WEIGHT MANAGEMENT ∙ 5 minutes read

Myth-busting: the low-down on which diets do and don’t work

By Kirsty Mason | Medically reviewed by Rupal Joshi

Our expert nutritionist, Shona, gives us the low-down on which diets do and don’t work.

Diets are notoriously hard to stick to. And even when we do, it’s a well-known fact that most of us will pile back on the pounds. In fact, a study that followed up with approximately 200 participants 3 years after they’d completed a diet programme found that a whopping 40% had gained more weight than they lost during the diet. Only 12% were able to maintain most of the weight loss.

It paints a bleak picture for those ready to start a new diet, especially when so many are overhyped and based on unfounded claims. But there’s good news: some diets actually work. 

We take a look at the science behind 7 of the most popular diets to get the low-down on which diets are worth chomping down on.

1. The paleo diet

What is a paleo diet?

A paleo diet is based on the foods that our ancestors ate millions of years ago. It argues that the modern diet doesn’t suit our genetic material and explains why we’re tackling a rising trend in obesity. The diet consists of food that was available for hunter-gatherers so this includes fish, lean meats, fruits, vegetables, nuts, and seeds. The diet excludes foods that are known to be unhealthy including processed foods and sugar. But it also excludes grains, legumes, and dairy products which are good sources of fibre and protein. This is the main drawback of the diet.

Does a paleo diet help you to lose weight?

Clinical trials have demonstrated that the paleo diet may be an effective method for weight reduction and fat loss. However, further studies are needed to truly understand if the diet is a suitable and healthy method of weight loss. In a study that compared the effects of intermittent fasting, the Mediterranean diet and the paleo diet, participants on the paleo diet lost the least amount of weight. It’s been theorised that the diet only leads to weight loss because of caloric restriction and the reduction in carbohydrates, and the weight loss benefits have been exaggerated. The diet excludes food groups that are known to be a healthy part of a weight loss regime, including whole grains and dairy products.

Paleo diet plan:

Breakfast: Banana and strawberry smoothie and a handful of mixed nuts

Lunch: Salmon salad with kale, spinach, peppers and grated carrot

Dinner: Steak, sweet potato and broccoli

What Shona the nutritionist says:

As dairy is eliminated from the paleo diet, so is calcium lactate, one of the best absorbed forms of calcium. The paleo diet also eliminates grains, including whole grains, which are a valuable source of prebiotics that help to keep gut microflora healthy. There is a tendency for modern paleo dieters to overconsume meat. In reality, our paleo ancestors would have consumed meat only after a successful hunt, which may have been as little as once a week. The majority of foods consumed by our paleo ancestors would have been plant-based foods such as fruits, vegetables and nuts. Excessive meat consumption can lead to multiple health complications.  

2. The keto diet

What is a keto diet?

A ketogenic diet (keto for short), is a low-carb, high-fat diet. The diet aims to put your body into a metabolic state called ketosis. This is where, in the absence of carbohydrates, your body burns fat for energy.

Does a keto diet help you to lose weight?

There is some evidence for the effectiveness of the ketogenic diet for weight loss in obese patients. A meta-analysis that looked at the effects of a very low-carbohydrate diet for weight loss concluded that the diet is a useful tool for fighting obesity. Lowering carbohydrate intake increases energy expenditure, meaning that your body naturally burns more calories when you’re following a ketogenic diet. There’s also evidence that the state of ketosis interacts with appetite-mediating nutrients and hormones in the body, resulting in reduced appetite.

Although there are clear benefits to following the keto diet for weight loss, there are some drawbacks. A low carbohydrate diet tends to lead to rapid weight loss but there’s no evidence to indicate that it’s a sustainable method in the long term. In practice, it’s extremely difficult to avoid carbohydrates. Carbs are a macronutrient (a major food group in the diet) and are a vital source of energy - especially if you’re exercising - and nutrients. 

Keto diet plan:

Breakfast: Avocado, scrambled eggs and bacon

Lunch: Tuna salad with kale, spinach and red onion

Dinner: Chicken stuffed with mozzarella cheese and wrapped in parma ham, with asparagus

What Shona the nutritionist says:

Dramatically reducing or cutting out carbohydrates reduces the level of prebiotics consumed which harms the probiotic levels and number of species in the gut. The higher consumption of saturated fat on the ketogenic diet further reduces probiotic numbers in the gut. It’s also very difficult to consume enough of some trace minerals such as selenium, so ensure you combine the ketogenic diet with a good multi and probiotic supplement. If you find yourself a little constipated on the ketogenic diet, you’re not eating enough fibre, and your gut will suffer in the long run. 

3. The Atkins diet

What is an Atkins diet?

