BMI and ideal body weight when you have kidney disease

Overview

Body mass index divides weight by height squared and knows nothing about fluid, muscle or fat distribution. In kidney disease all three of those can be abnormal at once.

Why it's done and who it helps

• Fluid overload inflates BMI without adding fat.
• Low muscle mass can hide excess fat at a normal BMI (sarcopenic obesity).
• Ideal body weight is commonly estimated with the Devine formula.
• On dialysis, always use post-dialysis dry weight for calculations.

How ideal body weight is calculated

The Devine formula estimates 50 kg plus 2.3 kg per inch over 5 feet for men, and 45.5 kg plus 2.3 kg per inch for women. It is a reference point for drug dosing and goal-setting, not a target you must hit.

Better measures alongside BMI

Waist circumference, waist-to-height ratio under 0.5, grip strength and, where available, bioimpedance body composition.

What we record

Weekly home weight, clinic weight, waist, and for dialysis patients the relationship between measured weight and prescribed dry weight.

Preparing for your appointment

Should I aim for my ideal body weight?

Rarely. A 10-15% loss delivers most of the health benefit.

Why does my weight jump 2 kg overnight?

That is fluid, not fat — one reason we look at trends, not single readings.

When to contact your care team

Contact the clinic promptly if you have any of the following:

• Vomiting or diarrhoea lasting more than 24 hours, or you cannot keep fluids down
• Passing much less urine than usual, or new swelling of the legs or face
• Severe pain in the upper abdomen that spreads to your back, with or without vomiting
• A weight change of more than 2 kg in a week that is not explained by fluid
• A missed weekly weight, a missed dose, or any hospital admission

If you are seriously unwell, contact NHS 111 or your renal unit directly rather than waiting for your next review.

Your care at KidneyWeight Clinic

Every dose change, weekly weight and kidney blood test is recorded in your clinical monitoring record, reviewed by Professor Mohammed Mahdi Althaf at six-weekly intervals and formally reassessed at 26 weeks. Booking and your initial payment are handled by professoralthaf.co.uk, medication supply by Healist Pharmacy, and follow-up appointment payments by Carebit.

References

• NICE TA1026: tirzepatide for managing overweight and obesity
• NICE TA875: semaglutide for managing overweight and obesity
• NICE CG189: obesity identification, assessment and management
• NHS: weight-loss medicines

This article is general patient information reviewed by a consultant nephrologist. It is not individual medical advice; treatment decisions are made at a face-to-face consultation.