Wednesday, December 15, 2010

Weekly Strength Training Provides Long-Term Cognitive and Economic Benefits

Joyce Mar works on her strength training at the Langara Family YMCA in Vancouver on Tuesday.

Photograph by: Steve Bosch, Vancouver Sun, Vancouver Sun

Today the Archives of Internal Medicine published results of a study that found that women aged 65 to 75 years who engaged in progressive strength training once or twice weekly over 12 months had improved executive cognitive functions and lower medical care costs than control women when evaluated again one year later.

Today's publication provides a follow-up on the Brain Power study which the Archives of Internal Medicine published inpublished in its January 2010 issue.  The original study demonstrated that 12 months of once-weekly or twice-weekly progressive strength training improved executive cognitive function in women aged 65- to 75- years- old.  

 One report of the the study results released today states:

Both studies were led by Teresa Liu-Ambrose, principal investigator at the Centre for Hip Health and Mobility and Brain Research Centre at Vancouver Coastal Health and UBC, and assistant professor in the Department of Physical Therapy at UBC's Faculty of Medicine. The one year follow-up study found the cognitive benefits of strength training persisted, and with two critical findings.

"We were very surprised to discover the group that sustained cognitive benefits was the once-weekly strength training group rather than the twice-weekly training group," says Liu-Ambrose, who's also a Michael Smith Foundation for Health Research scholar. "What we realized was that this group was more successful at being able to maintain the same level of physical activity achieved in the original study."

In this study, one group did once-weekly strength training, another did twice-weekly strength training, and a third group "control" group did something the authors refer to as "balance and tone" which according to a Vancouver Sun article featured "stretching, range of motion, core strength, balance and relaxation exercises." 

According to the report, only the once-weekly group maintained the cognitive benefits at the follow-up.  Strength training may keep you smarter than doing "balance and tone" training.

 Regarding economic benefits:

The second important finding relates to the economic benefits of once-weekly strength training. Using the data from the Brain Power Study and the one-year follow-up study, health economists Jennifer Davis and Carlo Marra, research scientists with the Collaboration for Outcomes Research and Evaluation at St. Paul's Hospital and UBC Faculty of Medicine, were able to show that the economic benefits of once-weekly strength training were sustained 12 months after its formal cessation. Specifically, the researchers found the once-weekly strength group incurred fewer health care resource utilization costs and had fewer falls than the twice-weekly balance and tone group.

"This suggests that once-weekly resistance training is cost saving, and the right type of exercise for seniors to achieve maximum economic and health benefits," says Davis.

The study found that the once-weekly strength training group had the fewest fall and lowest medical care utilization costs. 

Thus,  this study shows that standard strength training helps seniors maintain balance more effectively than exercises supposedly dedicated to "core" strength, balance, and range of motion.  That's partly because maintaining balance requires muscular strength.  If your inner ear detects that you are off balance, but you lack the strength required to correct the movement, you will fall.  Moreover, a properly designed strength training routine will itself provide so-called "core" strength, balance training, and movement through full ranges of motion.  

In other words, strength training does it all in just one session per week.

Stay strong, stay smart, stay healthy.

The Blood Type Diet: A Critical Perspective

01/20/14 UPDATE:   On January 15, 2014 Wang et al published an empirical test of the central claim of the blood type diet hypothesis, i.e. that each blood type benefit more from one particular diet than others.  Confirming what I wrote in this post in 2010, Wang et al concluded: "Adherence to certain ‘Blood-Type’ diets is associated with favorable effects on some cardiometabolic risk factors, but these associations were independent of an individual's ABO genotype, so the findings do not support the ‘Blood-Type’ diet hypothesis." Read the full text in PLOS One.  Read my blog about the study here.

Thanks to Peter J. D’Adamo, N.D. , author of the book Eat Right 4 Your Type, many people believe that blood type determines your dietary requirements and that only people with O-type blood should eat a paleo/primal diet.  

In this post I will discuss all the errors in this blood type hypothesis. 
The Blood Type Diet Hypothesis

D’Adamo’s hypothesis can be distilled down to four main claims and a conclusion drawn from these claims.

Claim A: Evolutionary adaptation to diet patterns resulted in the ABO blood groups, so each of the four types is adapted to a different type of diet and set of foods.
Claim B: People of different blood types have different antibodies in their blood and each blood type has a different susceptibility to diseases.
Claim C: Foods contain lectins that mimic blood group antigens and selectively cause blood agglutination (i.e. each food affects each blood group differently), and this causes diseases.
Claim D: Exposure to foods containing lectins incompatible with your blood type will cause agglutination of your blood which will cause diseases. As D’Adamo puts it, the lectins “target  an organ or bodily system and begin to agglutinate blood cells in that area.”

Conclusion: Therefore, people require diets tailored to their blood types, eliminating foods that have harmful lectins for their blood type.

The Four Diets

Blood type O

According to D’Adamo,  O-type blood is the “Original” blood type which evolved when humans lived by hunting supplemented by gathering.  He says these people should base their diets on lean meat and fish, supplemented with a selection of fruits and vegetables he deems suitable for this blood type.  O-types should avoid or greatly minimize dairy products and minimize or avoid grains and beans, particularly wheat.  According to D’Adamo, people with O-type don’t tolerate wheat “at all” yet he also says that they can eat sprouted wheat products (?).

