Limiting Dietary Phosphate Fails to Increase Lifespan of Patients on Hemodialysi

[YLGuy]

 
From Medscape Medical News
Limiting Dietary Phosphate Fails to Increase Lifespan of Patients on Hemodialysis

Nancy Fowler Larson

Authors and Disclosures

December 9, 2010 — Restricting phosphate intake in patients receiving hemodialysis does not prolong their lives, according to a study published online December 9 in the Clinical Journal of the American Society of Nephrology.

Physicians routinely advise patients with end-stage renal disease to limit the amount of phosphorous in their diet. Dialysis is unable to remove much of what is typically consumed, which results in hyperphosphatemia in 50% of the hemodialysis population.

"Observational studies have consistently demonstrated a potent and dose-dependent association between higher serum phosphate levels and mortality, cardiovascular mortality and morbidity, and increased rates of hospitalization," write Steven Brunelli, MD, MSCE, from Brigham and Women's Hospital and Harvard Medical School, in Boston, Massachusetts, and colleagues."However, there has been relatively little study of the effects of long-term dietary phosphate restriction among hemodialysis patients."

The investigators analyzed data regarding 1751 patients from the Hemodialysis study, conducted between 1995 and 2001. At the study's onset, the participants' mean age was 57.7 ± 14.0 years, with women making up 56.5% of the cohort.

Patients were tracked for an average of 2.3 years, during which time their dietary phosphate was restricted to 4 different quantities: 870 mg/day or less in 300 patients, 871 to 999 mg/day in 314 patients, 1000 mg/day in 307patients, and 1001 to 2000 mg/day in 297 patients. Intake was unlimited for 533 patients.

Findings and Limitations

Patients prescribed restrictive dietary phosphate had poorer nutritional status and an increased need for dietary supplements. In addition, patients with more liberally prescribed dietary phosphate (PDP) experienced lower mortality rates during the study period.

Specific findings were as follows:

    * serum phosphate levels remained unchanged during the tracking period (P = .77), although there was a tendency for levels to rise in patients in the 1000 mg/day PDP and 1001 to 2000 mg/day PDP groups, but these increases were statistically insignificant compared with the 870 mg/day or less PDP group (P for group-by-time interaction, .12 and .38, respectively);
    * using marginal structural analysis, the 1001 to 2000 mg/day PDP group was linked to reductions in mortality from all causes compared with the 870 mg/day or less PDP faction (hazard ratio , 0.73; 95% confidence interval [CI], 0.54 - 0.97);
    * the group with no phosphate limitations was similarly associated with decreases in mortality (HR, 0.71; 95% CI, 0.55 - 0.92); and
    * on prespecified subgroup analyses, the positive relationship between increased PDP and survival seemed to be greater among nonblacks, participants with serum phosphate levels lower than 5.5 mg/dL, and patients not taking vitamin D.

Compared with patients ingesting 870 mg/day PDP or less, those who were allowed 1001 to 2000 mg/day PDP were 27% less likely to die; those taking in unlimited amounts of PDP were 29% less likely to die.

"Our primary finding was that [PDP] restriction was not associated with survival benefit and in fact may have been harmful," the authors write. "One potential explanation for our findings is that prescribed phosphate restriction results in unintended reductions in intake of other beneficial macronutrients."

The researchers noted 3 limitations to their study:

    * because this was an observational study, results may have been influenced by residual cofounding;
    * data for phosphate binders, which have a suggested relationship with better survival, were not available; and
    * because the data were gathered from a clinical trial, the patients may have been healthier than the broader spectrum of hemodialysis patients.

"As such, further work is needed to examine the generalizability of our findings particularly to octogenarians, the obese, and patients with end-stage cardiac, hepatic, and pulmonary disease," the authors write.

The National Institute of Diabetes and Digestive and Kidney Diseases supported the study. Dr. Brunelli has served on advisory boards for Amgen and C.B. Fleet Company; also, Dr. Brunelli’s spouse is employed by Genzyme, the manufacturer of Renvela, a phosphate binder. Dr. Curhan is the incoming editor of the Clinical Journal of the American Society of Nephrology. The other study authors have disclosed no relevant financial relationships.

Clin J Am Soc Nephrol. Published online December 9, 2010.
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Authors and Disclosures
Journalist
Nancy Fowler Larson

Nancy Fowler Larson is a freelance writer for Medscape.
 

