Fad Diets — What’s the Harm?

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This article was first published in January 2020 Thriva Newspaper.

As we reflect on the past year and think about our future goals, the urge for self-improvement can be strong. This is why detoxes, cleanses and extreme weight loss diets really thrive in January.

Unfortunately, this quest for a “new me” does more harm than good when it involves extreme and unbalanced diets. This article will explore the impact of fad diets on both our physical and mental health.

The Impact on Physical Health

Nutritional deficiencies are a common feature of fad diets, although this depends on the type and severity of the diet.

For example, juice cleanses are low in calories, protein, fat, calcium, iron, iodine, selenium and vitamin B12.

Whereas the carnivore diet is deficient in carbohydrates, fibre and many vitamins, while being high in saturated fat – which is a very unhealthy balance of nutrients for heart and gut health.

Most of the current popular weight-loss diets are variations of low carbohydrate or very-low-calorie diets.

Consuming a very low amount of calories, particularly in those who are physically active, can lead to numerous physical issues such as: tiredness, muscle wasting, a weakened immune system, a higher risk of injury from sport, gut issues, worsened heart health, endocrine issues (impacting thyroid and hormonal function), fertility issues, weakened bones and a reduced resting metabolic rate (1).

The ketogenic diet (A.K.A. the keto diet) was originally used as a way of managing certain cases of childhood epilepsy, and specific genetic metabolic disorders (with the support of a specialist dietitian and medical team).

The keto diet is now a popular weight loss diet which involves consuming little to no carbohydrates. This restrictive diet can lead to a low intake of fruit and wholegrains, and a high intake of saturated fat.

‘Keto flu’ is another possible side effect, this includes symptoms like: weakness, exhaustion, headaches, nausea, diarrhoea and cramps.

Water fasting is an extreme approach which involves eating no food and only drinking water for 24 – 72 hours. Unsurprisingly this has been linked with low energy, headaches and nausea. Worryingly, water fasting has also been linked to low sodium levels, high blood pressure and serious dehydration (2).

Weight loss pills and supplements can also be very harmful. Some of these are basically just laxatives (e.g. weight loss teas) which can lead to diarrhoea and issues absorbing nutrients and medication.

‘Fat burners’ are weight loss supplements that have been associated with serious health issues. For example, there have been instances of liver failure related to the use of green tea supplements and illegal supplement dinitrophenol (DNP) has been linked with comas and even deaths due to its heart rate and temperature regulation (3-4).

Extreme weight loss can lead to a lower metabolic rate than expected.

For example, a study based on “The Biggest Loser” TV show found that the participants’ resting metabolic rate was roughly 500 calories per day lower than expected after six years (i.e. even when the expected reduction in metabolic rate due to having less body mass was taken into account) (5). It is thought that changes in fat tissue, hormones and appetite may play a role in this phenomenon, which is called metabolic adaptation.

The Impact on Mental Health

Although some people may feel empowered in the early days of a restrictive diet, this rarely lasts, as these diets are unsustainable which inevitably leads to feelings of failure.

In turn, this can lead to yo-yo dieting and cycles of gaining and losing weight.

This weight cycling has been linked with psychological issues such as: lower self-confidence, a higher risk of depression and binge eating disorder (6-7).

Similarly, restricting dietary intake is a common trigger for binge eating, and binge eating is associated with depression, anxiety and weight cycling (8). Therefore this can lead to a very difficult cycle of bingeing and restricting.

Furthermore, being on a restrictive diet is often exhausting, so this can lead to fatigue and irritability which gets in the way of living a healthy lifestyle.

If you are starving and worn-out it really isn’t easy to prioritise exercise, cook or socialise etc.

In some cases the feeling of control and inflexibility that often accompanies a fad diet can lead to an unhealthy obsession with healthy eating (which is known as orthorexia). This can be extremely damaging, as it leads to a lot of food anxiety as well as social isolation.

Even in less extreme cases, the mindset of being on a diet or ‘being good’ can create a very black and white relationship with food, which can trigger a lot of unnecessary guilt and anxiety.

What is the Alternative?

The best evidence for a health-promoting diet supports consuming:

  • Plenty of wholegrains, fruit, vegetables, beans and pulses
  • Healthy fats such as plant-based oils, avocado, nuts and seeds – rather than too many foods high in saturated fat like butter, coconut oil and fried foods.
  • Good sources of protein and calcium at meals.

Most people living in the UK and Ireland should also consider taking a 10mcg vitamin D supplement during the winter.

We don’t need to avoid any food in order to have a balanced diet, what matters is the overall balance and variety in our diet. Therefore, everything is fine in moderation.

Having a flexible mindset in terms of what you eat is also a key part of having a healthy and balanced relationship with food.

Those who have a history or yo-yo dieting or a poor relationship with food may benefit from seeking support from a psychologist or intuitive eating practitioner.

It is also just as important to think about our overall lifestyle and wellbeing by prioritising: sleep, rest, movement, relaxation, socialising, not smoking and not consuming too much alcohol. Here’s to a happy, healthy and fad-free 2020!


  1. Mountjoy et al. (2008) “IOC consensus statement on relative energy deficiency in sport (RED-S): 2018 update” [accessed December 2019 via: https://www.ncbi.nlm.nih.gov/pubmed/29773536]
  2. Finnell et al. (2018) “Is fasting safe? A chart review of adverse events during medically supervised, water-only fasting.” [accessed December 2019 via: https://www.ncbi.nlm.nih.gov/pubmed/29458369]
  3. LiverTox: Clinical and Research Information on Drug-Induced Liver Injury [accessed December 2019 via: https://www.ncbi.nlm.nih.gov/books/NBK547925/
  4. Grundlingh et al. (2011) “2,4-Dinitrophenol (DNP): A Weight Loss Agent with Significant Acute Toxicity and Risk of Death” [accessed December 2019 via: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3550200/
  5. Fothergill et al. (2016) “Persistent metabolic adaptation 6 years after “The Biggest Loser” competition” [accessed December 2019 via: http://onlinelibrary.wiley.com/doi/10.1002/oby.21538/full]
  6. Foster et al. (2012) “Psychological Effects of Weight Cycling in Obese Persons: A Review and Research Agenda“ [accessed December 2019 via: https://onlinelibrary.wiley.com/doi/full/10.1002/j.1550-8528.1997.tb00674.x]
  7. Madigan et al. (2008) “Is weight cycling associated with adverse health outcomes? A cohort study” [accessed December 2019 via: https://www.ncbi.nlm.nih.gov/pubmed/29277416]
  8. Hudson et al. (2008) “The prevalence and correlates of eating disorders in the National Comorbidity Survey Replication” [accessed December 2019 via: https://www.ncbi.nlm.nih.gov/pubmed/16815322]


Maeve has been consulting on The Food Medic Educational Hub for 12 months now and has been a huge asset to the team. Her ability to translate some very nuanced topics in nutrition into easy-to-follow, informative articles and infographics is really admirable.

Dr Hazel Wallace

Founder of The Food Medic

Maeve is incredibly talented at sharing scientific information in an easy to understand way. The content she shares with us is always really interesting, clear, and of very high quality. She’s one of our favourite writers to work with!

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Senior UX Writer at Thriva Health

Maeve has written extensively for NHD magazine over the last few years, producing a wealth of dietetic and nutritional articles. Always evidence based and factual, Maeve creates material that is relevant and very readable. She provides high quality work with a professional and friendly approach. Maeve is a beacon of high quality knowledge and work within the nutrition writing community; and someone NHD magazine is proud to work with.

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