Fad diets are trendy or popular diet plans that promise a ‘quick fix’ when it comes to weight loss. They typically involve cutting out certain food groups or drastically reducing calorie intake, often suggesting you eat far fewer calories than your body actually needs to function normally.

These diets usually gain attention quickly but might not have enough scientific evidence to back up their claims of being effective or safe. They could leave you lacking essential nutrients, exclude certain foods, or prioritise weight loss over overall health.

For these reasons, it’s really important to chat with your doctor or nutrition expert before starting any diet. They can help you weigh the ups and downs and offer advice on how to deal with any potential shortcomings, like which nutrients might be lacking and what supplements could help.

  • Fad diets promise quick weight loss but aren’t always backed up by scientific evidence and may lack essential nutrients.
  • Famous fad diets like Atkins, ketogenic, paleolithic, and intermittent fasting have potential weight loss benefits but also come with significant health risks.
  • A good diet prioritises a wide range of foods and promotes moderation for long-term health.
  • Weight loss medication often works best alongside diets that are low in fat, contain minimal spice or use few processed foods in order to keep side effects at bay.

What is a fad diet?

Fad diets are nothing new, with the first diet book being published in the 16th century.1 But their popularity soared during the 1800s and 1900s. Some diets to be developed during these periods have been dangerous to say the least. For instance, there was the ‘Arsenic Diet,’ where people were encouraged to take pills containing arsenic, often without knowing it was in there.2 Other fads were the ‘Smoking Diet,’ where cigarettes were advertised to women as a method to help them manage their weight3 and the ‘Sleeping Beauty Diet’, where people were sedated for days or weeks to promote weight loss.4

These are of course extreme cases but they share some key features with most fad diets. They promote fast weight loss and are popular within certain groups of people usually for short periods of time.

Fad diets often promise fast weight loss, with results supposedly achievable in just a few weeks. In comparison, healthy diet plans promote life-long habits and regular exercise. Naturally, a “quick fix” can be much more appealing than a commitment to long-term lifestyle changes.

Plus, diets like the keto or palaeolithic diets (more info below) give clear-cut guidelines on what to eat. Being told what to eat is often easier than making your own food choices, especially for those who don’t have the time or resources to research the nutritional value of what they eat.

On top of that, fad diets often tap into our social nature. People like to feel part of a group and when social media platforms are buzzing about a certain diet trend, it’s only natural to want to join in. So in a way, fad diets satisfy a social need.

Why are fad diets bad for you?

There are many reasons why fad diets are bad for you, and some vary from diet to diet. But generally speaking, since they often eliminate important foods, fad diets might lead to:

  • feeling weak and tired;
  • being dehydrated;
  • constipation;
  • nausea and headaches; or:
  • not getting enough vitamins and minerals.

Fad diets can also have long-term consequences. Since they’re all about quick fixes and don’t give you lasting healthy habits, you can get trapped in a “yo-yo” cycle of losing weight and then gaining it back. This “yo-yo” cycle is linked with an increased risk of heart disease, metabolic disorders5 and mental health issues like depression and anxiety.6

Many fad diets also promote the idea that certain foods are “good” while others are “bad,” leading to feelings of guilt, shame and stress when you eat. This way, they can make you develop “bad” eating habits and create unhealthy relationships with food or develop negative body image issues.

How to spot a fad diet

You can tell a fad diet apart from a healthy and balanced eating plan by looking at some key traits.7 For example, a fad diet often:

  • promises fast weight loss and doesn’t focus on creating long-lasting eating habits;
  • zeroes in on one food type or cuts out entire food groups and might not give you all the nutrients you need;
  • doesn’t include advice on exercising;
  • isn’t a way of eating you can stick to long-term;
  • doesn’t include warnings for people with chronic illnesses like diabetes; or:
  • doesn’t have much scientific proof to back up its claims.

Famous fad diets

There are many fad diets out there, whether they’re low-carb, low-fat, high-fat, high-protein, detox diets and so on. We’ll take a look at some of the most popular ones below, breaking down how each diet works and discussing their positives and negatives.

Atkins diet (AD)

It was introduced in the 1970s by cardiologist Dr. Robert Atkins as a low-carb, high-protein diet. The Atkins Diet (or AD for short) was designed on the belief that carbohydrates lead to weight gain by disrupting metabolism. It promotes cutting carbs down to less than 5% of total calories a day, while allowing unlimited protein and fat. The diet also encourages staying hydrated, taking vitamin and mineral supplements and regular exercise.