[MooseMom]

1.  What is "residual cofounding"?

2.  I have always suspected that the common dietary restrictions negatively impact a patient's nutritional status, an unintended consequence.

3.  I am not sure I understand the real value of this study if the use of phosphorus binders was not factored in.

4.  While I can understand how restricting dietary phosphorus intake might not save lives, surely reducing serum phosphate levels DOES, whether by longer dialysis and/or binders, hence the "suggested relationship with better survival" re binders.

5.  So, armed with this information, is anyone considering jettisoning the renal diet, at least in terms of phosphorus intake?

[YLGuy]

By posting this article I am in no way suggesting anyone should not follow the renal diet.  My ex-wife who is a scientist sends me articles once in awhile and if I find them interesting or pertinent, I post them here. 

[okarol]

It's posted here too http://ihatedialysis.com/forum/index.php?topic=21220.0

[YLGuy]

I did a search before I posted it because I know you are up on posting articles but it did not come up. Sorry for doubling up.

[okarol]

No problem, I think they are different. 

[MooseMom]

By posting this article I am in no way suggesting anyone should not follow the renal diet.  My ex-wife who is a scientist sends me articles once in awhile and if I find them interesting or pertinent, I post them here.

Oh, I understand that, but don't you all think this questions one of the cornerstones of the renal diet?  It's not that I think we should all suddenly be freed of the diet, but this would not be the first time in history that prevailing opinion and practice proved to be incorrect or flawed.

My mom struggled with malnutrition while on dialysis.  It got to the point where she was so thin that her clinic told her she needed to eat as many calories as possible and forget the renal diet.  I just felt that for her, the diet was counterintuitive.

Since I am pre-dialysis, I would assume that this study doesn't pertain to me, but if you ARE on dialysis, it just seems to me that in light of this study, it might be best to rely on binders and better dialysis to control serum phosphorus.  It seems to me that this just once again supports the idea that better dialysis enables one to be better nourished.  When you cut down on phos, you end up cutting down on many other nutrients, and you end up where my mother was.  But the dietary restrictions are so institutionally ingrained that I suspect that any conversation on this topic with a renal dietician would just be ignored.

[sb]

Hi,

I am one of the study's authors. Allow me to respond to your thoughtful quesitons (below).

1. Residual confounding means that patients who were prescribed different levels of phosphate restriction may have also differed in other ways that affect survival. In the analysis, we went through painstaking efforts to correct for these differences (so as to tease out the “independent” effect of phosphate restriction). However, we cannot exclude the possibility that we didn't/couldn't do this perfectly. Clinical trials are the best means to make sure that these differences do not "confound" results. However, due to limitations in funding and time (patients needed an answer sooner than in the 5 years it would have taken), we were not able to do a clinical trial in this instance.

2. Having taken care of many dialysis patients over the years, I share your concerns.

3. You are right, it would be better to do an analysis that compared dietary restriction versus phosphate binders. We did not have data on phosphate binders for this study, but we are attempting to plan a study that can make this comparison.

4. As you suggest, other means of reducing serum phosphate levels may be more beneficial. In particular, we advocate longer dialysis, which has other demonstrated benefits in terms of blood pressure, fluid removal, cardiovascular health and survival. Phosphate binders are also attractive, and there is at least one study that shows that their use is associated with better survival; that study shares many of the same limitations as ours.

5. We do NOT advocate that phosphate restriction be jettisoned at this time. We hope that these data call into question the advisability of a long-held practice and that subsequent research will enable use to identify what role, if any, phosphate restriction has for dialysis patients and how it fits in with other phosphate lowering strategies. Still, we think that these findings are important, because phosphate restriction is in widespread clinical use and has never been rigorously tested.

In response to another contributor: these data (unfortunately) do not apply at all to pre-dialysis chronic kidney disease patients. Although it would seem that many of the underlying principles may apply, dialysis is a real game-changer. It is important that this issue be looked at in a dedicated study or pre-dialysis patients.

Best,
Steve

1.  What is "residual cofounding"?

2.  I have always suspected that the common dietary restrictions negatively impact a patient's nutritional status, an unintended consequence.

3.  I am not sure I understand the real value of this study if the use of phosphorus binders was not factored in.

4.  While I can understand how restricting dietary phosphorus intake might not save lives, surely reducing serum phosphate levels DOES, whether by longer dialysis and/or binders, hence the "suggested relationship with better survival" re binders.

