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揭秘牛奶背后的真相!

放大字体  缩小字体 发布日期:2011-02-22  来源:译言网  浏览次数:1525
核心提示:本文作者在查阅大量科学文献基础上,分析了有关牛奶营养健康的是是非非,我们到底需不需要牛奶?看完本文,相信每个人都自会有答案了。


Milk is as pure white as fresh fallen snow and as familiar as a mother's warm touch.  Common sense once led me to believe that if a single food, milk, could sustain a baby as the sole source of nutrients, then it must be “nature's most perfect food.”  Milk builds strong bones – I have learned over and over again – and since the hardest parts of my body are made mostly of calcium, this liquid food must be essential for my strength and stability.  Milk is for life, because they tell me I never outgrow my need for milk.  All these “facts” were the “truth” until I took the trouble to think a little about the subject on my own and to look into the scientific research.  May I share with you some of my surprising discoveries?

Mother's Milk Can Be a Perfect Food
Within the same species – like cow for calf, cat for kitten, mare for foal – mother's milk can be the perfect food for the very young – not, after weaning, for older offspring, and certainly, not for the fully-grown.  All mammals nourish their developing young with this ready-to-eat liquid synthesized by specialized sweat glands, called the mammary glands.  This life-giving fluid contains the nutrients, antibodies and hormones that optimize the chances for growth and survival of the infant.

How essential is mother's milk? Human infants deprived of the advantages of human breast milk have:1
1、Two to four times the risk of sudden infant death syndrome (crib death),
2.  More than 60 times the risk of pneumonia in the first three months of life,2
3.  Ten times the risk of hospitalization during their first year
4.Reduced intelligence as measured by IQ score
5. Behavioral and speech difficulties
 6.An increased chance of suffering from infections, asthma, eczema, type I diabetes, and cancer (lymphoma and leukemia) in early life 
7.A greater risk of heart disease, obesity, diabetes, multiple sclerosis, food allergies, ulcerative colitis, and Crohn’s disease later in life

 
No one argues against the fact that human breast milk is nature’s most perfect food for human babies.  There is also no satisfactory substitute; therefore, every effort should be made to have every infant breast-fed exclusively for six months; and then, with the addition of healthy solid food choices, partially breast-fed until the age of two.  (More information on this is found in The McDougall Program for Women book).

Mother's Milk is Species Specific
The nutritional needs of very young animals are met by the unique qualities of the milk of that particular species.  The composition of this infant food has evolved over millions of years to be ideally suited for that animal.  Let me explain in terms of one essential nutrient: protein.

The amount of protein in the milk of an animal varies to meet the growth demands of the very young – the faster an animal grows the greater the protein needs.

Comparisons of Milk of Different Species3
Animal
Protein*
Growth Rate(days)**
Human
1.2
180
Horse
2.4
60
Cow
3.3
47
Goat
4.1
19
Dog
7.1
8
Cat
9.5
7
Rat
11.8
4.5
* Grams per 100 milliliters (in terms of % of calories, cow's milk has four times more protein than human milk; 21% vs. 5%4)
** Time required to double birth weight

In addition to the much higher protein content, consider the other nutrient differences between cow's milk and human:
Nutrient
Human
mg/100 Cal
Cow
mg/100 Cal
Calcium
45
194
Phosphorus
18
152
Sodium
23
80
Potassium
72
246

Not surprisingly, since a calf doubles its birth weight nearly four times faster than a human infant does, the concentrations of protein and calcium are nearly four times greater.  Rapid growth requires a much higher density of all kinds of nutrients.

Problems of Excess Nutrients
Most people think of health problems in terms of deficiencies of nutrients; this is the reason vitamin and mineral supplements are so popular.  However, I do not see diseases of deficiency in my patients.  For example, I see no vitamin C deficiency (scurvy), B1 deficiency (Beriberi), or protein deficiency in my patients.  Rather, I see diseases of excess – such as excess dietary fat (obesity), cholesterol (heart disease), and salt (hypertension).  Therefore, feeding an overly-concentrated food such as cow's milk to people (infants, children, and adults) promotes diseases of excess.  (Some of you are still thinking cow's milk corrects calcium deficiency in people, preventing osteoporosis.  Be patient, in a moment I will show you this is not true.)

Replacing human breast milk with cow's milk was once tried in the mid-1800s in the United States for emergency situations (such as when a mother died in childbirth).  The result was a quick death for most of the infants, because the high protein content of the cow's milk forced fluid losses from the infant's kidneys, resulting in dehydration.5 Once this problem was recognized, then infant formulas were developed which added sugar to the cow's milk in order to reduce the protein concentration of the cow's milk and make it more resemble human milk.  Some of you may be old enough to remember making or drinking infant formula made from Carnation evaporated cow's milk and Karo syrup (sugar).6 (This is a very unhealthy formula for infants – do not use this).