It has four phases:

  1. Induction. Lasts two weeks; carb intake is restricted to less than 20g a day, focusing on protein-rich foods like beef, poultry, fish and eggs, along with fats like olive oil.
  2. Ongoing weight loss. Continues until weight loss slows or stops; gradually increasing carb intake by 5g per week, incorporating nutrient-dense carbs, proteins and fats.
  3. Pre-maintenance. Involves adding 10g of carbs per week until weight loss stalls, then reducing carb intake by 5-10g to resume weight loss.
  4. Lifetime maintenance. Allows a wider range of foods while maintaining carb intake between 40-90g a day.

Pros:

There is some evidence to suggest that AD may lead to greater weight loss compared to traditional diets. For instance, in one study, 132 severely obese patients were split into two groups: one following AD and the other a low-fat diet (LFD) for 6 months. Those on AD lost an average of 3.8 kg more weight than the LFD group.8

Another study involving 63 obese participants found that after six months, the AD group lost 4% more weight than those on the conventional LFD.9

Also, AD has been linked to reducing seizures and improving cholesterol levels.7

Cons:

Compliance (“sticking” to the diet) seems to be a problem associated with AD, since the studies mentioned above often have many participants dropping out and sometimes don’t provide clear conclusions.

Plus, there are health concerns associated with following AD, such as an increased risk of developing kidney stones, chronic kidney disease, and metabolic acidosis (this happens when there’s too much acid in your body due to metabolic problems).7

Ketogenic diet (KD)

The classic KD was developed in 1923 by Dr.Russell Wilder. It’s moderate on protein, heavy on fats and low on carbs. It advises getting around 5–10% of your calories from carbs, 20–25% from protein and 65–80% from fats. KD also involves advice about fasting, keeping yourself well-hydrated, getting some exercise, electrolytes and nutritional supplements.7

KD works by changing your body’s metabolism. Normally, your body runs on glucose, which comes from carbs. But when you’re on the KD and cutting back on carbs, your body has to find another fuel source, ketone bodies, through a process called ketogenesis. This shift can boost fat breakdown and lead to weight loss, but also comes with a few risks for your health (see below).

Pros:

The KD has shown neuroprotective effects in conditions like Alzheimer’s, Parkinson’s disease, depression and autism.10

Also, there is some scientific proof that the diet works. A meta-analysis found that over 12 months or more, 1415 people on a modified KD lost on average 0.91kg more than people on LFD. Moreover, the modified KD group achieved greater long-term weight loss than the LFD group.11

Cons:

KD comes with common side effects that include nausea, vomiting, gastrointestinal discomfort, fatigue, feeling faint or dizzy, fluctuations in heartbeat and hypoglycaemia (low blood sugar levels). KD may also have a negative impact on your cholesterol levels and cause low bone mineral density, which could lead to fractures.7

Palaeolithic diet (PD)

The PD, also known as the Stone Age, caveman, or hunter-gatherer diet, was first presented in 1985 by Eaton and Konner. The idea behind this diet is that our bodies haven’t adapted as fast as our food systems, so we’re not genetically equipped to stay healthy eating foods our bodies are not adapted to (like processed foods, dairy products and grains). So the PD suggests that the foods our ancestors ate back in the Stone Age are better suited to our bodies than what we typically eat in modern times.

PD has a simple set of guidelines: it allows unlimited consumption of lean meats, fruits, and non-starchy vegetables, while restricting dairy products, legumes, cereals, and processed foods. Unlike some other diets, PD doesn’t typically include advise on portion control or calorie counting.7

Pros:

Some studies show that people following the PD experience weight loss of about 4%-6% over 10-12 weeks, although these studies involved a small number of participants, ranging from 29 to 70 people. Most of these studies also reported a slight decrease in blood pressure among participants.7

Cons:

The PD typically provides around 50% less calcium than the recommended daily intake. It’s also associated with lower levels of “good” cholesterol and higher levels of “bad” cholesterol. Plus, the long-term effects of this diet remain uncertain because most studies have only followed participants for a short period.7

Intermittent fasting (IF)

Compared to other diet plans, IF is more about scheduling your meals than what you eat and calorie counting. Key features of IF are restraining from eating for a period of time, followed by eating normally. There are a few different versions of IF, with the most commonly used being:

The 5:2 method, which involves eating normally for five days and ‘fasting’ for two non-consecutive days (for instance Monday and Thursday); on a ‘fast’ day, you’d normally eat around 500-600 calories;
The 16:8 method involves fasting for 16 hours a day and eating during the remaining eight hours each day.

