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{{Image|lactose.JPG|right|150px|A lactose molecule.}}
'''Lactose intolerance''' is "the condition resulting from the absence or deficiency of lactase in the mucosa cells of the [[gastrointestinal tract]], and the inability to break down [[lactose]] in milk for [[absorption]]. Bacterial fermentation of the unabsorbed lactose leads to symptoms that range from a mild indigestion ([[dyspepsia]]) to severe [[diarrhea]]. Lactose intolerance  may be an inborn error or acquired."<ref>{{MeSH}}</ref>


'''Lactose intolerance''' is due to a decreased production of the enzyme [[lactase]] in the cells lining the small intestine, resulting in an inability to break down or [[metabolize]] [[lactose]], the sugar in milk. In order to be digested, the [[disaccharide]] lactose must be broken down to the simpler sugars, [[glucose]] and [[galactose]]. Excess lactose causes [[enteral bacteria]] to adapt and lead to fermentation in the intestines. <ref>{{Cite book
Lactase is normally produced in the cells lining the small intestine and is required to break down the [[disaccharide]] lactose to the usable sugars, [[glucose]] and [[galactose]]. The loss of this function means that lactose, the major sugar in milk, cannot be broken down or [[metabolize]]d in the gut. Consequently, milk product cannot be digested by people who are lactose intolerant but the [[enteral bacteria]] adapt and ferment the sugar in the intestines, often leading to bloating and gas symptoms.<ref>{{Cite book | edition = 7 | pages = 70-71 | last = Campbell | first = N.A. | coauthors = J.B. Reece
| edition = 7
| title = Biology | publication = Library of Congress Cataloging in Publication Data | date = 2005
| pages = 70-71
}}</ref> Lactose intolerance is often referred to as lactase nonpersistence or lactase restriction since it is due to the lack of the lactase enzyme.
| last = Campbell
| first = N.A.
| coauthors = J.B. Reece
| title = Biology
| publication = Library of Congress Cataloging in Publication Data
| date = 2005
}}</ref>
 


Population studies suggest that the most common form of lactase intolerance is the ancestral state for humans<ref name=Wiley2004>{{Cite journal | volume = 106 | issue = 3 | pages = 506-517 | last = Wiley | first = Andrea S. | title = "Drink Milk for Fitness": The Cultural Politics of Human Biological Variation and Milk Consumption in the United States  | journal = American Anthropologist
| date = September 2004 }}</ref>; lactase is expressed during childhood but the activity decreases into adulthood. It is thought that new mutations led to variants of the lactase [[gene]] that remain switched on into adulthood. This is called lactase persistence and such variants are now abundant in populations that historically led a pastoral lifestyle, probably due to selective pressure for the new [[allele]]s.
__TOC__
__TOC__


== Symptoms ==
== Classification ==
Nausea, bloating, cramps, diarrhea, and gas are symptoms commonly included with lactose intolerance.  They typically occur 30 to 120 minutes after consuming [[lactose]]. <ref>{{Cite journal
| volume = 334
| issue = 2
| pages = 14-15
| last = Bhatnagar
| first = S.
| coauthors = R. Aggarwal
| title = Lactose intolerance
| journal = British Medical Journal
| publication = BMJ Publishing Group Ltd
| date = 2007
}}</ref>
 


== Types of Lactose Intolerance ==
Lactose intolerance is not the same as a milk allergy, which is a negative immune response to milk proteins.


=== Primary Lactose Intolerance ===  
=== Primary Lactose Intolerance ===  
 
Primary lactose intolerance is caused by genetic and environmental factors and occurs in adulthood. It occurs in populations where dairy products are not commonly available or consumed or have not been consumed for several generations. The [[allele]] that expresses the lactose intolerance [[phenotype]] (as the decline in the ability to produce [[lactase]]) is [[recessive]].
Primary lactose intolerance caused by genetic and environmental factors. It occurs in populations where dairy products are not commonly available or consumed. The [[allele]] that codes for lactose intolerance is [[dominant]].


