Juice Fasting

Naturopathic dietotherapy in Europe

Juice fasting is usually discussed as part of the dietary side of European and North American naturopathy. A historical study describes the Swiss physician Maximilian Bircher-Benner (1867 to 1939) as a leading figure in vegetarian dietetics and health reform, and a review of vegetarian history lists him among prominent vegetarians of the early twentieth century. A paper on German-language naturopathy reports that he coined the term Ordnungstherapie in 1937 for a broad concept of natural healing, with dietotherapy among its elements.

The sources reviewed for this page describe his emphasis on plant-based nutrition and do not document a juice-only fasting regimen attributed to him. Claims that Bircher-Benner or other early naturopaths founded juice fasting as a named method should therefore be treated as unverified here.

Gerson therapy and related cancer claims

The US National Cancer Institute summary of Gerson therapy states that Max Gerson, a German physician who began practicing in New York in 1938, developed a diet-based program from the 1930s and published his full theory in 1958. It combines a diet with supplements and enemas, and its supporters describe it as detoxifying the body. The summary reports no controlled human trials, and concludes that it cannot be recommended outside well-designed clinical trials.

This page treats Gerson therapy only as a related historical claim, since it is a cancer program with its own features rather than a juice fast. The summary also lists deaths and a case of dangerously high potassium reported in the literature in connection with the program, including electrolyte imbalance in two of the deaths.

Commercial detox and cleanse programs

A 2015 critical review describes the detox industry as booming and notes that detox diets are promoted as ways to eliminate toxins and lose weight. NCCIH lists juice-only diets among the many forms of detox and cleanse programs. The sources reviewed do not supply dated histories of Norman Walker's juicing writings or of the growth of retail juice-cleanse brands from the 1970s to the 2010s, so those episodes are not described here.

Fast, cleanse and detox

The terms juice fast, juice cleanse and juice detox overlap and have no standard definition in the sources reviewed. NCCIH groups juice-only diets with other detoxes and cleanses that it describes as including fasting, limited-food diets, supplements, herbs and colon cleansing. A review of popular weight loss strategies treats juicing and detoxification diets together as one category.

A juice program may be described by sellers as a fast even when it supplies energy, which sets it apart from water-only fasting, covered on the Machipedia page Water Fasting. Different again are the Master Cleanse, a named lemon-based program, and clinical programs of periodic fasting such as Buchinger fasting, which researchers report separately.

Place within dietary approaches

On Machipedia, juice fasting is a member of the family page Dietary Approaches. Related pages include Intermittent Fasting, Raw Food Diet, Colonic Hydrotherapy and Naturopathy, and the profession of Dietetics describes how registered dietitians assess diets. A 2017 review places juicing diets with intermittent fasting in a discussion of popular weight loss strategies.

General form

In general terms, a juice fast replaces most or all solid food with fruit and vegetable juices for a limited time. NCCIH names juice-only diets among detox and cleanse programs and describes the concerns as unpasteurized products, high-oxalate ingredients, low calorie intake and possible nutrient gaps. The contents, supplier and schedule vary widely between programs, and this page does not describe how to carry one out.

Clinical fasting programs kept separate

Some published studies use supervised fasting programs, such as Buchinger fasting, in which participants take small amounts of liquid nourishment under clinic guidelines. These research programs are medically supervised in a clinic setting and are distinct from consumer cleanse products sold for home use, so findings from one should not be carried over to the other.

Detoxification and weight management

Proponents promote detox diets, including juice-based ones, as ways to eliminate toxins, lose weight and promote well-being. A review of detox diets states that the industry makes these claims, then examines whether the diets are necessary, effective and dangerous.

NCCIH states that detox and cleanse programs are promoted to remove toxins, lose weight or improve health. Gerson therapy supporters likewise describe their diet as detoxifying and strengthening the immune system, a claim tied to cancer that the National Cancer Institute summary says has not been shown in controlled trials.

