There is no shortage of quick-fix weight-loss approaches these days. Even at this time of year you can flick through any glossy magazine and find celebrity-endorsed diets to help you shed that tummy fat for Christmas.

As much as we want to believe that losing weight is easy, it’s not. It doesn’t happen overnight and it requires planning, effort and motivation. Above all, it requires you to know yourself, and the reasons you became overweight in the first place.

The only way to lose weight effectively, and keep it off, is to make longstanding changes and build durable habits. We know this implicitly. Making lasting improvements to our eating and exercise habits, getting adequate sleep and managing stress are critical. Crafting and implementing these changes isn’t a quick process, and if you have substantial weight to lose, a structured six-month approach is necessary.

That’s why certain diets are so attractive: they work in the short term. However, the more extreme the diet, the less likely you are to stick to it.

A study carried out at Tufts Medical Center, in New England, found that four different approaches – the Atkins low-carb diet, the Ornish low-fat diet, the Weight Watchers method and the Zone diet – all produced a similar weight loss over 12 months, but few dieters could stick to their programmes for long enough to make a permanent change. Seventy-five per cent of dieters lost about 5 per cent of their weight over the year. They were successful at reducing their calories initially, but they slunk back up with time.

Out of the four tested, the Atkins diet produced the best weight-loss result over the 12 months, but it had the lowest adherence. People just could not stick with it in the long term.

In 2008 a randomised controlled trial designed to investigate the nutritional adequacy of four commercial weight-loss approaches – the Slim-Fast plan, the Weight Watchers Pure Points programme, Dr Atkins’s New Diet Revolution, and Rosemary Conley’s Eat Yourself Slim diet – found that there was no significant difference between the diets in terms of weight loss. The average weight loss was between 3.7kg and 5.2kg over eight weeks.

While the diets were found to be nutritionally adequate, the recommendation was that people with specific imbalances, such as a low folate or iron level, would benefit from seeing a qualified dietitian or medical professional for dietary guidance.

Low-carb, low-fat or Mediterranean?

A study by Direct compared a low-carbohydrate diet, a low-fat diet and a Mediterranean-style diet. It found that after two years, weight loss and maintenance was better on the low-carb and Mediterranean-style diets compared with the low-fat diets.

The low-carb diet had a more favourable effect on blood lipids, such as cholesterol and triglycerides, and the Mediterranean- style diet had better glycaemic control. However, researchers cautioned that comparing the effectiveness and safety of these weight-loss diets was an exercise limited by short follow-ups and high dropout rates.

Studies have raised concerns about ketosis and muscle-wasting brought on by eating a very low-carb diet. Low blood sugar and low glycogen stores cause the body to break down protein in the muscle for energy. Ketosis has been shown to upset the electrolyte balance in the body and there are concerns that this may cause cardiac arrhythmia. Young athletes thinking about ways to lose weight should seek professional help from a sports dietitian.

Intermittent fasting is the latest popular diet idea. The 5:2 diet involves eating normally for five days and then severely reducing calorie intake on two days of the week. In 2010, Michelle Harvie’s study found that women on the 5:2 diet achieved similar weight loss to those on a more standard calorie-controlled diet.

An additional paper by Harvie, published in Proceedings of the Nutrition Society 2012, suggested that a 5:2 diet may help lower the risk of certain obesity-related cancers, but concluded that further studies were required. Anyone wishing to try the 5:2 approach should make sure the version they follow is evidence-based. It should be avoided by people who are pregnant or have diabetes or a tendency to disordered eating.

There are so many different books and versions of the diet out there that it is difficult to comment on its safety in general. And please note that there is certainly no evidence that you can eat and drink anything you like for five days, restrict for two days and still lose weight, as some books suggest.

Essential daily nutrition

To lose weight and maintain health, we need a certain amount of essential nutrients on a daily basis. Fad diets, such as the cabbage-soup diet or the maple-syrup diet, are usually lacking in some nutrients as they tend to cut out entire food groups.

Being desperate to lose weight can lead people to do wretched things, such as starving and depriving their bodies of essential nutrition. Thankfully, diets like these aren’t sustainable, and the disruption they cause to an adequate supply of vitamins and minerals is short term.

Other symptoms that frequently arise from fad diets include fatigue and low energy levels, dehydration and headaches, constipation, irritability and mood swings.

The crazier fad diets focus more on inches and pounds than on improving overall health and fitness levels. The bottom line is that while fad diets may take the weight off, they are hard to adhere to and don’t teach people how to keep it off in the long term.

Repeated weight fluctuations have been linked to an increased risk of heart disease, secondary diabetes and gall-bladder disease. Yo-yo dieting may not slow your metabolism permanently, as we once thought, but it’s bad for your psychological health.

Every time you regain weight, you lower your confidence and self-esteem. If you have a significant amount of weight to lose, find a qualified coach, a personal trainer or a dietitian-led, evidence-based weight-loss programme. That way, you can reach a more comfortable weight for the long term and still enjoy your food.

Paula Mee works at Medfit Proactive Healthcare and is a member of the Irish Nutrition and Dietetic Institute. pmee@medfit.ie; Tweet @paula_mee

Low-fad dieting: myths and realities of weight loss

Rate of weight loss: Healthy plans aim for a loss of one or two lbs a week.

Quantities and limitations: Ditch diets that allow unlimited quantities of any food, such as grapefruit and cabbage soup. It’s boring to eat the same thing over and over, and it’s hard to stick with monotonous plans. Avoid any diet that eliminates or severely restricts entire food groups, such as carbohydrates. Even if you take a multivitamin, you’ll still miss some critical nutrients.

Food combinations: There is no evidence that combining certain foods or eating foods at specific times of the day will help with weight loss. Eating the “wrong” combinations of food doesn’t cause them to turn to fat immediately or to produce toxins in your intestines, as some plans claim.

Rigid menus: Limiting food choices or following rigid meal plans can be an overwhelming task. With any new diet, always ask yourself: "Can I eat this way for the rest of my life?" If the answer is no, the plan is not for you.

Exercise: Regular physical activity is essential for good health and healthy weight management. The key to success is to find physical activities that you enjoy and then to aim for 30-60 minutes of activity on most days of the week.

Source: American Academy of Nutrition and Dietetics