=== Secondary Lactose Intolerance ===  
=== Secondary Lactose Intolerance ===  
Secondary lactose intolerance is also caused by environmental factors.  It is often temporary and is a result of many gastrointestinal diseases from parasites or other causes.
Secondary lactose intolerance is also caused by environmental factors.  It is often temporary and is a result of many gastrointestinal diseases from parasites or other causes. It can also be caused by [[infant colic]], which damages the vili that produce lactase in the small intestine.<ref>{{Cite journal
| volume = 14
| issue = 5
| pages = 359-363
| last = Kanabar
| first = D.
| coauthors = M. Randhawa, P. Clayton
| title = Improvement of Symptoms in Infant Colic Following Reduction of Lactose Load with Lactase
| journal = FASEB Journal
| date = October 2001
}}</ref>


=== Congenital Lactase Deficiency ===  
=== Congenital Lactase Deficiency ===  
Congenital Lactase Deficiency is present at birth.  It is an [[autosomal]] [[recessive]] genetic disorder that prohibits the production of [[lactase]]. <ref>{{Cite journal
Congenital Lactase Deficiency is present at birth and is the rarest form of lactose intolerance.  It is an [[autosomal]] [[recessive]] genetic disorder caused by a mutation on the gene that produces lactase.<ref>{{Cite journal
| volume = 5
| volume = 5
| issue = 3
| issue = 3
Line 54: Line 46:
}}</ref>
}}</ref>


 
==Epidemiology==
== Geographic Variance ==
Table 1.1 Frequency of Adult Lactose Intolerance within Population Groups <ref name=Jurmain2005 />
Lactose intolerance is possibly an example of [[biocultural evolution]], human variation through multiple generations due to both biological and cultural forces. Lactose intolerance is inherited as the expression of the [[dominant gene]]. However, expression of the trait is also environmentally determined.  [[Enteral bacteria]] can often buffer the effects of lactose intolerance and can be increased with previous exposure, leading to acquired tolerance even in individuals are genetically lactose intolerant. 
[[Image:LacIntol-World2.JPG|right|thumb|350px|{{#ifexist:Template:LacIntol-World2.JPG/credit|{{lactose.JPG/credit}}<br/>|}}Global distribution of lactose intolerance.]]
 
Varience throughout populations is most likely due to a history of an economic reliance on pastoralism and, therefore, consumption of large quantities of milk after childhood.  Historically, the availabiliy of milk disappeared after weaning.  This rendered [[lactase]] useless and perhaps problematic for digestion of other foods in humans.  Therefore, there was a possible [[genetic advantage]] to ceasing production of [[lactase]].  This would change the [[allele frequency]] making the expression of lactose intolerance genetically dominant.  In populations with a history of pastoralism, however, there was a likely genetic advantage or [[allele]] shift toward lactose tolerance.  The descendants of these populations, most European groups, tend to retain lactose tolerance.  Distribution of lactose intolerance in [[Africa]] seems to be due to the same variation in economic history.  Most populations of [[Africa]] exhibit lactose intolerance.  However, individuals in groups that historically relied on pastoralism, such as the [[Fulani]] and [[Tutsi]], tend to show lactose tolerance. <ref>{{Cite book
| edition = 10
| pages = 416-419
| last = Jurmain
| first = Robert
| coauthors = Lynn Kilgore, Wenda Trevathan
| title = Introduction to Physical Anthropology
| publication = Thomson Learning, Inc
| date = 2005
}}</ref>
 
 
Another theory about the ability of people of Northern European descent has to do with [[vitamin D]]. Because the allele that codes for lactose tolerance or continued [[lactase]] production in adulthood is [[recessive]], selective forces keep it in existence. One selective force is the necessity of [[lactose]] consumption in pastoral communities. Another in Northern [[Europe]] is the reduced production of [[vitamin D]] due to the infrequnent direct sunlight in the region. The lack of [[vitamin D]] would make the population more vulnerable to bone diseases like [[rickets]] because of the poor absorbtion of calcium. The advantage of [[lactase]] production is the ability to consume milk, which is a good source of calcium, and contains [[lactose]], which allows for better calcium absorbtion. This theory has gained support because of its congruence with the theory that Northern European light skin color allows the most [[vitamin D]] production with little sunlight. <ref>{{Cite journal
| volume = 4
| issue = 5
| pages = 76-81
| last = Patterson
| first = K.D.
| title = Lactose intolerance
| journal = The Cambridge World History of Food
| publication = Cambridge University Press
| date = 1997
}}</ref>
 
 
Most other populations tend to exhiit lactose intolerance. Lactose intolerance is sometimes seen in groups that frequently consume dairy because they usually consume it as cheese or yogurt, forms in which bacterial action has already broken down the [[lactose]].
 
