The market for diet plans and weight loss solutions is a highly populated one.

And this is perhaps an unsurprising fact when you consider just how much of the UK population is overweight or obese.

A 2013 study by the Institute for Health Metrics and Evaluation (IHME) found that nearly two thirds of Britons had a BMI of 25 or above.

Consequently, diet plans are a big industry here, and have been since the 1980s. Every two to three years, a newer, better diet will seemingly appear from nowhere and take the headlines by storm, occasionally with the backing of celebrity endorsement.

For the consumer trying to find the most sustainable and healthy way to lose a few pounds, it can be difficult to know which plan will live up to its promises and work, and which might not suit them at all.

A programme of weight loss should always be undertaken with caution, and it’s always advisable to speak to a doctor before embarking on any diet or fitness plan which requires significant change.

Every individual is different; not just in terms of physical makeup and metabolism, but also in terms of attitude, willpower and motivation.

With this in mind, we thought it might be useful to compare ten of the most popular diet plans out there, and weigh up the advantages and disadvantages of each.

  1. Atkins diet
  2. Paleo diet
  3. 5:2 diet
  4. WeightWatchers diet
  5. Rosemary Conley diet
  6. Cambridge diet
  7. SlimFast diet
  8. South Beach diet
  9. Dukan diet
  10. Slimming World diet

Atkins diet

The Atkins diet was developed by Dr Robert Atkins in the 1960s and explained in his 1972 book, Dr Atkins’ Diet Revolution. It is perhaps one of the most famous and hotly debated low carbohydrate diets in history.

What does it involve?

Those following the Atkins plan go through four ‘phases’.

During phase one (or the ‘induction’ phase) the following rules must be observed:

  • A limit of 20g in ‘net carbs’ daily; sources of which are specified in the plan.
  • Protein can be sourced from red or white meat, fish, eggs and cheese.
  • Full-fat dairy such as butter, margarine or cream is permitted.
  • No carbs such as pasta, grains, bread and starchy vegetables including potatoes.
  • No nuts, seeds, legumes or pulses.
  • No caffeine or alcohol.

This phase is adhered to for a minimum of two weeks. Once you’ve reached a weight which is within a stone of your target, you can move on to phase two.

Also referred to as the ‘balancing’ phase, from the second phase you can begin to reintroduce more low carb fruit and vegetables into your diet, as well as grains and alcoholic drinks which are also low in carbohydrates. Net carb intake is increased by five grams per day until 50 grams is reached.

Phase three involves reintroducing yet more carbohydrates, again gradually each day, until daily net carb consumption reaches 80 grams. The final or ‘maintenance’ phase follows this pattern of slight daily increases, until you hit a daily net carb total of 100 grams. The idea is that your weight will stabilise at this level of carb intake.

Originally, the Atkins diet was not significantly discriminatory about the types of protein and fats which were suitable for consumption. The plan has since been revised, now emphasising the importance of choosing healthy fats and making nutritional choices.


  • The Atkins diet plan is a simple one to grasp the basic premise of.
  • Followers are not required to go to meetings.
  • Useful for those looking for quick results, and the consequent motivational boost.


  • Increasing protein intake can make food shopping more expensive.
  • For those who don’t manage to eat enough protein during the early phases of the diet, the body will burn muscle in order to get the energy it needs. This may have the effect of lowering metabolism and making weight loss more difficult.
  • Cutting out whole grains and dairy will inevitably cause a drop in calcium, potassium and fibre levels. These may need to be sourced from supplements instead.
  • Less carbs may increase the likelihood of headaches and irritability, and cause the body to produce ketones. This substance is an acid which may cause the breath to smell differently.

In summary

This plan is somewhat contradictory to more general health advice, which says that red and processed meat should only be consumed in moderation.

What’s more, results from studies comparing low fat and low carb diets are mixed. One study found that while carb intake reduction can help to lower overall weight (including fat and muscle), reducing fat intake is better for lowering fat.

Nevertheless, the Atkins diet may hold appeal for those looking to get quick results.

Paleo diet

The Paleolithic diet, also known as the caveman diet, is based on the premise of pre-agricultural ‘hunter-gatherer’ foods. It features only those items which could be ‘caught’ or naturally gathered by paleolithic humans.

What does it involve?

The reliance on natural foods means the exclusion of:

  • Processed meats
  • Wheat and dairy
  • Refined sugar
  • Grain-based food

And the inclusion of:

  • Lean meat
  • Fish
  • Fruit and vegetables
  • Nuts and seeds
  • Eggs

This naturally leads towards a diet which is high in protein and low in carbohydrates.


  • The omission of processed foods means little in the way of calorie-dense meals, and more in the way of nutritious fruit and vegetables.
  • Basic premise is one which is simple to follow, and does not require calorie budgeting.
  • 80/20 options (where you adhere to the rules 80 percent of the time) allow some flexibility.


