Newsgroup: it.salute.alimentazione
Titolo: Dieta senza latte

Togliendo il latte e i suoi derivati dall'alimentazione con
cosa si integra la quantita' di calcio perduta ?
grazie 

 cosa si integra la quantita' di calcio perduta ?
Se ne parla anche in un altro thread di oggi.
A quanto già scritto nell'altro thread, aggiungo che sull'argomento si
trovano su Internet molte informazioni diverse. Per esempio, i siti
vegetariani sono assai sbrigativi nel consigliare di fare del tutto a meno
del latte (accusato di ogni malanno) e sostituirlo con altri alimenti
fonti di calcio.
Quello che però non dicono, di solito, è che non basta sostituire una
fonte di calcio con un'altra, perché non tutte le fonti di calcio
permettono di assimilarlo alla stessa maniera.
Per esempio, il calcio si trova anche negli spinaci, ma gli spinaci
contengono anche acido ossalico che si combina con il calcio per formare
ossalato di calcio, un sale, rendendo il calcio meno disponibile
all'organismo. 
Oppure, i vegan consigliano bevande come il latte di soia fortificato,
dove però in realtà il calcio viene aggiunto in fabbrica... Tanto vale a
quel punto prendere un integratore di calcio e bere quel che più aggrada,
no? :)
Anche il calcio aggiunto, peraltro, non è al di sopra di ogni sospetto...
nella pagina di Harvard che cito più sotto si dice anche di non esagerare
con gli integratori, specie gli uomini: "supplements for men because of
questions about possible risks of prostate cancer."
Le raccomandazioni nutrizionali ufficiali, in America (da un sito Internet
di un ente governativo) dicono di bere tre "cups" (tre tazze da 250 ml
circa, più o meno quanto ne bevo io!) di latte al giorno (scegliendolo,
dicono, a ridotto tenere di grassi, per tenere sotto controllo l'apporto 
di grassi saturi... su questo aspetto peraltro ci sono diverse opinioni,
ma sarebbe un altro discorso... qui dico solo che bisogna guardare
all'apporto giornaliero complessivo, quindi d'accordo ridurre se si
esagera da un altra parte, ma sinceramente non vedo perché rinunciare a un
buon bicchiere di latte intero se non si sta a dieta e se non ci sono
altre fonti di grassi saturi, e si resta quindi al di sotto di quel 10-12
percento di grassi saturi di cui parlano anche le linee guida ufficiali,
se non sbaglio).
Ad ogni modo, le linee guida americane scrivono:
"Consume 3 cups per day of fat-free or low-fat milk or equivalent milk
products."
http://www.health.gov/dietaryguidelines/dga2005/recommendations.htm
Bisogna anche dire che la Harvard School of Public Health, dell'università
di Harvard, ha un approccio un po' diverso, meno entusiasta del latte, ma
neppure lo rifiuta... insomma una via di mezzo... Dice in sostanza di non
esagerare nelle quantità, e poi sempre il solito discorso di evitare
quello più grasso e scegliere latte e latticini "low-fat"... (peccato che
si perda il sapore, aggiungo io!)
 
A chi comunque non prende latte o latticini, per propri motivi, magari
perché non gli piacciono, Harvard consiglia direttamente integratori di
calcio.  
If you don't like dairy products, calcium supplements offer an easy and
inexpensive way to get your daily calcium. 
