Why can’t I stick to my diet?

Why do I impulsively eat? Do I lack self-control?

Have you ever made plans to start a new diet on Monday to avoid any junk food? Have you ever broken your diet by Monday evening?

If you have read my last blog post you will have been introduced to some behavioural terms and how they affect our choices. In today’s blog post we are highlighting issues of self-control on desires, and how they directly affect our food behavior.

Self-control is a  personality trait that many of us wish to possess and can exercise to varying degrees. One of the most famous experiments to convey this was the Stanford Marshmallow Experiment in the 1960s. The experiment involved young children who were given one marshmallow. They were told they can either eat the marshmallow now, or wait until the adult returns and they will receive another marshmallow (and therefore have two). The study showed the varying degrees of self-control in each child, with some pretending to eat it, others having ‘just one lick’, and some even eating parts and leaving some on the plate. Unfortunately for the latter, they did not receive the second marshmallow!

The study conveys the basic principles of short term pleasure versus a long term goal. Whilst many studies have been done showing variations of this and how these principles are affected, we tend to see this type of behaviour in diet culture. Individuals make a plan to start a diet and after coming into contact with a cookie or brownie, feel they simply can’t resist.

In Daniel Kahneman’s book ‘Thinking fast and slow’, he attributes this type of behaviour to two systems, System 1 & System 2. System 1 is your intuitive, fast and present orientated system. It is emotional, impulsive and often very automatic or unconscious. System 2 is quite the opposite in that it displays slow and deliberate choices. This is where your self-control lives and it is a mostly conscious cognitive process which is much more effortful. System 1 can often suffer from present bias (O’Donoghue & Rabin, 1999) where the payoff in the present outweighs those in the future. This means the pleasure you will receive from eating the forbidden food now will outweigh the pleasure of not eating it later.

Keeping all this in mind, there must be ways to stop yourself listening to your System 1 and be more successful at achieving your future goals. But how? By simply knowing when your System 1 is acting, you can send the supply of blood to the brain which activates System 2. By doing so you can reflect and act in a way which is more in line with your future goals, rather than giving in to the present bias you face. Instead of your choices being short-term, you can deliberately make choices for the long-term.

By building up the personality trait of self-control, we as humans can become more successful in controlling our impulses, and apply this to many other areas of our lives.


Kahneman, D. (2011). Thinking, fast and slow. Macmillan.

O’Donoghue, T., & Rabin, M. (1999). Doing it now or later. American economic review, 89(1), 103-124.

Stanford Marshmallow Experiment: https://www.youtube.com/watch?v=QX_oy9614HQ



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