  • Dependent on high levels of meat consumption, and not suitable for vegetarians.
  • Cuts out food groups such as dairy and grain, crucial aspects of a varied and balanced diet.
  • The diet is not based on hard evidence (there are obviously no accurate records of what paleolithic man used to eat) and more research is needed to determine its benefits.

In summary

The Paleo diet omits certain food groups that are essential, and might induce vitamin deficiencies as a result.

However, an adapted version of the Paleo diet which does not exclude dairy and grain may have significant nutritional value.

Those looking to lose weight through a variation of the Paleolithic diet should also make sure they’re getting enough exercise.

5:2 diet

Modelled on the concept of intermittent fasting, the 5:2 or the Fast Diet is one of the most popular plans of recent years. It gained significant attention after being featured on BBC documentary Horizon in 2012.

What does it involve?

The person following the plan has five days a week of eating ‘normally’ and two days of ‘fasting’, but thankfully in this scenario fasting doesn’t mean not eating at all. On each of these two days, which should be observed non-consecutively, women are allowed no more than 500 calories and men 600.

This might be:

  • A 300-calorie breakfast of two scrambled eggs with ham.
  • And another meal later in the day of grilled fish and vegetables, again amounting to no more than 300 calories.


  • Dieting for two days a week instead of seven is an easier task.
  • The plan is effective at reducing calorie-intake and helping to lose fat.
  • The rules are simple to follow.


  • Cutting out meals on fasting days can cause headaches, irritability and tiredness, which can harm performance at work, and may also cause dehydration and vitamin deficiencies.
  • Has been associated with problems sleeping at night.
  • May lead to overeating on non-fast days.
  • Not all versions of this plan are backed by scientific evidence.

In summary

More than one version of this diet exists, although they follow the basic premise of two drastically low-calorie days a week. It’s important to look up advice from a dietitian before attempting it, as some variations of the diet can be detrimental to health.

Furthermore, if you have a condition such as diabetes or if you are pregnant, then this diet will not be suitable for you.

WeightWatchers diet

The ProPoints plan is one of the most popular and established diet plans in the UK, considered by many to be one of the ‘big three’ (along with Rosemary Conley and Slimming World). Food items are attributed a points value, taking into account fibre, protein, carbohydrate and fat. The diet encourages steady weight loss at a rate of 2lbs per week.

What does it involve?

Adhering to the points allowance, and that’s about it. No specific items are off-limits, provided you remain under the threshold. The programme is accompanied by a weekly meetings and weigh-in schedule to help participants get support from others on the same plan.


  • The points system means that virtually no cap applies to the amount of fruit and some vegetables you can eat.
    Encourages a measured and consistent approach to weight loss and helps to develop lasting good habits.
  • ‘Safety net points’ can be accumulated for a special occasion, meaning that you can enjoy an occasional indulgence without feeling guilty.


  • The points system can be difficult and time-consuming for new starters, meaning that some may become discouraged early on.
  • Some may see the weekly meetings as an appointment they can’t commit to and thereby become demotivated.
  • WeightWatchers foods, which the programme promotes, may be more expensive than value brands. However, these are not integral to the programme.

In summary

The points system does provide an education on calorie values, as does the support network. The gradual rate of weight loss may not appeal quite as much to those who want to see fast results, but it does encourage those coming off the diet to stay at their target weight.

Rosemary Conley diet

The originator of the Hip and Thigh Diet, Rosemary Conley is a best-selling author whose eponymously named plan also includes an exercise regimen. Conley is reported to have first developed a low-fat diet plan after being diagnosed with gallstones, to help her manage symptoms without having to undergo surgery.

What does it involve?

Generally, Rosemary Conley’s diets and recipes consist of foods that are:

  • low in fat (five percent or less)
  • and have a low glycemic index (low-GI)
  • with the exception of oily fish and porridge oats which are allowed on the diet.

This is also accompanied by an online programme including fitness videos, cooking videos, a weight tracker and various other tools. The plan aims to help the user lose a stone (14 lbs) in seven weeks.


  • Encourages gradual and controlled weight loss.
  • Helps the user to improve their awareness of portion sizes (through the use of portion pots) and apply this in everyday situations.
  • Incorporates exercise to provide a more rounded and healthier approach to losing weight.


  • Low-fat foods will not automatically be healthier. Some may be higher in sugar than non low-fat foods.
  • Portioning when eating out may be difficult.

In summary

Success rates for this diet plan at three and 12 months have been shown as being ‘not inferior’ to those of WeightWatchers by one study; and like the WeightWatchers plan, it helps to increase the user’s knowledge of healthy eating, ultimately giving them a better chance at maintaining a healthy weight (and lifestyle) once they stop the programme.

Cambridge diet

Also known as the Cambridge Weight Plan, this diet is so-called as it was devised by a doctor at Cambridge University.

