One of the most common mistakes I see dieters make is to replace food with tea and coffee to quash hunger pangs and provide an energy boost. But this is a false economy, as the effect of caffeine on your blood sugar levels is similar to that of sugar. To understand this we need to look at how caffeine actually works:

To a nerve cell, caffeine looks like adenosine, a substance made in the brain which slows down nerve cell activity and makes blood vessels dilate, to cause drowsiness. Caffeine therefore binds to adenosine receptors on the nerve cells, blocking the adenosine from being able to bind to the cells themselves. This means that the adenosine cannot exert its action to slow down brain cell activity, or make blood vessels dilate, and as a result, cell activity actually speeds up. 

The pituitary gland sees this added activity and assumes that there is a good reason for it, so it releases hormones that tell the adrenal glands to produce adrenaline, the ‘fight or flight’ hormone, in order to respond to the apparent emergency. Adrenaline exerts a host of physiological effects to help you to face, or run away from danger, including making your heart beat faster, increasing blood flow to the muscles and making the liver release stores of sugar back into the bloodstream for extra energy. These stimulant effects are why caffeine is known as a pick me up, and why so many people can’t do without their dose of tea or coffee to get them started in the morning. But it is this last effect; the increase in blood sugar levels, that is of real interest to us in relation to dieting.

Anyone  who is familiar with low GL (Glycemic Load) or GI (Glycemic Index) eating to control weight and energy levels will recognise that increases in blood sugar are exactly what you should try to avoid when trying to lose weight. An increase in blood sugar, whether it is caused by a sugary snack or simply a cup of coffee, causes your body to release insulin. This hormone shifts excess sugar in the blood into cells, where it is either used as energy or, more likely, stored as fat. So by triggering the insulin response, you send your body into fat STORAGE mode. A low GL diet works specifically to keep your body in fat BURNING mode by making sugar blood sugar levels stay balanced. If you do not use up the extra energy provided via adrenaline to ‘fight or flight’ (for example if you are simply having a coffee with a friend), it gets stored as fat.

If you are trying to balance blood sugar to lose weight (or avoid gaining extra) and increase energy levels, you should avoid caffeine. Sources include tea, coffee, chocolate and energy drinks.