Do juice cleanses detox your body?

Who does the cleaning. The liver converts drugs and other compounds into more water-soluble forms, and the liver, gut, kidneys and lungs then remove them². A critical review of detox diets found very little clinical evidence for them. A handful of small, flawed studies claimed effects on liver detoxification or pollutant elimination, and the reviewers found no randomised trial of a commercial detox diet in humans¹.

What a juice cleanse does do. In a study of 20 healthy adults who drank only vegetable and fruit juices for 3 days, weight and BMI fell and stayed lower at day 17, gut bacteria shifted (partly reversing), and well-being scores rose. There was no control group⁸.

What you give up. Juicing removes most of the fibre. In a small randomised trial of 10 people, apple juice was swallowed 11 times faster than whole apples, was less satisfying, and produced a bigger insulin rise and a rebound drop in blood glucose³. In three large US cohorts, each three servings a week of fruit juice went with 8% higher diabetes risk, while whole fruit did not⁴. Higher fibre intakes, in contrast, were linked to 15% to 30% lower risk of death, heart disease, type 2 diabetes and colorectal cancer, and trials showed lower body weight, blood pressure and cholesterol⁹.

Juice is not poison. Across 19 adult trials, 100% juice did not significantly change body weight¹⁰, and an umbrella review found most outcomes unchanged and some, such as blood pressure, improved¹¹. The problem is replacing food with it for days.

The kidney risk. Oxalate is a natural compound in leafy greens and some other plants that can form crystals in the kidneys. Case reports describe acute kidney failure after heavy intake of oxalate-rich juices, including a "green smoothie cleanse"; the people involved had risk factors such as chronic kidney disease, gastric bypass or recent antibiotics^5,6.

A gentler plan. Eat the fruit and vegetables whole, add beans, oats and whole grains for fibre, and keep your usual meals. See our liver support article for food-based ways to support your body's own processes.

Detox claims

The critical review examined whether detox diets are necessary, what they involve, whether they work and whether they are dangerous. It found few clinical studies, hampered by flawed methods and small samples; preliminary signals for foods such as coriander, nori and olestra came mostly from animals; and it found no randomised controlled trials of commercial detox diets in humans¹. The absence of trials is not proof of harm or of no benefit, but it means the claims are unsupported.

The juice study

Henning and colleagues gave 20 healthy adults only vegetable and fruit juices for 3 days, then 14 days of their usual diet. On day 4 weight and BMI had fallen significantly (P = 2.0E-05) and remained lower on day 17 (P = 3.0E-04). Gut bacteria shifted (less Firmicutes and Proteobacteria, more Bacteroidetes and Cyanobacteria) and partly reversed by day 17. Plasma nitric oxide rose 244 ± 89% and a urinary marker of lipid oxidation fell 32 ± 21%⁸. It had no control group, lasted days, and the health meaning of these markers is unknown.

Fibre, satiety and blood sugar

In the classic randomised trial, 10 adults ate test meals of apples, purée or fibre-free juice, each with 60 g of available carbohydrate. Juice was consumed 11 times faster than intact apples and 4 times faster than purée. With eating speed equalised, juice was less satisfying than purée, and purée less than apples. Plasma glucose peaked similarly, but fell sharply after juice, and insulin was higher after juice and purée³. The cohort data come from Nurses' Health Study I and II and the Health Professionals Follow-up Study (66,105 women, 85,104 women, 36,173 men; 12,198 diabetes cases): per three servings a week, fruit juice carried HR 1.08 (95% CI 1.05 to 1.11), whole fruit 0.98 (0.97 to 0.99) and blueberries 0.74 (0.66 to 0.83)⁴.

Juice, weight and overall health

A meta-analysis of 42 studies found each daily serving of 100% juice went with 0.03 higher BMI in children. In adults, cohorts that ignored total energy found 0.21 kg more weight, those that adjusted found 0.08 kg less, and 19 trials showed no significant effect (-0.53 kg, 95% CI -1.55 to 0.48)¹⁰. The umbrella review of 15 reviews rated 10 of 51 meta-analyses as showing benefit, 3 as showing risk and the rest as neutral¹¹.

Kidney injury

A Mayo Clinic review of 65 patients with biopsy-proven calcium oxalate crystals in the kidney (1985 to 2010) identified three with presumed diet-induced oxalate nephropathy, including a patient with acute kidney failure after heavy juicing, and warned that oxalate-rich diets can precipitate failure in chronic kidney disease⁵. A 65-year-old woman with normal kidney function developed acute kidney injury that progressed to end-stage disease after a green-vegetable juice cleanse; gastric bypass and recent antibiotics were predisposing factors⁶. These are case reports, so the risk to healthy people is unknown.

Whole-food evidence

A dose-response meta-analysis of 95 studies found that, per 200 g a day of fruit and vegetables, risk fell for coronary heart disease (RR 0.92, 95% CI 0.90 to 0.94), stroke (0.84, 0.76 to 0.92), cardiovascular disease (0.92, 0.90 to 0.95), total cancer (0.97, 0.95 to 0.99) and all-cause mortality (0.90, 0.87 to 0.93), with benefits up to 800 g a day⁷. A series of reviews of 185 prospective studies and 58 trials (4,635 participants) found the greatest risk reduction at 25 to 29 g of fibre a day, with moderate-certainty evidence⁹.

Where the evidence disagrees

Observational diet studies can be confounded by healthier habits. The juice study shows short-term changes in weight and biomarkers, but those changes do not show that anything harmful left the body⁸. Whole juice is not harmful in most outcomes¹¹, so the case against cleanses rests on missing benefit, lost fibre and rare kidney injury, not on proven widespread harm.

Bottom line (confidence 2 of 5). There is no good evidence that juice cleanses remove toxins; your liver and kidneys already do that work. A short cleanse is unlikely to hurt a healthy adult, but it costs fibre and can be dangerous for kidneys. Eating whole plants is the better-supported option.