 
http://www.hsph.harvard.edu/nutritionsource/pyramids.html
Harvard ha anche una pagina di approfondimento sul calcio e sulla
prevenzione dell'osteoporosi, che come dicevo nell'altro thread non
dipende solo dall'assunzione di calcio ma da molti altri fattori... Per
esempio, una cosa interessante che dicono, un individuo che assume calcio
e fa attività fisica assorbe calcio nelle ossa nelle 30 ore seguenti, ma
dopo 30 ore comincia a perderlo! D'altra parte, si dice, non è del tutto
chiaro quale sia il fabbisogno giornaliero di calcio, quale sia il ruolo
delle proteine (accusate di "rubare" calcio alle ossa, nelle diete
iperproteiche non opportunamente compensate...), se ci siano rapporti tra
latte e tumore alla prostata (dagli studi che ho visto, però, pare semmai
 che il rapporto, se mai esiste, sia con i grassi animali in genere, non
solo con quelli del latte) e ci sono persino alcuni dubbi sul rapporto tra
calcio e prevenzione dell'osteoporosi! Insomma, molti dubbi e poche
certezze, alla fine... E anche per questo, tra parentesi, proliferano i
siti Internet dei "fissati" e degli allarmisti, che guardano solo allo
studio preoccupante ignorando magari la smentita del giorno dopo...
La mia personalissima conclusione è di attenersi a una dieta varia,
mangiando un po' di tutto, senza farsi mancare nulla ma senza esagerare in
nulla, non fissandosi in particolare su un alimento "miracoloso", ma senza
neppure escludere certi alimenti per allarmismi tutti da dimostrare...
E ricordarsi ogni tanto che il cibo è anche un piacere... :)
http://www.hsph.harvard.edu/nutritionsource/calcium.html
What's Best For Your Bones? 
Those advertisements pushing milk as the answer to strong bones are almost
inescapable. But does "got milk" really translate into "got strong bones?"
The pro-milk faction believes that increased calcium intake - particularly
in the form of the currently recommended three glasses of milk per day -
will help prevent osteoporosis, the weakening of bones. Each year,
osteoporosis leads to more than 1.5 million fractures, including 300,000
broken hips.
On the other side are those who believe that consuming a lot of milk and
other dairy products will have little effect on the rate of fractures but
may contribute to problems such as heart disease or prostate cancer.
Which view is right? The final answers aren't in. But here is a summary of
what's currently known about calcium and its effects on the body.
What is calcium?
Calcium is a mineral that the body needs for numerous functions, including
building and maintaining bones and teeth, blood clotting, the transmission
of nerve impulses, and the regulation of the heart's rhythm. Ninety-nine
percent of the calcium in the human body is stored in the bones and teeth.
The remaining 1 percent is found in the blood and other tissues.
Where do we get calcium? 
The body gets the calcium it needs in two ways. One is by eating foods
that contain calcium. good sources include dairy products, which have the
highest concentration per serving of highly absorbable calcium, and dark
leafy greens or dried beans, which have varying amounts of absorbable
calcium. 
The other way the body gets calcium is by pulling it from bones. This
happens when blood levels of calcium drop too low, usually when it's been
a while since having eaten a meal containing calcium. Ideally, the calcium
that is "borrowed" from the bones will be replaced at a later point. But,
this doesn't always happen. Most important, this payback can't be
accomplished simply by eating more calcium.
Growing healthy bones 
Bone is living tissue that is always in flux. Throughout the lifespan,
bones are constantly being broken down and built up in a process known as
remodeling. Bone cells called osteoblasts build bone, while other bone
cells called osteoclasts break down bone. 
In healthy individuals who get enough calcium and physical activity, bone
production exceeds bone destruction up to about age 30. After that,
destruction typically exceeds production.
What is osteoporosis? 
Osteoporosis, or "porous bones," is the weakening of bones caused by an
imbalance between bone building and bone destruction. People typically
lose bone as they age, despite consuming the recommended intake of calcium
necessary to maintain optimal bone health. An estimated 10 million
Americans - 8 million women and 2 million men - have osteoporosis. Another
34 million have low bone mass, placing them at increased risk for
osteoporosis.(1)
Achieving adequate calcium intake and maximizing bone stores during the
time when bone is rapidly deposited (up to age 30) provides an important
foundation for the future. But it will not prevent bone loss later in
life. The loss of bone with aging is due to several reasons, including
genetic factors, physical inactivity, and lower levels of circulating
hormones (estrogen in women and testosterone in men).