Consider the purpose of cow's milk.  This is an ideal food to grow a calf from its 60-pound birthweight to a 600-pound young cow, ready to wean.  This is a high “octane” fuel.  One obvious consequence of people eating “calf food” is rapid fat gain – and dairy products are one of the leading contributors to the epidemic of excess body fat affecting 25% of children and 65% of adults in Western populations.  Matters are made even worse when cow's milk is converted into even more concentrated products, like cheeses.

Cow's milk products have some important nutritional deficiencies.4  They are completely devoid of fiber; and contain insufficient amounts of vitamins, like C and niacin, and minerals, like iron, to meet the human body's needs.

False Promise #1: Milk Builds Strong Bones
If you ask people why they drink milk, they'll tell you it's for the calcium. Milk has lots of calcium and its supporters have "milked" that point for all it's worth. One of your first clues that cow's milk is not ideal for bone health comes from comparison of the calcium content of the two kinds of milk (shown above).  Cow's milk has more than four times the calcium content as human breast milk. If this exaggerated amount of calcium is not required during our greatest time of growth – babies double in weight in six months – then why should a concentration of calcium ideal for calves be required when we stop growing bones as adults?  Without a doubt growing the hefty skeleton of a cow takes much more calcium than growing relatively small human bones.

Billions of people worldwide do not consume milk after weaning and they grow normal adult skeletons.7 For example, Bantu women in Africa consume no dairy products at all, and take in only about 250 to 400 mg of calcium each day through vegetable sources8 (about half the recommended daily intake in the U.S.). These women typically have ten children each and breast-feed each one for about 10 months. Yet despite a diet with no dairy products and the tremendous calcium drain of pregnancy and breast-feeding, osteoporosis is virtually unknown among these women.8 When rural African women migrate to cities or move to Western counties and adopt rich, high-calcium diets, osteoporosis becomes common.9 You will soon understand this is because their new diet becomes very high in animal protein.10

The world picture fails to support benefits claimed by the dairy industry.  Countries that have the highest traditional consumption of dairy products (United States, Sweden, Israel, Finland, and the United Kingdom) also have the highest rates of osteoporosis-related hip fractures.11 Places in the world with a traditionally low intake of dairy - Hong Kong, Singapore, countries in rural Africa - have the lowest incidence of osteoporosis.

If calcium is the key and milk is such a great source, why are there still 10 million Americans with osteoporosis?  Long-standing recommendations to increase calcium intakes have had little or no effect on the prevalence of osteoporosis or fractures in the United States.7

Worldwide, the incidence of osteoporosis correlates directly and strongly with animal protein intake.  The highly acidic nature of animal protein is the major cause of bone loss.10 (You can read more about this at www.drmcdougall.com in the February 2003 McDougall Newsletter in the article, “Fish is not health food.”)

False Promise #2: Research Supports Dairy’s Benefits
In September of 2000, two researchers compiled a review of the 57 studies on dairy products and bone health which had been published in the scientific literature since 1985.  This review was published in the American Journal of Clinical Nutrition.12   Not surprisingly, most of this research was financed by the dairy industry.  The researchers reported that 53 percent of the studies showed no benefit from dairy.  Then they excluded studies with weak evidence or poor techniques, which eliminated more than half of the studies. Of the 21 remaining studies, 57 percent again showed no benefit from dairy, and another 14 percent found that dairy products actually weaken bones. Think about that – this means that 71 percent of the scientifically sound research did not support the bone building benefits of dairy products and some showed actual harm.

Randomized controlled studies compare an experimental group with a control group and are considered the most valid form of scientific research.   Of the seven randomized controlled studies which have been completed on the effects of dairy products on bone health, six were financed by the dairy industry.  Only one looked at the benefits of fluid milk on the health of the women most likely to benefit: postmenopausal women.13 At the conclusion of this study, the women in the experimental group, fed three eight-ounce glasses of skim milk daily for a year, were still losing more calcium from their bodies than they were absorbing (they were in negative calcium balance). Even though they consumed more than 1400 mg of calcium daily they still lost twice as much bone as the women in the control group, who were not getting the supplemental milk.  Yet the industry continues to proclaim its pro-milk message from every rooftop.

False Promise #3: Dairy Foods Make Meeting Calcium Recommendations Easy
Recommended intakes of calcium to prevent osteoporosis are now so high that it is difficult, if not impossible, to make up practical diets that meet these recommendations.7   The National Institutes of Health Consensus Conference and The National Osteoporosis Foundation support a calcium intake of 1,500 milligrams per day for postmenopausal women not taking estrogen, and for adults 65 years or older.  Assuming 300-400 mg of calcium comes from starches, vegetables, fruits, eggs, poultry, fish, and meats,4 then 1,200 mg would have to be obtained from dairy products daily.  An average postmenopausal sedentary woman consumes 1500 calories a day.  The amount of dairy required to meet her recommended calcium needs would be:4

* 6 ounces Cheddar cheese (which is 74% fat).  This would mean that 46% of the calories in her diet must be from cheese; or

* One quart (32 ounces) of whole milk (which is 50% fat) which would mean 40% of her diet is from milk; or
* One quart (32 ounces) of non-fat milk (which is 3% fat) which would mean 23% of her diet would be non-fat milk.

