Metabolica, cheto e salute

[Ct-7b]

CT, io NON ho mai trovato alcuno studio a riguardo e ne ho cercati per molto tempo.

il problema è il lungo periodo (decine e decine di anni) che ovviamente non possono essere studiati... tuttavia evidenze anedottiche riportano al fatto che la dieta sia sicura su soggetti sani e con un alimentazione e uno stile di vita comunque corretta (escludiamo quindi il caso si soggetti obesi, fumatori e consumatori di grosse quantità d'alccol che non fanno regolare attività fisica).

OT:
riapriranno il condominio molto presto
fine OT.

ci siamo..gli studi riguardano mesi...

Recentissime considerazioni su dieta iperproteica

Sports Nutrition Review Journal. 1(1):45-51, 2004. (www.sportsnutritionsociety.org)
Sports Nutrition Review Journal©. A National Library of Congress Indexed Journal. ISSN # 1550-2783
HIGH-PROTEIN WEIGHT LOSS DIETS AND
PURPORTED ADVERSE EFFECTS: WHERE IS THE
EVIDENCE?
Anssi H. Manninen
Department of Physiology, Faculty of Medicine, University of Oulu, Finland. Sports Nutrition
Review Journal. 1(1):45-51, 2004. Address correspondence to anssi.manninen@oulu.fi.
Received March 1, 2004/Accepted May 9, 2004/Published (online):
__________________________________________________ ______________________________
ABSTRACT
Results of several recent studies show that high-protein, low-carbohydrate weight loss diets indeed
have their benefits. However, agencies such as the American Heart Association (AHA) have some
concerns about possible health risks. The purpose of this review is to evaluate the scientific validity
of AHA Nutrition Committee´s statement on dietary protein and weight reduction (St. Jeor ST et al.
Circulation 2001;104:1869-1874), which states: “Individuals who follow these [high-protein] diets
are risk for… potential cardiac, renal, bone, and liver abnormalities overall. Simply stated, there is
no scientific evidence whatsoever that high-protein intake has adverse effects on liver function.
Relative to renal function, there are no data in the scientific literature demonstrating that healthy
kidneys are damaged by the increased demands of protein consumed in quantities 2-3 times above
the Recommended Dietary Allowance (RDA). In contrast with the earlier hypothesis that highprotein
intake promotes osteoporosis, some epidemiological studies found a positive association
between protein intake and bone mineral density. Further, recent studies studies suggest, at least in
the short term, that RDA for protein (0.8 g/kg) does not support normal calcium homeostasis.
Finally, a negative correlation has been shown between protein intake and systolic and diastolic
blood pressures in several epidemiological surveys. In conclusion, there is little if any scientific
evidence supporting above mentioned statement. Certainly, such public warnings should be based
on a thorough analysis of the scientific literature, not unsubstantiated fears and misrepresentations.
For individuals with normal renal function, the risks are minimal and must be balanced against the
real and established risk of continued obesity. Sports Nutrition Review Journal. 1(1):45-51, 2004
Key Words: high-protein diets, adverse effects, American Heart Association
__________________________________________________ ______________________________
INTRODUCTION
Certainly, living organisms thrive best in the
milieu and on the diet to which they were
evolutionarily adopted. From all indications,
Homo sapiens sapiens (anatomically modern
humans) has remained biologically
unchanged during at least the last 50,000
years.39 It was not until some 10,000 years
ago that the transition from a roaming hunter
and gatherer to a stationary farmer began.
Consequently, our diet has become
progressively more divergent from those of
our ancient ancestors. The typical Paleolithic diet
compared with the average modern American
diet contained 3 to 4 times more protein.40
It is implausible that an animal that adapted to a
high protein diet for 5 million years suddenly in
10,000 years becomes a predominant
carbohydrate burner. Indeed, counter to the
current U.S. Dietary Guidelines which promotes
diet high in complex carbohydrates, recent
clinical investigations support the efficacy of
high-protein diets for weight loss/fat loss, as well
as for improved insulin sensitivity and blood
lipid profiles. Thus, the popularity of highprotein
diets for weigh loss is unquestionable.
However, there are always some concerns
about high-protein diets.
In 2001, the American Heart Association
(AHA) Nutrition Committee published
statement on dietary protein and weight
reduction.2 According to this statement,
“Individuals who follow these [high-protein]
diets are risk for… potential cardiac, renal,
bone, and liver abnormalities overall.
However, it should be noted that there is little
if any evidence supporting these contentions.
Thus, this review deals with the relationship
between protein intake and renal function,
bone health, blood pressure, heart disease and
liver function. Also, effects of very-low
carbohydrate diet on lean body mass loss are
discussed.