Postmenopausal women account for 80 percent of all cases of osteoporosis
because estrogen production declines rapidly at menopause. Of course, men
are also at risk of developing osteoporosis, but they tend to do so 5-10
years later than women, since testosterone levels do not fall abruptly the
way estrogen does in women. It is estimated that osteoporosis will cause
half of all women over age 50 to suffer a fracture of the hip, wrist, or
vertebra.
How can osteoporosis be slowed down?
Preventing osteoporosis depends on two things: making the strongest,
densest bones possible during the first 30 years of life and limiting the
amount of bone loss in adulthood.
There are a number of lifestyle factors that can help with the latter:
Getting regular exercise, especially weight-bearing and muscle
strengthening exercise. 
Getting adequate vitamin D, whether through diet, exposure to sunshine, or
supplements. 
Consuming enough calcium to reduce the amount the body has to borrow from
bone. 
Consuming adequate vitamin K, found in green-leafy vegetables. 
Not getting too much preformed vitamin A. 
Preventing bone loss in adulthood
Several complementary strategies can help prevent or minimize bone loss
during adulthood and old age. These include:
Getting regular exercise
Physical activity that puts some strain or stress on bones causes the
bones to retain and possibly even gain density throughout life. Cells
within the bone sense this stress and respond by making the bone stronger
and denser. Such "weight-bearing" exercises include walking, dancing,
jogging, weightlifting, stair-climbing, racquet sports, and hiking. 
Swimming is a useful form of exercise for the heart and cardiovascular
system. But because water supports the bones, rather than putting stress
on them, it's not considered a good "weight-bearing" exercise for bone
strength. In addition, physical activity doesn't strengthen all bones,
just those that are stressed, so you need a variety of exercises or
activities to keep all your bones healthy. 
Another function of physical activity, probably at least as important as
its direct effect on bone mass, is its role in increasing muscle strength
and coordination. With greater muscle strength, one can often avoid falls
and situations that cause fractures. Making physical activity a habit can
help maintain balance and avoid falls.
Getting enough calcium
Despite the debates surrounding milk and calcium, one thing is clear:
adequate calcium - both for bone development and for non-bone functions -
is key to reducing the risk of osteoporosis. However, the healthiest or
safest amount of dietary calcium hasn't yet been established. Different
scientific approaches have yielded different estimates, so it's important
to consider all the evidence. 
Balance studies - which examine the point at which the amount of calcium
consumed equals the amount of calcium excreted - suggest that an adequate
intake is 550 mg/day. To ensure that 95 percent of the population gets
this much calcium, the National Academy of Sciences established the
following recommended intake levels:
1,000 mg/day for those age 19-50 
1,200 mg/day for those age 50 or over 
1,000 mg/day for pregnant or lactating adult women 
But most balance studies are short-term and therefore have important
limitations. To detect how the body adapts to different calcium intakes
over a long period of time - and to get the big picture of overall bone
strength - requires studies of longer duration. 
The results from such long-term studies may be surprising to some. While
they do not question the importance of calcium in maximizing bone
strength, they cast doubt on the value of consuming the large amounts
currently recommended for adults. 
In particular, these studies suggest that high calcium intake doesn't
actually appear to lower a person's risk for osteoporosis. For example, in
the large Harvard studies of male health professionals and female nurses,
individuals who drank one glass of milk (or less) per week were at no
greater risk of breaking a hip or forearm than were those who drank two or
more glasses per week.(2, 3) Other studies have found similar results.
Additional evidence also supports the idea that American adults may not
need as much calcium as is currently recommended. For example, in
countries such as India, Japan, and Peru where average daily calcium
intake is as low as 300 mg/day (less than a third of the US recommendation
for adults, ages 19-50), the incidence of bone fractures is quite low. Of
course, these countries differ in other important bone-health factors as
well - such as level of physical activity and amount of sunlight - which
could account for their low fracture rates.