The dairy industry is happy about these grand recommendations, but consuming that much cow's milk product daily would replace too many other more filling (satisfying) and nutritious foods, and be unhealthy.

False Promise #4:  We Require 1500 mg of Calcium a Day
Our requirements for calcium are far less than recommended.   Scientific research demonstrates people need as little as 150 to 200 mg/day, even when pregnant or lactating.14

Consider the great variation in calcium intakes and recommendation:
Minimum Requirement Based on Research
150-200 mg
Calcium Intake for Underdeveloped Countries
300-500 mg
Calcium Intake for Average American
500-600 mg
World Health Organization Recommendation
400-500 mg
USA Food and Nutrition Board
1000- 1300 mg
A National Institutes of Health
1000-1500 mg

Why the large variation in figures for calcium intakes and recommendations?  The simple answer is the amount of calcium in the foods you eat has little effect on the quantity of calcium that is eventually taken into the body and on the health of your bones.15

Your intestine will always absorb sufficient calcium to meet your needs from the foods you eat. On a diet low in calcium, the efficiency of mineral absorption is increased, and the intestine takes in more calcium. On a high-calcium diet, more calcium is left in the intestine to be excreted, unused, in the feces.16  The intestine is so “smart” about calcium that it never fails to meet the body’s needs.  If you look over the last hundred years of scientific and nutritional literature you will find there is no evidence that dietary calcium deficiency occurs in humans, even though most people in the world don't drink milk after weaning – because of custom, lactose intolerance, or simply because milk is not generally available in their part of the world. 7,14, 17-20  This means there is no such disease as “dietary calcium deficiency” – think again if your mind drifts to osteoporosis – remember, populations with the lowest calcium intakes have the strongest bones; the least osteoporosis, worldwide.11

False Promise #5: Milk is the Best Food for Bones
The truth is, milk is not the only source of calcium and it is not the best source of calcium.  Consider that the original source of calcium is the ground.  Calcium, and other minerals, are dissolved in watery solutions and absorbed by the roots of plants.  These minerals are then incorporated in the roots, stems, leaves, flowers, and fruits of the plants.  Humans can get plenty of calcium the same way it gets into cow's milk; from the plant foods they eat.

Inappropriate concern about calcium intake may divert attention and resources from more important nutritional issues. Calcium isn't the only nutrient that affects bone health. Studies have shown that potassium and magnesium may be even more critical in preventing bone loss, and that beta-carotene, phosphorus, and fiber play important roles as well.21,22 Plants are excellent sources of these nutrients.  Milk provides no beta-carotene and no dietary fiber.4 Most important, bone health can be more about what you don't eat than what you do eat. Certain foods and substances – like animal proteins, cigarettes, soft drinks, caffeine, and salt – all affect your body's ability to absorb and use calcium vs. the loss of calcium from the body. 23,24

False Promise #6: Milk is Necessary for vitamin D
Some people will point out milk's vitamin D content as evidence of its critical place in a healthy diet. Well, that's a fabrication, too. Vitamin D is not really a vitamin; it's a hormone that the body produces in reaction to sunlight. And it isn't present naturally in milk – it's added as a supplement at the dairy processing factory. This addition was supposedly done to prevent rickets, a painful, deforming bone condition that is caused by vitamin D deficiency. But rickets is really caused by limited exposure to sunlight, and the body levels of vitamin D are only slightly affected by dietary sources.25,26 The amount of sunlight we get during the summer holidays is reflected in our vitamin D levels all year long.  More than 90% of the vitamin D in the body is produced by sunlight.  Exposing the face and arms for as little as 15 minutes 3 times a week provides adequate amounts of vitamin D.  However, this activity is modified by the use of sunscreens and by skin pigmentation.27 So nearly everyone gets enough vitamin D every day just through normal activities – we don't need to drink milk to get it. Plus, vitamin D is fat-soluble, which means it is stored in our body fat for long periods of time – and most importantly, for periods of low sun exposure in the winter months.

Myth #7:  Milk Cures Hypertension
A grant from the National Dairy Council supported a large review of the influence of dietary (dairy products) and nondietary (supplements) calcium supplementation on blood pressure and came to the conclusion “that calcium supplementation leads to a small reduction in systolic (top number) and diastolic (bottom number) blood pressure.”28  Of the 67 studies published, 47 proved eligible for review.  The actual decrease in blood pressure was paltry:  Decreases of 1.44 mmHg systolic and 0.84 mmHg diastolic.  The mechanism causing this almost undetectable reduction in blood pressure from consuming calcium is unknown.

By comparison, our results from the McDougall residential center show a 23/14 mmHg decrease in blood pressure in people with high blood pressure (150/90 mmHg or greater) in less than 10 days; and almost all of these people were taken off all of their blood pressure medication during the 10 days.

