Read any alt med website or magazine and you can guarantee they will be recommending things like: 'Detox today; 10 ways to detox after Christmas' or '8 best foods to detox today'. Loads of books offer a '3 Day Detox Diet' or a 2 day or a 7 day one. Most of them advise you need to remove dangerous toxins that build up in your body from overindulging in alcohol, junk foods, caffeine, sugar, cigarette smoke or pollution and they can show you how. For instance, in their book '7-Day Detox Miracle', Sara Faye, Stephen Barrie, N.D.,(Naturopathic 'Doctor') and Peter Bennett, N.D., explain that "detoxing with a whole-body cleanse can enhance the body’s systems". According to the authors: "Detox drink recipes can assist in ridding your body of toxins and bringing it back into healthy balance."
The problem is that the word 'Detox' is a buzzword with no consistent medical meaning, at least when used by health-food companies trying to get you to buy their latest fad diet book, juice machine or vitamin products. It it just marketing. Your body does a reasonable job of removing everyday unwanted 'toxins' via your liver, kidneys and lungs. If they weren't working properly then you would soon know about it and no amount of wheatgrass juice will fix it - certainly not in three days! The effects of junk food, smoking etc take many years to build up in your body and these detox fads discourage us from taking a long term view, making it about short-term solutions to long term problems.
Many people report benefits when 'detoxing' and it is true that giving up smoking, eating healthier, cutting alcohol consumption and taking more exercise will show fairly immediate benefits to things like sleeping, energy levels and concentration but this is not because your body is somehow 'detoxifying' harmful substances, it is simply the effects of the changes. And, of course, recovering from a hangover can be helped by drinking plenty of liquid but this is because alcohol dehydrates you. There are huge benefits from improving your diet, reducing alcohol and tobacco, and increasing exercise but taking multivitamins, expensive exotic juices or specialized "detox liquids" for a few days will just dent your wallet and give you expensive urine. There is a great interview between Ben Goldacre and someone marketing "Detox in a Box" on Radio 4 back in 2009: https://www.badscience.net/wp-content/uploads/detoxradio4.mp3