5.  So, armed with this information, is anyone considering jettisoning the renal diet, at least in terms of phosphorus intake?

[YLGuy]

Thank you very much for responding Steve.  It is not often that we get our questions answered by one of the actual authors of the studies.  I hope MooseMom and others benefit from your post.

[MooseMom]

Steve, I am extremely grateful that you would answer some of our questions arising from your study.  So often we get snippets of information here and there and then are left with practically nothing other than more questions.  It is extremely frustrating to those of us who want to be educated.  And all too often, a study concludes with "More studies need to be done."

I agree entirely that your findings are important because widespread clinical use of dietary phos restriction in dialysis patients never seems to have been either rigorously tested or even questioned.  Certain practices are maintained simply because "it has always been this way."  In saying that, it does make sense for pre-dialysis patients to curb phosphates in our diet since most of us are not yet either on D or on binders, so obviously dietary restrictions are the only option for us at this time.

Since undernourishment is such a problem with many dialysis patients, it seems to be common sense to prescribe more dialysis and fewer dietary restrictions.  But money (or lack of it) decides what nephs prescribe, so we are back to square one which is merely "adequate" dialysis.

Thank you again for replying in person, and any other research you do on this subject would be eagerly read by all of us on this forum.  Congrats on a job well done.

[RightSide]

Gee, why am I not surprised at this.

One way to restrict dietary phosphate is to restrict protein intake.  (After you've done the easy things like eliminating cola drinks and so on.)

But that's really cutting off your nose to spite your face.

Restricted protein intake can lead to malnutrition, which together with the chronic inflammation from ESRD and dialysis can be a lethal combination.  (google for "malnutrition inflammation complex")

I assume that's what this study looked at--restricted protein intake to reduce phosphate intake.  (I doubt that "poorer nutritional status" resulted from eliminating cola drinks.)

[MooseMom]

Davita has a web page listing some superfoods for kidney patient that I think might be useful.

http://www.davita.com/diet-and-nutrition/lifestyle/top-15-healthy-foods-for-people-with-kidney-disease/a/2113

[sb]

Right Side,

You are correct. It is important to distinguish between foods that are intrinsically high in phosphate (often good protein sources) versus those that have additive phosphate.  The latter include products such as cola, but also a number of processed foods to which phosphate-containing preservatives have been added, and which you wouldn't necessarily expect to be high phosphate (such as certain snack cakes). These products are not necessarily as nutrient rich as foods with intrinsic phosphate. The other bugaboo about additive phosphate is that it is absorbed into the body much more readily than intrinsic phosphate. So, it stands to reason that cutting out additive phosphate should be safe and beneficial. Colleagues of mine at U Miami and U Alabama Birmingham are studying this very issue, and I hope will present preliminary findings in the near future.

The data were collected approximately a decade ago. At that time, there was much less use of additive phosphate in food packaging; also, the medical community was not tuned into this issue. So, with the exception of colas, the dietary phosphate restriction prescribed to patients in the study centered on foods such as dairy, meat and legumes. Therefore, our findings only indicate that restriction of these foods is unhelpful/harmful.


For now, it is probably advisable to avoid foods with high additive phosphate. One other cautionary message: phosphate is not listed on the nutrition labels of many products, so you have to look at the ingredients themselves.

Best,
Steve

Gee, why am I not surprised at this.

One way to restrict dietary phosphate is to restrict protein intake.  (After you've done the easy things like eliminating cola drinks and so on.)

But that's really cutting off your nose to spite your face.

Restricted protein intake can lead to malnutrition, which together with the chronic inflammation from ESRD and dialysis can be a lethal combination.  (google for "malnutrition inflammation complex")

I assume that's what this study looked at--restricted protein intake to reduce phosphate intake.  (I doubt that "poorer nutritional status" resulted from eliminating cola drinks.)

[MooseMom]

Yes, added phosphates are the real bugbear.  While restricting normally healthy foods like legumes can certainly contribute to undernourishment, avoiding processed foods which will almost certainly contain blahdyblahphosphate won't compromise your nutritional status.  We can all live without deli meats.  And we can certainly read ingredient lists.  If the word "phosphate" appears, I don't buy it.  Of course, even renally healthy people should avoid such foods.