False Promise #8:  Milk Prevents Colon Cancer
Colon cancer is one of the most common cancers in the United States and other places where people eat the Western diet.  There is general agreement in the scientific community that this form of cancer is due to the high-meat, high-fat, low-dietary fiber, low-vegetable diet that people eat.29,30  However, among those unfortunate people who eat this unhealthy diet, those who have a higher calcium intake also have a lower risk of colon cancer.  The reason for this may be that calcium in the colon binds and neutralizes cancer-causing substances, such as fats and bile acids, which are produced by the Western diet.31

The recommendation to increase your calcium intake, rather than change to a healthy diet, makes good economic sense for the dairy and calcium supplement industry.  However, as a sensible person, you would come to the conclusion that stopping the cause of colon cancer – the Western diet – should be the focus of your attention.

False Promise #9:  Low-fat Dairy Products are Health Food
Low-fat or skim milk and dairy products are widely consumed today, but in some ways they may be even more of a health hazard than the high-fat versions. The process of skimming the fat from the milk increases the relative proportions of protein and lactose.

Making Low-fat Milk
When the fat is removed from whole milk to make low-fat and skim milk the relative amounts of proteins and carbohydrates (sugars) are increased.4
 
Whole
Low-fat
Skim
Fat
49%
31%
2%
Protein
21%
28%
41%
CHO
30%
41%
57%
CHO = carbohydrate = lactose = milk sugar

Protein causes calcium loss10,11 and is the #1 source of food allergies in people; and the milk sugar (lactose) results in lactose intolerance (diarrhea, stomach cramps and gas). Although skim milk may have less fat, it is still devoid of fiber; and contains insufficient amounts of vitamins, like C and niacin, and minerals, like iron, to meet the human body's needs.4

False Promise #10: Milk Is As Pure White As Fresh Fallen Snow
Milk may be white but it is far from pure.  Unfortunately, some of that white comes from white blood cells – commonly referred to as “pus cells” – which are cells produced by the cow's immune system to fight off infections, especially those of bacterial origin, such as mastitis.  The dairy industry calls these somatic cells and refers to their presence as the somatic cell count (SCC).  The SCC is the number of (mostly) white blood cells per milliliter (cells/ml) of milk.  (There are 20 drops per milliliter; 30 milliliters to an ounce)

Beginning July 1, 1993, the SCC level in milk must be less than 750,000 SCC to comply with the State and Federal Pasteurized Milk Ordinance.32   This means one 8 ounce glass of milk (240 milliliters) can contain 180 million white blood cells and still be fine for you to drink and feed to your family.  In a recent study of milk sold in New York State the average SCC was 363,000 cells/ml.33 These white blood cells were produced by the cow to fight off the 24,400 bacteria/ml found in this milk.

I realize this is a disgusting way to end this article, but I must prepare you for next month’s article concerning the health risks you take for yourself and your family by consuming dairy products, such as obesity, heart disease, cancer, type-I diabetes, food allergies, and the potential for infections with AIDS and leukemia viruses found in almost all vats of milk in the United States.

