Dialysis is a medical treatment that takes over the work of failing kidneys, which can no longer effectively filter waste products and excess fluid from the blood. This process is necessary to sustain life for individuals with end-stage kidney disease. While dialysis is life-saving, it introduces complexities that lead to significant changes on the scale. Weight changes experienced by people on dialysis can be temporary, resulting from fluid shifts, or more permanent, involving changes in body fat and muscle mass.
Weight Fluctuations Caused by Fluid Retention
The most immediate and common cause of weight increase in dialysis patients is the accumulation of excess body water between treatments. Healthy kidneys continuously manage the body’s fluid balance by producing urine to remove water and salts. When the kidneys fail, this ability is severely diminished or lost entirely, causing fluid to build up in the body’s tissues.
This temporary increase is known as interdialytic weight gain (IDWG), which is the weight difference measured from the end of one session to the start of the next. Every liter of retained fluid weighs approximately 2.2 pounds, meaning a few extra liters quickly add up on the scale. This weight gain is expected to be removed during the next dialysis session through ultrafiltration, which pulls the excess fluid out of the blood.
Excessive fluid retention poses serious health risks that go beyond a number on the scale. Too much fluid places a significant strain on the cardiovascular system, potentially leading to high blood pressure, swelling in the limbs, and fluid accumulation in the lungs, causing shortness of breath. Limiting fluid and sodium intake between sessions is a major focus of care, as keeping IDWG within a safe range (often less than 5% of the target weight) is necessary for effective treatment.
Dietary and Metabolic Contributors to True Weight Gain
While temporary fluid gain is common, many patients also experience a long-term, structural weight increase involving the accumulation of fat and muscle mass. For many individuals, starting dialysis marks an improvement in overall health. Before treatment begins, patients with kidney failure often suffer from poor appetite and nausea due to the build-up of toxins.
Once dialysis begins to effectively clear these toxins, appetite often improves, leading to a higher caloric intake. Patients are typically advised to increase their protein intake to account for losses during dialysis and to maintain muscle mass. If this higher consumption is not balanced by physical activity, the resulting caloric surplus can lead to a gradual increase in body fat.
Metabolic changes related to kidney failure can further contribute to this permanent weight increase. Some patients experience changes in how their body processes sugar, potentially leading to insulin resistance and a greater tendency to store fat. The combined effect of improved appetite and consumption, along with shifts in metabolism, accounts for “true” weight gain, distinct from temporary fluid retention. Managing this type of weight gain requires a careful balance of diet and exercise, which a renal dietitian can help monitor.
How Different Dialysis Types Impact Weight
The specific type of dialysis a person receives can uniquely influence both fluid and true weight changes. For people undergoing hemodialysis (typically performed several times a week in a clinic or at home), weight management focuses primarily on controlling interdialytic fluid gain and balancing calorie intake. The weight removed during a hemodialysis session is almost entirely excess fluid, pulled from the blood by the machine.
Peritoneal dialysis (PD) presents a distinct mechanism for true weight gain due to the nature of the dialysate solution used. This treatment involves introducing a fluid into the abdominal cavity to filter the blood. The solution contains dextrose, a type of sugar, which creates the osmotic pressure necessary to draw out fluid and waste. A portion of this dextrose is absorbed directly into the patient’s bloodstream, providing a significant number of unexpected calories daily.
For some patients, this absorbed dextrose can contribute hundreds of extra calories per day, which, if not compensated for by dietary changes, leads to fat mass accumulation. Studies show that patients transitioning from PD to hemodialysis often experience a significant reduction in body weight. This suggests that fluid overload and the caloric impact of the dextrose solution are significant factors in the PD process. While weight gain in hemodialysis is largely fluid-driven, the caloric contribution from the dialysis fluid makes permanent fat gain a more predictable challenge for those on peritoneal dialysis.