=== Frequency of Lactose Intolerance within Population Groups ===
 
{| class="wikitable"
{| class="wikitable"
|-
|-
! Population Group
! Population Group
! Percent
! Percent
|-
|-
| United States Whites
| United States Whites
Line 104: Line 66:
| 4
| 4
|-
|-
| United States Blacks
| United States Blacks
| 70-77
| 70-77
|-
|-
Line 122: Line 84:
| 99
| 99
|-
|-
| Asian Americans
| Asian Americans
| 95-100
| 95-100
|-
| United  States Jews
| 69
|-
|-
| Native Australians
| Native Australians
| 85
| 85
|-
|-
| Native Americans
| Native Americans
| 99
| 99
|} <ref>{{Cite book
|}  
| edition = 10
 
| pages = 416-419
Because most  adult Americans of Western European descent exhibit lactase persistence,  it is commonly assumed that it is the most common gene expression. As  shown in Table 1.1, however, United States Whites are one of few  population groups that show high levels of lactase persistence. Lactase  persistence is only common in adults with ancestry in pastoral  populations. This is supported by the low levels of lactose intolerance  in the United States Whites and the African Fulani and Tutsi  populations. The ancestry of a large percentage of United States Whites  is in Western Europe, where pastoralism was a common means of  sustenance. The nomadic Fulani tribe of East, Central, and West Africa  and the Tutsi tribe of Rwanda and Burundi are two populations in Africa  that, unlike most other African populations, have a history of  pastoralism.<ref>{{Cite journal
| volume = 66
| issue = 4
| part = 1
| pages =  944-947
| last = Flannery
| first = Kent  V.
|  title = Man and Cattle: Proceedings of a Symposium on Domestication
| journal =  American Anthropologist
| date = August 1964
}}</ref>  Because of this, they are among the few populations of African descent  that evolved independently to genetically favor lactose tolerance.
 
 
===  Geographic Variance ===
 
Lactose  intolerance is possibly an example of [[biocultural  evolution]], human  variation through multiple generations due to both biological and  cultural forces.  Lactose intolerance is inherited as the expression of  the [[recessive gene]].  However, expression of the trait is also environmentally determined.  [[Enteral bacteria]]  can often buffer the effects of lactose intolerance and can be  increased with previous exposure, leading to acquired tolerance even in  individuals are genetically lactose intolerant. 
 
Variance  throughout populations is most likely due to a history of an economic  reliance on pastoralism and, which results in the increased consumption  of milk after childhood.  Historically, the availabiliy of milk had  disappeared after weaning.  This rendered [[lactase]] useless and perhaps problematic  for the digestion of other foods in humans.  Therefore, there was a  possible [[genetic advantage]] to ceasing the production of [[lactase]].  This would change the [[allele frequency]]  making the expression of lactose intolerance genetically dominant.  In  populations with a history of pastoralism, however, there was a likely  genetic advantage or [[allele]]  shift toward lactose tolerance.  The descendants of these populations,  most European groups, tend to retain lactose tolerance.  Distribution of  lactose intolerance in [[Africa]]  seems to be due to the same variation in economic history.  Most  populations of [[Africa]]  exhibit lactose intolerance.  However, individuals in groups that  historically relied on pastoralism, such as the [[Fulani]] and [[Tutsi]] of Africa, tend to show lactose  tolerance. <ref  name=Jurmain2005>{{Cite book
| edition = 10
| pages = 416-419
| last = Jurmain
| last = Jurmain
| first = Robert
| first = Robert
| coauthors = Lynn Kilgore, Wenda Trevathan
| coauthors = Lynn Kilgore, Wenda Trevathan
| title = Introduction to Physical Anthropology  
| title = Introduction to Physical Anthropology  
| publication = Thomson Learning, Inc
| publication = Thomson Learning, Inc
| date = 2005
| date = 2005
}}</ref>
}}</ref>