The Atkins diet is a low-carb diet that was popularised by Dr Robert Atkins. There’s an emphasis on the consumption of fat and protein instead of carbohydrates. The Atkins diet is similar to the keto diet but there’s more flexibility around reintroducing carbs. There are variants in versions of the Atkins diet but the method tends to follow a four-phase plan where carbohydrates are initially severely restricted before slowly being reintroduced.

Does an Atkins diet help you to lose weight?

Low-carbohydrate diets have proven to be effective but experts have questioned whether the diet is beneficial in the long term. Carbs are a vital source of energy and contain key nutrients. That said, there are several reasons why the Atkins diet can lead to weight loss. For one, as carbohydrates are restricted, the body will burn glycogen stores for energy. This leads to the depletion of water which, unfortunately, will be easily regained but explains the rapid weight loss. It’s also thought that your appetite is suppressed when you’re in ketosis (a metabolic state where your body uses reserved fat stores for energy). The Atkins diet does reintroduce a level of carbs into the diet so is more flexible when compared to the keto diet, but, like the keto diet, your body may be starved of key nutrients.

Atkins diet plan:

Breakfast: Scrambled eggs and smoked salmon

Lunch: Chicken and avocado salad with lemon dressing

Dinner: Cheesy cauliflower steak with kale

What Shona the nutritionist says:

It can be tricky to get all the nutrients you need when following the Atkins diet. Research has found that less than half of the nutrients needed were consumed in adequate quantities in participants on the Atkins diet. As with the ketogenic diet, the reduction in carbohydrates also reduces the prebiotics which our gut flora relies on. This is made worse by the increase in saturated fats. Not only do saturated fats negatively influence the gut flora and possibly trigger constipation, but they’re also detrimental to heart health.

4. Mediterranean diet

What is a Mediterranean diet?

The Mediterranean diet emerged when researchers noted that people living on the coast of the Mediterranean sea (such as France, Spain, Italy and Greece) were at lower risk of cardiovascular disease, obesity, type 2 diabetes, and cancer. Although there are slight variances in the diet (mainly down to differences in each country), it’s generally agreed that the diet should be rich in healthy fats (such as olive oil), vegetables, fruits, nuts, seeds, whole grains, and legumes. The diet should also include a moderate amount of fish, seafood, and dairy. Red meats, processed foods and added sugars should be avoided.

Does a Mediterranean diet help you to lose weight?

There is plenty of evidence to support the role the Mediterranean diet plays in weight loss. A comparison of Mediterranean, low-carbohydrate and low-fat diets found that, while all led to weight loss, the Mediterranean and low-carbohydrate diets were superior to a low-fat diet. There’s also evidence to support the role the diet plays in long-term, healthy weight loss. Greater adherence to the diet is associated with an increased likelihood of weight loss maintenance.

Mediterranean diet plan:

Breakfast: Greek yoghurt with berries and almonds

Lunch: Lentil salad with cucumber, pepper, feta cheese, parsley and lemon dressing

Dinner: Herb salmon with whole grain rice and grilled Mediterranean vegetables

What Shona the nutritionist says:

Studies have demonstrated the beneficial effect on health that the traditional Mediterranean diet provides and is widely recommended.  The increased intake of vegetables, fruits, nuts, seeds, whole grains and herbs is beneficial for the gut and waistline, while the fish and extra virgin olive oil are beneficial for the heart and brain. There are some limitations to this diet, however. There are no guidelines on portions, with most instructions saying ‘limit’, ‘moderate’ and ‘abundance’ which may be confusing for some people. Wine is also recommended which is not suitable for everyone. Overall, the Mediterranean diet is healthy and well-balanced. 

5. The Dukan diet

What is a Dukan diet?

The original Dukan diet has four phases. During the first phase, there are just 72 foods to choose from. These foods are high-protein, low-fat and contain virtually no carbohydrates, even those that are in vegetables. These protein-rich foods include lean meat, fish, poultry, eggs, shellfish and fat-free dairy products. Foods are slowly reintroduced during the next three phases and eventually, you can introduce carbs back into the diet, as long as weight maintenance continues.

Does a Dukan diet help you to lose weight?

The Dukan diet is an effective method of weight loss in obese patients. However, there are dangers when it comes to following this severely restrictive diet as your body is missing key nutrients. A study on the nutritional implications of following the Dukan diet found that protein intake was excessive and participants were vulnerable to many nutrient abnormalities and imbalances, including low levels of vitamin C and folates. These vitamin and mineral deficiencies may continue following the discontinuation of the diet.

