Proteine: quante ne occorrono veramente?

Ok un altro studio che ho trovato:
Effects of resistance training and dietary protein intake on protein metabolism in older adults

W. W. Campbell , M. C. Crim , V. R. Young , L. J. Joseph , W. J. Evans
American Journal of Physiology - Endocrinology and MetabolismPublished 1 June 1995Vol. 268no. E1143-E1153

ABSTRACT

Nitrogen (N) balance, fed-state leucine kinetics, and urinary 3-methylhistidine (3-MeH) excretion were examined in 12 men and women, aged 56–80 yr, before and during 12 wk of resistance training (RT). Subjects were randomized to groups that consumed diets providing either 0.80 +/- 0.02 g protein.kg-1.day-1 (lower protein, LP) or 1.62 +/- 0.02 g protein.kg-1.day-1 (higher protein, HP).
At baseline, mean N balance was negative for LP (-4.6 +/- 3.4 mg N.kg-1.day-1) and positive for HP (13.6 +/- 1.0 mg N.kg-1.day-1). N retention increased similarly in LP and HP at the 11th wk of RT by 12.8 and 12.7 mg N.kg-1.day-1, respectively.

Thus LP had an increased efficiency of N retention. LP had decreased leucine flux (P < 0.001), oxidation (P < 0.001), and uptake for protein synthesis (P < 0.02), relative to HP, both at baseline and after RT. Leucine flux increased with RT in both diet groups (P < 0.05) and was associated mainly with an increase in protein synthesis in LP (91% of change in flux) and an increase in oxidation in HP (72% of change in flux; RT-diet interaction, P < 0.05). RT increased actomyosin protein breakdown (increased 3-MeH-to-creatinine ratio, P < 0.01).

Diet-related differences in protein metabolism did not influence body composition changes with RT. These data show that the efficiency of N retention and protein utilization during RT is higher in older subjects who consume 0.8 vs. 1.6 g protein.kg-1.day-1 dietary protein.
http://ajpendo. physiology.org/ … ent/268/6/E1143

Lo studio riguarda persone over 56 sottoposte ad un allenamento per la forza. Un gruppo è stato nutrito con 0,8 proteine x kg di peso corporeo, un altro con il doppio delle proteine. Nessuna differenza in termini di risultati nella composizione corporea è stato notato nei due gruppi; in più, il gruppo con meno proteine aveva una migliore utilizzazione delle proteine disponibile, con minore escrezione di aminoacidi nelle urine. Quindi, per i soggetti over 56 è meglio utilizzare poche proteine che molte. Se questo sia trasferibile sui soggetti più giovani non possiamo legittimamente inferirlo dallo studio, ma i risultati restano comunque interessanti secondo me.

In realtà gli androgeni causano solo una marea di effetti indesiderati, per questo (ovviamente sempre a seconda del risultato che uno intende perseguire) di solito si cercano combinazioni fra steroidi che massimizzino l’effetto anabolizzante lasciando contenuta la componente androgena (che poi è anche quella che di solito viene aromatizzata - convertita in estrogeni = ritenzione idrica + tette).
Ma qua stiamo parlando di proteine e poichè io non intendo essere holdato mi sento di dare un consiglio al nostro Leader Marinera: 175 cm x 90 Kg….. Mettiti a dieta e non pensare alle proteine !!!!!!
Guarda come mi holda….

Non sono poi tanto grasso eh. Magari un giorno posto una foto. Comunque restiamo sul tema.

:-) non intendevo insinuarlo !

Uno studio simile al precedente:
"Physical activity improves protein utilization in young men

BY GAIL E. BUTTERFIELD AND DORIS H. CALLOWAY
Department of Nutritional Sciences, University of California, Berkeley,
California 94720, USA
(Received 10 March 1983 - Accepted 8 September 1983)

Abstract
………..
To illuminate these relationships and to determine if physical activity does influence
protein utilization, we measured N retention in men assigned two different amounts of
exercise of equivalent load, such that any training effect would be minimized. Energy intake
was either sufficient to maintain body-weight or in excess under both conditions of activity.
The findings to be reported here show that both activity and excess energy intake favour
N retention.