==References==
Another  theory about the ability of people of Northern European descent has to  do with [[vitamin D]].  Because the allele that expresses in the lactose tolerance [[phenotype]] or continued [[lactase]] production in adulthood is [[recessive]], selective forces keep it in  existence. As mentioned previously, one selective force is the necessity  of [[lactose]]  consumption in pastoral communities. Another in Northern [[Europe]] is the reduced production of [[vitamin D]] due to the lack of direct  sunlight in the region. The lack of [[vitamin D]] would make the population more  vulnerable to bone diseases like [[rickets]] because of the poor absorption of  calcium. The advantage of continued [[lactase]] production is the ability to  consume milk after childhood. Milk contains high levels of calcium,  which would help to counter the [[vitamin D]] deficiency. This theory has  gained support because of its congruence with the theory that Northern  European light skin color allows the most [[vitamin D]] production with little sunlight. <ref>{{Cite journal
| volume = 4
| issue = 5
| pages =  76-81
|  last = Patterson
| first = K.D.
| title =  Lactose intolerance
| journal = The Cambridge World History of  Food
|  publication = Cambridge University Press
| date = 1997
}}</ref>  However, this theory is not relevant south of the equator, nor is it  supported with archaeological or osteological evidence.
 
Lactase  persistence is sometimes seen in groups that frequently consume dairy  because they usually consume it as cheese or yogurt, forms in which  bacterial action has already broken down the [[lactose]].
 
==Etiology / cause==
=== Related Foods ===
 
==== Dairy Products ====
Dairy products tend to contain higher levels of lactose in the liquid components versus the fat components. Therefore, lower fat dairy products and those that have not been processed as much, such as whole milk, tend to have more lactose. Fermented dairy products tend to have more fat and lactose, such as yogurt or sourcream. Consumption of dairy products is recommended for the calcium they contain.
 
==== Nondairy Products ====
Lactose is often added into medications or foods like bread, margarine, and processed meat. While dairy products are recommended for calcium consumption, there are some lactose-free nondairy products that contain high levels of calcium, such as green leafy vegetables, fish, and legumes.<ref name=Cohen1997>{{Cite book
| pages = 189-270
| last = Cohen
| first = Robert
| title = Milk: The Deadly Poison
| publication = Argus Publishing
| publication location = Englewood Cliffs, NJ
| date = 1997
}}</ref> Many nondairy foods are also fortified with calcium such as orange juice, cereal, and many dairy substitutes made with rice or soy.
 
 
=== Genetic Factors ===
 
Lactose intolerance is an [[autosomal recessive trait]]. The allele variations differ in the temporal aspect of their expression. The dominant allele is expressed later and, therefore, the [[phenotype]] for the [[dominant allele]] is the persistence of production of the lactase enzyme. The recessive allele is expressed only early in life and results in lactose intolerance. The gene that codes for the lactase enzyme is located on [[chromosome]] 2. This is the case in all populations, but the reguation of the gene varies. The lactase gene has four common [[haplotypes]]- A, B, C, and U. The A haplotype is usually found in populations that exhibit lactase persistence. Increased haplotype diversity occurs in populations that exhibit lactose intolerance. The expression of the lactase persistence [[phenotype]] gives genetic advantage to members of populations that consume milk. This is why most express the [[dominant allele]] in milk consuming populations. While it is still unclear, it is likely that lactase regulation occurs during [[DNA]] [[transcription]] because there is variation in [[mRNA]] levels between lactase persistent and impersistent individuals. <ref name=Wiley2004 /> Genetic drift probably also played a role in latase gene diversity. The more homogeneous populations are probably as such because of genetic drift, this is why African cultures have more diversity in the haplotypes. Gene flow, mainly due to colonization, is probably the cause of continued frequencies of lactose intolerance and tolerance within populations. Lactose tolerance is rare in a worldwide sense, but it exists in scattered populations that have no contact. As shown by the low levels of lactose intolerance in United States Whites and the Fulani and Tutsi tribes, the genes evolved independently in different populations around the world.
 
== Symptoms ==
 
Nausea, bloating, cramps,  diarrhea, and gas are symptoms commonly experienced with lactose  intolerance.  They typically occur 30 to 120 minutes after consuming [[lactose]].<ref  name="pmid17599979">{{cite journal| author=Bhatnagar S, Aggarwal R|  title=Lactose intolerance. | journal=BMJ | year= 2007 | volume= 334 |  issue= 7608 | pages= 1331-2 | pmid=17599979
|  url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=clinical.uthscsa.edu/cite&retmode=ref&cmd=prlinks&id=17599979  | doi=10.1136/bmj.39252.524375.80 }} </ref>
 
