Low-Carb Diets Tax Kidneys, May Weaken Bones
 

I found this article at Yahoo. It worries me. Does anyone know more about this?

Low-Carb Diets Tax Kidneys, May Weaken Bones
Tue Aug 13, 2:36 PM ET

NEW YORK (Reuters Health) - Diets that are heavy on protein-rich foods and skimp on carbohydrates can increase the risk of kidney stones and reduce the body's ability to absorb calcium after just 6 weeks, researchers report.

Their findings come at a time when an increasing number of Americans, seduced by anecdotal accounts of fast weight loss, are turning to low-carbohydrate, high-protein (LCHP) diets. With an estimated 50% of American adults either overweight or obese, many are looking for a surefire way to shed pounds.

But while LCHP diets have been shown to get the pounds off in the near term, these diets are less successful over the long run and may even be hazardous to health, researchers warn.

For one, protein-rich foods can be high in fat, which increases the risk of heart disease and type 2 diabetes. A dearth of carbohydrate-rich foods such as fruits and vegetables can leave the body hungry for essential vitamins and minerals, while insufficient glucose (sugar) from carbohydrates, the body's preferred fuel source, can lead to fatigue and dizziness.

And according to the new study, 6 weeks on an LCHP diet increased the acid load to the kidneys, raising the risk of kidney stones. Animal protein has been shown to boost urinary excretion of oxalate, a compound that combines with calcium and other compounds to form the deposits commonly known as kidney stones.

At the same time, adults in the study had higher levels of calcium in their urine, suggesting a decreased absorption of the bone-building mineral and an increased risk of osteoporosis, according to the report in the August issue of the American Journal of Kidney Diseases.

"Consumption of an LCHP diet for 6 weeks delivers a marked acid load to the kidney, increases the risk for stone formation, decreases estimated calcium balance, and may increase the risk for bone loss," write Dr. Shalini T. Reddy from the University of Chicago, Illinois, and colleagues.

Their study included 10 healthy adults aged 21 to 52 who consumed their usual diet for 2 weeks, followed an LCHP diet for 2 weeks, and then followed a diet that restricted carbohydrates only moderately for 4 weeks. The protein-restricted diets included 3 liters of fluid a day.

Study volunteers lost an average of 9 pounds, but most developed ketones--compounds that are formed when the body uses its own fat as fuel and can raise acid levels in the blood. Acid excretion, a marker of acid levels in the blood, rose by 90% in some volunteers but none of the dieters developed metabolic acidosis, a potentially life-threatening condition caused by excessive breakdown of fats, the report notes.

There was also a sharp rise in urinary calcium levels during the LCHP and maintenance diets despite only a slight decrease in calcium intake. Urinary citrate, a compound that inhibits kidney stone formation, decreased.

While it is not clear from the study whether bone mass was affected, the findings indicate that such diets may increase the risk of bone loss over the long term.

"We already know that osteoporosis is going to be a major issue as the population ages, and if people are going to eat this kind of diet on a long-term basis, it's unknown what the implications would be for your bones," Dr. Chia-Ying Wang, a study author, said in a prepared statement.

SOURCE: American Journal of Kidney Diseases 2002;40:265-274.

Dr. Atkins has challenged the medical community to produce one person who has developed kidney disease as a direct result of low carb. So far, no one has produced any (perhaps because there aren't any to produce). When you see things like "can" and "may" in reports such as this, what they are saying is "I'm giving you my opinion, but I can't back it up with any long-term studies". So what you have here is opinion, not medical fact. You might also want to note that the study participants were only doing "very low" carb for a total of two weeks out the the 6 weeks of the study (in the middle). For two, they were eating "normally", for two very low carb and the last two on only moderately restricted carb, so I wonder how they can attribute the results to soley very low carb?
I've been following low carb for about 17 months now and so far, my liver and kidney function are both normal. If they had bother to run the study longer, like 6 months to a year, I believe they would have found that all those "horrible" conditions that they metioned would have disappeared as the calcium situation has a tendency to do; equilibrium is re-established within a few months in the normal range. Perhaps they thought if they ran the study longer they wouldn't have gotten the results they were after? Both Dr. Atkins and Dr. Bernstein have been low carbing for 30 and 40+ years respectively and I don't think either one of them has osteoporosis or kidney disease. 10 people do not a study make...at least not one of any significance.

This has been addressed in these threads on the research forum:

http://forum.lowcarber.org/showthre...&threadid=52311

http://www.benbest.com/health/kidney.html

This study shows that raising dietary protein in a healthy person raises risk of dying from kidney disease less than 1%.

http://www.ncbi.nlm.nih.gov/entrez/...9&dopt=Abstract

On the other hand, kidney stones (which are not life-threatening) are a possibility on a long-term ketogenic diet as evidenced in epileptic children who must use the ketogenic diet to control seizures. The risk is greater when a person doesn't drink enough water or eat enough green vegetables.