PROTEIN INTAKE AND RENAL
FUNCTION
Healthy individuals. Despite its role in
nitrogen excretion, there are presently no data
in the scientific literature demonstrating the
healthy kidney will be damaged by the
increased demands of protein consumed in
quantities above the Recommended Dietary
Allowance (RDA). Furthermore, real world
examples support this contention since kidney
problems are nonexistent in the bodybuilding
community in which high-protein intake has
been the norm for over half a century.3
Recently, Walser published comprehensive
review on protein intake and renal function,
which states: “it is clear that protein
restriction does not prevent decline in renal
function with age, and, in fact, is the major
cause of that decline. A better way to prevent
the decline would be to increase protein
intake... there is no reason to restrict protein
intake in healthy individuals in order to
protect the kidney.” 4
The study by Poortmans and Dellalieux
investigated body-builders and other welltrained
athletes with high- and mediumprotein
intake, respectively.5 The athletes
underwent a 7-day nutrition record analysis as
well as blood sample and urine collection to
determine the potential renal consequences of a
high protein intake. The data revealed that
despite higher plasma concentration of uric acid
and calcium, bodybuilders had renal clearances
of creatinine, urea, and albumin that were within
the normal range. To conclude, it appears, at
least in the short term, that protein intake under
2.8 g/kg does not impair renal function in welltrained
athletes.
More recently, Knight et al. determined whether
protein intake influences the rate of renal
function change in women over an 11-year
period.32 1624 women enrolled in the Nurses’
Health Study who were 42 to 68 years of age in
1989 and gave blood samples in 1989 and 2000.
Ninety-eight percent of women were white, and
1% were African American. In multivariate
linear regression analyses, high protein intake
was not significantly associated with change in
estimated glomerular filtration rate (GFR) in
women with normal renal function (defined as an
estimated GFR 80 mL/min per 1.73 m2). Thus,
the authors concluded that high protein intake
does not seem to be associated with renal
function decline in women with normal renal
function. As pointed out by Lentine and
Wrone33, the generalizability of these findings is
limited by sampling characteristics to white midadulthood,
but this limitation is overshadowed
by strong internal validity grounded in a large
sample size, prospective outcomes
ascertainment, and adjustment for multiple
covariates.
Chronic Renal Failure. Historically, dietary
protein restriction has been recommend as a
therapeutic approach for delaying the
progression of chronic renal failure (CRF).
However, as pointed out by Ikizler,6 it is
important to reassess the applicability of this
approach. Indeed, the results of the largest
randomised clinical trial, The Modification of
Diet in Renal Disease (MDRD), did not
demonstrate a benefit of dietary protein
restriction on progression of renal disease.7
Further, CRF patients have been shown to
require a protein intake of 1.4 g/kg/day to
maintain a positive or neutral nitrogen
balance during nondialysis days, and even this
intake may not be adequate for dialysis days.6
Diabetics. According to American Diabetes
Association (ADA), there is no evidence to
suggest that usual protein intake (15-20% of
total calories) should be modified if renal
function is normal.8 The long-term effects of
consuming > 20% of energy as protein on the
development of nephropathy has not been
determined, and therefore ADA nutritionists
felt it may be prudent to avoid protein intakes
> 20% of total daily energy.8 More recently,
the metabolic effects of a high-protein diet
were compared with those of the prototypical
healthy (control) diet, which is currently
recommended to persons with type 2
diabetes.31 The ratio of protein to
carbohydrate to fat was 30:40:30 in the highprotein
diet and 15:55:30 in the control diet.
The high-protein diet resulted in a 40%
decrease in the mean 24-h integrated glucose
area response. Further, glycated hemoglobin
decreased 0.8% and 0.3% after 5 weeks of the
high-protein and control diets, respectively.
Finally, fasting triacylglycerol was
significantly lower after the high-protein diet
than after the control diet. The authors
concluded that a high-protein diet lowers
blood glucose postprandially in persons with
type 2 diabetes and improves overall glucose
control. Cleary, longer-term studies are
necessary to determine the total magnitude of
response and possible adverse effects.

