Introduction: Chronic kidney disease is a degenerative and increasingly prevalent condition that includes metabolic abnormalities and is associated with a higher risk of sarcopenia. The conservative approach points primarily to controlling metabolic issues and reducing the risk of malnutrition and sarcopenia, slowing the progression of kidney disease. The present study aims to evaluate the effect of a low-protein diet on malnutrition and sarcopenia. Methods: A total of 45 patients (33 male and 12 female) aged over 70 with chronic kidney disease stage 4–5 in conservative management were considered. All patients had a dietary assessment and prescription of personalized low-protein dietary plans (≤0.6 g protein/kg) and a follow-up control between 4 and 6 months. In preliminary and follow-up evaluations, anthropometric data, blood examinations, body composition results, muscle strength, physical performance, and a 3-day food diary were collected. Results: In the follow-up period, a significant weight loss (p = 0.001) and a decrease in body mass index (p = 0.002) were recorded. Food diaries revealed a significant reduction in protein, sodium, potassium, and phosphorus intake (p < 0.001), with a significant reduction in urea (p < 0.001) and proteinuria (p = 0.01) without any impact on lean mass (p = 0.66). Considerable variations in adherence between food diaries and the prescribed diet were also noted. Conclusions: Providing a personalized low-protein diet led to significant benefits in a short period without worsening the patient’s nutritional status.