Ideally, these issues might be resolved by randomizing a large group of
adults to get different amounts of calcium and following them to see how
many would eventually break a bone. In fact, a few such studies have been
conducted, but they have not provided clear results because they were
small or of short duration, or they provided calcium in combination with
vitamins, which could obscure the true effects of calcium.
To illustrate the different conclusions drawn from examining the same body
of data, a British committee that is comparable to the U.S. group that
established calcium requirements here concluded that 700 mg/day was enough
for individuals aged 19 and older.
Getting enough vitamin D
Vitamin D plays a critical role in maintaining bone health. When blood
levels of calcium begin to drop, the body responds in several ways. It
promotes the conversion of vitamin D into its active form, which then
travels to the intestines (to encourage greater calcium absorption into
the blood) and to the kidneys (to minimize calcium loss in the urine).
For bone health, an adequate intake of vitamin D is no less important than
calcium. Vitamin D is found in milk and vitamin supplements, and it can be
made by the skin when it is exposed to sunlight in the summertime. But not
all sunlight is created equal. Above 40 degrees latitude (north of San
Francisco, Denver, Indianapolis, and Philadelphia), the winter sunlight
isn't strong enough to promote vitamin D formation. Sunscreens also
prevent the formation of vitamin D, although they are still recommended to
reduce risk of sun-induced skin cancer and skin damage.
An examination of clinical trials of vitamin D for the prevention of
osteoporosis found that the vitamin decreases vertebral fractures and may
decrease nonvertebral fractures.(4) A similar analysis of the effect of
vitamin D on falls indicated that supplementation with vitamin D reduces
the risk of falls among ambulatory or institutionalized older individuals
with stable health by more than 20%.(5) 
Getting enough vitamin K
Vitamin K, which is found mainly in green, leafy vegetables, likely plays
one or more important roles in calcium regulation and bone formation.(6)
Low intake of the vitamin has been associated with low bone mineral
density in women, but not men.(7) Getting one or more servings per day of
broccoli, Brussels spouts, dark green lettuce, collard greens, or kale
should be enough to meet the daily recommended target of 120
micrograms/day for men and 90 micrograms/day for women. 
Some other factors may also help lower the risk of osteoporosis:
Take care with caffeine. Although the votes aren't all in, there is some
evidence that drinking a lot of coffee - about four or more cups per day -
can increase the risk of fracture. Caffeine tends to promote calcium
excretion in urine. 
Avoid too much protein. Getting too much protein can leach calcium from
your bones. As your body digests protein, it releases acids into the
bloodstream, which the body neutralizes by drawing calcium from the bones.
Animal protein seems to cause more of this calcium leaching than vegetable
protein does.(3) Just how important protein is as a risk factor for
osteoporosis is still up in the air. 
Get enough vitamin A, but not too much. Long-associated with good vision,
vitamin A has also been found to direct the process of borrowing and
redepositing calcium in bone. However, too much preformed vitamin A can
promote fractures. Avoid vitamin supplements that have a full RDA (5,000
IU) of vitamin A as preformed vitamin A, unless prescribed by your doctor.
Vitamin A in the form of beta-carotene does not increase one's fracture risk. 
Postmenopausal women may also want to talk to a health care provider about
taking a medication that can strengthen bones. The estrogen in
postmenopausal hormones can compensate for the drop in estrogen levels
after menopause, helping to prevent - and perhaps even partially reverse -
bone loss. However, hormone replacement therapy has fallen from grace as
the mainstay for preventing osteoporosis after results from several
studies showed that it increased the risk of heart disease, stroke, and
blood clots.(8) Other medications such as alendronate (Fosamax),
risedronate (Actonel), calcitonin (Miacalcin), raloxifene (Evista), and
parathyroid hormone (Fortéo) have been approved for the prevention or
treatment of osteoporosis.
Should you get calcium from milk? 
