Fasting

A pooled analysis whose designs were not recorded reported small triglyceride reductions with alternate-day fasting compared with time-restricted eating; a meta-analysis of randomized trials found a change of WMD: -0.12 mmol/l in 2,032 people. Results differ across comparisons: another pooled analysis whose designs were not recorded found no significant difference in triglycerides (MD = 0.03 mmol/L; 95% CI, −0.05 to 0.11; p=0.452).

A meta-analysis of randomized trials found an HDL increase of WMD: 0.04 mmol/l in 2,032 people, while another pooled analysis whose designs were not recorded reported +0.1 mmol/L. A separate pooled analysis whose designs were not recorded found no significant difference in HDL-C (MD = 0.03 mmol/L; 95% CI, −0.16 to 0.21; p=0.783).

A meta-analysis of randomized trials found that intermittent fasting and calorie restriction combined with exercise increased handgrip strength by WMD = 1.707 kg compared with exercise alone; the authors said its clinical relevance is unclear. A randomized controlled trial in 90 people found repeated chair stand time improved by approximately 1 second in both the RCR (−1.14, 95% CI: −1.81, −0.47) and TRE (−1.04, 95% CI: −1.76, −0.32) groups; a separate review said strength was not compromised by intermittent fasting.

A pooled analysis whose designs were not recorded reported that total FACIT-F score increased by 9.3 ± 13.3 points following the intervention, indicating improvements in fatigue (p < 0.001, ES = 0.50).

A 2026 review reported that lean muscle mass was consistently preserved across the studies it included. The review’s pooled-analysis designs were not recorded.

A pooled analysis whose designs were not recorded found a memory SMD of 0.60 (95% CI: 0.43–0.77), assessed primarily by MoCA and Digit Span versus Rey Auditory Verbal Learning Test.

A review of randomized and non-randomized human studies reported improvements in overall sleep quality, daytime dysfunction, and subjective sleep quality during Ramadan, more evident among amateur athletes. A separate pooled analysis whose designs were not recorded found a trivial effect on total sleep time (g = 0.07, 95% CI: −0.23 to 0.37).

A randomized controlled trial in 64 healthy people found that participants in the MFP group entered ketosis rapidly from day 2 onwards, measured by urine ketone test strips (morning ketonuria Δ −8.25 ± 0.73 mg/dL vs control, p < 0.001).

A 3-week alternate-day fasting regimen improved MFR in a randomized controlled trial of 16 people with overweight. Separately, a review of observational studies involving 1,345 people found fasting was not associated with increased rates of major cardiovascular events or mortality relative to non-fasting periods.

A pooled analysis whose designs were not recorded reported that menstrual cycles normalized in over 70% of 30 patients.

A randomized controlled trial in 41 people found differences between intermittent fasting with probiotics and calorie restriction for 15 metabolites (p.adj ≤ 0.089), including increased malonic acid and acetylcarnitine consistent with fatty acid oxidation. In a separate randomized controlled trial, myocardial substrate metabolism remained unaltered following alternate-day fasting.

A randomized controlled trial in 41 people reported an increase in fat-free mass percentage (~2×; p ≤ 0.030), and another trial in 20 people found arm circumference increased by ∼4% in the C/RT and ∼6% in the IF/RT groups. Results are not consistent: a meta-analysis of randomized trials involving 761 people found a slight but non-significant increase in fat-free mass following the fasting-mimicking diet (WMD = 0.885 kg, 95% CI: −0.059, 1.830, p = 0.066).

In a randomized controlled trial in 60 people with fatty liver, the 5:2 intermittent fasting diet decreased the proportion with hepatic steatosis ≥moderate compared with daily calorie restriction eating (29.6% vs. 59.3%, p = 0.028).

A randomized controlled trial in 41 people with obesity found greater reductions in gastrointestinal symptom rating scores with intermittent fasting plus probiotics than with calorie restriction: −9.3% vs. −5.4% and −13.2% vs. −3.9%, respectively.

In a randomized controlled trial in 44 people with breast cancer, grade III vomiting occurred more often in the control group than in the fasting-mimicking diet group (P = <0.001). The study also found neutropenia was more frequent in the control group (p = 0.04).

A randomized controlled trial in 90 people with obesity found that 400-m walk time improved by approximately 20 seconds in both the RCR (−19.8, 95% CI: −29.3, −10.2) and TRE (−19.2, 95% CI: −29.8, −8.6) groups. In contrast, a meta-analysis of randomized trials found that intermittent fasting and calorie restriction combined with exercise did not significantly affect VO_2max (SMD = 0.005, p = 0.94).

