Could that coffee be giving you more than a kick in the butt?

The latest advice from weight-loss experts will be a jolt to those who think it's a diet wonder as it gives a hit of energy with next to no calories.

It's all the more reason, dietitians say, to cut back to just one cup of coffee a day - or cut the habit completely.

Because rather than kick-starting the metabolism, as commonly believed, caffeine causes the body to pile fat on.


Rushing Woman's Syndrome author Dr Libby Weaver says this happens because caffeine forces the body to shift into "fight or flight" mode.

"Your stress hormones are telling your body that your life is in danger and, to fuel your escape, you need a fuel you can access fast. When adrenalin is released, blood glucose elevates to provide more energy, blood pressure and pulse rate rise to provide more oxygen to the muscles, and your muscles tense, which provides readiness for action," she says.

This was useful for cavemen needing to flee from wild animals, Weaver says, but for those slamming back coffee or Diet Coke from behind a desk, the glucose flows around the body before being stored as fat.

New Zealand's medicine safety authority, MedSafe, warns many coffee drinkers may be unknowingly overdosing on caffeine.

Its guideline states a busy professional, drinking around six cups of filter coffee a day, is likely to hit "toxic levels of caffeine". Symptoms include indigestion and jitteriness.

MedSafe also warns a heavy coffee drinker is likely to experience caffeine withdrawal on weekends and when on holiday. Symptoms include headaches, reduced alertness and a depressed mood.

Generally, it is advised to have no more than 600mg of caffeine a day. But Weaver says caffeine tolerance varies and, in some people, the symptoms of overdose can start to set in after just two cappuccinos.

"Reaching for another cup of coffee is a common response to these feelings. There's a huge lack of awareness about what caffeine is doing inside your body," she says.

"Almost everyone who used to have coffee every day for energy will ... tell me they have so much more energy now they have cut it out."

One cup a day - max

Nova nutrition director Catherine Sissons says people wanting to lose weight should keep an eye on caffeine in the same way they monitor calories.

"People ... don't think about the way the caffeine is going to be processed," she says.

"The body goes into panic mode and the adrenal glands respond by releasing sugar from the muscles. All this sugar flows around in the blood, overloads the pancreas and then gets stored as fat. Alcohol, caffeine and stress all have the same effect."

Sissons, who has degrees in sports medicine and human nutrition, says caffeine is a diuretic, "so it's dehydrating you. It also knocks out your B vitamins, which ironically enough are for stress control and energy, and Vitamin A, which is for immunity".

Sissons says one coffee a day is the maximum anyone should be having if they want to lose weight.