References:
1)  McDougall J. The McDougall Program for Women. Plume, 2000. Pages 59-70.
2)  Cesar JA.  Impact of breast feeding on admission for pneumonia during postneonatal period in Brazil: nested case-control study.  BMJ. 1999 May 15;318(7194):1316-20.
3)  McDougall J.  The McDougall Plan. New Win Publ. 1983; page 101.
4)  J Pennington.  Bowes & Church’s Food Values of Portions Commonly Used.  17th Ed. Lippincott. Philadelphia- New York. 1998.
5)  Abrams CA.  Hazards of overconcentrated milk formula. Hyperosmolality, disseminated intravascular coagulation and gangrene.  JAMA. 1975 Jun 16;232(11):1136-40.
6)  Belton NR.  Clinical and biochemical assessment of a modified evaporated milk for infant feeding.  Arch Dis Child. 1977 Mar;52(3):167-75.
7)  Hegsted D.  Fractures, calcium and the modern diet.  Am J Clin Nutr 74: 571-3, 2000.
8)  Walker A. The influence of numerous pregnancies and lactations on bone dimensions in South African Bantu and caucasian mothers.  Clin Science 42:l89-196, l972.
9)  Smith R. Epidemiologic Studies of Osteoporosis in Women of Puerto Rico and Southeastern Michigan with Special Reference to Age, Race, National Origin, and to Other Related or Associated Findings. Clin Orthop 45:31-48, 1966.
10)  Barzel US, Massey LK. Excess dietary protein can adversely affect bone.  J Nutr. 1998;128:1051‑3.
11)  Abelow B.  Cross-cultural association between dietary animal protein and hip fracture: a hypothesis.  Calcific Tissue Int 50:14-8, 1992.
12)  Weinsier R.  Dairy foods and bone health: examination of the evidence.
Am J Clin Nutr.
2000 Sep;72(3):681-9.
13)  Recker R.  The effect of milk supplements on calcium metabolism, bone metabolism and calcium balance.  Am J Clin Nutr. 1985 Feb;41(2):254-63.
14)  Paterson C. Calcium requirements in man: a critical review.  Postgrad Med J 54:244-8, 1978.
15)  Kanis J.  The use of calcium in the management of osteoporosis.  Bone 24:279-90, 1999.
16)  Spencer H. Influence of dietary calcium intake on Ca(47) absorption in man. Am J Med 46:197-205, 1969.
17)  Hegsted D.  A study of minimum calcium requirements of adult men.  J Nutr 46:181-120, 1952.
18)  Symposium on human calcium requirements. JAMA 185:588-93, 1963.
19)  Goodhart and Shils, Modern Nutrition in health and disease (Dietotherapy), 5th ed. 1973 p. 274.
20)  Walker A. Osteoporosis and calcium deficiency. Am J Clin Nutr 16:327, 1965.
21)  Tucker KL.  Potassium, magnesium, and fruit and vegetable intakes are associated with greater bone mineral density in elderly men and women.  Am J Clin Nutr. 1999 Apr;69(4):727-36.
22)  New S. Dietary influences on bone mass and bone metabolism: further evidence of a positive link between fruit and vegetable consumption and bone health.   Am J Clin Nutr 71:142-151,2000.
23)  Ilich J. Nutrition in bone health revisited: a story beyond calcium. J Am Coll 19:715-37, 2000.
24)  Cohen A. Review of risk factors for osteoporosis with particular reference to a possible aetiological role of dietary salt.  Food Chem Toxicol. 38:237-53, 2000.
25)  Holick M. Environmental factors that influence the cutaneous production of vitamin D.  Am J Clin Nutr. 1995 Mar;61(3 Suppl):638S-645S.
26)  Stamp T.  Comparison of oral 25-hydroxycholecalciferol, vitamin D, and ultraviolet light as determinants of circulating 25-hydroxyvitamin D. Lancet. 1977 Jun 25;1(8026):1341-3.S
27)  Norris J.  Can the sunshine vitamin shed light on type 1 diabetes?  Lancet 2001 358:1476-77.
28)  The influence of dietary and nondietary calcium supplementation on blood pressure: an updated metaanalysis of randomized controlled trials. Am J Hypertens. 1999 Jan;12(1 Pt 1):84-92.
29)  Weisburger J.  Causes, relevant mechanisms, and prevention of large bowel cancer.
Semin Oncol
. 1991 Aug;18(4):316-36.
30)  Mason JB.  Nutritional chemoprevention of colon cancer.  Semin Gastrointest Dis. 2002 Jul;13(3):143-53.
31)  Holt R.  Dairy foods and prevention of colon cancer: human studies.  J Am Coll Nutr. 1999 Oct;18(5 Suppl):379S-391S.
32)  Adkinson RW.  Implications of proposed changes in bulk tank somatic cell count regulations.  J Dairy Sci. 2001 Feb;84(2):370-4.
33)  van Schaik G.  Trends in somatic cell counts, bacterial counts, and antibiotic residue violations in New York State during 1999-2000.  J Dairy Sci. 2002 Apr;85(4):782-9.

参考译文:
牛奶如从天而降的雪一样洁白,让人想起母亲温暖的怀抱。常识曾让我相信,既然牛奶可以作为婴儿唯一的营养来源,那么它一定是天然的最完美的食品。牛奶强壮骨骼──我反复被告知──既然体内最坚硬的骨骼大多由钙组成,那么富含钙质的牛奶对于维持我骨骼的力量和平衡来说,是必不可少的。你终生都需要牛奶,因为你身体对牛奶的需求是永不满足的,乳制品业如此宣传。这些"事实"一直是"真的",然而,当我花点时间去认真地思考牛奶的作用,并查阅大量的科学文献后,我得出了一些让我感到意外的结果。

一、母乳才是最佳食品
例如牛奶对小牛、猫奶对小猫、马奶对小马,只有在同一物种之内,母乳才是婴儿的最佳食品,对于断奶后、青少年、成年人来说,母乳也不是最佳食品。哺乳动物用乳腺分泌的乳汁来哺育成长中的婴儿。乳汁含有利于成长和生存所需的营养、抗体、激素。

母乳有多重要?人类婴儿如果没有乳汁:
1.患婴儿猝死综合症的机率大2~4倍。
2.在出生后三个月内,患肺炎的风险大60倍。
3.出生后一年内,住院机率大10倍。
4.IQ下降。
5.行为和语言障碍。
6.在生命前期,患感染、哮喘、湿疹、1型糖尿和癌症(淋巴瘤和白血病)的风险加大。
7.在生命后期,有较大机率患心脏病、肥胖症、糖尿病、多发性硬化症、食物过敏、溃疡性结肠炎和克罗恩病。

母乳是人类婴儿最理想的食品这一点是毋容置疑的。迄今为止,还没有满意的母乳替代品,因此,在出生后前6个月应该尽量只用母乳喂养,然后,在两岁以前,以健康的固体食品加上一部分母乳喂养。(更多信息请查阅麦克杜格尔妇女手册)