A review of randomized and non-randomized human studies reported improvements in fat mass while lean mass was maintained. The authors noted that effects depend on caloric deficit and adherence.

In a randomized controlled trial of 16 people with overweight, a 3-week alternate-day fasting regimen reduced blood pressure and MVO2 and improved MFR.

A 2025 review reported that religious fasting during Ramadan and Orthodox Christian fasting periods were associated with greater perceived spiritual meaning and affective modulation.

A 2025 review reported that supervised Buchinger-type programs were associated with increases in high-frequency heart-rate variability (HF-HRV), alongside lower State-Trait Anxiety Inventory-State (STAI-S) scores and lower morning salivary cortisol.

A review of randomized and non-randomized human studies reported that 16:8 or 18:6 time-restricted eating protocols in men with obesity were associated with total testosterone increases of +0.8 to +1.6 nmol/L alongside body-weight reductions of −3–7 kg. Findings differ: a meta-analysis of randomized trials involving 127 people found a non-significant effect of fasting on testosterone (WMD: −0.88; 95% CI: −2.37 to 0.61 ng/mL; p = 0.24).

A 2025 review reported modest reductions in perceived stress with fasting.

A 2026 review reported that intermittent fasting restored serum testosterone levels, preserved testicular histology, and maintained sperm parameters that were otherwise impaired by HFD.

A narrative review reported preservation of subchondral bone microarchitecture and attenuation of cartilage degeneration. Human evidence was not reported for this effect.

A narrative review reported mean reductions of 2.1 and 2.3 points in HADS-A and HADS-D, respectively, alongside reduced anxiety and depressive symptoms. Human evidence was not reported for this effect.

A narrative review suggested that adding a fasting-mimicking diet to first-line carboplatin-based chemotherapy may improve overall survival in advanced triple-negative breast cancer, but said the findings need validation in larger Phase II/III trials before clinical recommendations can be made. Human evidence was not reported for this effect.

A fasting-related rise in growth hormone secretion has been described, with roughly a 5-fold rise

Intermittent fasting may reduce plasma homocysteine levels in middle-aged adults, possibly through improved methylation and B-vitamin metabolism.

Studies did not support improved physical function: a meta-analysis of randomized trials found no significant effect on gait speed (WMD = 0.005 m/s, p = 0.82).

Fasting may reduce substrate load and enhance phase I and phase II enzyme activity, mechanisms proposed to support liver detoxification pathways.

Studies did not support appetite suppression as an effect: a randomized controlled trial in 209 people found greater increases in dietary restraint with calorie restriction than with intermittent fasting or standard care at month 2, 6 and 18.

Studies did not support improved concentration: a quasi-experimental study in 35 healthy people found no significant Group × Time interaction for any attention subdomain (all p > 0.05), with interaction effect sizes ranging from r = 0.03 to r = 0.23.

Studies did not support improved sleep onset: a review of randomized and non-randomized human studies found sleep latency and disturbance remained unaffected by Ramadan.

Studies did not support improved pregnancy outcomes: a pooled analysis whose designs were not recorded, involving 2,040 people, found no significant difference in gestational age at birth (pooled mean difference 0.05 weeks, 95% CI –0.22 to 0.31 weeks) or association with preterm birth risk (OR 0.93, 95% CI 0.60–1.44) for Ramadan fasting during pregnancy.

Studies did not support faster reaction speed: a quasi-experimental study in 35 healthy people found no significant Group × Time interaction for any PVT parameter (all p > 0.05), with small to trivial interaction effect sizes.

Pooled analyses whose designs were not recorded reported reductions in body weight, glucose and insulin, without an increase in chemotherapy toxicity; however, a 2025 review found no demonstrated impact on treatment outcomes or chemotherapy-related toxicities, so findings disagree. In a small, single-centre randomized trial of 44 people, the fasting-mimicking diet group had lower rates of grade III vomiting and neutropenia and more frequent tumor response.

Pooled analyses whose designs were not recorded found reductions in several pro-inflammatory markers, including TNF-α, CRP and leptin, among adults.

Pooled analyses whose designs were not recorded found that PF reduced LDL by -6.80 mg/dL versus the usual diet; other intermittent fasting methods were not significantly better than the usual diet.