It is a (very) low-calorie plan focussing on weight loss through reduced calorie intake, utilising meal replacement products including bars, soups, shakes and porridges.

What does it involve?

It depends what your goal is. Programmes start at as a little as 415 calories-a-day and can go up to and over 1,500 calories-a-day. You’ll consult with a Cambridge representative regularly and they will discuss the most suitable plan with you before commencing the diet.

Meal replacement products can be used:

  • in conjunction with regular meals for gradual weight loss,
  • or on their own for rapid weight loss.

There are six steps to the plan. Where you start is determined by how much weight you want to lose.

These are:

  • Sole Source, the first stage, whereby three to four meal replacement products are consumed per day. A variation of this, Sole Source Plus, involves eating a meal of no more than 200 calories in addition to the three branded items.
  • Total daily calorie goals for this stage are between 415 and 615, and it should be undertaken for between 1 and 12 weeks.
  • The second stage involves three meal replacement products, in addition to a daily allowance of high-protein foods, along with selected vegetables and skimmed milk. This adds up to a total of 810 calories a day (one week minimum).
  • Stage three consists of two Cambridge items per day, along with milk, breakfast and salads for lunch and evening meals. This 1000 calorie a day stage should be adhered to for two weeks.
  • The fourth stage permits a balanced low-calorie lunch and dinner in addition to two meal replacement items. This stage can last for as long as the user desires.
  • 1500 calories are permitted each day at the fifth stage. During this stage, three meals (breakfast, lunch and dinner), a snack and one diet product is consumed daily, for as long as the person following it feels comfortable.
  • The final stage is the one which the user will adopt once they’ve reached their target weight and achieved stability. This entails eating a healthy balanced diet, and having just one diet product a day while continuing to see a specialist Cambridge diet consultant.


  • The meal replacement plan produces results quickly, and helps to generate weight loss at a fast pace.
  • These diet products allow the user to get the vitamins and nutrients they require.
  • Users don’t have to start at the beginning of the plan. They can pick up at a later stage depending on their target.


  • As a very low-calorie diet, users might experience dizziness and headaches during the early stages.
  • This may make it more difficult for some users to stick to.
  • The range of meal replacement items isn’t huge, meaning that if you don’t like what’s on offer your choice is fairly limited.

In summary

The speedy results may appeal to those who have a BMI of 30 or more, and are looking to lose a significant amount of weight for health reasons.

However, those who lose weight at a fast pace may experience difficulty keeping the pounds off when the programme is over.

Furthermore, the NHS advises against following a very low calorie diet (1,000 calories or less) for more than 12 weeks continuously. Some may be put off by the need for consultant supervision, but for such a low-calorie diet this is nonetheless a medical necessity.

Slim Fast diet

The Slim Fast plan is another programme based around meal replacement products. It is aimed at those with a BMI of 25 or above and it was first conceived by a doctor in California in 1977.

What does it involve?

The range of products has changed over the years, but today it has been streamlined into the 3-2-1 programme. This consists of:

  • 3 snacks per day. These can be SlimFast noodles or other snack items
  • 2 SlimFast meals, shakes or bars
  • and 1 balanced meal containing no more than 600 calories (800 for men)

This rate of weight loss is around 1-2 lbs per week, and is followed every day until the target weight is reached. To maintain a healthy weight after this, the plan recommends having:

  • one meal replacement shake per day
  • two snacks which are low in fat
  • and two sensible meals.


  • The plan is easy to follow and understand. Downloadable menus are available to help the user choose appropriate healthy meal options.
  • No specific foods are out of bounds, although the user is encouraged to eat lean meat, as well as fruit and vegetables.
  • Offers a steady and controlled rate of weight loss.


  • Reliance on meal replacement products doesn’t necessarily introduce the user to healthy cooking and dieting practices. Consequently, the user may be more susceptible to regaining the weight they’ve lost when they come off the plan.
  • Unlike other diets, which may not impose a limit on the amount of fruit and vegetables one can eat, the user may find this plan requires more planning when it comes to getting their 5-a-day.
  • The range of meal replacement items is varied, but users who don’t find them enjoyable may be less encouraged to stay on the plan.

In summary

Meal replacement products provide an easy route to losing weight, and the SlimFast plan allows for a more gradual, sustainable rate of weight loss than the earlier stages of the Cambridge Diet.

But those undertaking this diet will still need to make use of the resources available to develop their knowledge of healthy eating and cooking practices.

South Beach diet

This plan was developed by Dr Arthur Agatston, a preventive cardiologist, and Marie Almon, a dietitian specialist. It was initially designed to help patients with heart disease, and developed as a lower-fat alternative to the Atkins diet.

What does it involve?

