Diet

The 5:2 diet is based on a principle known as intermittent fasting (IF) – where you eat normally five days a week and fast on the other two days. On top of losing weight, fans claim the 5:2 diet can improve lifespan, brain function and protect against conditions such as dementia and Alzheimer’s. However, evidence on the effectiveness of the 5:2 diet is limited when compared to other types of weight loss techniques.

One 2010 study found that women placed on a 5:2 diet achieved similar levels of weight loss as women on a calorie-controlled diet and were also less likely to develop chronic diseases such as type 2 diabetes. A 2012 study suggested that the 5:2 model may help lower the risk of certain obesity-related cancers, such as breast cancer. If you are considering it then you should first talk to your GP to see if it is suitable for you. Not everyone can safely fast.

Many of the diets listed here are quick fixes and may not be sustainable or healthy in the long term. They could make your weight more likely to fluctuate or ‘yo-yo’.

Find out how to lose weight the healthy way with our 12-week weight loss plan.

Pros:

Sticking to a regimen for two days a week is more achievable than seven days so you are more likely to persevere with this way of eating and successfully lose weight. Two days per week on a restricted diet can lead to greater reductions in body fat, insulin resistance and other chronic diseases.

Cons:

The non-restricted days do not mean unlimited feasting. While you don’t need to be as strict about your calorie consumption, you still need to make healthy choices and be physically active. Skipping meals could make you feel dizzy, irritable, give you headaches and make it hard to concentrate, which can affect work and other daily tasks. Other reported side effects are difficulties sleeping and daytime sleepiness, bad breath and dehydration.

BDA verdict:

The 5:2 is a simple way to reduce calorie intake. There are lots of versions of this diet, with some less safe than others. Many studies on intermittent fasting are short-term, involve small numbers of subjects, or are animal-based. If you choose to follow it, choose an evidence-based plan based on healthy, balanced eating and written by a dietitian like the "2-Day Diet". It’s vital for your health to avoid nutritional deficiencies, dehydration and overeating on non-fast days. Never attempt to delay or skip meals if you are pregnant, have had, or are prone to, eating disorders or diabetes.

 Dukan diet

The Dukan diet is a low-carbohydrate (carb), high-protein diet. There’s no limit to how much you can eat during the plan’s four phases, providing you stick to the rules of the plan. During phase one, you’re on a strict lean protein diet. This is based on a list of 72 reasonably low-fat protein-rich foods, such as chicken, turkey, eggs, fish and fat-free dairy. This is for an average of five days to achieve quick weight loss. Carbs are off limits except for a small amount of oat bran. Unlike the Atkins diet, Dukan’s phase one bans vegetables and seriously restricts fat. The next three phases of the plan see the gradual introduction of some fruit, veg and carbs and eventually all foods. The aim is gradual weight loss of up to 2lb a week and to promote long-term weight management. There’s no time limit to the final phase, which involves having a protein-only day once a week and taking regular exercise.

Pros:

You can lose weight very quickly, which can be motivating. It’s a very strict and prescriptive diet and some people like that. It’s easy to follow. You don’t need to weigh food or count calories. Apart from keeping to low-fat, low-salt and high-protein foods, there’s no restriction on how much you can eat during your first two weeks.

Cons:

At the start of the diet you may experience side effects such as bad breath, a dry mouth, tiredness, dizziness, insomnia and nausea from cutting out carbs. The lack of wholegrains, fruit and veg in the early stages of the diet could cause problems such as constipation.

BDA verdict:

Rapid weight loss can be motivating but it is unsustainable and unhealthy. The Dukan diet isn’t nutritionally balanced, which is acknowledged by the fact that you need a vitamin supplement and a fibre top-up in the form of oat bran. There’s a danger this type of diet could increase your risk of long-term health problems if you don’t stick to the rules. The diet lacks variety in the initial phases so there’s a risk you’ll get bored quickly and give up.