二、母乳是物种特异性的
婴儿所需的营养只有在同样物种的母乳中才含有。母乳的成分通过上万年的进化才使得其符合该物种婴儿的需求。让我以蛋白质这个必需营养成分为例来解释。

因不同物种婴儿的生长速度不同,母乳中的蛋白质含量也不同──生长速度越快,所需蛋白质越多。

不同乳汁的蛋白质含量

* 每毫升所需克数(以卡路里的百分比计算,牛奶比人乳的蛋白质含量高4倍:21%比5%)
** 出生后体重增加一倍所需时间

除了蛋白质含量的不同,还有其它营养成分的含量也不同:


不出意料,因为小牛增加一倍出生体重的速度比人类婴儿快4倍,牛奶中的蛋白质和钙含量也比人乳高4倍。高的生长速度对于各种营养成分的需求也更多。

三、营养过剩的问题
大多数人认为健康问题是因为缺乏营养而引起的,这是维生素和矿物质补充剂如此畅销的原因。但是,我的患者中没有一个是因缺乏营养而患病,比如维生素C缺乏症(坏血病)、维生素B1缺乏症(脚气病)或蛋白质缺乏症。相反,其中有很多富贵病──比如超量饮食脂肪酸(肥胖)、胆固醇(心脏病)、盐分(高血压)。因此,人们(婴儿、小孩、成人)摄取如牛奶一样的含有多余营养成分的食品会导致富贵病。(可能你还认为牛奶可以预防钙缺乏症,防止骨质疏松。请耐心地往下读,我会向你证明这是不可信的。)

十九世纪中期,在美国,牛奶只是作为紧急情况下人乳的替代品(比如,母亲死于难产)。结果因为牛奶的蛋白质含量过高导致婴儿肾脏功能障碍,水分从肾脏流失而引发脱水症,引起大量婴儿的死亡。该问题发生后,人们在婴儿配方奶中加入糖分以降低牛奶中蛋白质的含量,使其成分比更接近人类。如果你年纪比较大,可能还会记得冲调或饮用康乃馨牌的奶粉和卡罗牌糖浆组成的婴儿配方奶(这对于婴儿来说,是非常不健康的配方奶,请不要再使用)。

考虑一下牛奶的真正用途。它是从出生体重60磅长到600磅准备断奶的小牛的最佳食物。牛奶是高"辛烷值"的燃料。人们饮用牛奶就会导致一个明显的结果──快速变胖。在西方国家中,乳制品对于影响25%儿童和65%成年人的超重的流行负主要责任。如果牛奶被制成更高营养含量的食品,如奶酪,其带来的问题更多。

牛奶中也缺乏一些重要的营养成分。其中,完全缺乏纤维素、缺少维生素和矿物质,比如维生素C、尼克酸、铁,这些都是人体所需的营养成分。

谎言1:牛奶强壮骨骼
如果你问人们,为什么要喝牛奶?他们通常会说为了其中的钙。牛奶中含有大量的钙,于是它的支持者将此证据"挤"出来了。其实,与上面表格中的其它两种乳汁的钙含量相比,牛奶不是维持骨骼健康的理性选择。牛奶中的钙含量比人乳中的高四倍。如果在我们生命中生长最快的阶段(婴儿在六个月内体重增倍)都不需要如此高含量的钙,当我们成人停止生长后,为什么还需要如此多的钙?当然,相对于人类较小的骨骼,牛的骨骼较大,所需的钙也就多。

世界范围内上数十亿的人断奶后不再饮用牛奶,成人后,他们的骨骼也是正常的。比如,非洲的班图妇女完全不饮奶,而是通过蔬菜来获取每天所需的250~400毫克的钙(大约是美国推荐摄入量的一半)。这些妇女大多有十个孩子,每个孩子的哺乳期大约是10个月。尽管不饮奶,而且在怀疑和哺乳期间还消耗大量钙质,她们几乎都不会出现骨质疏松。但是,当土著非洲妇女移居到大城市或移民到西方国家,遵循富含钙质的饮食后,骨质疏松症开始发生。你可能会马上想到这是因为她们的饮食变得富含动物蛋白了。

不同国家的数据不支持乳制品业宣称的益处。传统高消费乳制品的国家(美国、瑞典、以色列、芬兰、英国)通常有较高的骨质疏松引起的髋骨骨质,而传统低消费乳制品地区(香港、新加坡、非洲农村)的骨质疏松症发生率较低。
如果摄取钙很关键,而牛奶又是钙质的良好来源,为什么还有一千多万的美国人患骨质疏松症?增加钙摄入的这个存在已久的建议对于降低美国骨质疏松或骨质的流行只有有限或完全没有作用。

世界范围内,骨质疏松症的发生与动物蛋白的摄取量有直接和有力的联系。高度酸性的动物蛋白是引起骨质流失的重要原因。(你可以在www.drmcdougall.com 阅读麦克杜格尔2003年2月份上的"鱼肉不是健康食品"。)