In a randomized trial of 60 people with early-to-mid-stage Alzheimer's disease, the primary cognitive outcome improved within the intervention group and differed between groups over time. Reduced amyloid-β accumulation and tau phosphorylation were reported in preclinical models, but direct human evidence for these biomarker changes is lacking.

In a randomized trial of 97 adults with mild-to-moderate Crohn's disease, clinical response, clinical remission and fecal calprotectin improved.

In a randomized trial of 88 people with hypothyroidism, 74.4% achieved TSH stability with fasting LT4 ingestion, comparable to nonfasting ingestion with dose adjustment.

A 2025 review of pooled analyses whose designs were not recorded reported that randomized trials and pilot trials showed modest benefits when intermittent fasting was used as an adjunct.

In a randomized trial of 20 people, weight loss from baseline to 6 months was reported in each study arm.

Pooled analyses whose designs were not recorded reported reductions in DAS28 with intermittent fasting in randomized and observational studies, and reductions in VAS in observational studies. Inflammatory markers showed non-significant trends.

A randomized trial in 59 children under 3 years found that shortened fasting, with water allowed up to 1 h before sedation, did not increase the measured gastric antral area compared with standard 4-h fasting.

A 2025 review described intermittent fasting as a potential approach for anxiety, but said effects varied and the evidence was preliminary; the review drew on cited literature rather than original data.

A study of 202 patients found no significant effect of fasting on liver function tests, while medication adherence was better in the non-fasting group. The review stated that fasting was acceptable for people who were stable and adhered to antiviral therapy.

A 2025 review of animal and preliminary clinical evidence suggested that intermittent fasting may improve pain, physical function and joint structure in osteoarthritis.

Intermittent fasting produced behavioral and molecular improvements in VPA-exposed rats, but this is an animal model and there is no human evidence.

Alternate-day fasting improved salivary flow and gland function in a mouse model of Sjögren's disease. A review described the evidence as scarce, preclinical and partly inconsistent.

In the GAERS animal model, alternate-day fasting improved several bladder and kidney outcomes, including tissue findings, oxidative markers, mast cells and bladder contractility. This is preclinical evidence only.

A vote-count synthesis of animal studies reported that approximately 80% found cardiovascular improvement under cardiac stress. This is animal evidence only.

A review reported improvements in periodontal inflammation and clinical measures with caloric restriction and intermittent fasting in animal models and small trials, mostly among healthy or obese adults and in experimentally induced disease; the evidence was described as preliminary.

Intermittent fasting may lower triglycerides in adults with overweight or metabolic syndrome, potentially through weight loss and improved insulin sensitivity. Evidence in severe hypertriglyceridemia is lacking.

Intermittent fasting may improve IBS symptoms by reducing gut inflammation, promoting gut motility and altering the microbiome, though evidence is preliminary.

Time-restricted eating may reduce migraine frequency in some people by stabilizing glucose and circadian rhythms.

Fasting may slow cyst growth in autosomal dominant polycystic kidney disease by reducing mTOR pathway activation, but clinical evidence is preliminary.

The studies did not support a settled cognitive benefit: a 3-year cohort of older adults with mild cognitive impairment reported cognitive improvements with regular intermittent fasting, but a review characterized the findings as exploratory and heterogeneous.

The studies did not support an effect on fasting blood glucose, fasting insulin, HOMA-IR or 2-hour postprandial glucose; pooled analyses whose designs were not recorded reported non-significant results.

The studies did not support a pregnancy benefit: pooled analyses whose designs were not recorded found a mean difference of −94 g in birthweight and a relative risk of 0.96 for low birthweight (95% CI 0.88–1.05), with no increased low-birthweight risk.

The studies did not support a clear benefit for type 1 diabetes: pooled analyses whose designs were not recorded found no significant effect of Ramadan fasting on HbA1c (SMD -0.12, 95% CI -0.38 to 0.14) or body weight (SMD 0.05, 95% CI -0.30 to 0.40). Hypoglycemia was common, at 50.79 per 100 observations.

The studies did not establish a benefit or contraindication: a 2026 review of observational studies found no increase in decompensation, cardiovascular events, mortality or worsening of cardiac markers with fasting in stable chronic heart failure.

The studies did not support a kidney-disease benefit: pooled analyses whose designs were not recorded found no significant change in serum creatinine or estimated glomerular filtration rate in transplant groups compared with non-fasting controls. A small serum creatinine decrease after Ramadan in uncontrolled studies was not considered convincing.