When most people in the United States think of calcium, they immediately
think of milk. But should this be so? Milk is actually only one of many
sources of calcium, and there are some important reasons why milk may not
be the best source for everyone. These include:
Lactose intolerance
Many people have some degree of lactose intolerance. For them, eating or
drinking dairy products causes problems like cramping, bloating, gas, and
diarrhea. These symptoms can range from mild to severe. Certain groups are
much more likely to have lactose intolerance. For example, 90 percent of
Asians, 70 percent of blacks and Native Americans, and 50 percent of
Hispanics are lactose-intolerant, compared to only about 15 percent of
people of Northern European descent. 
One alternative for those who are lactose intolerant but who still enjoy
consuming dairy products is to take a pill containing enzymes that digest
milk sugar along with the dairy product, or to consume milk that has the
lactase enzyme added to it.
High saturated fat content
Many dairy products are high in saturated fats, and a high saturated fat
intake is a risk factor for heart disease. And while it's true that most
dairy products are now available in fat-reduced or nonfat options, the
saturated fat that's removed from dairy products is inevitably consumed by
someone, often in the form of premium ice cream, butter, or baked goods. 
Strangely, it's often the same people who purchase these higher-fat
products who also purchase the low-fat dairy products, so it's not clear
that they're making great strides in cutting back on their saturated fat
consumption. For more information on dietary fats, click here.
Possible increased risk of ovarian cancer
High levels of galactose, a sugar released by the digestion of lactose in
milk, have been studied as possibly damaging to the ovaries and leading to
ovarian cancer. Although such associations have not been reported in all
studies, there may be potential harm in consuming high amounts of dairy
products.(9, 10)
Possible increased risk of prostate cancer
A diet high in calcium has been implicated as a potential risk factor for
prostate cancer. In a Harvard study of male health professionals, men who
drank two or more glasses of milk a day were almost twice as likely to
develop advanced prostate cancer as those who didn't drink milk at
all.(11) Moreover, the association appears to be with calcium itself,
rather than with dairy products in general. 
Clearly, although more research is needed, we cannot be confident that
high milk intake is safe.
The bottom line-recommendations for calcium intake and bone health
Adequate, lifelong dietary calcium intake is necessary to reduce the risk
of osteoporosis. Consuming adequate calcium and vitamin D and performing
regular, weight-bearing exercise are also important to build maximum bone
density and strength. After age 30, these factors help slow bone loss,
although they cannot completely prevent bone loss due to aging.
Milk and dairy products are a convenient source of calcium for many
people. They are also a good source of protein and are fortified with
vitamins D and A. At this time, however, the optimal intake of calcium as
well as the optimal sources of calcium, are not clear. As noted earlier,
the National Academy of Sciences currently recommends that people ages
19-50 consume 1,000 mg of calcium per day, and that those age 50 or over
get 1,200 mg per day. Reaching 1200 mg per day would usually require
drinking two to three glasses of milk per day over and above an overall
healthy diet. 
However, these recommendations are based on very short-term studies, and
are likely to be higher than what people really need. Currently, there's
no good evidence that consuming more than one serving of milk per day in
addition to a reasonable diet (which typically provides about 300
milligrams of calcium per day from nondairy sources) will reduce fracture
risk. Because of unresolved concerns about the risk of ovarian and
prostate cancer, it may be prudent to avoid higher intakes of dairy products.
At moderate levels, though, consumption of calcium and dairy products has
benefits beyond bone health, including possibly lowering the risk of high
blood pressure and colon cancer.(12-14) While the blood pressure benefits
appear fairly small, the protection against colon cancer seems somewhat
larger, and most of the latter benefit comes from having just one glass of
milk per day. Getting more than this doesn't seem to lower risk any further.
For individuals who are unable to digest - or who dislike - dairy products
and for those who simply prefer not to consume large amounts of such
foods, other options are available. Calcium can also be found in dark
green leafy vegetables, such as kale and collard greens, and in dried
beans and legumes. 
