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Why diets fail

Fad diets can be a losing battle for people intent on shedding kilos. But if you win the mind over matter battle and consider the flaws in quick-fix dieting you'll have a better chance of keeping weight off long-term, reports MiNDFOOD.

Why diets fail

We are all familiar with the evidence that proves the latest diet is a winner. A photo of an overweight person in baggy clothes looking glum next to another picture of them at a more healthy weight looking well-groomed and happy.

Fewer people are aware that dieters routinely fail to achieve their long-term weight-loss goals. A review published in the journal American Psychologist in 2007 stated there was “little support for the notion that diets lead to lasting weight-loss or health benefits”. Diets do produce short-term weight loss of 5-10 per cent of body weight, but studies consistently show that weight 
is regained, with some people even ending up heavier than when they started.


Diet programs can be divided into two groups – the outlandish and the reasonable. Many diet fads rely on a gimmick (“Eat as much cabbage soup as you want!”) or an unproven manipulation of normal eating patterns (eliminating fat or carbohydrates, or increasing protein). These diets often promise a quick fix and promote a too-good-to-be-true solution.  

A balanced diet is a healthier way to lose weight, particularly when combined with exercise. A 2006 Cochrane review declared that exercise was effective as a weight-loss intervention, particularly when combined with dietary change. And the same research shows that even if no weight is lost, exercise improves health.

Healthy eating? Exercise? You’ve heard it all before, right? So why, despite all your efforts, doesn’t it seem to work for you?


Dr Judith Beck is a world-famous clinical psychologist and researcher who has applied her specialist knowledge to 
the problem of healthy weight loss. 
Dr Beck’s area of expertise is cognitive behaviour therapy (CBT). CBT looks at people’s problems from a number of angles including their thoughts, feelings and behaviours. Dr Beck concluded that people struggle with diets because they haven’t been taught important skills to combat sabotaging thoughts, emotions and behaviours. She came to believe that changing behaviours, such as eating patterns, without changing thoughts (why you reach for the chips after a hard day) 
can lead to a return to those behaviours.

And CBT seemed to work. A Swedish study of 54 adult women who enrolled in 
a 10-session cognitive therapy for weight loss lost an average of 8.5kg compared with a loss of 0.6kg for those who received advice regarding diet and exercise but did not learn cognitive therapy techniques. After 18 months, the cognitive therapy group maintained their weight loss (average 5.9kg) whereas the non-cognitive group put on weight, ending up heavier. Another Cochrane review in 2005 found support for behavioural and cognitive-behavioural strategies to enhance weight reduction in 
a sample of 3495 participants. 

Let’s look at some examples of how our thoughts can undermine weight loss no matter how determined we are to succeed.



A good diet and exercise plan works right up until: the night where you work late and decide to order takeaways; a miserable rainy day when it’s easier to stay in your warm bed than hit the gym; or the dinner party where you have two helpings of irresistible chocolate mousse, plus crackers and camembert afterwards. Then what happens? The problem begins when you say to yourself: “I was weak, this is exactly what always happens”; “I can’t do it”; “It’s not fair, other people don’t have to do this”; “Oh, what the hell, the diet is broken now anyway, I may as well enjoy myself”. In other words, the catastrophic interpretation of the event (breaking your diet) leads you to feel worse, and you are therefore prone to eating more and exercising less.

Sabotaging thoughts, emotions, behaviours and even hunger sensations can be overwhelming if you are not trained in how to respond to them. Unless you examine your particular triggers and then use psychological skills to combat them, 
it doesn’t matter what healthy food plan 
you are on. Preparation is the key.


People typically overestimate the influence of their own willpower and underestimate the other factors that impact on their behaviour. The sight and smell of food (psychologists call these external cues) seem to invite you to take a bite. How should you handle the smell of hot chips when you’re at the bar, have a Mediterranean platter right in front of you, or see your friends eating ice-cream? Contrary to popular opinion, it’s not as simple as relying on willpower and telling yourself ‘just don’t eat it’.

CBT teaches ways of talking back to your inner saboteur. CBT and mindfulness skills (becoming aware of what we pay attention to) can help us regulate our emotions without reaching for the 
nearest or most tempting food offerings.


At the same time as over emphasising willpower, we are bombarded with the ‘easiness’ of dieting – “If I can do it, you can too, just follow this diet …” It is interesting that we try to solve complex problems  
with simple solutions. By doing this we run the risk of oversimplifying significant health problems such as obesity, and make people feel worse and less likely to pick themselves up and have another go.

Often we view food as fuel and wolf down our lunch before quickly getting back to our work or other tasks. Studies have found that by eating slowly your brain has time to register that you’re full. Research in 2008 also found that people eat less when they eat slowly and, when they notice and enjoy every mouthful, they feel more satisfied when the food is gone.

The effects of distraction on volume of food eaten also make for engaging reading. A study by Georgia State University found people ate more when watching TV, or were having a conversation or listening to music. A Bristol University study showed that when participants focused on the process of eating, they lost the desire to have dessert, while a group eating the same amount but playing a video game at the same time reported a high desire to continue to eat 10 minutes after finishing the same portion.

There is also evidence that plate sizes and plate shape can influence how much we eat without being aware of it. Having 
a visual cue of your plate not being empty is possibly a stronger cue to continue eating than the feeling of a full stomach (which does not register the sensation of ‘full’ 
until 20 minutes after eating).

So what are the ways of combating these thoughts and environmental/cultural  factors that sabotage healthy dieting?


If we take into account the above, the ‘how to’ becomes much easier. Here’s an example: Jack is overweight, does no exercise, works long hours and then has 
a long commute home. When he gets home he feels hungry, irritable because of the traffic and exhausted from the day’s work so he reaches for the salted peanuts and 
a beer. He follows this with a takeaway pizza and promises himself that it will be the last time, just as he did last week.

If Jack could acknowledge that long hours and the stressful commute were triggers for his irritability, he would then be in a position to choose whether to do something about changing them. For example, he could take a 10-minute break from work every 90 minutes to recharge 
or walk for a half-hour during his lunch break. He could have fruit and nuts available as snacks in the afternoon and have ingredients for a stir-fry in the fridge at home. He might also choose to involve his family or friends in his weight-loss efforts or have a buddy join him at the 
gym before or after work.


In clinical psychology, treatments are based on science. However, clients are encouraged to try out experiments each week to see how a theory relates to them. Everything is treated as ‘grist for the mill’ and any result is seen in this light rather than the success or failure mindsets many people hold.

Responding to binges or mistakes 
as temporary setbacks rather than a reason to give up is the key to long-term success. Instead of believing the thought “I’m so weak, I might as well give up”, 
try to be more compassionate towards yourself (“I had one slip up, I’m now 
back on track”). Changing your thoughts this way is likely to prevent binge eating 
next week.

This orientation to new behaviours 
is far more likely to work than the perfectionistic striving common in many of us, and you are far more likely to be the person in the photo happy you have achieved your weight-loss goals.

Dr Mary Grogan is a clinical psychologist and director of Change it psychology. To find out more about CBT and mindfulness seminars for dieting, visit  

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