On Sat, 2 Jul 2005 15:33:15 +0200, Enrico C wrote in
<news:
[email protected]> on
sci.med.nutrition,sci.bio.food-science :
> On Sat, 02 Jul 2005 12:47:37 GMT, Jeff wrote in
> <news:[email protected]> on
> sci.med.nutrition,sci.bio.food-science :
>
>> "Enrico C" <[email protected]> wrote in message
>> news:[email protected]...
>>>I am trying to understand if there is some truth in the acid-base diet
>>> theory. I've been reading different opinions on the net.
>>>
>>> Anyway, I see there are studies on Pubnet about acid-base balance in diet.
>>> What do you make of this article, for instance?
>>>
>>>
>>> http://www.nutrition.org/cgi/content/full/128/6/1051
>>> The Journal of Nutrition Vol. 128 No. 6 June 1998, pp. 1051-1053
>>> Excess Dietary Protein Can Adversely Affect Bone1,2
>>
>> The acid-base diet has been disprove.
>
> I see there are lots of web sites about "acid-base diet", and my impression
> was that there is some (at least) inaccurate information on the topic.
>
> Yet, I read a few studies on Pubmed bringing proofs to the hypothesis of a
> link between high protein diets, renal PRAL, and calcium loss in bones.
>
>
>> Humans evolved in such a way that they
>> can have a very varied diet.
>
> No doubt, imho.
> Yet a healthy diet has to be "balanced", hasn't it?
> not too much of this, not too little of that...
>
> We all try and balance our diet in terms of calories, protein, fat, carbs,
> fiber, glycemic load, contents in vitamins,, and so on...
>
> My simple question is: should we care and balance our diet in terms of PRAL
> as well?
>
>> We have kidneys that are excrete acid (or base)
>> to keep our acid/base balance in check.
>
> Fine, but how do they achieve that result?
> Don't they need some calcium in the process, getting it from bones, if
> needed?
>
> http://www.nutrition.org/cgi/content/full/128/6/1051
> [...]
> "The kidneys respond to this dietary acid challenge with net acid
> excretion, as well as ammonium and titratable acid excretion. Concurrently,
> the skeleton supplies buffer by active resorption of bone. Indeed,
> calciuria is directly related to net acid excretion. Different food
> proteins differ greatly in their potential acid load, and therefore in
> their acidogenic effect. A diet high in acid-ash proteins causes excessive
> calcium loss because of its acidogenic content.
>
>
>> The acid/base diet, IMHO, is total ****.
>
> Some references?
>
Here is a "contrary" study, for instance.
Even they say "The role of dietary protein in bone metabolism is
controversial.", though, and show some prudence in their conclusions.
http://www.ajcn.org/cgi/content/full/77/6/1517
American Journal of Clinical Nutrition, Vol. 77, No. 6, 1517-1525, June
2003
© 2003 American Society for Clinical Nutrition
ORIGINAL RESEARCH COMMUNICATION
Protein intake: effects on bone mineral density and the rate of bone loss
in elderly women1,2,3,4
Prema B Rapuri, J Christopher Gallagher and Vera Haynatzka
1 From the Bone Metabolism Unit (PBR and JCG), Creighton University, School
of Medicine (VH), Omaha.
2 Presented at the 23rd Annual Meeting of the American Society for Bone and
Mineral Research, Phoenix, AZ, October 12-16, 2001.
3 Supported by research grants UO1-AG10373 and RO1-AG10358 from the
National Institutes of Health.
4 Address reprint requests to PB Rapuri, Bone Metabolism Unit, Creighton
University, School of Medicine, 601 North 30th Street, Room 6718, Omaha, NE
68131. E-mail:
[email protected].
Background: The role of dietary protein in bone metabolism is
controversial.
Objective: We investigated the associations of dietary protein intake with
baseline bone mineral density (BMD) and the rate of bone loss over 3 y in
postmenopausal elderly women.