Pros:

One positive of IF is that it’s effective for weight loss, but similarly effective to a calorie restricting diet after six months.12 On top of that, a meta-analysis found that IF caused a significant decrease in glucose levels, fat mass and improvements in the “appetite-regulating hormones” adiponectin and leptin.13

Cons:

IF can cause increased free fatty acids, up to three times greater than normal levels. Higher amounts of these molecules can lead to conditions like type 2 diabetes and cancer, but more research is needed to nail down a solid link between IF and these health issues.14

Fatigue, constipation and headaches were also more frequently reported in people following the IF diet compared to a calorie restriction diet or no restrictions.12

And lastly, some studies have found evidence to suggest that IF can lead to decreased testosterone levels in both men and women, as well as decreased thyroid hormone levels and increased cortisol (the hormone associated with stress) levels.21, 22

But research on the long-term effects of IF have only scratched the surface and more studies are needed to understand them.

Juice cleanses (JC)

This is a type of diet that involves only drinking juices from fruits and vegetables. Fruit and veg are high in nutrients, so there are some positives to this diet. Some people believe that consuming only juices can work as a way to detoxify their bodies and flush out toxins.

Pros:

Consuming lots of liquids can be good for your kidneys and improve overall hydration so long as the juice diet you follow isn’t too high in oxalates (contained in green leafy vegetables, potatoes, grains, almonds, soy) and doesn’t recommend the use of laxatives.

Cons:

Many juice cleanse diets last less than two weeks and may result in weight loss, but they don’t suggest lasting lifestyle recommendations so this change is only likely to be temporary. Plus, this type of diet doesn’t contain enough fibre, proteins or fats, which are crucial for a normal functioning of your body.

Although there isn’t enough research on humans, low-calorie JC diets may increase cortisol levels and appetite, resulting in difficulty in losing weight, followed by binge eating and weight gain.15

In some cases, juice cleanse diets have been found to be extremely dangerous and have caused kidney failure due to oxalate nephropathy (when your body can’t eliminate enough oxalate, leading to its accumulation in the kidneys).16

What constitutes a ‘good’ diet?

A ‘good’ diet is one that prioritises a wide range of foods eaten in moderation. It’s basically one that gives advice that you can stick to long-term. Typically, a healthy and balanced diet should include these groups of foods:17

  • Plenty of fruit and veg, as they are essential sources of nutrients and fibre. You need at least five portions a day, one portion of fresh fruit or veg being 80g (that’s one medium sized banana or two small fruits like plums or kiwis).
  • Protein sources either from animal sources like fish, meat, eggs and dairy, or plant-based sources like beans and lentils.
  • Wholegrain starchy foods like bread, pasta, rice or cereals like bulgur and quinoa.
  • Dairy products in moderation.
  • Unsaturated fats including nuts and seeds, oily fish like salmon or trout, sunflower, olive, avocado or rapeseed oil.

The Mediterranean diet (MD) is often considered a healthy diet, although some articles categorise it as a fad diet. It recommends eating lots of fruit and veg, nuts, wholegrains, fish, olive oil and smaller amounts of meat, eggs and dairy.

It’s also linked to long-term positive health outcomes like reduced risk of heart disease. The effects of various diets, including the American Diabetic Association (ADA) diet, traditional Mediterranean diet (tMD), or low carbohydrate Mediterranean diet (LCM) were compared in a clinical trial involving 259 participants. After 12 months, the LCM group had the highest weight reduction (10.1kg compared to 7.7kg for ADA and 7.4kg for tMD). The LCM group also had improved cholesterol and glucose levels.18

Which diet should I follow on weight loss medication?

Weight loss treatments work in various ways, but can be generally classed as appetite suppressants (which curb your hunger) or anti-absorption medication (which work by reducing the amount of fat you absorb from food).

Gastrointestinal effects like nausea and vomiting are common side effects for both groups and in order to avoid them, it’s often best to take weight loss medication alongside diets that follow the recommendations for a ‘good’ diet, and are low in trans and saturated fats, spicy or processed foods. These foods can make nausea and vomiting worse and cause people to stop the treatment. Carbonated drinks and some dairy products should also be avoided if they make your symptoms worse.

Instead, it’s recommended that you consume foods that are easy to digest, including sources of protein like lean meat and healthy foods. Plus, you need to make sure you drink plenty of water in small portions. If you still suffer from side effects like nausea you could try to add ginger or mint (such as in ginger or peppermint tea) to your diet, as there is some evidence to show that these foods can help.19, 20