Shoulder pads, sequins, and a seven-day diet plan that asks you to eat eight bananas in one day - the 80s certainly gifted us with some weird and wonderful trends. And now (along with the shoulder pads and sequins), that diet plan is making a comeback.

Supposedly the brainchild of General Motors (GM), the GM diet plan was developed to help their employees lose weight - although the automotive company has never actually confirmed the connection. A quick Google search reveals pages of fans of the diet, who rave about their 11lb weight loss after just seven days.

So what's behind this 'miracle' diet plan - and is it actually good for you?

In short, the GM diet is an extremely strict seven-day plan that suggests you drink 12-15 glasses of water a day while cutting out alcohol, tea and coffee; and restrict your calorific intake from food. The breakdown of each day looks like this:

Day One: You eat only fruit (but not bananas)

Day Two: You eat only vegetables and start your day with a large baked potato

Day Three: You can eat both fruit and vegetables but no bananas or potatoes

Day Four: Up to eight bananas, three glasses of milk, and a 'GM wonder soup' that consists of cabbage, onion and other green vegetables

Day Five: Two portions of lean protein (beef, chicken or fish) and six tomatoes

Day Six: Unlimited lean protein and vegetables

Day Seven: Unlimited fruit, vegetables and brown rice - but no protein

"This is a low calorie diet plan that works by giving you a negative energy balance," says Dr Frankie Phillips, registered dietitian and nutritionist and spokesperson for the British Dietetic Association. By restricting those calories, especially in the first few days, the body is forced into fat burning mode; while the high water intake also offers detoxifying benefits.

The restrictive nature of the GM plan means dieters miss out on vital food groups. On the first 'fruit only' day, for example, you're consuming a lot of naturally occurring sugars but your iron intake is low - which can account for a lack of energy. Eating just vegetables on the second day, you'll be missing out on soluble fats and omega 3, which are good for heart health.

"As it's only seven days, the lack in vitamins and minerals won't make a drastic difference," says Dr Phillips. "But there's a noticeable shortage of fibre over the week, so people may experience less movement when it comes to going to the toilet."

Blogger Morgan Hegarty, 22, says she felt lost six pounds on the GM diet. "Eating only vegetables for a whole day was by far the hardest," she says. "Waking up to carrots or a baked potato for breakfast in place of my normal porridge was hardly appetising." At the time, she was doing a mile-and-a-half walk to and from her work place each day. "Arriving at work, I felt exhausted. I really noticed a lack of energy. I often felt light headed in the afternoons which made it hard to focus at work and I didn't even attempt a work out."

Clearly, the GM diet has weight loss potential, but Dr Phillips warns that it might not be sustainable. "The rapid weight loss is partly down to the lack of carbohydrates, therefore a lack of glycogen and a loss of 'water weight', which quickly returns when you resume eating a normal diet."

Current guidelines by the Association of UK Dietitians tell us that gradual weight loss is the way to go. We've heard it before, of course: small changes in lifestyle over time result in sustainable weight loss. However, a 144 week-long study of 204 people within the same BMI range, published in the Lancet, stands to question this dietary advice. It found that the rate of weight loss did not affect the proportion of weight regained. Whether participants lost weight on a crash diet or a long-term diet plan, they still regained the same amount of weight over the same period.

If that's the case, why are we warned against crash diets such as the GM diet? It seems that it is actually the speed of weight loss and weight gain that can be harmful. "My biggest concern with losing weight so rapidly is the affect it has on someone's mental wellbeing," says Dr Frankie. "Crash diets like the GM often leave people feeling demoralised when they start to regain weight so quickly." A review published by Yale University's Department of Psychology acknowledges the correlation between yo-yo dieting (or weight cycling) and mental health issues. "Weight cycling appears linked to increased psychopathology, lower life satisfaction, more disturbed eating in general and perhaps increased risk for binge eating," it says.

But Morgan's experience on the GM diet was a good one. She says she actually picked up healthier habits following the diet. "I carried on eating fruit in the mornings and generally eating more vegetables." Impressed by the results, she's done the diet twice over the past year. "It really helps me kick-start a healthy regime," she says.

Despite dietitians and nutritionists criticising the lack of science behind the GM diet, its appeal among dieters is clearly still strong. If you are thinking of trying it, be wary of how much you exercise during the week because your energy levels will be low. Once the weeklong diet plan is over, re-introduce carbohydrates into your diet slowly.

(China Daily 08/12/2017 page23)