Does A High-Protein Diet Tax The Kidneys? (Repost)

(This is a repost from December 14, 2009.)

A study in this month's AJCN suggests it does:

Effect Of Short-Term High-Protein Compared With Normal-Protein Diets On Renal Hemodynamics And Associated Variables In Healthy Young Men, American Journal of Clinical Nutrition, December 2009

"The glomerular filtration rate, filtration fraction ... blood urea nitrogen, serum uric acid, glucagon, natriuresis, urinary albumin (protein in the urine), and urea excretion increased significantly with the high-protein diet.

Conclusions: A short-term high-protein diet alters renal hemodynamics and renal excretion of uric acid, sodium, and albumin. More attention should be paid to the potential adverse renal effects of high-protein diets."

These were healthy young men with presumably healthy kidneys, kidneys designed to hold onto protein. Yet they still lost more protein when they ate a higher-protein diet.

Fortunately, people with diabetes, kidney disease, and high blood pressure (diseases that damage kidneys) get their serum creatinine and urinary protein checked regularly throughout the year. Unfortunately, many people don't know they have diabetes, kidney disease, or high blood pressure because all are silent in the early stages.

It's not a good idea to increase protein intake without undergoing kidney function tests before and throughout a period of increased protein intake.

Side Notes

Active Vitamin D
Damaged and failing kidneys produce less of a substance called calcitriol, the active form of vitamin D produced in the body. Calcitriol is made from the vitamin D we eat or make in our skin, so it can't be replaced by supplements, unless that supplement is calcitriol itself. I wrote about active vitamin D here.

Edema
One sign of early kidney damage is puffiness and swelling, called edema. Fluid accumulation occurs when protein losses increase, such as happened above. When blood has less protein it doesn't hold onto fluid as well, so blood volume decreases. The kidneys counter that low volume by retaining sodium. That can lead to fluid build-up in tissues. A unique characteristic of this kind of edema is that it "pits" or holds an indentation when poked.

Other Signs Of Early Kidney Damage:

• Frequent urination or frequent urge to urinate but it's not productive - especially at night.
  
• Colored or foamy urine.
  
• Back pain (location of kidneys).
  
• Fatigue (caused by lack of red-blood-cell forming erythropoietin which is made by the kidney).
  
• Foul or metallic taste in mouth (waste buildup).
  
• Itching and rashes (waste buildup).

High Protein
The subjects in the above study were eating a diet that included 2.4 grams of protein per kg body weight per day (2.4g/kg/d). The average intake for Americans, and the compare dose in this study, is 1.2g/kg/d. The DRI or Dietary Reference Intake is 0.8g/kg/d.

• High protein: 2.4g/kg/d for a 160 lb person works out to 173 grams protein.
  
• Average protein: 1.2g/kg/d for a 160 lb person works out to 86 grams protein.
  
• DRI/RDA: 0.8g/kg/d for a 160 lb person works out to 58 grams protein (for a 120 lb person: 43 grams).

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