Our levels of willpower are directly linked to our consumption of sugar or glucose, says a new book.
It promises not only to help people learn self-control, but also to explain why so many of us find it so difficult to say no.
The book titled Willpower: Rediscovering The Greatest Human Strength, by Roy F. Baumeister and John Tierney is a bestseller in the U.S, the Daily Mail reported.
"Ask people to name their greatest strengths and they'll often credit themselves with honesty, kindness, humour, creativity and even modesty - but not self-control," wrote the authors.
"Conversely, when people were asked about their failings, a lack of self-control was top of the list," they stated.
They found that the moments when our glucose levels are at their lowest are the moments when we make poor decisions or fail to get anything done.
By analysing studies performed on groups as diverse as convicts in Finland and children at primary school in America, the authors found the lower our blood sugar levels, the angrier we feel and, in turn, the less control we have over our actions.
According to the book, using the part of our brain that determines self-control, the fronto-median cortex, uses up more of our body's glucose supplies than normal.
This causes us to crave sweet things to replenish our blood sugar levels, making us reach for biscuits rather than healthier savoury foods.
All of which sounds like bad news for dieters and explains why healthy eating plans can be so hard to stick to.
The book also claims if we want to improve our resolve, our sleeping habits need to be altered as well - those who sleep longer at night have more willpower as they are more rested.
"Adults routinely short-change themselves on sleep and the result is less self-control," the authors added.