Calcium is also found in spinach and chard, but these vegetables contain
oxalic acid, which combines with the calcium to form calcium oxalate, a
chemical salt that makes the calcium less available to the body. A variety
of calcium-fortified foods, such as orange juice, are now on the market.
Calcium (and vitamin D) can also be ingested as a supplement. Antacids
contain calcium as well. However, men may want to avoid calcium
supplements for men because of questions about possible risks of prostate
cancer.
An extensive list of the calcium content of foods is available online from
the U.S. Department of Agriculture. These foods are good sources of calcium:
Food Amount Calcium 
Yogurt, plain, low fat 8 oz 415 
Collards, frozen, boiled 1 cup 357 
Skim milk 1 cup 306 
Spinach, frozen, boiled  1 cup 291 
Yogurt, plain, whole milk 8 oz 275 
Cheese food, pasteurized American 1 oz 162 
Cottage cheese, 1% milk fat 1 cup 138 
Baked beans, canned 1 cup 154 
Iceberg lettuce 1 head 97 
Canned salmon 3 oz 181 
Oranges 1 cup 72 
Trail mix (nuts, seeds, chocolate chips) 1 cup 159 
Almonds 1 oz (24 nuts) 70 
Blackeye peas, boiled 1 cup 211 
Green peas, boiled 1 cup 94 
 
 
References
1. Osteoporosis facts. National Osteoporosis Foundation. 
2. Owusu W, Willett WC, Feskanich D, Ascherio A, Spiegelman D, Colditz GA.
Calcium intake and the incidence of forearm and hip fractures among men. J
Nutr 1997; 127:1782-7. 
3. Feskanich D, Willett WC, Stampfer MJ, Colditz GA. Milk, dietary
calcium, and bone fractures in women: a 12-year prospective study. Am J
Public Health 1997; 87:992-7. 
4. Papadimitropoulos E, Wells G, Shea B, et al. Meta-analyses of therapies
for postmenopausal osteoporosis. VIII: Meta-analysis of the efficacy of
vitamin D treatment in preventing osteoporosis in postmenopausal women.
Endocr Rev 2002; 23:560-9. 
5. Bischoff-Ferrari HA, Dawson-Hughes B, Willett WC, et al. Effect of
Vitamin D on falls: a meta-analysis. JAMA 2004; 291:1999-2006. 
6. Weber P. Vitamin K and bone health. Nutrition 2001; 17:880-7. 
7. Booth SL, Broe KE, Gagnon DR, et al. Vitamin K intake and bone mineral
density in women and men. Am J Clin Nutr 2003; 77:512-6. 
8. Manson JE, Hsia J, Johnson KC, et al. Estrogen plus progestin and the
risk of coronary heart disease. N Engl J Med 2003; 349:523-34. 
9. Cramer DW. Lactase persistence and milk consumption as determinants of
ovarian cancer risk. Am J Epidemiol 1989; 130:904-10. 
10. Cramer DW, Harlow BL, Willett WC, et al. Galactose consumption and
metabolism in relation to the risk of ovarian cancer. Lancet 1989; 2:66-71. 
11. Giovannucci E, Rimm EB, Wolk A, et al. Calcium and fructose intake in
relation to risk of prostate cancer. Cancer Res 1998; 58:442-447. 
12. Martinez ME, Willett WC. Calcium, vitamin D, and colorectal cancer: a
review of the epidemiologic evidence. Cancer Epidemiol Biomarkers Prev
1998; 7:163-8. 
13. Hyman J, Baron JA, Dain BJ, et al. Dietary and supplemental calcium
and the recurrence of colorectal adenomas. Cancer Epidemiol Biomarkers
Prev 1998; 7:291-5. 
14. Cappuccio FP, Elliott P, Allender PS, Pryer J, Follman DA, Cutler JA.
Epidemiologic association between dietary calcium intake and blood
pressure: a meta-analysis of published data. Am J Epidemiol 1995; 142:935-45. 