Design: Women aged 65-77 y (n = 489) were enrolled in an osteoporosis
intervention trial. We studied the associations of protein intake as a
percentage of energy with baseline BMD and the rate of bone loss in 96
women in the placebo group (n = 96). We also examined the effect of the
interaction of dietary calcium intake with protein intake on BMD.
Results: In the cross-sectional study, a higher intake of protein was
associated with higher BMD. BMD was significantly higher (P < 0.05) in the
spine (7%), midradius (6%), and total body (5%) in subjects in the highest
quartile of protein intake than in those in the lower 2 quartiles. This
positive association was seen in women with calcium intakes > 408 mg/d.
There was no significant effect of protein intake on hip BMD. In the
longitudinal study of the placebo group, there was no association between
protein intake and the rate of bone loss.
Conclusions: The highest quartile of protein intake
72 g/d) was
associated with higher BMD in elderly women at baseline only when the
calcium intake exceeded 408 mg/d. In the longitudinal study, no association
was seen between protein intake and the rate of bone loss, perhaps because
the sample size was too small or the follow-up period of 3 y was not long
enough to detect changes.
Key Words: WORDS Protein * bone mineral density * bone loss * calcium
intake * bone markers * calciotropic hormones * elderly * parathyroid
hormone
ABSTRACT
The relation between dietary protein intake and bone metabolism is
controversial, and questions about this relation are unresolved. Excess
dietary protein was shown to cause urinary calcium loss, negative calcium
balance, and bone loss in young and elderly men and women, and these
effects are mainly attributable to high acid load from metabolism of animal
protein (1-11). It has been proposed that bone buffers the excess acid
load, which results in urinary calcium loss that leads to reduced bone
mineral content and bone mass (12). The type of dietary protein has also
been suggested to play a role, but the results of studies on this aspect
remain unclear (13-19). At the other end of the spectrum, protein
undernutrition is suspected to be a risk factor for bone loss and
osteoporosis. There is convincing evidence from the literature that
indicates that low protein intake is associated with low bone mineral
density (BMD) (20-23) and greater fracture risk (24, 25). Studies of
protein supplementation after hip fracture in the elderly further
substantiate the importance of adequate protein intake in bone biology
(26-28).
The relations of dietary protein intake with BMD and bone loss in
postmenopausal women and the elderly, who have the highest risk of
developing osteoporosis, are not very clear. Among cross-sectional studies,
some showed a positive association between protein intake and BMD (20-22,
29, 30), whereas others did not find any such association (23, 31-34).
There are few longitudinal studies that examined the relation between
dietary protein intake and bone loss in postmenopausal women and the
elderly, and the results of these studies are conflicting. Freudenhiem et
al (32) and Hannan et al (18) reported that higher protein intake is
associated with lower rates of bone loss, whereas Nordin and Polley (35)
and, more recently, Sellmeyer et al (15) reported contrasting results.
Studies examining the association between dietary protein intake and
fracture risk also reported conflicting observations (14-16, 19, 26, 27).
Dietary calcium was shown to influence the association between dietary
protein and BMD by some researchers (17, 19, 36-39) but not by others (21).
Promislow et al (17) reported that under conditions of low calcium intake,
increasing protein intake increased BMD. On the other hand, Dawson-Hughes
and Harris (38) reported that in elderly subjects supplemented with calcium
and vitamin D, dietary protein was inversely associated with the rate of
bone loss. Feskanich et al (19) and Meyer et al (39) observed a positive
association between protein intake and fracture risk when calcium intake
was < 540 mg/d. In contrast, Kerstetter et al (21) reported that the
association between dietary protein intake and BMD is not related to
calcium intake.
In the present study, we examined the association at baseline between
different dietary protein intakes and bone metabolism in postmenopausal
elderly women. Furthermore, in women receiving the placebo treatment, we
prospectively studied whether different baseline protein intakes influence
the rate of bone loss and changes in biochemical markers. In addition, we
examined whether dietary calcium intake influences the associations of
protein intake with BMD, biochemical variables, and the rate of bone loss
in both the population studied cross-sectionally and the population studied
longitudinally.
[...]
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