nutrition, as there is an imbalance of food intake of proteins, carbohydrates and essential fats,' she explains.
'It may lead to malnutrition and most certainly energy problems as calorie intake is limited to 600 to 1000 calories per day, which is less than half the recommended calories for men and women.'
Alix goes on to raise her concerns about the meals the Copenhagen Diet consists of.
'It encourages only coffee with sugar - an anti nutrient - for breakfast. This may send stress hormone soaring, and increase circulating glucose, causing blood sugar spikes and energy dips,' she says.
'Other meals are laden with proteins from red meat which could potentially encourage an increase in 'bad' or LDL cholesterol and may lead to other cardiovascular complications.'
Alix concludes by pointing out another negative of the plan and explains how physical activity would be extremely tricky.
'With such a diet, water is lost and not fat and as soon as one eats normally, the weight is likely to resume,' she adds.
'Without sufficient nutrients, exercise in most cases is impossible and may lead to muscle wastage and may effect bone health and metabolism.
'This again, confirms that it is not a healthy way to diet, being so restricted and it would be best to be monitored by a practitioner should it be "advised".'