Part II

• Drawbacks include lack of evidence, nutritional deficiencies, one-size-fits-all approach, among other factors

• This is the second part of a multiple-part series of articles. The first was published in the 20 February issue

The drawbacks of fad diets are the lack of evidence, nutritional deficiencies, a one-size-fits-all approach without considering the individual differences which may adversely affect those with serious illnesses and comorbidities, eating disorders and other health risks specific to diet types, the absence of one or more food groups, yo-yo dieting (rapid weight loss followed by regaining weight), unsustainability, and there being few or no recommendations for physical activities.

These concerns were pointed out in an editorial on ‘Revisiting fad diets to separate science from fiction’ which was authored by the Co-Editor of the Sri Lanka Journal of Medicine and Specialist Community Physician and Professor in Community Medicine attached to the Peradeniya University's Community Medicine Department, Prof. S. Navaratna and published in the said Journal's 33rd volume's fourth Issue, in January 2025.

Evaluating the benefits and drawbacks of fad diets

Fad diets often appeal to individuals seeking rapid results, as they can facilitate noticeable weight loss in a short period. For instance, low-carbohydrate diets, such as the ketogenic diet, work by inducing ketosis, where the body burns fat for energy, leading to quick reductions in body weight and fat mass. 

This initial success can act as a strong motivator for individuals to pursue further dietary changes. Another advantage is that many fad diets, like intermittent fasting, simplify meal planning by reducing the number of meals or limiting the time window for eating, which can make adherence easier for some people. Additionally, certain fad diets offer short-term improvements in specific health markers. For example, plant-based diets have been shown to lower cholesterol levels and reduce blood pressure, contributing to cardiovascular health.

The psychological boost provided by rapid results is another notable advantage of fad diets. People often feel empowered and encouraged when they see visible changes in their weight or body composition early in the process. This sense of achievement can inspire continued commitment to healthier lifestyle choices, at least temporarily.

Despite their appeal, fad diets are associated with significant disadvantages, including nutritional imbalances. 

Many of these diets restrict entire food groups, and sometimes one or more macronutrients, such as carbohydrates, fats, or proteins, as the main strategy for achieving rapid weight loss, leading to an imbalance in the nutrient intake. This restriction often leads to an imbalance in the nutrient intake, which can result in short-term weight loss but may compromise long-term health by causing deficiencies in essential macro- and micro-nutrients.

The elimination or severe reduction of specific macronutrients in these diets disrupts the balance needed for optimal metabolic function and overall wellbeing (Y. Schutz, J.P. Montani and A.G. Dulloo's ‘Low-carbohydrate ketogenic diets in body weight control: A recurrent plaguing issue of fad diets?’). 

For example, low-carbohydrate diets like the ketogenic diet significantly limit the carbohydrate intake to induce ketosis, while high-protein diets like the Dukan diet promote protein at the expense of carbohydrates and fats. The paleo diet excludes dairy, which is a primary source of calcium for many people, raising concerns about bone health over time. Similarly, plant-based diets, while beneficial for heart health, can lead to deficiencies in vitamin B12 and iron if not carefully managed (A. Niklewicz, A.D. Smith, A. Smith, A. Holzer, A. Klein, A. McCaddon, A.M. Molloy, B.H.R. Wolffenbuttel, E. Nexo, H. McNulty, H. Refsum, J-L. Gueant, M-J. Dib, M. Ward, M. Murphy, R. Green, K.R. Ahmadi, L. Hannibal, M.J. Warren and P.J. Owen's ‘The importance of vitamin B12 for individuals choosing plant-based diets’).

Another major disadvantage is the unsustainability of most fad diets. Their restrictive rules can make them difficult to maintain in the long-run, often leading to feelings of deprivation and eventual abandonment. This can result in a cycle of weight loss and regain, commonly referred to as ‘yo-yo dieting’ which has been shown to negatively impact metabolism and psychological wellbeing. Some fad diets limit the daily calorie intake to 1,000-1,200 kilocalories (kcal) or restrict carbohydrate consumption to less than 100 grams per day. 

This can lead to several negative effects, including fatigue, constant hunger, muscle loss, and disruptions to metabolism. Additionally, such severe restrictions can push the body into ‘starvation mode’ where the metabolism slows down, making it increasingly difficult to sustain weight loss over time (L. Mattson’s ‘Fad diets or exercise? Maintaining weight among millennials’). This phenomenon has been linked with increased cortisol levels.