………
EXPERIMENTAL
Subjects and experimental design

Six male non-smokers aged 24-27 years (Table 1) were recruited from a local community.
All were in good health as determined by physical examination, routine blood and urine
analyses and dietary history. They were housed for 108 d in the residential metabolic unit
at the University of California and left the unit only when necessary to perform tests. At
such time, they were accompanied by a member of staff. Environmental conditions and
general procedures followed were similar to those in previous studies (Calloway & Margen,
1971).
Throughout the study, 1 h of treadmill walking at 4.8 km/h (3 miles/h), 10% grade, was
assigned in three 20 min bouts daily (standard exercise 1.OX). Energy intake and assigned
exercise were varied to produce four treatments which included periods with and without
both surfeit energy and added work (for details, see Table 2).

During an 18 d pre-period, the men were given 1.0 g egg-white proteinlkg body-weight,
and energy intake was varied to approximate the amount required by each man to maintain Physical activity and protein utilization
a stable body-weight. In period 1, protein intake was lowered to 0.57 g/kg body-weight (the
FAO/WHO (1973) safe level of protein) and energy intake was further adjusted to establish

. This period allowed adequate time for adap-
tation to the lowered protein intake, which remained at the FAO/WHO (1973) safe level
throughout the rest of the study. Period 2 was the control condition of energy balance with
light exercise (l.OE+ 1.OX).
Subsequently, energy intake was increased to 1.15 or 1 *3 times the 1 SO E level. In periods
4 and 5, two 30 min bouts of daily bicycle work (700 Kp; 60 rev./min) were added to
produce an assigned energy output of 1 -0 X plus 0.15 of the 1 -0 E value for each man. As
a consequence of these manipulations, energy intake in periods 3 and 5 was greater than
energy output; in period 4, energy intake and output were balanced, as in period 2, but
the total energy intake was greater

………
First, when untrained individuals receiving energy intakes approximating need are
started on a new exercise regimen, especially one which is strenuous and of long duration,
there is a transient period of increased N loss (MolC & Johnson, 1971 ; Gontzea et al. 1974,
1975) which may be minimized by increasing protein intake (Gontzea et al. 1974) or energy
intake (Consolazio et al. 1975). After this initial period, urinary N decreases (Marable et
al. 1979).

Total N retention is ostensibly higher in individuals given higher protein intakes
(Consolazio et al. 1975; Gontzea et al. 1974), yet careful examination of the information
available suggests that change in N retention from control to experimental conditions may
be no greater on higher than on lower N intakes (Conzolazio el al. 1975; Marable et al.
1979) and that the efficiency of retention of dietary N (proportion of ingested dose retained)
is markedly higher on the lower N intakes.

The general consensus, based on these and other
biochemical findings, has been that physically active individuals may require a greater
protein intake to maintain N balance than do sedentary persons. However, our review of
our own and other evidence suggests to us that chronic physical activity promotes an
improvement in the over-all N economy and that, after some initial period of adaptation,
the physically active individual consuming adequate energy to cover the increase in energy
expenditure can maintain body protein better with more exercise than with less

In the experiment reported here, physical activity was found to affect N metabolism in
the following ways: (1) negatively, by increasing SN and FN losses; (2) positively, by
requiring an increased energy intake which allows protein sparing; (3) by an effect of the
physical activity itself on N retention. The cumulative effect of all these is to increase N
retention of even a small protein intake (0.57 g/kg) in the short-term in the more active
individual.
…."
http://journals .cambridge.org/ … cb278dbfe6e39fd

6 giovani uomini sono stati studiati per 108 giorni, sottoposti ad allenamenti di treadmill (camminate in montagna a passo spedito?) e bicicletta. Inizialmente un incremento di proteine ha migliorato il bilancio azotato (cioè di nitrogeno, la componente in cui vengono scisse le proteine per essere utilizzate nei muscoli), dopo di che però nessun vantaggio è stato notato con maggiori quantità di proteine ed anzi più esercizio facevano più il bilancio azotato migliorava, tanto che anche un quantità così bassa come 0.57gx kg corporeo al giorno era sufficiente.

