A century of fad diets – from the F-plan to Keto and the raw food movement – what really works?

For the past century, our pursuit of the “perfect body” has been fuelled by ever-changing, often bizarre diet trends. Some stemmed from desperation, others from questionable science, and a few, well, from outright madness.

From grapefruit-fuelled dreams in the 1920s to the keto craze of today, let’s take a look at the wild world of fad diets.

The “grapefruit diet”, also known as the “Hollywood diet”, promised weight loss by eating half a grapefruit with every meal, a meagre intake of toast, eggs and a touch of protein. Grapefruits were thought to contain a magical fat-burning enzyme, which – spoiler alert – does not exist.

While fruit is great for weight loss (it’s high in fibre and nutrients and low in calories), the real reason this diet worked was starvation – we’re talking 500 calories a day. Yes, that’ll make you lose weight, but it’s neither safe nor sustainable long term.

The “master cleanse”, also known as “the lemonade diet”, involved consuming nothing but lemon juice, water, maple syrup and cayenne pepper for 10 days, along with a bedtime laxative tea.

While yes people lost weight quickly on this so-called “detox” diet, much of it was water and muscle loss, and as soon as you resumed eating, it came right back.

Nutrition experts aren’t fans. “It sounds obvious, but our bodies need all the essential nutrients to function,” says Jo Travers, a registered dietitian for Love Your Gut. “So if we don’t get them because a diet restricts lots of food groups, then these essential things can’t happen.” Depriving yourself just slows your metabolism and sets you up for failure as your body then holds on harder to the calories when they do arrive.

Despite this, this is a diet that is often revived in various reiterations – because apparently, misery loves company.

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The “sleeping beauty diet” took calorie restriction to a new level: if you’re asleep, you can’t eat. The solution? Sedatives. Lots of them. Reportedly, even Elvis Presley was into it.

Besides being wildly unsafe, prolonged sedative use leads to malnutrition, muscle loss and in extreme cases – coma. And while sleep is important, research suggests both too little and too much can contribute to weight gain in the long term.

In short? Sleeping within the recommended seven to nine hours is great – knocking yourself out for days to avoid meals? Not so much.

The “Scarsdale diet” was a strict, low-carb, high-protein meal plan, designed to be followed for 14 days with militant control. Devised by Dr Herman Tarnower of the Scarsdale Medical Group, it was based on chemical reactions between foods rather than quantities of foods per se and promised weight losses of up to 20 pounds in 14 days.

Followers were told to use lean meat only, prepare all foods without butter and all salads without oil or mayonnaise and use both lemon and vinegar on salads. No snacking, except for raw carrots and celery, was allowed and neither was alcohol. It promised to help followers lose up to 20 pounds in just 14 days Compared to previous starvation-level diets, it at least had some structure, but it was still miserable and unsustainable, meaning once the diet was “over”, people would resort to old habits and gain back the weight.

On the other end of the lunacy spectrum, we had the “egg and wine diet” – which involved eating eggs, black coffee and wine for breakfast and lunch, followed by steak and wine for dinner.

The science behind the Scarsdale diet set the stage for the low-carb craze, paving the way for protein-focused Atkins and keto. The egg and wine diet, however, was just malnutrition with a hangover.

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The “cabbage soup diet” had dieters eating nothing but cabbage soup for a week, with a few extra foods (bananas one day, beef the next). While low in calories, it was also low in nutrients and high in social isolation – thanks to the infamous digestive side effects.

Meanwhile, the “F-plan diet” promoted high-fibre foods like bran and legumes to keep you full and aid digestion. It was more nutritionally sound, but still extreme – people quickly grew tired of eating mountains of bran, and excessive fibre led to bloating and discomfort.

Both diets reinforced quick-fix thinking, but fibre’s reputation as a weight-loss ally endured, shaping more balanced approaches in the decades to come.

The “zone diet” introduced strict macronutrient balancing – 50 per cent carbs, 30 per cent protein, 20 per cent fat – to keep the body in peak metabolic condition. While more scientific than previous trends, it required rigid portion control and meal planning, making it hard to maintain.

The “blood type diet”, however, was pure pseudoscience – claiming that diet should be tailored to your blood type. Despite no scientific backing, it became wildly popular.

However, the trend towards “personalised nutrition” took off, but by the 2000s, more research-backed approaches – like the Mediterranean diet – started taking centre stage.

Two diets dominated the 2000s, and they couldn’t have been more different.

The “raw food diet” promoted eating only uncooked, plant-based foods, claiming these preserved enzymes and nutrients. While eating more plants is undeniably good, a strict raw diet posed risks – some nutrients are actually more bioavailable after cooking, and it lacked essential micronutrients like B12 and iron.

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Meanwhile, the Atkins diet brought low-carb dieting back with a vengeance, convincing people that carbs – not calories – were the enemy. Rapid weight loss was common, but cutting out whole grains and fibre-rich foods had long-term digestive and metabolic consequences.