谎言2:研究支持乳制品的益处
2000年九月份,两位研究者总结了1985年以来发表的关于乳制品和骨骼健康的科学文献。该综述发表在美国临床营养杂志上。不出所料,大多数科学文献都是由乳制品业提供资金。研究者称,其中53%的文献表明乳制品的益处无科学证据。然后,研究者排除了证据差或技术差的研究,这样至少将一半的研究给排除了。剩下的21个研究中,57%的显示乳制品的益处无科学证据,其它14%甚至显示乳制品有害骨骼健康。想一下这意味着什么──71%的科学性良好的研究不支持乳制品的益处,甚至一些显示有害。

随机对照实验比较实验组和对照组,它被认为是最科学的科学研究。在7个关于乳制品对骨骼健康的随机对照实验中,有6个由乳制品业资助。只有一个研究能从液体牛奶中获益最大的妇女:绝经后的妇女。在这个研究中,实验组的妇女一年中每天三次饮用8盎司的脱脂牛奶,但是她们仍然流失比吸收更多的钙(她们的钙平衡处于负的状态)。尽管她们每天摄入1400多毫克的钙,但是和对照组的非饮奶妇女相比,她们的钙流失速度快两倍。虽然如此,乳制品业还是继续不遗余力地宣传乳制品对骨骼健康的好处。

谎言3:乳制品使你的钙的摄入量简单地达到推荐量
防止骨质疏松症的钙的推荐摄入量如此之高,以致要通过正常饮食来达到该标准变得很困难(如果不是不可能)。美国国立卫生研究所和国家骨质疏松基金会推荐对于绝境后而又没有服用雌激素的妇女每天摄取1500毫克的钙,对于65岁或以上的老年人也要每天摄取1500毫克的钙。如果其中300~400毫克的钙来源于碳水化合物、蔬菜、水果、蛋类、禽类、鱼肉、肉类,剩下的1200毫克就不得不从乳制品中获得。一个静坐生活方式的绝经后的妇女评价每天消耗1500卡路里。如果要达到推荐的钙摄入量,她所需要食用的乳制品量:

6盎司的切达乳酪(脂肪含量74%)。从乳酪中获得卡路里将占总卡路里46%;
1夸脱(32盎司)的全脂牛奶(脂肪含量50%),从全脂牛奶中获得的卡路里将占总卡路里的40%;
1夸脱的脱脂牛奶(32盎司)的脱脂牛奶(脂肪含量3%),从脱脂牛奶中获得的卡路里将占总卡路里的23%;

乳品业对这些过高的推荐量持乐观态度,但是每天消耗这么多的牛奶替代其它更加饱腹(满意)和营养的食物,这是不健康的。

谎言4:每天我们需要1500毫克的钙
我们真正所需钙远远少于推荐量。科学研究证明我们每天只需150~200毫克的钙,即使在怀孕或哺乳期间也是如此。

考虑下钙摄入量和推荐量不同:


为什么关于钙的摄入量和推荐量如此不同?简单地解释就是你在食物中摄取的钙对最终吸收进身体和骨骼健康的影响是微小的。

你的肠道总是会从进食的食物中获取满足你需求的足量的钙。如果饮食中的钙含量低,肠道对钙吸收的效率增加,这样就能吸收更多的钙。如果饮食中钙含量高,多余的钙就会在未吸收的状态下以排泄物的形式排出体外。肠道系统对于钙吸收的调节十分智能,总是能满足机体对钙的需求。如果你追溯营养研究的科学文献到最近的一百年前,你会发现没有证据表明食物中钙缺会发生在人类身上,尽管世界上的大多数人断奶后并不饮牛奶──可能出于风俗、乳糖不耐受、牛奶不在本地区生产等原因。所以说并不存在"钙缺乏症"这个疾病──如果你又想到骨质疏松症──请记住,世界上,钙摄入量最低的国家的人却拥有最强壮的骨骼,最低的骨质疏松发生率。

谎言5:牛奶是骨骼健康的最佳食品
事实上,牛奶并不是钙的唯一来源,而且也不是最佳来源。钙的源头是大地。钙和其它矿物质溶于水后被植物的根所吸收。然后钙从根传递到茎、叶、花、果。人类也可如钙进入牛奶的途径一样,从植物性饮食中获取钙。

对钙的摄入量的过度关注可能会将人们的注意力和有限的资源从更加重要的营养问题上转移。钙不是唯一影响骨骼健康的营养元素。研究显示,钾和镁对于防止骨质流失起到更大的作用,此为β-胡萝卜素、磷、纤维素也具有重要作用。植物性饮食是获得这些营养的良好来源。牛奶中不含β-胡萝卜素和膳食纤维。更为重要的是,你不吃什么要比你吃什么对骨骼健康的影响大。某些食物和物质──比如动物蛋白、烟草、碳酸饮料、咖啡、盐──都会影响你机体对抗钙流失,影响你吸收和利用钙的能力。