Insomma nel lungo periodo succede il contrario di quello che succede nel breve, sono necessarie meno proteine all’atleta che al sedentario.

Lo studio è solo su 6 soggetti ma in questo caso dubito ciò abbia grande influenza sui risultati.

Mari, ma quale è il risultato che vuoi ottenere ?

Fvecchio, è scritto nella prima post di questa discussione il tema del thread. Non c’è ‘un risultato che voglio ottenere’, strettamente parlando, sarebbe anzi un’idea sbagliata iniziare una discussione solo per affermare un punto di vista preconcetto.

Infatti non lo insinuavi, lo stai affermando :D :D

Comunque vi state scannando per bene. Sappiate che mi siete di grande aiuto! Grazie ragazzi.

Ci stiamo scannando?

Termine poco appropriato in effetti, ma nella mia mente non è così :D

Ve lo spiego: intendo dire che ci state dando dentro su questo argomento, mettendoci impegno e tutta la conoscenza che avete. :)

Beh buono no?

Si diciamo che leggendo questi studi effettivamente sembrerebbe che 200g di proteine per noi sarebbero troppe ma rimane la questione del grasso. Cioè o mangio meno e patisco la fame ma se sostituisco alle proteine io carboidrati o i grassi ingrasso. Quindi?

Dunque, mi sembrano due punti differenti; uno è la quantità di proteine minime o ottimali, l’altro è qual è una dieta che consenta di dimagrire o non ingrassare. Con meno di 200 g di proteine al giorno patisci la fame? Cioè hai la tendenza ad ingrassare con una dieta normale?

Per quanto mi pare di ricordare i grassi sono quelli che richiedono più dispendio calorico per essere digeriti, infatti tempo fa una dieta consigliata agli atleti era 40/30/20, cioè 40% grassi 30% proteine e 20% carboidrati. Anche perchè la maggior parte dei cibi proteici contengono molti grassi.

Ci sono popoli che mangiano in questo modo, ad esempio gli eschimesi. Non mi pare che siano particolarmente magri o muscolosi.

Ho trovato altri due studi; sono interessanti perchè focalizzano l’attenzione sui culturisti.

Ecco il primo:
Proceedings of the Nutrition Society (1994), 53, 223-240 223
Physical activity, protein metabolism and protein requirements
BY D. JOE MILLWARD', JOANNA L. BOWTELL2.3, PAUL PACY3
AND MICHAEL J. RENNIE2*3