This is the study the article is referring to:

Am J Kidney Dis 2002 Aug;40(2):265-74

Effect of low-carbohydrate high-protein diets on acid-base balance, stone-forming propensity, and calcium metabolism.

Reddy ST, Wang CY, Sakhaee K, Brinkley L, Pak CY.

Department of Internal Medicine, Section of General Internal Medicine, The University of Chicago, IL 60637, USA. sreddy~medicine.bsd.uchicago.edu

BACKGROUND: Low-carbohydrate high-protein (LCHP) diets are used commonly for weight reduction. This study explores the relationship between such diets and acid-base balance, kidney-stone risk, and calcium and bone metabolism. METHODS: Ten healthy subjects participated in a metabolic study. Subjects initially consumed their usual non-weight-reducing diet, then a severely carbohydrate-restricted induction diet for 2 weeks, followed by a moderately carbohydrate-restricted maintenance diet for 4 weeks. Results: Urine pH decreased from 6.09 (Usual) to 5.56 (Induction; P < 0.01) to 5.67 (Maintenance;P < 0.05). Net acid excretion increased by 56 mEq/d (Induction; P < 0.001) and 51 mEq/d (Maintenance; P < 0.001) from a baseline of 61 mEq/d. Urinary citrate levels decreased from 763 mg/d (3.98 mmol/d) to 449 mg/d (2.34 mmol/d; P < 0.01) to 581 mg/d (3.03 mmol/d; P < 0.05). Urinary saturation of undissociated uric acid increased more than twofold. Urinary calcium levels increased from 160 mg/d (3.99 mmol/d) to 258 mg/d (6.44 mmol/d; P < 0.001) to 248 mg/d (6.19 mmol/d; P < 0.01). This increase in urinary calcium levels was not compensated by a commensurate increase in fractional intestinal calcium absorption. Therefore, estimated calcium balance decreased by 130 mg/d (3.24 mmol/d; P < 0.001) and 90 mg/d (2.25 mmol/d; P < 0.05). Urinary deoxypyridinoline and N-telopeptide levels trended upward, whereas serum osteocalcin concentrations decreased significantly (P < 0.01). CONCLUSION: Consumption of an LCHP diet for 6 weeks delivers a marked acid load to the kidney, increases the risk for stone formation, decreases estimated calcium balance, and may increase the risk for bone loss. Copyright 2002 by the National Kidney Foundation, Inc.

It should be noted that Lisa was right about ten people not making a large enough sample size for a proper study. There is a thing called "statistical power".

http://www.ama-assn.org/public/peer/7_13_94/pv3037x.htm

In Westman's study of the Atkins Diet, he concluded:

"To detect this amount of weight reduction with 80% power (2-sided alpha of 0.05), about 50 subjects were required for the study."

The study with 10 people did not have enough statistical power to be valid.

Besides, one study doesn't prove anything. It is not considered science, but only an hypothesis. For something to become proven, it must be duplicated in many laboratories by many scientific observers under properly controlled circumstances.

In science, as more and more studies back up a hypothesis, it becomes accepted as a powerful or even reigning theory--but rarely as undeniable fact. (The connection between smoking and cancer is regarded as nearly incontrovertible--but only after 30 years of painstaking research.)

We are all familiar with "breaking news" (that seems to break nearly every day!) about a new miracle drug or herbal remedy. In most cases, this "breaking news" was released by a single source--usually a source with financial stakes in the new miracle. Look for multiple sources to confirm a hypothesis before you hand your money over for a new product. If possible, also try to discover where the funding came from in these experiments. You may have three different lab reports, all confirming that Drug A is the most effective cure, but if all three laboratories are funded by the same drug company-you may want to raise an eyebrow.

In the case of this low-carb, high-protein study, I highly question their motives considering the short-term nature of the study and the small sample size, it seems rather quickly put together to attack the diet while minimizing the fact that 10 people lost an average of 9 pounds in 6 weeks.

It should be noted that no one in their study actually got kidney stones or actually got osteoporosis or actually got kidney disease.

http://www.journaloftheoretics.com/.../Vol-1/e1-3.htm

http://www.businessweek.com/1996/33/b348827.htm

Wow, thanks for your replies. I thought the two week period was odd when I read it, but I didn't notice that the study was performed on only 10 participants.

Three things I know for sure:

1) Whenever I've tried a low-carb diet I just feel much better.

2) The health consequences of obesity are far worse than the unsubstantiated claims of kidney stones and osteoporosis.

3) Low fat diets have made me fatter and fatter and have given me blood sugar problems.