 
==  Sociopolitical Issues ==
 
While  the American dairy industry holds that the frequency of lactose  intolerance is overestimated, recent research in gastrointestinal  problems shows that it is likely underdiagnosed in the United States.<ref  name=Wiley2007>{{Cite journal
| volume = 109
| issue = 4
| pages =  666-677
| last = Wiley
| first =  Andrea S.
| title = Transforming Milk in a Global  Economy
| journal = American Anthropologist
| date =  November 2007
}}</ref>  It has also been  argued that despite its depiction as a "perfect food" by the dairy  industry and government funded health organizations, milk is in fact bad  for the health of all adults due to added hormones and biological  defects in many farmed dairy cows. <ref  name=Cohen1997 /> Still, government supported medical  associations advocate the consumption of 2 to 3 servings of dairy daily  as a source of calcium. Also, it is typically recommended that those who  experience symptoms of lactose intolerance test the amount of dairy  they can consume without experiencing negative effects. This is funded  and widely accepted information despite the high incidence of lactose  intolerance (as it is the more common expression of genes worldwide) and  the many foods that contain calcium without lactose (for example, leafy  greens).<ref name=Wiley2007 />
 
==Treatment==
Most patients can tolerate 12 to 15 g of lactose.<ref name="pmid20404262">{{cite journal| author=Shaukat A, Levitt MD, Taylor BC, Macdonald R, Shamliyan TA, Kane RL et al.| title=Systematic Review: Effective Management Strategies for Lactose Intolerance. | journal=Ann Intern Med | year= 2010 | volume=  | issue=  | pages=  | pmid=20404262
| url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=clinical.uthscsa.edu/cite&retmode=ref&cmd=prlinks&id=20404262 | doi=10.1059/0003-4819-152-12-201006150-00241 }} </ref>
 
==Lactose Content of Selected Dairy Products==
1 cup whole, reduced fat or nonfat milk 11 grams; 1 cup chocolate milk 11 grams; 1 cup buttermilk 10 grams; 1/2 cup ice cream 6 grams; 1/2 cup sherbet 2 grams; 1 cup low fat yogurt 5 grams; 1/2 cup creamed cottage cheese 3 grams.<ref name="urlwww.healthsystem.virginia.edu">{{cite web
|url=http://www.healthsystem.virginia.edu/internet/digestive-health/nutrition/lactosecontent.pdf
|title=www.healthsystem.virginia.edu
|format=
|work=
|accessdate=2010-10-26
}}</ref>
 
 
== References ==
<references/>
<references/>

Revision as of 21:08, 26 October 2010

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PD Image
A lactose molecule.

Lactose intolerance is "the condition resulting from the absence or deficiency of lactase in the mucosa cells of the gastrointestinal tract, and the inability to break down lactose in milk for absorption. Bacterial fermentation of the unabsorbed lactose leads to symptoms that range from a mild indigestion (dyspepsia) to severe diarrhea. Lactose intolerance may be an inborn error or acquired."[1]

Lactase is normally produced in the cells lining the small intestine and is required to break down the disaccharide lactose to the usable sugars, glucose and galactose. The loss of this function means that lactose, the major sugar in milk, cannot be broken down or metabolized in the gut. Consequently, milk product cannot be digested by people who are lactose intolerant but the enteral bacteria adapt and ferment the sugar in the intestines, often leading to bloating and gas symptoms.[2] Lactose intolerance is often referred to as lactase nonpersistence or lactase restriction since it is due to the lack of the lactase enzyme.

Population studies suggest that the most common form of lactase intolerance is the ancestral state for humans[3]; lactase is expressed during childhood but the activity decreases into adulthood. It is thought that new mutations led to variants of the lactase gene that remain switched on into adulthood. This is called lactase persistence and such variants are now abundant in populations that historically led a pastoral lifestyle, probably due to selective pressure for the new alleles.

Classification

Lactose intolerance is not the same as a milk allergy, which is a negative immune response to milk proteins.

Primary Lactose Intolerance

Primary lactose intolerance is caused by genetic and environmental factors and occurs in adulthood. It occurs in populations where dairy products are not commonly available or consumed or have not been consumed for several generations. The allele that expresses the lactose intolerance phenotype (as the decline in the ability to produce lactase) is recessive.

