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Weight-loss fad diets: a quick fix or a danger to health?

The potential link between obesity and COVID-19 complications has driven increased interest in extreme diets. But are they quick fixes or dangerous for your health? Nutritionist Rob Hobson takes a look.

With recent research showing that being obese or overweight puts you at greater risk of death or serious illness from COVID-19, as well as the unveiling of the Government's new obesity strategy, online searches for diets have skyrocketed. But with so many different types of diet out there, it's difficult to know the best way to lose weight – and to keep it off.

Here nutritionist Rob Hobson takes a look at the evidence (or lack of it) behind some of the most popular eating plans.

Raw food diet

Also known as the 'raw vegan diet', the raw food diet is made up of uncooked, unprocessed, organic foods. Some also include unpasteurised dairy, raw eggs, meat and fish.

The main concept behind this diet is that cooking food reduces the natural levels of vitamins and minerals, and therefore only raw foods (or foods cooked below 118 degrees Fahrenheit (48 degrees Celsius) are consumed.

Raw foods, such as fruits, vegetables, nuts, seeds and sprouted grains are certainly a highly nutritious, valuable addition to the diet, but cooking certain foods is beneficial. Studies suggest that cooking tomatoes makes the lycopene more readily available, while cooking carrots in oil does the same for its beta carotene.

'Raw foodies' also frequently talk of beneficial enzymes found in raw foods, but in fact these are only necessary for plant survival and not essential for human health. Although our bodies couldn't function without enzymes, we can continue to make them throughout life, meaning we're never in short supply.

Will you lose weight on a raw food diet? Probably, given the potential low-calorie content of this diet, but you may be restricting important food groups, such as protein and healthy fats. Following this type of diet requires a lot of planning, learning, and may also require supplements and even protein shakes.

Overall, the raw food diet is actually very healthy, as it promotes eating lots of fresh fruits, vegetables and other plant-based foods, while avoiding processed junk.

Juice cleanses/detox

To be clear, there is no such thing as a detox. Juice cleanses have become very popular, but they only offer you a way to starve yourself of valuable nutrients.

The general idea is that by avoiding solid food the body switches into 'cleanse mode', excreting toxins and supposedly healing itself.

Firstly, there is no such process known as 'cleanse mode'. The body is actually in a constant state of cleanse, which is what the liver, lungs and kidneys are for. This diet in fact lacks fibre and the nutrients that form the essential components of a healthy diet required to support life.

Unpleasant symptoms associated with this diet include dizziness and fatigue and, despite what some think, a 'juice diet' is more likely to slow down your metabolism than kick-start it.

Will you lose weight? Yes, as a result of a dramatic reduction in calories. Will you keep the weight off? Very unlikely, as this is more of a quick fix and offers no insight into maintaining a healthy weight through healthy eating.

Intermittent fasting

This type of diet still remains popular, and includes the 5:2, 6:2 and 16-hour fast. The 5:2 involves two fasting days during the week, which are restricted to 500 calories for women and 600 for men. The evidence for the 5:2 is limited, and weight loss has been shown to be similar to that in people following a calorie-controlled diet.

The 6:1 diet involves avoiding food completely for one day of the week, while the 16-hour fast involves only eating during an eight-hour time frame, and fasting for the remaining 16 hours.

At their core, these diets are basically about reducing the overall number of calories you eat across the week. Each variety comes with pros and cons, which are generally about how you fit them into your lifestyle. For example, you should plan your exercise schedule carefully on fasting days to make sure you still have enough energy left over from your previous meal for training.

There is also some evidence to suggest that intermittent fasting may help to reduce the risk of certain diseases such as diabetes.

Will you lose weight? This depends on what you eat on the non-fasting days, which would still need to be calorie-controlled to reduce your overall intake across the week.

Sirtfood diet

This diet has received quite a bit of interest in the media, given its popularity among celebrities and the fact that you can diet and include foods such as chocolate and red wine.

'Sirtfoods' are those high in sirtuin activators, and sirtuins are a type of protein that protect cells in the body from inflammation. Research also suggests that they may help to regulate metabolism, burn fat and increase muscle, hence their use in this weight-loss diet plan.

On this diet you are encouraged to increase your intake of sirtfoods, including apples, walnuts, buckwheat, dates, olive oil, rocket and kale. Although all these listed foods are healthy, there are still restrictions of certain food groups, which may encourage nutrient imbalances.

Creators of this diet claim it switches on your 'skinny gene' by eating high levels of sirtfoods, but this is not backed up by strong research.

There is nothing really wrong with this diet, but there is no evidence to suggest it is any more effective than a calorie-controlled way of losing weight.

Carnivore diet

This diet is the antithesis of plant-based eating, as it consists entirely of meat and animal products, excluding all other foods. The diet promises weight loss, as well as blood glucose regulation and mood elevation, but is highly restrictive.

This diet also offers no guidance on calorie intake, serving size or meal timing, although it is difficult to eat large amount of these foods in a single sitting as they are very filling. Aside from feeling full, protein is thought to increase metabolic rate, contributing to calories burnt.

You may lose weight on this diet, but you do not need to go to such extremes; there are healthier weight-loss methods. Cutting out all other groups may leave you short of micronutrients and fibre, as well as increasing your intake of saturated fat.

Meal replacement diets (NUUT and Soylent)

Meal replacement diets are nothing new, but these are two that have become more popular over recent years.

The Soylent diet has been created completely out of shakes, each of which contains a source of fat, carb, protein and fibre, along with a spectrum of micronutrients.

The meal replacements come as premixed drinks, including a regular or café version made with caffeine and L-carnitine, as well as a powder form. Each shake is 400 calories, so you can map out your intake based on a given number of drinks per day.

NUUT provides meal replacement drinks in powder form to help support intermittent fasting – for example, ensuring a good nutritional intake on the fasting days of the 5:2 diet when it may be tricky to get what you need from the low-calorie guidelines.

NUUT promotes the quality of these drinks and the provenance of the ingredients. The company also includes pro- and prebiotics in its powders, as well as powders that support keto and paleo dieting.

Meal replacements contain everything your body needs, but they don't excite the palate in the way real food does, and they do nothing to teach you about heathy eating – which is not good in the long term.

There are also other beneficial compounds in foods which cannot be created in a supplemented shake. This is why NUUT may be the better option out of the two, as it involves both shakes and real food.

Either way, meal replacements will probably help you to lose weight, but may not help you to keep it off if you do not learn to change your behaviour when it comes to eating normally again.

Noom diet

This diet is based around eating low-calorie foods with a high nutrient density while tracking your progress and supporting you via a mobile app. Entering your personal details allows the app to calculate your calorie needs, which it then adjusts for weight loss based on your goal weight and timeframe.

This approach and support from professionals offers a long-term solution which promotes behaviour change. Nothing is off the menu, but some foods are recommended to be eaten more than others to promote an overall healthy balanced diet.

It's still important to focus on a balanced diet, and some people may not feel comfortable using the app – so if you're not very techy then this is probably not the diet for you.

Rob Hobson MSc RNutr is a Registered Nutritionist who has worked with some of the UK’s largest food and health companies and performs training in the public health sector (including government agencies and the NHS). Rob contributes regularly to UK press publications and has a monthly column in Women's Health magazine.

Find out more at Rob Hobson's website, or read more about Healthspan's health experts.