Pooled analyses whose designs were not recorded reported headaches with alternate-day fasting and mild headache in a separate analysis. The findings do not quantify how often headaches occurred.

Pooled analyses whose designs were not recorded reported dizziness in fasting studies, including analyses involving people with Diabetes Type 2, fatty liver, Metabolic Syndrome, Overweight, or Prediabetes. The findings do not quantify its frequency.

Pooled analyses whose designs were not recorded reported hypoglycemia, including hypoglycemia with a fall, in fasting studies involving people with Diabetes Type 2. The findings do not quantify the frequency.

Pooled analyses reported diarrhea in fasting studies, including one analysis pooling randomized trials. The findings do not quantify its frequency.

A 2026 pooled analysis whose study designs were not recorded found an LDL-C increase of 6.75 mg/dL (95% CI [3.15, 10.34]) in the under-30 cohort. A separate 2025 pooled analysis reported triglycerides increased by 8.56 mg/dl (95% CI: 0.50, 16.62) across 11 experiments.

Pooled analyses whose designs were not recorded reported hunger in studies of fasting. The findings do not quantify how often it occurred.

Pooled analyses whose designs were not recorded reported constipation in fasting studies, including analyses involving people with Diabetes Type 2, fatty liver, Metabolic Syndrome, Overweight, or Prediabetes. The findings do not quantify its frequency.

A pooled analysis whose study designs were not recorded reported fatigue. In a 2026 randomized controlled trial involving 57 people with fatty liver, fatigue was reported more often in the intervention group as a self-reported mild symptom.

In a 2026 randomized controlled trial involving 90 people, usual 4-m gait speed declined by an average of 0.15 (95% CI: −0.24, −0.06) m/sec in the calorie restriction group and 0.12 (95% CI: −0.19, −0.04) m/sec in the time-restricted eating group.

A 2023 systematic review of observational studies in people with fatty liver reported increased fasting blood sugar after Ramadan fasting. A 2025 meta-analysis reported 38.87 total events per 100 observations for hypoglycemia, hyperglycemia, and DKA combined, with high heterogeneity (I² = 95%); this combined figure is not an estimate of blood sugar increases alone.

A pooled analysis whose study designs were not recorded reported irritableness with time-restricted eating; a 2026 review also described irritability. The findings do not quantify its frequency.

In a 2026 randomized controlled trial involving 28 people, fatigue was reported during Fasting Mimicking Diet cycles alongside headache, nausea, and constipation. A 2026 pilot involving 9 people described transient side effects, mostly grade 1, including fatigue and muscle weakness.

A pooled analysis whose study designs were not recorded reported vomiting. Vomiting was also reported in a 2026 randomized controlled trial involving 23 people.

A pooled analysis whose study designs were not recorded reported lack of concentration with time-restricted eating. It did not quantify the change.

A pooled analysis whose study designs were not recorded reported upper abdominal pain with time-restricted eating. The finding does not establish how often it occurred.

A pooled analysis whose study designs were not recorded reported low sodium alongside high bilirubin. The finding does not quantify either change.

A pooled analysis whose study designs were not recorded reported low potassium. The finding does not quantify the change.

A 2026 systematic review associated very restrictive eating windows (≤10 h) and prolonged fasting (>12.38 h) with lower cognitive scores. One example reported MMSE scores of 22.45 ± 4.63 versus 24.97 ± 4.24 (p<0.001) in the time-restricted feeding group; the review also reported 58% increased cardiovascular mortality.

A 2023 systematic review of observational studies in people with fatty liver reported increased ALT levels after Ramadan fasting; it did not give the size of the increase.

A 2025 systematic review described anxiety exacerbation in relation to fasting; the finding did not quantify how often it occurred.

A 2026 systematic review described reduced sexual desire in a clinical population; the finding did not quantify the change.

A 2025 systematic review described mood destabilization in relation to fasting; the finding did not quantify how often it occurred.

In a 2026 randomized controlled trial involving 57 people, drowsiness was reported in free-text responses; its frequency was not stated.

A 2025 systematic review described psychotic or manic decompensations in relation to fasting; the finding did not quantify how often they occurred.

A 2026 systematic review reported a decline in muscle strength among sedentary older adults during Ramadan. The reported finding concerns strength and does not describe rhabdomyolysis.

