10-second takeaway: Fad diets frequently fail and can harm mental health, exacerbated by societal pressures and ultra-processed foods. Health professionals should encourage sustainable, health-focused goals and positive nutrition education.

Diet, weight loss and fitness goals consistently rank top of New Year’s resolutions, driving huge marketing activities to capitalise on this annual trend. But given the high “failure” rates of January diets, what sort of impact are fad diets having on the mental health of our population?

Why are fad diets an increasing problem for patients?

According to The Health Survey for England 2021, an estimated 25.9% of the population were recorded as obese, and 37.9% were considered to be ‘overweight’. Given the increasing use of these terms and our national battle with weight gain, quick-fix fad diets are rising in popularity, especially around January. 

Some of the latest research highlights a few of the difficulties in following these plans. It invites us to reflect on issues such as weight stigma, our food environment and how these are intricately linked with our mental health.

The impact of fat and sugar on the brain

Our food environment presents patients with tempting, cleverly-marketed ultra-processed food options, making weight gain very easy. We already know that these foods, which are usually high in fat and sugar, can be hard to resist and recent research now gives us further evidence as to why.

McDougle et al. (2024) provide insights into the mechanisms of gut-brain communication. The group demonstrated in mice that vagal nerve neurons located in the gut trigger dopamine release via distinct nigrostriatal circuits, thereby generating a “reward” in response to certain dietary stimuli. When consuming fat and sugar together, these circuits are stimulated to a greater degree compared to just one macronutrient alone, even when controlling for calorie numbers. 

Ultra-processed foods are typically high in both fat and sugar, so this research highlights how cravings for these types of food could develop. This can provide a difficult barrier for patients looking to lose weight on fad diets that are typically restrictive, leading to feelings of guilt when these diets inevitably fail. 

Fad diets and mental health

Research by Romo et al. (2024) looked into the effect of weight cycling on long-term mental wellbeing. They found that most participants were initially motivated to diet to conform to societal pressure or to combat weight stigma, rather than for health reasons. When starting a diet with this motivation, the participants were more likely to undergo weight cycling (rapid weight loss, regain, and so on) with damaging effects on mental wellbeing including feelings of shame, unhappiness, overall preoccupation with weight and disordered eating.

How should health professionals advise patients on fad diets? 

From the research, it is probably good to discourage patients from pursuing quick-fix fad diets at all, and to ensure that the motivations for dieting do not stem predominantly from non-health-related reasons as this could kickstart a potentially addictive cycle. For those who need to lose weight to improve their health, researchers also hope that research into how fat and sugar communicate with the brain is promising for the future of anti-obesity treatment.

There are some positive steps being made. It was recently announced that the Australian curriculum is being changed to educate children and young people in a more positive light about nutrition and the body, in a bid to combat diet culture and weight stigma. In the UK, to limit the popularity of ultra-processed food, some places (including Bristol, Transport for London and Brighton and Hove) are leading the way by restricting advertising of some ultra-processed foods. More solutions, particularly around awareness and education could help improve the nation’s relationship with food and limit those January diets, shifting towards more sustainable health-orientated goals.

The bi-directional influence of the brain and our food choices is clear, the food we eat can communicate with our brain and societal pressure can dictate how we eat and feel about food. This invites us to an increased understanding of how our diet, weight loss and mental health are so intricately linked.

Key takeaways

• Fad diets often fail, leading to negative mental health effects such as guilt and shame, especially when driven by societal pressures and weight stigma.
• Ultra-processed foods high in fat and sugar trigger brain reward circuits, making them hard to resist and contributing to weight gain, complicating weight loss efforts.
• Health professionals should discourage quick-fix diets and focus on health-oriented goals, promoting positive nutrition education and addressing societal pressures around weight.

 

Looking for more high-quality lifestyle medicine education? Make sure to explore our free CME-accredited webinars and the latest series of our Nutritank podcast.

 

About the author

Elisa Daly is a current MSc student in Nutrition and Behaviour, having already gained a PG cert in the Neuroscience and Psychology of Mental Health at King’s College London. She is particularly interested in the bi-directional links between nutrition and the brain and is keen to contribute to and raise awareness of the research in this field. Her passion is to bring together nutrition and mental health knowledge with her training background to make an impact on mental health outcomes, particularly in young adults.

Reference list
McDougle, M., de Araujo, A., Singh, A., Yang, M., Braga, I., Paille, V., Mendez-Hernandez, R., Vergara, M., Woodie, L. N., Gour, A., Sharma, A., Urs, N., Warren, B. and de Lartigue, G., 2024. Separate gut-brain circuits for fat and sugar reinforcement combine to promote overeating. Cell Metabolism, 36 (2), 393-407.e397. Doi: https://doi.org/10.1016/j.cmet.2023.12.014 

Romo, L., Earl, S., Mueller, K. A. and Obiol, M., A Qualitative Model of Weight Cycling. Qualitative Health Research, 0 (0), 10497323231221666. Doi: https://doi.org/10.1177/10497323231221666