By Sarah Berry
What happens to your body when you do a juice cleanse?
My first juice "cleanse" was a bit of an anti-climax.
Green juices are good, but what is juice fasting doing to your body?Credit: Paul Aguirre / EyeEm
According to the two sides of the argument, I was either going to mess madly with my metabolism and make myself sick, fat or both, or I was curing my toxic body and would emerge a leaner, cleaner, more radiant version of myself.
Nothing extreme happened. I was hangry [hungry and angry] for a few days and felt better when I started eating again.
I dropped a few kilos, but put them back on when I began eating again. No more, no less. It did however help to kick food panic – the irrational fear that you will not survive if no snacks are on hand. I've become a green juice fiend over the years, but moved away from extremes of alternating indulgence (pleasure) with fasting (punishment).
This is a peak time of year with people wanting to drop their Christmas trimmings and "detox", but what does it really do to your body when you do a juice fast?
Your metabolism will slow
"Once you stop eating enough food to meet your basic energy requirements, your metabolism will slow," according to TIME magazine. "For most people, that threshold of calorie intake is around 1200 calories [about 5000 kilojoules] per day."
TIME also says that we will become sensitive to cold during our "cleanse".
These claims are inaccurate, says Amanda Salis, Senior Research Fellow in the Boden Institute of Obesity, Nutrition, Exercise & Eating Disorders, University of Sydney.
"First, it is not necessarily true that your metabolic rate (or energy expenditure) and sensitivity to cold will drop when your energy intake goes below around 5000 kJ," Salis says.
"Body temperature and sensitivity to cold are directly related to energy expenditure. We have been measuring energy expenditure in people under various types of regimes involving fasting, semi fasting and mild energy restriction inducing rapid to moderate weight loss, and energy expenditure only drops when the body perceives a lack of overall energy deficit in the body.
"So if you have been eating and drinking to excess in the past, then a semi-fasting diet for a week or so will not necessarily result in a reduction in your energy expenditure.
"In some people, energy expenditure does not drop despite many weeks on a semi-starvation diet."
You will eliminate the toxins in the body
This statement, made by virtually all companies offering detoxes or cleanses, needs some context.
"Most everything is toxic at some level. We can't avoid it," says Precision Nutrition dietitian Ryan Andrews.
"Yet the body 'cleanses' itself. Our major organs of detoxification include the digestive tract, kidneys, skin, lungs, liver, lymphatic system, and respiratory system."
When the body's self-cleaning systems are strained however through poor diet, medication, alcohol, lack of sleep, environmental toxins etc, the idea is that they work less efficiently, so decreasing the burden and increasing your intake of vegetables is not a bad idea.
"The reality is that the liver is constantly detoxifying, so juicing is not something that starts a detox process," explains British nutritionist Kyla Williams. "However, what juicing does is give your digestive system a break, and provides plenty of antioxidants which will be well received by your hard-working liver to keep up its ongoing job."
You will lose weight
"Any weight loss from a detox diet is probably water, carbohydrate stores, and intestinal bulk – all of which come back in a few hours after the detox ends," Ryan Andrews says.
"Still, there is an important connection between body fat and toxins, because fat cells don't merely contain fat. They're also a storage site for certain fat-soluble toxins we ingest.
"So, the leaner you are, the less real estate you have available for toxins.
"This may help explain why many people feel lousy when they're going through a period of rapid fat loss.
"Since fat-soluble chemicals can be stored in fat, when fat is broken down, the chemicals can enter the bloodstream, contributing to fatigue, muscle soreness, even nausea."
Symptoms like headaches can also be the result of caffeine withdrawal. Or too much of a good thing.
"Many juices incorporate high quantities of celery and beets," Andrews explains. "Neither of these vegetables is typically eaten in such large quantities; both, meanwhile, are rich in nitrates.
"Nitrates promote vasodilation. And dilated blood vessels can lead to some pounding headaches."
While doing a "detox" for weight loss is probably futile, it may not be a bad idea if you are looking to make long-term lifestyle changes.
"If you are looking to kick start a completely different way of eating by following a new weight loss programme, a juice cleanse for a few days is actually a great way to reset your dietary habits," Williams says. "For example, let's say you are the type of person who grabs a snack on the go without keeping track of what you are eating: a juice cleanse, even for just three days will really make you realise just how often you go for that snack without realising it."
A short-term kickstart, sure. For long-term weight and lifestyle changes, incorporating more green juice into your diet may be a good thing, but regular juice cleanses may not.
"The trouble with juice cleanses is that their nutritional value is very low and so they are dangerous in the long term," Amanda Salis says. "In terms of 'detoxing' the body, it is far better to do a weight reducing diet, such as a very low energy diet based on products designed and approved to be used as complete meal replacements, and supervised by a health care professional with experience in their use, such as a doctor or dietitian."