I'm a personal trainer – this is why diets don’t work

• Ben Carpenter has been a personal trainer since 2006, and has gained a loyal Instagram following by debunking health and fitness myths online. His book Everything Fat Loss: The Definitive No Bullsh*t Guide was released last year.

• As January comes to a close, it is estimated that about 80% of people who made new year diet pledges will have abandoned them. And with multiple studies showing that diets are hard to stick to in the long term, Carpenter says the 'common pattern' of diets means they don't work in the long term.

I entered the fitness industry 19 years ago as a young, oily-faced teenager. I didn’t know what my career path would look like. I just knew that I enjoyed working out and I loved the idea of coaching people face-to-face to help them with their fitness goals.

To begin with, my clients were very diverse. It didn’t matter if you were young or old, a professional athlete or a complete beginner, I was happy to train you if we both thought I could help you. My client roster contained teenagers wanting to get in shape for their upcoming holiday, fitness models who wanted to diet for their upcoming show, billionaires who just wanted to squeeze an exercise routine into their busy schedule and elderly people who just wanted to improve their quality of life and hopefully live a bit longer.

It didn’t take long for it to become increasingly clear that the most popular client request was to lose body fat. Sure, some people wanted to improve their fitness levels, get stronger, or build some muscle but, ultimately, the overwhelming majority of people who hired me wanted to diet in some shape or form. If you asked everyone who joined the gym in January what their fitness goals were, I would bet good money that the most common answer would relate to weight loss.

This forced me to shift my focus. In an attempt to better serve my clients, fat loss became the topic that I researched most heavily, the topic I started specialising in when talking about nutrition science on social media and the topic that I eventually wrote a whole book about.

In my opinion, diets don’t work. At least, not the way they are typically prescribed and followed. Historically, diets have been utilised as a temporary phase of food restriction. For example, if you want to lose weight in January you might buy the latest diet book and find yourself following whatever plan is trending at the time. Maybe it’s a low-fat, low-carb or ketogenic diet. Maybe it’s intermittent fasting (like the 5:2 diet, the 16:8 diet, or one meal a day diet). Maybe it’s the latest, greatest revolutionary-sounding DNA genotype diet or whatever plan a big weight loss company is selling you.

Whichever you choose, there is an unfortunately common pattern: you change what you eat, see results for a little while before it starts to feel like the diet plan gets harder and harder to stick. Eventually, sooner or later you realise you have lost weight, but the diet has also robbed you of a lot of the joy in your life, so you jack it in and go back to what you were doing before.

It is estimated that nearly half of all adults are proactively trying to lose weight every single year. A plethora of scientific studies have shown that although people tend to lose weight easily in the short-term, a majority of people do not maintain that and they regain at least some of the weight they originally lost.

We probably all instinctively suspect this, right? After all, the term ‘yo-yo dieting’ is well known for a reason. Although there is a never-ending conveyor belt of different weight loss diets, there is a distinct lack of data showing that any specific diet type produces significantly better results in the long term (think several years, rather than a few months).

All weight loss diets seem to work in the short term, but they often fizzle out later to the point that even after 12 months, no specific diet clearly reins superior over the rest.

Why is this? Well, that’s a complicated question to answer, but if we simplify it right down it’s because fundamentally people don’t want to follow that plan forever. It doesn’t matter what the diet is, people’s adherence rates tend to decrease over time which correlates with diminishing weight loss results.

Basically, if you start a diet plan that you dislike in the short term, the likelihood of you sticking with it in the long term is only a smidge or two above absolutely zero. This is an extra huge problem because people commonly report that not losing weight is a primary reason why they decide to stop exercising altogether.

What happens if a load of people join the gym in January feeling determined to lose weight and they shortly hit a weight loss plateau because they stopped wanted to follow their (often overly-restrictive) diet plan?

Unfortunately, they don’t just stop the diet, they frequently stop exercising as well. This is likely one reason why a huge chunk of people who join the gym in January stop exercising regularly by the end of the year, with some gyms estimating that 60% of new members stop coming within the first three months.

Traditional diets do work, at least in the sense that they reliably deliver results in the short term. However, most people don’t actually want short term results, do they? When you combine the high dropout rates and the lack of long-term weight loss success, I find it very difficult to support the practice of people randomly buying the latest, greatest diet book hoping it will magically lead to better results than the last diet they tried.

It is currently common practice for people to start dieting by abruptly switching to overly aggressive practices that they cannot sustain for long periods of time, often perpetuating a yo-yo weight cycling pattern.

If you are like most people and you want to improve your health and change your body composition for life, it makes sense that you don’t approach your long-term goals with habits you can only maintain in the short term. I think the health and fitness industry would be a healthier place for everyone if this became more common knowledge.

So, if you are someone who sits in the subgroup of people who feels trapped in a constant yo-yo dieting cycle, what could you do instead? Perhaps it would be a smart idea to shift your focus towards sustainable behaviours that you can (hopefully) do for many years or even decades to come. For example:

• Try to find any form of exercise you enjoy and use this to increase your physical activity levels. Don’t worry whether it is the ‘best’ exercise modality or not. A majority of people do not hit basic exercise targets for aerobic and resistance training, so doing something is inevitably better than nothing. If you actually enjoy something, the likelihood of you sticking with it is bound to increase, right?

• Instead of focusing solely on weight loss when you exercise, shift your focus to something else which is health-promoting, like getting stronger or improving your cardiorespiratory fitness levels which can improve your health even if the number on the scale does not change.

• Increase or decrease individual habits that will likely improve your health. For example, eating more fruits and vegetables, decreasing or stopping smoking, and minimising alcohol consumption are all things smart ideas, even if you do not lose weight.

Of course, if you get into a good groove with these habits, your body composition might change as a side effect, which you might appreciate. But, you can feel reassured that these are all healthy ideas, regardless of whether the number on the scale moves or not.

Edited by Harriet Sinclair