It’s not your willpower...
Food is a funny thing...it is something that we need for nourishment. Technically we should just be making food choices based on what would give us optimum nutrition. However, it is also something that gives us pleasure...especially the highly processed, sugary/salty foods that have been designed specifically to maximise the pleasure we derive from food (and are therefore incredibly addictive). So it is no wonder that willpower alone often won’t let you change your diet or lifestyle. Why would your brain just let you stop doing something that you derive so much pleasure from - it just doesn’t make sense - you can’t blame your mind (or your willpower) for not wanting to let go of the short-term joy it gets from food.
The food industry has therefore had a huge role to play in the current epidemic of obesity - and the highly processed, very addictive (yet nutritionally-devoid) foods it has created are certainly to blame for why people are going back for more and more of foods their bodies don’t need and getting sicker and sicker. Studies have actually shown that refined sugar, for example, lights us the same reward centres in our brain that are stimulated by recreational drugs and can be just as addictive as cocaine. This stuff is really addictive - no wonder willpower alone won’t help you to cut down. The food industry is also to blame for why eating intuitively (only eating when. you are hungry and stopping when you are full) and listening to your bodys' hunger cues is very difficult these days - you can’t tell when you are full these days because sugary foods don’t stimulate the hormones which tell you that you are full...meaning that you can keep eating this unhealthy stuff (seeking those short-term hits of pleasure) and never feel satisfied.
This is why, if you want to change your lifestyle and diet, you cannot just follow a meal plan and lose weight. You may be able to stick to it for a while...but imagine putting a recovering alcoholic in situations where they are surrounded by alcohol at every turn ....they would relapse pretty fast. In the same way, you have processed food available to you on every street corner, in every restaurant/supermarket, in every shop...it is only a matter of time before you have a low or weak moment in your life and seek out the pleasure and comfort you get from eating something you know is “bad” for you. Eating is also something that you have to do - you can’t just abstain from food, like an alcoholic would do from alcohol, so it can be very easy to fall back into unhealthy habits unless you have appropriate support to break your addiction to unhealthy food.
Therefore, if you want to change your eating habits for good - you will need psychological support. There are psychological techniques and tools that can be used to help you to break free of your eating habits and addiction to unhealthy food. You can still enjoy lots of delicious food - but will find that you naturally want to make much healthier choices. However, you will also need to look at your life more generally and ask yourself if there is another reason you are trying to get pleasure/comfort from your food - is it because you feel sad/unhappy in your relationship/bored at work/lonely etc...because these issues also need to be resolved to ensure that you do not keep seeking pleasure from food as a coping mechanism. One part of this process is ineffective without the other - to fully resolve food issues - you need (1) psychological help to break an addiction/unhealthy habit and (2) to look in more depth at what is going on in the rest of your life. If you fix what is causing you to over-eat but don’t break the habit/addiction, the next time you suffer a low point in life (which will happen, because life has its ups and downs) you will just relapse and over-eat. If you only treat the habit but not the underlying issue in your life, you may just form another unhealthy addiction to help you cope e.g. shopping/gambling/alcohol/drugs etc.