Secondary Lactose Intolerance

Secondary lactose intolerance is also caused by environmental factors. It is often temporary and is a result of many gastrointestinal diseases from parasites or other causes. It can also be caused by infant colic, which damages the vili that produce lactase in the small intestine.[4]

Congenital Lactase Deficiency

Congenital Lactase Deficiency is present at birth and is the rarest form of lactose intolerance. It is an autosomal recessive genetic disorder caused by a mutation on the gene that produces lactase.[5]

Epidemiology

Table 1.1 Frequency of Adult Lactose Intolerance within Population Groups [6]

Global distribution of lactose intolerance.
Population Group Percent
United States Whites 2-19
Finnish 18
Swiss 12
Swedish 4
United States Blacks 70-77
Ibos 99
Bantu 90
Fulani 22
Tutsi 7
Thais 99
Asian Americans 95-100
United States Jews 69
Native Australians 85
Native Americans 99

Because most adult Americans of Western European descent exhibit lactase persistence, it is commonly assumed that it is the most common gene expression. As shown in Table 1.1, however, United States Whites are one of few population groups that show high levels of lactase persistence. Lactase persistence is only common in adults with ancestry in pastoral populations. This is supported by the low levels of lactose intolerance in the United States Whites and the African Fulani and Tutsi populations. The ancestry of a large percentage of United States Whites is in Western Europe, where pastoralism was a common means of sustenance. The nomadic Fulani tribe of East, Central, and West Africa and the Tutsi tribe of Rwanda and Burundi are two populations in Africa that, unlike most other African populations, have a history of pastoralism.[7] Because of this, they are among the few populations of African descent that evolved independently to genetically favor lactose tolerance.


Geographic Variance

Lactose intolerance is possibly an example of biocultural evolution, human variation through multiple generations due to both biological and cultural forces. Lactose intolerance is inherited as the expression of the recessive gene. However, expression of the trait is also environmentally determined. Enteral bacteria can often buffer the effects of lactose intolerance and can be increased with previous exposure, leading to acquired tolerance even in individuals are genetically lactose intolerant.

Variance throughout populations is most likely due to a history of an economic reliance on pastoralism and, which results in the increased consumption of milk after childhood. Historically, the availabiliy of milk had disappeared after weaning. This rendered lactase useless and perhaps problematic for the digestion of other foods in humans. Therefore, there was a possible genetic advantage to ceasing the production of lactase. This would change the allele frequency making the expression of lactose intolerance genetically dominant. In populations with a history of pastoralism, however, there was a likely genetic advantage or allele shift toward lactose tolerance. The descendants of these populations, most European groups, tend to retain lactose tolerance. Distribution of lactose intolerance in Africa seems to be due to the same variation in economic history. Most populations of Africa exhibit lactose intolerance. However, individuals in groups that historically relied on pastoralism, such as the Fulani and Tutsi of Africa, tend to show lactose tolerance. [6]

Another theory about the ability of people of Northern European descent has to do with vitamin D. Because the allele that expresses in the lactose tolerance phenotype or continued lactase production in adulthood is recessive, selective forces keep it in existence. As mentioned previously, one selective force is the necessity of lactose consumption in pastoral communities. Another in Northern Europe is the reduced production of vitamin D due to the lack of direct sunlight in the region. The lack of vitamin D would make the population more vulnerable to bone diseases like rickets because of the poor absorption of calcium. The advantage of continued lactase production is the ability to consume milk after childhood. Milk contains high levels of calcium, which would help to counter the vitamin D deficiency. This theory has gained support because of its congruence with the theory that Northern European light skin color allows the most vitamin D production with little sunlight. [8] However, this theory is not relevant south of the equator, nor is it supported with archaeological or osteological evidence.

Lactase persistence is sometimes seen in groups that frequently consume dairy because they usually consume it as cheese or yogurt, forms in which bacterial action has already broken down the lactose.

Etiology / cause

Related Foods

Dairy Products

Dairy products tend to contain higher levels of lactose in the liquid components versus the fat components. Therefore, lower fat dairy products and those that have not been processed as much, such as whole milk, tend to have more lactose. Fermented dairy products tend to have more fat and lactose, such as yogurt or sourcream. Consumption of dairy products is recommended for the calcium they contain.

Nondairy Products

Lactose is often added into medications or foods like bread, margarine, and processed meat. While dairy products are recommended for calcium consumption, there are some lactose-free nondairy products that contain high levels of calcium, such as green leafy vegetables, fish, and legumes.[9] Many nondairy foods are also fortified with calcium such as orange juice, cereal, and many dairy substitutes made with rice or soy.