PROTEIN INTAKE AND BONE
HEALTH
Increasing dietary protein increases urine
calcium excretion such that for each 50 g
increment of protein consumed, and extra 60
mg of urinary calcium is excreted. It follows
that the higher the protein intake, the more
urine calcium is lost and the more negative
calcium balance becomes. Since 99% of the
body´s calcium is found in bone, one would
hypothesize that high protein induced
hypercalciuria would results in high bone
resorption and increased prevalence of
osteopenia or osteoporotic-related fractures.
However, the epidemiological and clinical data
addressing this hypothesis are controversial. In
fact, some epidemiological studies found a
positive association between protein intake and
bone mineral density (BMD).9,37,38 Further, there
is growing evidence that a low protein diet has a
detrimental effect on bone. For example,
Kerstetter et al. reported that in healthy young
women, acute intakes of a low-protein diet (0.7 g
protein/kg) decreased urinary calcium excretion
with accompanied secondary
hyperparathyroidism.10 The etiology of the
secondary hyperparathyroidism is due, in part, to
a significant reduction in intestinal calcium
absorption during a low protein diet.
In a recent short-term intervention trial,
Kerstetter et al. evaluated the effects of graded
levels of dietary protein (0.7, 0.8, 0.9, and 1.0 g
protein/kg) on calcium homeostasis.11 Secondary
hyperparathyroidism developed by day 4 of the
0.7 and 0.8 g protein/kg diets (due to the
decreased intestinal calcium absorption), but not
during the 0.9 or 1.0 g protein/kg diets in eight
young women. There were no significant
differences in mean urinary calcium excretion
over the relatively narrow range of dietary
protein intakes studied, although the mean value
with the 0.7-g/kg intake was lower than that with
the 1.0 g/kg intake by 0.25 mmol (10 mg).
According to authors of this study, the lack of
change may be due to the small sample and the
inherent variability in urinary calcium excretion.
Similarly, when Giannini et al. restricted dietary
protein to 0.8 g protein/kg, they observed an
acute rise in serum parathyroid hormone (PTH)
in 18 middle-aged hypercalciuric adults.12 Taken
together, both of studies suggest, at least in the
short term, that the RDA for protein (0.8 g/kg)
does not support normal calcium homeostasis.
Furthermore, dietary protein increases
circulating IGF-1, a growth factor that is thought
to play an important role in bone formation.
Indeed, several studies have examined the
impact of protein supplementation in patients
with recent hip fractures. For example, Schurch
et al. reported that supplementation with 20 g
protein/day for 6 months increased blood
IGF-levels and reduced the rate of bone loss
in the contralateral hip during the year after
the fracture.28 More recently, the Cochranereview
assessed the effects of nutritional
interventions in elderly people recovering
from hip fracture.41 Seventeen randomised
trials involving 1266 participants were
included. According to reviewers, the
strongest evidence for the effectiveness of
nutritional supplementation exists for oral
protein and energy feeds, but the evidence is
still weak.
Moreover, many of these early studies that
demonstrated the calciuric effects of protein
were limited by low subject numbers,
methodological errors and the use of high
doses of purified forms of protein.35 Indeed,
the recent study Dawson-Hughes et al. did not
confirm the perception that increased dietary
protein results in urinary calcium loss.36
According to Dawson-Hughes et al., “The
constellation of findings that meat
supplements containing 55 g/d protein, when
exchanged for carbohydrate did not
significantly increase urinary calcium
excretion and were associated with higher
levels of serum IGF-I and lower levels of the
bone resorption marker, N-telopeptide,
together with a lack of significant correlation
of urinary N-telopeptide with urinary calcium
excretion in the high protein group (in
contrast to the low protein) point to the
possibility that higher meat intake may
potentially improve bone mass in many older
men and women.”
Finally, the cross-cultural and population
studies that showed a positive association
between animal-protein intake and hip
fracture risk did not consider other lifestyle or
dietary factors that may protect or increase the
risk of fracture.35 It is of some interest that the
author of the most cited paper favoring the
earlier hypothesis that high-protein intake
promotes osteoporosis no longer believes that
protein is harmful to bone.34 In fact, he
concluded that the balance of the evidence seems
to indicate the opposite.34