Gut health and other proposed effects

Small studies have measured changes in gut bacteria, blood lipids and body composition during juice-based fasts. These are reported in the evidence section and are measurements of physiological markers, not demonstrations of health benefit.

What reviews state about detoxification

A critical review by Klein and Kiat (Journal of Human Nutrition and Dietetics) found very little clinical evidence for detox diets. A handful of clinical studies suggested that commercial detox diets enhance liver detoxification and eliminate persistent organic pollutants, but these were limited by flawed methods and small samples. The authors found no randomized controlled trials of commercial detox diets in humans.

The British Dietetic Association describes detox diets as a marketing myth rather than nutritional reality and states that the liver, kidneys, gut and skin already remove waste. NCCIH reports that few human studies exist, most of low quality, and that a 2015 review found no compelling research supporting detox diets for weight management or removing toxins. These are statements by a dietitian body and a federal agency and are not trial findings.

Weight and body composition

A 2017 review reports that juicing and detoxification diets lead to weight loss because of very low calorie intake for short periods, with weight gain once a normal diet resumes, and that studies are limited. The BDA similarly states that rapid weight loss on such plans is mostly water and glycogen and is often regained. An uncontrolled study of 50 healthy people given a lemon and honey juice fast in a naturopathy setting reported reductions in weight, body mass index, fat mass and triglycerides compared with baseline, without a comparison group.

Small studies of juice fasting and the gut

A Freiburg pilot crossover study of six healthy volunteers on a juice fast, with and without added inulin, found no significant uniform change in the gut microbiome. It reported a trend toward a larger decrease in diversity without inulin and called for larger studies. An older cohort of five healthy men on a modified juice fast reported changes in blood lipids and insulin that returned to baseline within a week of stopping.

A separate study of 15 healthy men on a supervised Buchinger fast reported shifts in gut bacteria linked to energy metabolism that reversed after three months, and a rise in inflammatory markers when food was reintroduced. Buchinger fasting differs from consumer juice cleanses in supervision and design, and these findings should not be attributed to juice cleanses. No source reviewed reported a randomized trial of juice fasting for disease outcomes.

Kidney injury from oxalate

Case reports describe acute oxalate nephropathy, with deposits of calcium oxalate crystals in the kidney, after juice programs. A 2017 report describes a 65-year-old woman with prior gastric bypass and recent antibiotic therapy who developed acute kidney injury that progressed to end-stage renal disease after a green smoothie juice cleanse. A 2022 report describes a 68-year-old man on a spinach-heavy juice diet who became dependent on dialysis, and a 2023 report describes a man with diabetes who needed dialysis after a juice diet.

Case reports cannot show how often this occurs. The authors name predisposing factors including chronic kidney disease, gastric bypass, antibiotic use, diabetes, age and dehydration. NCCIH notes that high-oxalate ingredients such as leafy greens and beets can be a problem for people prone to kidney stones.

Other reported effects

NCCIH states that severe calorie restriction can cause electrolyte imbalances, that fasting can cause headaches, fainting, weakness and dehydration, and that unpasteurized juices can cause serious illness, especially in children, older adults and people with weakened immune systems. The BDA lists fatigue, dizziness and poor concentration as common on fasting and extreme detox plans.

The sources reviewed do not give case series on low blood sugar, sugar load, diarrhea or medicine interactions during juice fasting, so those points are not quantified here. The kidney case reports above note antibiotic use as a predisposing factor in one patient.

Who is advised to take care

NCCIH flags people with diabetes, who should follow their care team's eating plan and consult providers before major diet changes, people with kidney disease or a tendency to kidney stones, and children, older adults and those with weakened immune systems in relation to unpasteurized juices. The sources reviewed do not address pregnancy or eating disorders, so no statement is made for them here, and the page does not suggest that absence of a statement means absence of risk.

NCCIH advises discussing any detox or cleanse with a health care provider. Juice fasting is not a replacement for assessment or for prescribed treatment of any condition. The sources reviewed describe dietitian positions but do not document training pathways or registers, and no jurisdiction-specific regulation was verified for this page.