 
-- 
Enrico C
=======================================
http://www.lillathedog.net/icling/dizionari_inglese.html

 Se ne parla anche in un altro thread di oggi.
Si ho visto adesso che c'era un link a una tabella
di dove si trova il calcio.
Per adesso dietro consiglio medico si prova a togliere
latte e tutti i suoi derivati per 1 mese
Volevo sapere in questo mese dove trovavo una fonte
di calcio alternativa, sicuramente in un'acqua minerale
un po' dura visto che con il caldo si beve di piu' e forse
basta questa.
Comunque a me piace il latte e ne bevo(bevevo) almeno 500ml
al giorno + spesso anche formaggi .
grazie ciao

 basta questa.
Non credo che la semplice acqua possa garantire un grammo di calcio al dì. E 
il calcio contenuto in molte verdure è difficilmente assimilabile. Io 
valuterei la possibilità di integrarlo, diciamo 0.5g al giorno (così fai 
metà integrazione e metà alimentazione), a meno che non trovi qualcosa che 
non ti irriti il colon e che ne contenga comunque. Non riesci proprio a 
mangiare alcun latticino?? 

 grazie
Prova con il  Latte Crudo ....
molti soggetti che avevano disturbi con il latte pastorizzato ( coliti
, mal di pancia etc ) risolvono i loro problemi con il latte
consumandolo crudo !
dai uno sguardo a 
http://www.biola.it/le-intolleranze.aspx
 ...
Giuseppe Brandizzi
www.biola.it

Non riesci proprio a  mangiare alcun latticino??
Diciamo che stiamo provando a vedere cosa succede ad eliminare tutti
i latticini , sicuramente adesso c'e' meno 'rivoluzione' nel colon poi si
puo' provare a reintegrare formaggi stagionati ad alto contenuto di
calcio ma senza lattosio.
grazie 

*Alessandro Morelli* wrote:
:: il calcio contenuto in molte verdure è difficilmente assimilabile.
Di quali verdure parli, tanto per capire?
A me risulta che il calcio contenuto nei vegetali sia più assimilabile
di quello contenuto nell'acqua o nel latte.

 di quello contenuto nell'acqua o nel latte.
http://www.sinu.it/larn/mineral1.asp
L'assorbimento del calcio avviene attraverso due meccanismi: trasporto
attivo transcellulare (saturabile) e diffusione passiva paracellulare (non
saturabile). L’assorbimento transcellulare avviene nell'intestino
prossimale, mediante una proteina legante il calcio che trasferisce il
minerale attraverso l'enterocita verso la membrana basale o laterale dove
viene espulso dalla calcio magnesio ATPasi. Una piccola quota di calcio può
essere assorbita nell'intestino distale. Solo il 35-45% del calcio della
dieta viene assorbito. La quota assorbita dipende dallo stato fisiologico
del soggetto e dalle interazioni con altri componenti della dieta. Oltre
all'influenza favorevole sull’assorbimento esercitata dalla vitamina D, la
biodisponibilità del calcio alimentare può essere aumentata dalla presenza
di zuccheri, in particolare di lattosio (Allen, 1982; Spencer & Kramer,
1986), di alcuni aminoacidi (lisina, arginina) e da un aumento del pH
intraluminale (Wilkinson, 1976). La biodisponibilità viene invece diminuita
da alcuni costituenti dei vegetali: ossalati, fitati, fosfati ed alcune
frazioni della fibra alimentare (acidi uronici) (Heaney & Weaver, 1989;
Heaney et al., 1991, James et al., 1978). Alcuni di questi composti
indigeribili a cui il calcio è legato possono però essere degradati ad
opera della flora batterica intestinale a livello della regione ceco-colon
(Favus et al., 1980). La degradazione batterica di questi composti può
pertanto essere un fattore importante nella valutazione globale della
biodisponibilità del calcio.
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