Dukan diet plan (phase 1):

Breakfast: Salmon and boiled eggs

Lunch: Baked cod with shrimp

Dinner: Chicken breast stuffed with cottage cheese

What Shona the nutritionist says:

The Dukan diet has its limitations and problems. The very fact that vegetable intake is limited decreases micronutrient intake substantially, and antioxidants will be severely limited. Although carbohydrates and carbohydrate-rich vegetables are reintroduced back into the diet, it’s hard to control the way in which the gut microflora will recover. If you are going to follow this diet, it makes sense to supplement with a good multi-nutrient, a probiotic and a prebiotic to limit the damage caused to your gut. 

6. Intermittent fasting

What is intermittent fasting?

There are different methods of intermittent fasting but the general concept is to eat during a specific time frame and fast for the remainder. The most popular method of intermittent fasting is the 16:8 method. This is where you eat within an 8-hour window, usually between 12pm-8pm. Essentially, you’ll be asleep for the majority of the fasting period and will just need to skip breakfast. Another popular method of intermittent fasting is the 5:2 method. This is where you eat normally for 5 days then severely restrict your diet on two non-consecutive days where you consume around 500 calories. A more extreme method of intermittent fasting is alternate-day fasting where you eat normally on one day and then either fast entirely the next day or limit yourself to 500 calories.

Does intermittent fasting help you to lose weight?

There is evidence for the effectiveness of time-restricted fasting, the 5:2 method, and alternate-day fasting. One study that compared intermittent fasting with the Mediterranean diet and Paleo diet found that intermittent fasting led to the greatest amount of weight loss. It’s also thought that intermittent fasting leads to a range of health benefits including cardiometabolic health, as well as improvements in insulin sensitivity, blood pressure, and oxidative stress. That said, many studies have noted that intermittent fasting isn’t superior to calorie restriction when it comes to weight loss. The diet may not be appropriate for everyone as severe calorie restriction may lead to dizziness and fatigue, although your body usually adapts to the new behaviour over time.

Intermittent fasting diet plan (500 calorie day):

Breakfast: Greek yoghurt and raspberries (200 calories)

Lunch: One small orange (50 calories)

Dinner: Chicken breast marinated in orange with broccoli (250 calories)

What Shona the nutritionist says:

Intermittent fasting reduces calorie intake, promotes a reduction in weight and encourages the use of ketones as fuel as well as improving insulin sensitivity. It may be more beneficial for some people than other diet types. During fasts between food, human growth hormone increases which promotes fat loss and the building of muscle. It is, however, a good idea to take a good multi-nutrient formula to ensure a good nutrient intake is achieved. Taking branched-chain amino acids including valine, leucine and isoleucine may help to protect against muscle loss when fasting for long hours at a time. Intermittent fasting may not be recommended for everyone so if you have any health conditions make sure you speak to a professional before starting intermittent fasting. 

7. Very low-calorie diet

What is a very low-calorie diet?

A very low-calorie diet consists of around 800 calories a day but is only recommended in extreme circumstances. If someone is obese or extremely obese, they may be recommended the diet on the basis that their current health risk is greater than the risk of following the diet and immediate weight loss is critical. Under NHS advice, you should follow the diet for a maximum of 12 weeks with medical supervision throughout.

Does a very low-calorie diet help you to lose weight?

A very low-calorie diet is a quick method of weight loss for obese or severely obese patients who need to lose weight imminently. The diet should not be followed long-term as a very low-calorie diet will lead to nutrient and vitamin deficiencies. The diet can also make you feel hungry, dizzy, and lead to hair thinning. You should only follow a very low-calorie diet for a maximum of 12 weeks, under medical supervision.

Very low-calorie diet plan (800 calories):

Breakfast: Two boiled eggs and a handful of tomatoes (200 calories)

Lunch: Cottage cheese on low-calorie crackers (250 calories)

Dinner: Lean beef salad with spinach and red onion (350 calories)

What Shona the nutritionist says:

A low-calorie diet, although it makes sense scientifically for weight loss, has some pitfalls. Many participants focus on reducing fat intake as fats are highest in calories per gram. Some fats are needed by the body to stay well, and if you eliminate fats you may find your mood decreases. Fats are also needed as they contain fat-soluble vitamins such as vitamins A, D, E and K, all of which play an essential role in health. Some healthy foods have a higher fat and calorie content, such as nuts, seeds and avocados. And some foods which are low calories are not necessarily healthy, so a low-calorie diet does take some navigating as to the best foods to choose. 

The bottom line

It’s clear that dieting isn’t easy and most people give up when restrictive eating becomes too challenging. Many diets have been overhyped and can lead to dangerous nutrient or vitamin deficiencies. Losing weight essentially boils down to a calorie deficit. Except for extreme circumstances, a healthy, balanced diet with a calorie deficit of around 500 calories a day is recommended. To achieve sustainable weight loss, it’s critical that you change your relationship with food.