Thursday, June 02, 2011

Longterm Use of Low-Carb, High-Protein Diets May Risk Health

This post on the New York Times Well blog has been making rounds:

Eating Fat, Staying Lean

What do you think? Is a "meatier, cheesier, high-fat, low-carbohydrate spread" better for health? While I think low-carb diets are effective for weight loss in the short term, I don't believe they are healthful in the long term.

A low-carbohydrate diet is, by default, a high-protein diet (as well as a high-fat diet). That protein, often from animal foods, may cause problems.

High-protein diets make demands on the liver and kidneys, which have to work harder to get rid of the extra nitrogen. Ammonia, the nitrogen compound produced after proteins are deaminated, is toxic in even small amounts (it raises blood pH). So ammonia is combined in the liver with carbon dioxide to make the less-toxic urea. Urea is then sent to the kidneys for excretion.

People with diabetes, kidney disease, and high blood pressure can have compromised kidneys which, when presented with excess urea from high-protein diets, may fail to adequately dispose of it. They often have elevated blood urea nitrogen (BUN) levels.

Remember this study I blogged about? It found elevated BUN not just in people with compromised kidneys ... but in healthy young men fed a high-protein diet:

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."
A more recent and longer term study found kidney damage in pigs fed a high-protein diet:

Long-Term High Intake of Whole Proteins Results in Renal Damage in Pigs, Journal of Nutrition, September 2010
"The [high protein] compared with [normal protein] diet resulted in enlarged kidneys at both 4 and 8 months. Renal and glomerular volumes were 60–70% higher by the end of the study. These enlarged kidneys had greater evidence of histological damage, with 55% more fibrosis and 30% more glomerulosclerosis. Renal monocyte chemoattractant protein-1 levels also were 22% higher in pigs given the HP diet. Plasma homocysteine levels were higher in the HP pigs at 4 mo and continued to be elevated by 35% at 8 mo of feeding.

These findings suggest that long-term intakes of protein at the upper limit of the AMDR* from whole protein sources may compromise renal health."

* Acceptable macronutrient distribution range
The pigs on the high-protein diet were getting 35% of their calories from protein (as opposed to 15%), primarily egg and dairy protein.

Unfortunately, many people don't know they have diabetes, kidney disease, or high blood pressure because all are silent in the early stages. Eating a high-protein diet with any of these conditions may accelerate organ failure. Even Loren Cordain, author of the Paleo Diet concedes this.1

If you're not young and healthy and would like to experiment with a low-carb diet, it would be sensible to get your serum creatinine and urinary protein, as well as blood glucose and blood pressure, checked periodically.
1 The Protein Debate: Loren Cordain, PhD, T. Colin Campbell, Phd


Anonymous said...

Bix, there've actually been a few NY Times
articles that are relevant (and have
seemed more pro-protein than anti-protein).
e.g. take a look at:

More later,

Bix said...

Thanks for this, K.

I think some people process protein better than others. The population I'm interested in is older. These folks often present with established chronic conditions. Even the study in your link recognizes the risk of higher-protein in this group:

"However, high total protein intake, particularly high intake of nondairy animal protein, may accelerate renal function decline in women with mild renal insufficiency."

Since many chronic conditions are relatively symptomless in the early stages (diabetes, kidney disease, hypertension), I think it's a good idea to get tested.

Bryant Ford said...

I should say, thanks for this article..I would have never known that high protein low carb diet may still affect one's health. This could be helpful to people who are use in low carb diet.