Background: Obesity is associated with metabolic syndrome and fat accumulation in various organs such as the liver and the kidneys. Our goal was to assess, using magnetic resonance imaging (MRI) Dual-Echo phase sequencing, the association between liver and kidney fat deposition and their relation to obesity. Methods: We analyzed MRI scans of individuals who were referred to the Chaim Sheba Medical Center between December 2017 and May 2020 to perform a study for any indication. For each individual, we retrieved from the computerized charts data on sex, and age, weight, height, body mass index (BMI), systolic and diastolic blood pressure (BP), and comorbidities (diabetes mellitus, hypertension, dyslipidemia). Results: We screened MRI studies of 399 subjects with a median age of 51 years, 52.4% of whom were women, and a median BMI 24.6 kg/m². We diagnosed 18% of the participants with fatty liver and 18.6% with fat accumulation in the kidneys (fatty kidneys). Out of the 67 patients with fatty livers, 23 (34.3%) also had fatty kidneys, whereas among the 315 patients without fatty livers, only 48 patients (15.2%) had fatty kidneys (p < 0.01). In comparison to the patients who did not have a fatty liver or fatty kidneys (n = 267), those who had both (n = 23) were more obese, had higher systolic BP, and were more likely to have diabetes mellitus. In comparison to the patients without a fatty liver, those with fatty livers had an adjusted odds ratio of 2.91 (97.5% CI; 1.61–5.25) to have fatty kidneys. In total, 19.6% of the individuals were obese (BMI ≥ 30), and 26.1% had overweight (25 < BMI < 30). The obese and overweight individuals were older and more likely to have diabetes mellitus and hypertension and had higher rates of fatty livers and fatty kidneys. Fat deposition in both the liver and the kidneys was observed in 15.9% of the obese patients, in 8.3% of the overweight patients, and in none of those with normal weight. Obesity was the only risk factor for fatty kidneys and fatty livers, with an adjusted OR of 6.3 (97.5% CI 2.1–18.6). Conclusions: Obesity is a major risk factor for developing a fatty liver and fatty kidneys. Individuals with a fatty liver are more likely to have fatty kidneys. MRI is an accurate modality for diagnosing fatty kidneys. Reviewing MRI scans of any indication should include assessment of fat fractions in the kidneys in addition to that of the liver.

Background: The term “fatty kidney” refers to the accumulation of fat within the kidney. There is no clear definition of a fatty kidney. In our previous study, we defined a fatty kidney as one with fat accumulation of more than 4% in the kidney as detected by magnetic resonance imaging (MRI). This condition is associated with renal inflammation and contributes to the development of kidney dysfunction. Fat accumulation in the kidney can be detected using imaging modalities such as computed tomography (CT) or MRI. Given the clinical importance of renal fat deposition, the aim of this review was to investigate how imaging findings in this condition correlate to disease prevalence and metabolic disorders. Methods: A systematic review was conducted in accordance with the PRISMA guidelines. The databases searched included PubMed, Scopus, Web of Science, and Cochrane Library up to August 2024. Studies employing MRI or CT for renal fat quantification were included. Data were extracted, and their quality was assessed using the QUADAS-2 tool. Results: Twenty-eight studies comprising 6994 participants met the inclusion criteria. Most studies used MRI (75%) for fat quantification, with CT limited to renal sinus evaluation. Renal fat fractions (FFs) ranged from 0.4% to 55.3%, with higher values consistently observed in individuals with obesity, diabetes, chronic kidney disease, and hypertension. A consistent positive association was observed between fatty kidney and fatty liver, suggesting shared pathogenic mechanisms. Conclusions: Fatty kidney appears to be a distinct and clinically relevant entity with strong links to metabolic dysfunction. Imaging-based quantification—particularly MRI—offers a promising tool for early detection, yet standardization is needed. The findings underscore the need for further research into fatty kidney as a modifiable risk factor for renal and cardiovascular disease.