Health risks associated with consumption include strain on the kidneys and increased cholesterol levels, potentially leading to long-term health issues. Detox diets, which claim to eliminate toxins, lack scientific evidence to support their efficacy and may cause adverse effects like electrolyte imbalances, fatigue, and muscle loss. Plant-based diets including vegan diets are often associated with cardiovascular health benefits but can lead to nutrient deficiencies if not carefully planned.

The evidence regarding the impact of fad diets on lipid profiles remains inconsistent. Both intermittent fasting and the ketogenic diet share mechanisms that include inducing lipolysis (the breakdown of fats and other lipids by hydrolysis to release fatty acids) and generating ketone bodies, which may offer cardiovascular benefits. However, intermittent fasting is generally considered a safer option compared to the ketogenic diet, as it carries a lower risk of causing hyperlipidaemia (M.S. D'Souza, T.A. Dong, G. Ragazzo, D.S. Dhindsa, A. Mehta, P.B. Sandesara, A.M. Freeman, P. Taub and L.S. Sperling's 'From fad to fact: Evaluating the impact of emerging diets on the prevention of cardiovascular disease’).

In contrast, the ketogenic diet has been associated with elevated low-density lipoprotein cholesterol (LDL-C) levels, which can be detrimental to cardiovascular health (J.S. Noain, A. Minupuri, A. Kulkarni and S. Zheng's ‘Significant impact of the ketogenic diet on LDL-C levels’). Fad diets have been linked to serious adverse events, such as ketosis, and in extreme cases, even death. Prolonged adherence to these diets has also been linked to ketosis and various other metabolic issues (J. Singh, P. Rasane, V. Tomer, S. Kaur, Y. Gat, K. Dhawan, D.K. Mahato and V. Kumar's ‘Fad diets: Dietary dilemmas, predicaments, and recommendations for its use’).

Psychological effects

In addition to physical problems, fad diets can lead to various psychological issues, including disordered eating patterns, such as binge eating or orthorexia (an obsession with eating healthy food). The restrictive nature of these diets often exacerbates body image disturbance, increasing dissatisfaction with one’s appearance and contributing to low self-esteem (B. Puspita, A. Lestari and T.R. Andayani's ‘The relationship between fad diet, body image, stress, and peer pressure with eating disorders in adolescent girls aged 16-18 years’ and the ‘Relationship between fad diet and eating disorders in female adolescents aged 16-18 years’). 

Additionally, the pressure to adhere to strict food rules can result in anxiety, stress, and feelings of guilt when individuals deviate from the prescribed eating patterns. Social isolation may also occur, as individuals on fad diets tend to avoid social events that involve food, which can lead to feelings of loneliness (L. Bacon and L. Aphramor's ‘Weight science: Evaluating the evidence for a paradigm shift’). Emotional dependence on dieting, where self-worth becomes linked to dieting success, may further perpetuate a cycle of dieting and self-criticism, potentially leading to depression.

Accordingly, health risks associated with fad diets are well-documented, and adherence to these restrictive and imbalanced eating patterns can pose serious risks to one's health, including nutrient deficiencies, fatigue, weight regain, and the development of disordered eating behaviours (J.M. Phelan, J.M. Joyce, K. Bode and S.K. Rosenkranz's ‘Opportunities for maximising the dietary quality of fad diets’). Instead, the best approach to weight loss and improved health is to follow a long-term, healthy, and balanced eating plan while maintaining an active lifestyle. The lack of scientific validation for many fad diets raises concerns about their safety and effectiveness. These diets may even exacerbate health problems. 

The appealing characteristics of fad diets are weight loss (many fad diets induce rapid weight loss by creating calorie deficits or altering metabolic processes); simplicity (fad diets often have simple rules, making them easy to follow initially); short-term health benefits (certain diets, like plant-based or low-carb diets, may improve markers like blood sugar levels, cholesterol, or blood pressure in the short term); and motivational boost (visible, rapid results can motivate individuals to maintain dietary changes). 

The drawbacks of fad diets are the lack of evidence (based on subjective opinion rather than scientific evidence); nutritional deficiencies (restrictive diets may lead to imbalances or deficiencies in essential nutrients); a ‘one-size-fits-all’ approach without considering the individual differences, which may adversely affect those with serious illnesses and comorbidities); eating disorders and other health risks specific to diet types; the absence of one or more food groups; yo-yo dieting (rapid weight loss followed by regaining weight is common, negatively affecting metabolism and psychological health); unsustainability (many fad diets are difficult to maintain in the long-term due to strict rules or social limitations); and few or absent recommendations for physical activities.