Genetic Factors

Lactose intolerance is an autosomal recessive trait. The allele variations differ in the temporal aspect of their expression. The dominant allele is expressed later and, therefore, the phenotype for the dominant allele is the persistence of production of the lactase enzyme. The recessive allele is expressed only early in life and results in lactose intolerance. The gene that codes for the lactase enzyme is located on chromosome 2. This is the case in all populations, but the reguation of the gene varies. The lactase gene has four common haplotypes- A, B, C, and U. The A haplotype is usually found in populations that exhibit lactase persistence. Increased haplotype diversity occurs in populations that exhibit lactose intolerance. The expression of the lactase persistence phenotype gives genetic advantage to members of populations that consume milk. This is why most express the dominant allele in milk consuming populations. While it is still unclear, it is likely that lactase regulation occurs during DNA transcription because there is variation in mRNA levels between lactase persistent and impersistent individuals. [3] Genetic drift probably also played a role in latase gene diversity. The more homogeneous populations are probably as such because of genetic drift, this is why African cultures have more diversity in the haplotypes. Gene flow, mainly due to colonization, is probably the cause of continued frequencies of lactose intolerance and tolerance within populations. Lactose tolerance is rare in a worldwide sense, but it exists in scattered populations that have no contact. As shown by the low levels of lactose intolerance in United States Whites and the Fulani and Tutsi tribes, the genes evolved independently in different populations around the world.

Symptoms

Nausea, bloating, cramps, diarrhea, and gas are symptoms commonly experienced with lactose intolerance. They typically occur 30 to 120 minutes after consuming lactose.[10]


Sociopolitical Issues

While the American dairy industry holds that the frequency of lactose intolerance is overestimated, recent research in gastrointestinal problems shows that it is likely underdiagnosed in the United States.[11] It has also been argued that despite its depiction as a "perfect food" by the dairy industry and government funded health organizations, milk is in fact bad for the health of all adults due to added hormones and biological defects in many farmed dairy cows. [9] Still, government supported medical associations advocate the consumption of 2 to 3 servings of dairy daily as a source of calcium. Also, it is typically recommended that those who experience symptoms of lactose intolerance test the amount of dairy they can consume without experiencing negative effects. This is funded and widely accepted information despite the high incidence of lactose intolerance (as it is the more common expression of genes worldwide) and the many foods that contain calcium without lactose (for example, leafy greens).[11]

Treatment

Most patients can tolerate 12 to 15 g of lactose.[12]

Lactose Content of Selected Dairy Products

1 cup whole, reduced fat or nonfat milk 11 grams; 1 cup chocolate milk 11 grams; 1 cup buttermilk 10 grams; 1/2 cup ice cream 6 grams; 1/2 cup sherbet 2 grams; 1 cup low fat yogurt 5 grams; 1/2 cup creamed cottage cheese 3 grams.[13]


References

  1. Anonymous (2024), Lactose intolerance (English). Medical Subject Headings. U.S. National Library of Medicine.
  2. Campbell, N.A.; J.B. Reece (2005). Biology, 7, 70-71. 
  3. 3.0 3.1 Wiley, Andrea S. (September 2004). ""Drink Milk for Fitness": The Cultural Politics of Human Biological Variation and Milk Consumption in the United States". American Anthropologist 106 (3): 506-517.
  4. Kanabar, D.; M. Randhawa, P. Clayton (October 2001). "Improvement of Symptoms in Infant Colic Following Reduction of Lactose Load with Lactase". FASEB Journal 14 (5): 359-363.
  5. Montgomery, R.K.; H.A. Buller, E.H Rings., R.J Grand (1991). "Lactose intolerance and the genetic regulation of intestinal lactase- phlorizin hydrolase". FASEB Journal 5 (3): 70-73.
  6. 6.0 6.1 Jurmain, Robert; Lynn Kilgore, Wenda Trevathan (2005). Introduction to Physical Anthropology, 10, 416-419. 
  7. Flannery, Kent V. (August 1964). "Man and Cattle: Proceedings of a Symposium on Domestication". American Anthropologist 66 (4): 944-947.
  8. Patterson, K.D. (1997). "Lactose intolerance". The Cambridge World History of Food 4 (5): 76-81.
  9. 9.0 9.1 Cohen, Robert (1997). Milk: The Deadly Poison, 189-270. 
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