It’s January; the detox fantasies are in full force. One-week regimes, 24-hour plans, pills, potions, kits, devices and diets. Programmes from a bizarre array of “authority” figures, presented by the media as immaculate experts, despite their correspondence-course qualifications. And a barrage of sciencey-sounding claims, the majority revolving around short-term health drives that make no lasting difference.

The notion of detox is medically meaningless. A vast army of marketers and lifestyle gurus has erected an entirely new physiological system. Look at a metabolic flow chart, the wall-sized maps of all the molecules in your body: you can see the way food is broken down into its constituent parts, and the way those components are converted between each other, and the way those new building blocks are then assembled into muscle and bone and everything else you are made of.

It is impossible from this chart to pick out the “detox system”. There is nothing on the subject in a medical textbook. That burgers and beer can have negative effects on your body is certainly true, for any number of fascinating reasons; but the notion that they leave a specific residue — “toxins” — that can be extruded by a specific physiological mechanism is nothing more than a marketing invention.

Detox regimes career from the superficially plausible to the laughably absurd. The Aqua Detox foot bath — you put your feet in a warm bath of salty water that an electric current is passed through — claims to extrude toxins from your body, which flow theatrically out of your feet, turning the water into brown sludge. I’ve pulled the machine apart: the water goes brown through basic chemistry, whether your feet are in the bath or not, through electrolysis of the metal electrodes in the saltwater. It’s GCSE-level stuff, and yet the fabulous benefits of this device have been widely reported.

Many would argue that simply critiquing the science misses the point: detox plays out a ubiquitous and ancient cultural role, blending a modicum of common sense with huge doses of ritual and personal melodrama.

When you go through busy periods of partying, drinking, sleep deprivation and excessive eating, you may decide, eventually, that you need a rest. Perhaps you will have a few nights in, reading at home, going to bed early, eating more salad than usual. Models and celebrities, in the same circumstances, “detox”.

Of course it is sensible to eat healthily and abstain from various risk factors for ill health, such as excessive alcohol use, but the notion of “detox” does not stretch to this. Instead we indulge ourselves in fantasies about peculiarly modern, quick-fix, short-term health drives and, with our hands over our ears, deny the reality that lifestyle risk factors for ill health exert their influence over an entire lifetime.

Now, it might be a good thing to remind ourselves what it’s like to eat vegetables, but we do ourselves a psychological disservice when we pretend that these rituals are based in science or that they are new. Almost every religion and culture has some form of purification or abstinence ritual built around fasting, alterations in diet, bathing and public announcements of personal change. They’re not presented as science, because they use the language and ideas of their own times. And they’re always precise: Hindu fasts, for example, if strictly observed, run from the previous day’s sunset until 48 minutes after the next day’s sunrise.

Purification and redemption are recurring themes in religious rituals, as they are in our own rituals around detox, because we all do regrettable things as a result of our own circumstances, and new rituals are frequently invented in response to new circumstances. In Angola and Mozambique, for example, former child soldiers can be purged and purified of sin and guilt, of the “contamination” of war and death, with a public declaration of renewal, which protects them from the consequences of their previous actions and retaliation from the avenging spirits of those they have killed.

In our own country, we seek purification from material indulgence. We fill our faces with drink, bad food, drugs and more. We know it’s wrong, so we crave ritualistic protection from the consequences, performing public “transitional rituals”, commemorating our return to healthier behavioural norms.

That is what happens at this time of year. Ceremonial acts are being performed up and down the country with pills, gadgets, rituals, fad diets and holy books filled with arbitrary instructions on how to live.

The tragedy is that, captivated by this distraction, we avoid the need to think about the real, lifelong changes we could make to our lifestyles, and continue to live the rest of the year as unhealthily as before.

Ben Goldacre is an NHS doctor and the author of Bad Science (Fourth Estate £12.99)

IMPLAUSIBLE HEALTH PLANS

- The Lemon Detox Also known as the Neera Super Cleanse. As used by Beyoncé. Find inner peace by downing Southeast Asian palm syrups. Curiously, if you don’t ingest anything else for up to seven days, you’ll probably lose some weight. Based on the cannily trademarked Madal Bal Natural Tree Syrup. A litre tin costs about £40. From sap, for saps?

- Martha’s Vineyard Diet Detox A juice fast: a berry drink, a vegetable drink, a “green drink”, an “inner cleanse” and some protein start you off on this three-week detox. Shelling out £140 to lose 21lb in 21 days, as its “guru” Roni DeLuz claims you will, is a snip — not.

- Detox in a Box Healthy breakfasts, lunches and dinners delivered to your door. Shock horror, you’re allowed potatoes, but there’s no salt or sugar. Its claims were roundly trashed on Radio 4’s Today earlier this month. A week’s supply of blood-purifying, mucus-cleansing nutrition is yours for £115.50.

- Dr Joshi’s Holistic Detox Beloved of Gwynnie, Cate and Sadie, this detox promises you’ll be thinner and happier in 21 days by “flushing toxins from your system” and avoiding many substances commonly known as food. “Within the first 48 hours, you could experience headaches, stomach pains, nausea and fatigue.” Yum. An initial consultation with the man himself costs £180; the book is £12.99.

- Boots Detox 5 Day Plan It works “in harmony with your body to flush away toxins”. Consists of five phials of apple or strawberry-flavoured powder containing vitamins C and E and selenium, mixed with glycerol. Add one to a litre of water and drink throughout the day. Detoxers should avoid caffeine and dairy. Yours for £13.21 — not bad for a few vitamins.