Both diets were hard to maintain, but influenced future trends – Raw evolved into “clean eating”, and Atkins laid the groundwork for keto.

The “paleo diet” insisted we eat like our hunter-gatherer ancestors, eliminating grains, dairy and legumes while prioritising meat, fish and vegetables. The whole-food focus was a step forward, but avoiding entire food groups without cause was unnecessary.

Meanwhile, juice cleanses became the ultimate “detox”, with people drinking nothing but juice for days. While juices are rich in vitamins, they lack fibre, causing sugar spikes and crashes. Plus, most weight loss was just water and muscle depletion, being that fat wasn’t burned and weight would return as soon as food was reintroduced.

Both trends reinforced the obsession with “clean eating”, though modern nutritionists advocate for balance rather than restriction.

The keto diet took low-carb to new extremes, shifting the body into ketosis by eliminating nearly all carbohydrates. While it’s effective for weight loss and managing epilepsy, it’s highly restrictive, tough to sustain and cuts out many gut-friendly plant foods.

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Then came Ozempic – a diabetes drug turned viral weight-loss miracle, thanks to its appetite-suppressing effects. While effective, it raises ethical concerns, especially since off-label use has led to shortages for diabetic patients.

On the other end of the spectrum, gut health has emerged as a key focus. Experts like Tim Spector, professor of genetic epidemiology and co-founder of the ZOE app, advocate for diversity in diet – aiming for 30 different plants per week – which benefits digestion, immunity and overall wellbeing.

Together, these trends highlight the modern paradox of health – an embrace of both nature and science in the pursuit of wellness.

While each decade has brought its own diet obsessions, nutritionists remain unconvinced by most quick-fix trends. Fad diets often make bold promises – whether it’s rapid weight loss, detoxification or optimised performance – but as experts point out, the fundamentals of healthy eating haven’t changed much over the years.

Some of these diets weren’t entirely wrong. Many pushed for more fruit, vegetables and fibre, which dietitians widely support. The grapefruit diet of the 1920s, for example, exaggerated the fruit’s supposed fat-burning properties, but as Travers points out, eating a variety of plant-based foods is key.

“Fad diets don’t tend to be balanced, often missing out food groups entirely, which is ultimately not good for our overall health,” she explains. Instead, she advocates for a portion-controlled diet based on vegetables, fruit, proteins, healthy fats and whole grains, with the addition of some dairy and fermented foods to support gut health.

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Fibre has also been a recurring theme, from the F-plan diet of the 1980s to today’s focus on gut health. Conrad Astley, of the Good Food Institute, highlights the benefits of plant-based meat alternatives – which, despite falling into the ultra-processed category, have been shown to reduce LDL (bad) cholesterol. “The example of plant-based meat is a good one – while it is generally UPF, it is a source of fibre, low in saturated fat and shown to reduce LDL cholesterol in clinical trials,” he explains.

Protein has also been central to many diet trends, from high-meat, low-carb plans like Scarsdale, Atkins and keto to the blood type diet’s claims about different protein needs. But while high-protein diets often deliver quick results, Roberta Alessandrini, director of the dietary guidelines initiative at PAN International, warns that some versions push excessive meat consumption, which isn’t just bad for the environment – it can be harmful to long-term health.

“Most nutrition scientists agree that carbohydrates – especially from whole plant-based foods – should form the foundation of our diet,” she explains. That doesn’t mean carbs should be eaten in excess, but completely avoiding whole grains and legumes deprives the body of essential fibre and nutrients.

Alessandrini notes that fad diets often appeal because they remove decision-making – even if they aren’t sustainable. “Following a fad diet might remove some of the stress and work, as some diets require eating the same foods every day, which can feel simpler. However, many of these diets are just trendy and, for some, less boring than the healthy, sustainable eating patterns that nutrition and health organisations recommend.”

This brings us to today’s biggest weight-loss trend: Ozempic. Instead of a meal plan, the drug is a pharmaceutical intervention, designed to suppress appetite and promote rapid fat loss. While it’s highly effective, Amy Williams, nutrition lead at the Good Food Institute, warns that quick fixes don’t support long-term habit change.

“Any approach focused solely on rapid weight loss – whether a restrictive meal plan or a drug – misses the bigger picture of sustainable health.” The drug’s rising popularity has also led to shortages for diabetic patients and comes with potential side effects like nausea and thyroid complications.

Spector, however, argues that the best approach is simpler – eat more plants and less meat. “Just trying to eat more plants and less meat, or a greater variety of plants, is key,” he explains. “Rather than one big blob of something, you’ve got multiple little ones, and you realise that, hey, it tastes good, and then it’s also better for you and fills you up more.”

Ultimately, fad diets come and go, but the best advice stays the same – focus on variety, prioritise whole foods and build habits that are sustainable for life. As Williams puts it, “There isn’t a single path to being healthy, and much of the evidence hasn’t changed in decades – eat a diverse plant-rich diet, consume the same amount of energy as you burn and keep active.”