……
Physical activity can influence growth of LBM through stimulation of height growth in
children (see Torun, 1993). The increase in height, over 6 weeks, of exercised children
was 22 mm, but that of control children fed on the same diet was only 14 mm; the
respective increases in urinary creatinine were 42 and 31 mg/d. Since the energy content
of the weight gain by exercised children was calculated to be lower than that of controls
(21 kJ/g v. 39 kJ/g) the authors concluded there was a 50% increase in LBM growth. For
a 1-year-old child accreting N at 30 mg/kg per d (0.19 g protein), a 50% increase in
growth amounts to an extra 0.095 g proteidd, which is still less than 10% of the DRV for
a child of that age.
Thus, in the absence of steroid-induced growth, rates of protein accretion with
exercise in adults are trivial accounting for up to 30 mg/kg per d, i.e. 3% of the mean
adult protein intake in the UK (1.15 g/kg per d). Even for steroid abusers exhibiting
maximal rates of growth of LBM, the accretion would only rise to 20% of these average
intakes and of course would be a much lower proportion of the high-protein diet which
such individuals generally take. In any case the increased energy expenditure that
accompanies increased physical activity requires increased food intake and that would
supply increased protein. In the UK at present, average energy intake by males is 1.39
times the resting metabolic rate (RMR) (Gregory et al. 1990). Our studies of body
builders indicate an energy expenditure of 1.97 x RMR (Quevedo et al. 1991), requiring
a 42% increase in energy intake for balance. The average protein intake by the adult
male in the UK is 1.12 g/kg (Gregory et al. 1993), so that assuming that the
protein-energy density in the increased food intake of the body builders is the same as
that of the average UK diet (140 kJ/MJ total energy), they would have a protein intake of
1-58 g/kg, i.e. an extra 0.46 g/kg. Thus, the increased protein intake associated with
satisfying the energy needs on a normal mixed diet will supply at least 50% more protein
than the maximum rate of accretion recorded in the literature for steroid-induced weight
gain. For normal non-drug-abusing athletes, the extra protein intake will be fifteen times
the likely maximum rate of protein accretion.

In sostanza, si dice che la dieta normale di un Inglese dà un surplus di proteine superiore del 50% di quello che sarebbe richiesto per il massimo tasso di accrescimento mai riportato in un culturista sotto steroidi e ben 15 volte superiore a quello richiesto ad un culturista natural, dato che in realtà, dati alla mano, l’aumento di proteine utilizzato è minimo. (Il 50% e il 1500% è riferito al surplus, non alla quota totale; cioè se le proteine in più fornite dalla dieta normale sono per esempio 15 g quelle richieste ad un culturista sotto steroidi sono 7 g al giorno). Quello che conta è aumentare il numero di calorie.

Lo stesso studio della post precedente inoltre ha altri punti interessanti: guardate questo:
”. In a group
of twenty-six body builders of both sexes we studied, dietary protein intakes averaged
1.93 (SD 0.46) g/kg per d, values ranging from 0.63 (a lacto-ovo vegetarian) to 3.05 g/kg
with diets of protein-energy densities ranging from 82 to 280 kJ/MJ total energy, with no
discernible impact. However, as is often the case with the nutrition literature the key
experiments are to be found described in the classic texts written decades ago.
Chittenden (1907) took a group of elite University of Yale athletes and persuaded them
to reduce their protein intake by 50% over 5 months, mainly by switching to a vegetarian
diet of about 0.75 g protei d kg per d. Extensive measures of strength were made. Over
the 5 months their strength increased on average by 35% (see Table 31, coupled with a
fall in perceived fatigue.

Similar studies with soldiers over 6 months resulted in an 85%
average increase, although these were untrained at the outset so that their final strength
was similar to the athletes at the start of their experiment. Chittenden (1907) concluded
that his experiments ‘afford reasonable proof of the beneficial effects of a lowered
protein intake upon the muscular strength of man,’ and that ‘man can profitably maintain
nitrogen equilibrium and body weight upon a much smaller amount of proteid food than
he is accustomed to consume.’ In the context of minimal and optimal protein require-
ments, Chittenden (1907) defined an optimal daily requirement of about 0.75 g/kg,
equivalent to the current UK DRV (Department of Health, 1991) and significantly less
than the average UK intake. “

In un esperimento fatto all’inizio del secolo scorso, un gruppo di atleti di elite della Yale University venne convinto a ridurre progressivamente nel corso di 5 mesi la loro assunzione calorica del 50%, principalmente passando ad una dieta vegetariana, con circa 0.75g x kg peso al giorno. Nei cinque mesi la loro forza incrementò del 35%. Uno studio similare fu fatto su soldati; in questo caso i soggetti non erano allenati all’inizio dell’esperimento e ottennero un incremento del 85%, portandosi allo stesso livello di coloro che erano allenati all’inizio dell’esperimento.