Contact us
Back to articles

Weight loss diets don’t work, a registered dietitian explains why

Weight loss diets don't work. A registered dietitians explains why failing a diet is not you're fault

It’s not willpower. Strong physiological and psychological changes from dieting stop you losing weight long term.

Over 90% of women have tried some sort of weight loss diet in their life, yet, for up to 97% of us, we don’t “lose weight and keep it off”. Although you may have been told you just need to try harder, it’s actually your body’s biological changes in response to dieting that make the weight go back on. Learn more about the changes that happen in your body so you can stop the yo-yo weight and diet cycle.

Listen on the podcast!


It’s not calories in, calories out

Calories are simply the units of energy a food supplies to our bodies. So in the same way metres measure distance, calories measure the amount of energy supplied to our cells.

But, we are not "calorie in, calorie out machines". We have strong biological drives that influence how we use and store energy and this changes depending on how much energy or calories are coming in.  When you eat less, your body uses less calories.

Initially, when you start a diet your body will likely draw on some energy stores. But if you keep eating less calories than your body needs, it will biologically switch over to saving energy mode. It will limit the amount of processes going on in your body so as to use less energy. This will happen at any body weight not just what we perceive as a low weight.

This slowing of metabolism or burning less calories from dieting will trigger a cascade of other symptoms you may notice when you are dieting or limiting your food.


You’re not failing the diet, the diet is failing you


You’ll find it difficult to focus

One area your body will “save” calories on is your brain function. It will keep essential processes going but things like focus and concentration are not essential for short term survival.

When your body enters survival mode, things like work tasks, self care routines, exercise and feeling engaged in conversation with friends will be put on the back burner. These things are all important for our health and wellbeing. But keeping your heart beating, your basic brain functioning and your immune system working is more important so when energy supplies are limited, your brain chooses to sacrifice your focus and concentration.


 It's harder to concentrate and focus when you are weight loss dieting


You’ll get sick and run down

Speaking of your immune system, this another area that doesn’t get the energy it deserves when food is limited. Your body will keep it running at a basic level, but there may not be enough energy to keep it running at it’s best. Some people notice they get more frequent colds, feel constantly run-down or take longer to recover from illness when dieting.


Your bathroom schedule can become a pain

Another bodily function that is commonly compromised when dieting is your gut functionThe limited energy available means less energy goes to digestion and movement within the bowel and the muscles of the bowel are broken down to use as a protein or energy source causing the gut to become weaker.

For these reasons, gut symptoms such as bloating, constipation or other IBS- like symptoms are more common when dieting.

It’s stressful

When low calorie dieting, your body produces an increase in your stress hormone cortisol. Cortisol is a hormone that is ideally produced in response to short term stress to help us respond quickly such as to avoid being hit by an oncoming car.

Nowadays, many people have long term elevated cortisol from work stress or other life stress, such as from dieting. Cortisol makes us more alert and ready to act by increasing blood pressure and heart rate. It also shuts off non urgent processes such as digestion because we don’t want to be weighed down by other processes when we need to be alert to respond to a threat.

When raised long term such as when dieting, it makes it more difficult to relax, makes it harder to sleep, affects our immune function and mental health as well as increasing our risk of future chronic disease such as heart disease.

Yep, dieting is not so healthy.


Dieting increases cortisol, your stress hormone


You feel obsessed with food

As well as having body processes to reduce the energy our body uses when dieting, our body also has biological mechanisms to help increase the amount of food we eat. 

Many people report obsessively thinking about food when they are dieting. And although it can feel like your body has it in for you and is trying to sabotage your diet, it’s actually a sign your body is working with you. It’s on your side

We often think of hunger as a grumbling in the stomach or other physical sensations we feel. But actually your body has many ways of communicating hunger with you, one of the main ones is thinking about food. When eating without a diet, it is natural to start thinking about food when you start feeling hungry again and after eating, to stop thinking about food and have headspace for other things.

But if we are following a diet and not eating enough most days, your body is going to make you think about food a lot of the time! It’s a natural response to hunger, whether you feel it physically or not.


 You go all out with food in the evenings

Some people may also experience periods of binge eating, emotional eating or out of control eating. Such as eating a large amount of food in one go despite feeling uncomfortably full and unwell.

We often expect our body to feel full and satisfied at a comfortable level of fullness even when we are not honouring our body’s hunger and eating regularly throughout the day. But if your body doesn’t know when the next meal or snack is going to come, of course it is going to want to eat as much as possible right now while food is available!

To connect back with hunger, your body first needs to feel safe that it has enough food coming in.

To stop binge eating and emotional eating, you firstly need to ditch the diet rules


What you can do instead of dieting

If you have been getting frustrated that you can’t stick with a diet or your weight is cycling up and down from the diet cycle, maybe explore some of these biological processes and how you may relate to them. Because, you don’t fail the diet, the diet fails you.

It really is possible to eat in a way that feels good and to feel good in your body. But food rules and dieting are not the way to get there. To feel at peace with food and eat consistently in a way that feels good, without guilt, you need to stop fighting against your body and instead start working with your body.

Intuitive eating is an approach that focuses on creating a peaceful connection with your body’s appetite cues and emotional needs and supports you to develop a healthy relationship with food.



Author Bio:

Written by Emma Townsin, Registered Dietitian and Certified Intuitive Eating Counsellor

Emma is the founder of Food Life Freedom and the host of the Food & Life Freedom Podcast. You can listen to a more detailed version of this article in episode 1 of the podcast “Why diets don’t work”. For personalised support to stop stressing over health and heal your relationship with food and your body, learn how you can fast track your way food and life freedom.




  1. An evidence-based rationale for adopting weight inclusive health policy. Hunger et al. 2020.
  2. Intuitive eating 4th edition, 2020. Evelyn Tribole and Elyse Resch.
  3. Centre for Clinical Interventions. WA Health. What is Starvation Syndrome PDF.
  4. Gut, 2015. Giula Enders 
  5. Tomiyama et at. 2010. Low calorie dieting increases cortisol
  6. Mind over milkshakes: Mindsets, not just nutrients, determine ghrelin response, 2011. Crum and Corbin.

Want 1-to 1 support?

Learn how you are supported to feel good around food.

Learn more here


5 Reasons You Feel Out of Control Around Food

Jun 06, 2024

Should you be worried about blood sugar spikes?

Mar 08, 2024

How to know if you are overeating

Oct 11, 2023

Why mind-body connection is so important for intuitive eating