The plan is separated into three phases:

  • During phase one, the user will eat lean meat and fish, vegetables with a low glycemic index and non-saturated fats. This lasts for two weeks, and is the recommended start point for those looking to shed 10 lbs or more. Users will lose weight rapidly during this phase (up to an estimated 13 lbs).
  • Phase two sees the gradual reinsertion of low-GI carbohydrates into the user’s diet, such as vegetables and whole grains. Weight loss will begin to slow down during this step, but this regimen will continue until the user’s target weight is reached.
  • Phase three is the maintenance phase. By this point, the user has developed a knowledgeable eating regimen observing the importance of healthy choices and moderation.


  • The second and third phases help to educate the user on making sustainable choices.
  • These are useful places to start for those who don’t need to lose more than 10 lbs, and encourage dietary consistency.
  • No essential food groups are off-limits during the latter two phases.


  • Phase one involves a drastic reduction in calorie consumption which may cause headaches, tiredness and irritability.
  • This may make the plan during the initial two weeks more difficult to stick to.

In summary

The loss of 13 lbs in the first phase will make this a tough ask for many, but from phase two onwards, the plan becomes more manageable. Those who aren’t looking for drastic or speedy results might find phase two a useful starting point.

Dukan diet

Put together by French doctor Pierre Dukan, this plan focuses on high protein and low carbohydrates. The rationale is that the body will be forced to burn fat in lieu of the presence of carbohydrates, and weight loss is intended to start off quickly then become gradual.

What does it involve?

Four phases:

  • The first, also known as the ‘attack’ phase, lasts for 1-10 days and involves eating lean protein (from an approved list). In addition to this, the user will also eat a tablespoon and a half of oat bran per day, and drink six glasses of water. No vegetables or other carbs are allowed.
  • The ‘cruise’ phase comes next. During this phase which can last for a number of months, non-starchy vegetables can be reintroduced, along with an extra half teaspoon of oat bran.
  • The third phase is ‘consolidation’. This is followed for five days per lb of weight lost. Vegetables are allowed each day, as is one serving of fruit and a serving of hard cheese. Two slices of whole grain bread per day are also permitted. On one or two occasions during this phase, the user is allowed a ‘celebration’ meal where any food is permitted.
  • ‘Stabilisation’ is the name given to the last phase. From this point onwards in the plan, the user can eat as they please for six days a week. On the remaining day, they must observe the restrictions from the first phase and eat only lean protein. Three tablespoons of oat bran are eaten every day, and twenty minutes walking a day is also encouraged.


  • The rapid rate of weight loss at the start of the plan may be a significant motivational factor for many.
  • It’s easy to grasp and the user can refer to the approved foods list, without having to check calorie amounts.
  • There is no limit on the amount of approved foods the user is permitted during the attack phase provided they follow the rules.


  • The attack phase can be hard to sustain.
  • A lack of carbs may cause tiredness and dizziness, and the lack of fibre from vegetables and grain could induce constipation.
  • It may be unsuitable for those with certain health conditions (such as heart or kidney disease), and those with other conditions (such as diabetes) will need to consult with their doctor before embarking on this diet, as their medication administration may need to be adjusted.

In summary

The first phase of this diet is perhaps among the most difficult to follow, and the restrictions are such that it should certainly not be undertaken lightly by those with dietary conditions.

More research is needed to determine whether diets such as this one are sustainable and healthy in the long term.

Slimming World diet

The premise of this plan is ‘food optimisation’. This means substituting high-fat items with those low-fat items which will still satisfy appetite and leave users feeling full. The aim is to help the user lose weight at a rate of one to two pounds per week.

What does it involve?

There are three main categories of food on this plan:

  • Free foods. Users choose from a list of which they can eat how ever much they want. This list contains fruit and vegetables, rice and pasta, potatoes, lean meat, fish and eggs.
  • Healthy extras. These are allowed in daily portions in order to ensure balance. These include foods such as bread, cereals, and dairy such as cheese and milk.
  • Syns. Less healthy and more calorific foods, such as chocolate and sauces, are given a ‘syn’ value. Those on this diet are allotted a daily allowance of syns.

The programme can be followed online, but local support groups are also located up and down the country and provide weekly meetings.


  • No items are strictly off-limits, meaning that the diet is a varied one.
  • Encourages gradual and sustainable weight loss.
  • The weekly meeting option offers motivational support and may help some to stay on track.


  • Doesn’t necessarily provide users with wider applicable knowledge on calories and portion sizes.
  • Users may therefore be less able to maintain their target weight after leaving the programme.

In summary

Slimming World is an established programme, and has had comparable success rates to plans offered by WeightWatchers and Rosemary Conley (see above).

The concepts of ‘Free foods’ and ‘Syns’ may not easily translate into a wider knowledge of calories and nutrition however, meaning that participants will have to learn this themselves in order to maintain a healthy weight once they have finished this plan. 

Page last reviewed:  25/10/2019