**Background:** Obesity is a growing health concern in Japan, where individuals tend to accumulate visceral fat even at lower BMIs compared to Western populations. In Japan, a system exists allowing registered dietitians to provide nutritional guidance to patients with BMI >30 kg/m², with additional compensation. However, it is unclear whether patients with moderate obesity—especially those visiting general hospitals for other conditions—receive adequate nutritional guidance or ongoing follow-up. This study aimed to investigate the provision of nutritional guidance interventions and evaluate their effectiveness on obesity and metabolic parameters over a short-term period.
**Methods:** This retrospective study was conducted at the Department of Nutrition of Kawasaki Medical School General Medical Center, Japan. From April 2018 to March 2020, 636 patients with BMI >30 kg/m² were identified through medical record review. Among these, 164 received nutritional guidance from a registered dietitian at least once, while 472 did not. For the effectiveness analysis, 70 patients who underwent blood examination before receiving nutritional guidance and again 3–6 months after were compared with 54 patients who had blood examinations at diagnosis and 3–6 months later without receiving guidance. Patients with cancer, secondary obesity, mental disorders, or steroid use were excluded. The Mann–Whitney U test and chi-square test were used for statistical analysis, with p<0.05 considered significant.
**Key Results:** Among the 636 patients, only 164 (25.8%) received nutritional guidance. Most guidance was ordered from internal medicine (81.1%), followed by surgery (6.7%), orthopedic surgery (3.0%), otorhinolaryngology (2.4%), dermatology (1.8%), neurosurgery (1.8%), and others (3.0%). Internal medicine was also the most common department not ordering guidance (49.2%). Patients receiving guidance had higher rates of comorbidities: diabetes mellitus (68.3% vs. 26.7%), dyslipidemia (52.4% vs. 23.7%), hypertension (47.0% vs. 36.2%), liver dysfunction (31.7% vs. 13.3%), and hyperuricemia (13.4% vs. 7.6%). At baseline, the guidance group had significantly higher total cholesterol (192.9±37.8 vs. 176.2±35.5 mg/dL, p=0.0253) and LDL cholesterol (115.9±35.1 vs. 99.6±30.4 mg/dL, p=0.0052). After 3–6 months, the guidance group showed significant improvements in total cholesterol (−9.7±29.3 vs. +2.3±22.0 mg/dL, p=0.0208) and LDL cholesterol (−10.4±30.5 vs. −2.0±26.0 mg/dL, p=0.0147) compared to the non-guidance group. BMI changes were not significantly different (−0.3±1.0 vs. −0.1±1.4 kg/m², p=0.3965). Other metabolic markers (glucose, HbA1c, triglycerides, liver enzymes) trended favorably but did not reach statistical significance.
**Clinical Implications:** This study reveals a substantial gap in the provision of nutritional guidance for patients with moderate obesity in general hospitals, with only about one-quarter receiving dietitian-led interventions. The finding that even short-term nutritional guidance (one session with 3–6 month follow-up) can significantly improve lipid profiles—despite no significant BMI change—suggests that dietary counseling may confer metabolic benefits independent of weight loss. This is particularly relevant for Japanese patients, who are prone to visceral fat accumulation and obesity-related complications at lower BMIs. The authors recommend that physicians across all departments, not just internal medicine, should refer patients with obesity for nutritional guidance. However, the study's limitations—single-center retrospective design, small sample size, lack of standardized intervention protocols, and absence of adherence verification—limit generalizability. Further prospective, multicenter studies with standardized nutritional guidance programs are needed to confirm these findings and establish optimal intervention strategies for patients with moderate obesity.