In a 2026 randomized controlled trial involving 23 healthy people, body aches were reported; the finding did not quantify their frequency.

A 2026 review described randomized trials of alternate-day fasting and time-restricted eating reporting reduced intake of calcium, magnesium, potassium, folate, vitamin C, and B-complex vitamins. A 2025 systematic review also associated Ramadan fasting during the third trimester, or during both the second and third trimesters, with birth weight reductions of 60 g (P < 0.007) and 80 g (P = 0.03), respectively.

A 2026 systematic review reported that some intermittent fasting protocols reduced testosterone in lean, physically active young males, without affecting muscle mass or strength.

A 2026 systematic review reported decreased FSH (p = 0.016) in 45 people in its FSH analysis.

A pharmacology reference explains that fasting can raise serum uric acid because ketones compete with urate for renal excretion; this may trigger flares in susceptible people, especially during prolonged fasts or refeeding.

A pharmacology reference links dry mouth during fasting to dehydration and reduced salivary flow.

A pharmacology reference notes that dehydration and reduced citrate excretion during prolonged fasting can increase the risk of calcium oxalate kidney stone formation.

A pharmacology reference notes that electrolyte imbalances during fasting, particularly magnesium and potassium depletion, can cause muscle cramps.

Fasting lowers insulin, which can lead the kidneys to excrete more salt and water; the resulting reduction in blood volume can lower blood pressure and cause dizziness on standing, particularly with blood-pressure medicines.

A pharmacology reference notes that ketosis during fasting can rarely trigger an itchy red rash on the chest and back, called prurigo pigmentosa.

A pharmacology reference describes fainting during fasting as potentially related to low blood sugar, loss of fluid and salt, or lower blood pressure, particularly when standing up quickly or in heat.

A pharmacology reference links cold intolerance during fasting, especially in the hands and feet, to reduced metabolic rate and blood flow to the extremities. Two of 425 community reports discussing fasting mentioned this effect.

A 2024 review described decreased appetite in a clinical population, but did not quantify the change.

A 2026 review described increased serum creatinine in clinical populations that included people with cancer, fatty liver, and viral hepatitis; it did not quantify the change.

A 2026 review described menstrual disturbances in relation to fasting but did not specify their form or frequency.

A 2026 review noted that fasting may complicate medication use when a medicine requires food for absorption or tolerability; this finding concerns medication-food requirements rather than demonstrated nutrient malabsorption.

A 2026 study in animals found elevated red cell distribution width, described as an erythropoietic stress pattern and a possible mild anemia-like phenotype. This animal finding does not establish the same effect in people.

Because food restriction is central to Anorexia Nervosa, fasting can reinforce restrictive behavior and risk medical instability.

Fatty acid oxidation disorders impair the fuel switch fasting depends on; fasting can cause life-threatening hypoglycemia and metabolic crisis in MCAD Deficiency. Prolonged fasting must be avoided.

Fasting can reduce milk supply and alter nutrient composition, potentially compromising infant nutrition and hydration.

Fasting can trigger or worsen hypoglycemia when there is no incoming glucose, especially when counter-regulatory responses are impaired.

In advanced Liver Disease, impaired glucose production and detoxification increase the risk of hypoglycemia and encephalopathy during fasting.

Calorie restriction and fasting can activate the hepatic heme pathway and precipitate acute porphyria attacks; carbohydrate loading is part of attack treatment.

Fasting imposes metabolic stress that may destabilize cardiac function during early recovery after a heart attack.

With limited cortisol reserve, prolonged fasting raises the risk of hypoglycemia, hypotension and adrenal crisis, particularly during illness or stress.

Prolonged fasting and rapid weight loss reduce gallbladder emptying and increase cholesterol saturation of bile, which can raise the risk of stone formation and biliary colic in people who already have Gallstones.

A review notes a potential risk of hypoglycemia during fasting for people with diabetes who use insulin or insulin secretagogues.

A review advises caution or medical supervision for frail older adults who fast.

A review advises caution or medical supervision for children and adolescents who fast.

A review warns that prolonged fasting during prolonged caloric restriction may worsen frailty or sarcopenia, and says it is not suitable for people with low body mass index or advanced chronic illness.

In established wasting, a further energy deficit can accelerate lean-mass loss and worsen outcomes.

Strict fasting windows can increase hunger and loss-of-control eating, potentially triggering or maintaining binge cycles.