A 'reset' for your body? Scrutinizing the hype over juice cleanses

Who doesn't want to wake up in the morning full of energy and feeling great? This is what makers of juice cleanses - or juice fasts - promise you: a "reset" for your body. Sounds enticing, especially at the start of a new year.

There are pre-packaged juice plans with everything already mixed and instructions on when to drink what. Or if you're willing to put in the effort, you can save some money by switching on your juicer if you've got one.

Are juice cleanses really beneficial to health? Two experts field some questions:

How does a juice cleanse work?

A simple juice cleanse - not to be confused with therapeutic fasting or so-called detox products - generally lasts between two and five days, and no longer than a week.

"During this period you only drink fruit and vegetable juices," says Niklas Schwarz, an instructor at the German University of Applied Sciences for Prevention and Health Management (DHfPG) in Saarbrücken, Germany. "In addition can be tea, water and vegetable broth. You eat no solid foods."

You drink from three to six servings of juice per day, each a mixture of various types of fruits and vegetables. A serving contains between 250 and 500 millilitres of juice. "The total amount ranges from 1 to 1 1/2 litres," Schwarz says.

You can start immediately. Some people indulge in their favourite foods the day before, while others avoid foods such as meat and white flour products.

For whom are juice cleanses inadvisable?

People with a pre-existing medical condition should consult their GP first, says Antje Gahl, spokesperson for the German Nutrition Society (DGE). They include those with high blood pressure, disorders of the liver, kidneys or thyroid gland, and also cancer patients and diabetics.

"Women who are pregnant or nursing shouldn't fast either," Gahl says. "Nor is it suitable for the elderly and children, because they have a high nutrient requirement."

A juice cleanse is unproblematic for healthy persons. Both Gahl and Schwarz say it can be the start of an overhaul of your eating habits. "Then it's a launch pad that makes changing your diet easier," remarks Schwarz.

Are juice cleanses healthy?

"The juices provide the body with many vitamins and secondary plant metabolites along with minerals and fibre," says Gahl, adding that the cleanses also lighten your bowels' workload thanks to the juices' easy digestibility.

As to whether they make you feel better, she says it's purely subjective: "Establishing a direct connection is difficult."

On the negative side, juice cleanses deprive your body of many nutrients, for example proteins and essential fatty acids. "So in some respects it's an unbalanced diet," she says.

This is why it's important not to do juice cleanses for longer than a week, and to spread the servings over the day rather than drinking everything at once. "Otherwise," she warns, "your blood sugar levels will rise relatively high and then quickly fall," which can cause an energy slump, not an energy surge.

Can a juice cleanse help you lose weight?

A one-week juice cleanse usually results in a weight loss of between 1 and 1 1/2 kilograms, and even as much as 3 to 5, depending on your baseline, according to Schwarz.

"It's not only fat though, but to a large extent the water that you always lose when you start a diet," he explains. "The drop in digestive tract content reduces your weight too, and the lack of protein intake causes your muscles to break down some protein."

So the key to losing weight is to overhaul your diet after you've finished the juice cleanse. "If you then resume your old eating habits, you'll regain the weight in a week or two," Schwarz says.