谎言6:牛奶对维生素D的获取是必需的
有些人支持牛奶中的维生素D在健康饮食中扮演一个很重要的角色。但是这不是事实。维生素D不算是真正的维生素,它是一种机体对阳光反应而产生的激素。而且维生素D并不天然存在于牛奶中,他是在牛奶加工过程中被添加的。这是为了预防佝偻病而添加的,佝偻病是一种因维生素D缺乏而引起痛苦的畸形骨骼。实际上,佝偻病是因为日照不足引起的,机体内的维生素水平受饮食因素的影响很小。我们在夏季获得的日照会影响我们全年的维生素D水平。机体中90%以上的维生素D来源于日照。每周只需3次日照脸部和手臂15分钟,我们就能获得足量的维生素D。但是,这个作用会受到防晒霜和肤色的影响。基本上,通过日常活动,我们就能获得满足每天所需的维生素D,我们并不需要通过饮用牛奶来获取它。再说,维生素D是脂溶性的,这样它就可以储存在我们的机体内很长一段时间,在冬天低日照的情况下,我们也能获得足量维生素D。

谎言7:牛奶可以治疗高血压
国家奶业委员会通过评价饮食钙(乳制品)和非饮食钙(补充剂)的补充对血压的影响,从而得出一个可以保证的结论"钙的补充可以轻微降低血压的收缩压(最高值)和舒张压(最低值)"。在67个研究中,有47个符合评价标准。血压的实际下降值毫无意义:收缩压降低1.44mmHg,舒张压降低0.84mmHg。摄入钙导致血压轻微下降的机制还不清楚。

相对的是,麦克道格尔居民中心的结果显示高血压(150/90mmHg或更高)的人群饮用植物性饮食不到10天,血压就下降了23/14mmHg。这些人大多数在这10天内都没服用抗高血压药物。

谎言8:牛奶预防结肠癌
结肠癌是美国和其它西方饮食流行地区人们的常见癌症。科学界一致认为结肠癌是由高动物蛋白、高脂肪、低膳食纤维、低蔬菜饮食引起的。但是,在这些食用不健康饮食的人群中,钙摄入量高的人患结肠癌的风险也低。可能的原因是结肠中的钙结合和中和了引起癌症的物质,例如西方饮食中存在的脂肪和胆汁酸。

乳制品业建议你摄取更多的钙,而不是改变饮食习惯,这对于乳制品业和钙补充剂生产商来说,是有利的。但是,作为理性的人,你应该已经得出结论:停止结肠癌的根本原因──西方饮食──才该是你注意力的中心。

谎言9:低脂牛奶是健康食品
低脂牛奶或脱脂牛奶和其它乳制品如今被广泛消费,但是从某种意义上说,它们可能比全脂牛奶对健康危害更大。脱脂的过程使得牛奶中的蛋白质和乳糖含量相对地增高。

生产低脂牛奶
当脂肪从全脂牛奶中去除而获得低脂牛奶和脱脂牛奶后,蛋白质和碳水化合物的量相对应地增加:

CHO = 碳水化合物 = 乳糖 = 牛奶中的糖

牛奶中的蛋白质引起钙流失,而且是人群中食物过敏的首要原因,牛奶中的糖(乳糖)还会引发乳糖不耐受(腹泻、胃痛、胃胀气)。尽管脱脂牛奶含有的脂肪很低,但是还是缺乏纤维素,也缺乏一些重要的维生素和矿物质,例如维生素C和尼克酸、铁,来满足人体的需求。

谎言10:牛奶如同天降的雪一样纯洁
牛奶是白色的,但是绝对不是纯洁的。不幸的是,牛奶的白色有些来自于白细胞──通常称为脓细胞──白细胞于牛的免疫系统抵抗感染时产生,特别是因细菌引起的感染,比如乳腺炎。乳制品业把这些细胞称为体细胞,并通过体细胞计数(SCC)来测量。体细胞计数表示牛奶中每毫升中所含白细胞数。(20滴大约为1毫升,30毫升为1盎司)

从1993年7月1日起,根据国家和联邦巴氏杀菌奶条例,牛奶中的体细胞计数必须小于750000。这意味着,即使一杯8盎司(240毫升)的牛奶中含有1.8亿的白细胞,对于你和家人也是安全的。最近一项对于纽约州销售的牛奶的调查发现平均体细胞计数大约是363000个/毫升。与此同时发现的还有,牛奶中产生这些白细胞的原因──24400个细菌/毫升。

虽然作为文章的结尾,这个事实可能会令你反胃,但是这是为下个月我们将讨论因消费乳制品,你和家人所面临的健康风险做准备,比如肥胖、心脏病、癌症、1型糖尿病、食物过敏和因牛奶中含有的病毒而患上艾滋病和白血病。

原文链接:http://www.nealhendrickson.com/mcdougall/030400pudairyproductsfalsepromises.htm
编辑:foodtrans

 
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