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12 Aug, 2023

Why extreme diets fail

Studies show that 95% of diets fail and most people will regain their lost weight in 1-5 years. Here we look at why these extreme diets tend to fail, and how we should approach weight management instead.


Everybody is different when it comes to weight loss and there is no one size fits all. Our behavioural habits and the psychology around food has a huge role to play in weight loss, but our diet is essential. Weight loss is essentially caused by a deficit in calories which cause the body to use up fat stores. As Nutritionist Rob Hobson explains, there are generally two common ways to lose weight and most diets fall into one or the other. These are low fat and low carbohydrate.

The low-fat diet is very much calorie based and includes eating lower fat versions of food, because fats contain more calories than carbohydrate and protein. This way of losing weight still requires someone to choose healthy foods rich in lean proteins and healthy fats alongside plenty of vegetables. But simply focusing on calories alone does not ensure a healthy diet. Not all calories are created equally – it’s important to make sure every calorie counts by eating nutritious meals made up of mostly whole foods.

The low carbohydrate approach involves eating a diet which is high in fat and moderate amounts of protein. The lack of carbohydrate puts people in a state of ketosis which is when their body is using fat for energy instead of glucose. This can lead to quick initial weight and fat loss, however research into the long-term effects is lacking.

Can crash diets slow down my metabolism?

Yes! This is to say, as Nutritional Therapist Phoebe Liebling explains, that unhealthful approaches to weight loss, those that force the body into a prolonged stressed state, will negatively impact our natural body mass balancing mechanisms. If someone were to follow a well-managed regime that helped them to lose weight progressively over time then that wouldn’t have the same effects.

Our body works on a number of ‘set points’ which it determines based on its previous experiences. You have your normal, resting state (AKA parasympathetic nervous system dominant) points which is where you will sit with things like your pulse, blood pressure and breathing rate on any given day, and then you have your sympathetic nervous system dominant (AKA fight or flight response/stressed state) situation which will alter these. Instead of having to adjust each time you swap between the two imagine your body has marks on a wall - when it needs to quickly switch because it thinks there’s a threat to your survival (which is what our sympathetic nervous response is there to do) it just jumps to that new mark as opposed to climbing a ladder rung by rung.

The link between the above and how crash dieting influences your metabolism refers mainly to how and how much additional energy we hold as fat, and consequently the ease with which we can burn it off. Yo-yo dieting is seen as a form of threat because you are depriving the body of energy in a sudden way, and your brain is just a control centre in a black box, it can’t tell that the danger signal you have created is because you’ve decided you need to quickly drop X number of pounds at speed, so it says to your body that it should hold on to extra energy stores (usually around our middles as it’s easier to access if it’s in one place) because we are living in a time with uncertain food supply. This would also link with an incremental slowing of the energy we use overall in an attempt to preserve what we have for longer.

This is why those who diet in this way will progressively find it more difficult to lose weight over time, their body has taken their set points up the wall so they will hold more fat as a baseline, and plus when they return to eating in a more normal pattern they then find they put on more weight as their body is in storage mode using up the fuel they put in at a slower pace. This is something well documented in clinical studies and in fact those who had never dieted always come out as the leaner group when compared to yo-yo dieters.

So what is a healthy way to lose weight?

As Hobson notes, needless to say, dieting is rarely successful and can cause unhealthy eating habits and attitudes towards foods that are difficult to shake off. Many people who like to follow diet regimes often fail to keep the weight off in the long term. A better approach is to think about making lots of small changes to the way you eat and focus on choosing to eat healthy meals based around whole foods (mostly plants).

You can read more about our nutrition philosophy here. Our mission is to make the healthy choice the easy choice, to help you adopt a vibrant and healthy lifestyle that you'll enjoy so much you won't even have to think about your weight. We have hundreds of recipes on our blog to inspire you to create delicious healthy food, or if you need more of a helping hand, our meal plans have got you covered.


Rob Hobson is a registered nutritionist (BSc, MSc, AFN), published author and food writer. Rob has 15 years of experience working with some of the UK’s leading food companies, government agencies, NHS and private clients as well as regularly writing in the media for publications including the Daily Mail online.

Phoebe Liebling is a London based Nutritional Therapist and award winning product and recipe developer. She splits her time between seeing clients for clinical consultations and her work as a consultant which can have her doing anything from formulating therapeutic supplements and training other practitioners, to getting into the kitchen and creating wonderfully delicious and nutritious things. A running theme through everything Phoebe does is a passion to empower others to understand how dietary and lifestyle choices impact our health and wellbeing, and to show that eating in a health minded way does not mean sacrificing on flavour or enjoyment! More information on her clinical services can be found on her website, and you can find endless foodie inspiration with that added educational spin to it on her Instagram feed as @_naturalnourishment.