Blood type A

D’Adamo claims that A-type blood arose as an adaptation to agriculture; conveniently, A is for agriculture.  He claims that this type can eat grains (except wheat), beans, most seafoods, many vegetables and  fruits, but should avoid dairy, meat, wheat, kidney beans, and lima beans.  He states that only people with A-type blood can and should eat a vegetarian diet.
Blood type B

D’Adamo refers to B-type as  “The Nomad.”  He implies that this type arose as an adaptation to pastoral lifestyles based on use of dairy products and meat from domesticated animals.  He states that B-types are adapted to a “balanced omnivore” diet that meat (but no chicken), eggs, dairy, beans, fruits, vegetables.  He advises people having the B blood type to avoid chicken, corn, lentils, peanuts, sesame, buckwheat, and wheat.

Blood type AB

D’Adamo calls type AB blood “The Enigma” and states that people having this blood type are adapted to a “mixed diet in moderation.   He advises that they can safely eat lamb, mutton, rabbit, turkey, pheasant, most seafood, dairy, beans, grains,             fruits,             and vegetables, but should avoid beef, chicken, kidney beans, lima beans, seeds, corn, buckwheat.

Basic Errors

As someone basing his whole approach to diet on blood types, D’Adamo appears disturbingly ignorant of basic facts about the evolution of the ABO types.

First, he claims that the O-type is the original blood type. He published his book in 1994, but by 1990 molecular biologists had determined that A-type is the original blood type.   In “Evolution of Primate ABO Blood Type Genes and Their Homologous Genes [full text available free],” Saitou and Yamamoto state [p. 405]:

“..the common ancestral gene for the hominoid and Old World monkey ABO blood
group is A type, and three B alleles evolved independently on the human, gorilla, and baboon lineages.”

The fact that both A-type and B-type antedate O-type seems predictable from the fact that O-type blood carries antibodies to A-type and B-type blood; for this to happen, O-type blood had to have emerged in an environment in which A-type and B-type antigens (the markers on A- and B- type blood cells) already existed. 

D’Adamo suggests that the blood types arose in humans as adaptations to dietary variations, implying that they are unique to humans.  In fact, ABO blood types occur not only in humans, but also in other primates.  Again, according to Table 5 in Saitou and Yamamoto, which presents data dating to 1964, more than 30 years before D’Adamo published his books:
·      The A phenotype occurs in chimps, orangutans, gibbons, baboons, Java macaques, sulawesi crested macaques, and squirrel monkeys (7 speicies).
·      The B phenotype occurs in gorillas, orangutans, gibbons, baboons, Rehsus macaques, pigtailed macaques, Java macaques, sulawesi crested macaques, and cebus monkeys (9 species).
·      The AB phenotype occurs in oragutans, gibbons, baboons, and Java macaques (4 species).
·      The O phenotype occurs in chimps, Java macaques, squirrel monkeys, and cebus monkeys (4 species).

Since none of these primates have ever practiced agriculture or domesticated dairy animals, it is clear that the A allele did not evolve as an adaptation to agriculture nor did the B allele emerge as an adaptation to consumption of dairy products. 

As noted above, the B-type has been found in the largest selection of species (9), followed by the A-type (7), and both O- and AB- type occur in the smallest selections (4 species each).  According to Saitou and Yamamoto, among this list of primates checked for ABO blood type, A phenotype occurred in 191 individuals, B in 75 individuals, AB in 44 individuals, and O in 20 individuals. 

According to Saitou and Yamamoto “It seems that the time of gene dupulication producing ABO and GAL genes may be around the emergence of vertebrates (ca. 500 MYA).”  [p.408]  In other words, these blood types have a much longer history than human dietary variations. 

Human Data

Its possible that D’Adamo did not mean to imply that the blood types arose only in humans.  Perhaps he meant that human adoption of hunting lifestyle selected for O-type, agriculture for A-type, and pastoralism for B-type.  In this case, we should find a predominance of O-type among all ethnic groups with a long history of living by hunting, especially those eating little plant food; a predominance of A-type among  ethnic groups having the longest histories of practicing agriculture; and a predominance of B-type among ethnic groups with long histories of pastoralism.

Unfortunately, the available data does not support this either.  So far as we know, Eskimos have never practiced agriculture or animal husbandry, and have long lived primarily by hunting, a diet enforced by their environment.  D’Adamo’s hypothesis would predict that Eskimos would have predominantly O-type blood.  According to, this is true of Greenland Eskimos (54% O, 36% A), but not of Alaskan Eskimos (38% O, 44% A), who have more A-type than O-type individuals, contradicting D'Adamo's hypothesis.

According to Wikipedia and, people of the Blackfoot or Niitsítapi tribe traditionally lived primarily on buffalo meat; classic hunters.  From Wikipedia:

“While the Niitsitapi were in the Great Plains, they came to depend on the buffalo (American bison) as their main source of food. The bison are the largest mammals in North America and stand about 6 ½ feet tall and weigh up to 2,200 pounds.[6] Before the introduction of horses, the Niitsitapi had to devise ways of sneaking up close to the buffalo without the animals' noticing so they could get in range for a good shot. The first and most common way for them to hunt the buffalo was using the buffalo jump. The hunters would round up the buffalo into V-shaped pens and drive them over a cliff (they hunted prong-horned antelopes in the same way). After the buffalo went over the cliff, the Indians would go to the bottom and take as much meat as they needed and could carry back to camp. They also used camouflage for hunting.[6] The hunters would take buffalo skins from previous hunting trips and drape them over their bodies to blend in and mask their scent. By subtle moves, the hunters could get close to the herd. When close enough, the hunters would shoot the bison with arrows, or use lances and spears to bring them down.

They used virtually all parts of the body and skin. They prepared the meat for food: by boiling, roasting and drying for jerky. This prepared it to last a long time without spoiling, and they depended on bison meat to get through the winters.[7] The winters were long, harsh, and cold due to the lack of trees in the Plains, so the people stockpiled the meat when they had the chance.[8] The hunters often ate the bison heart minutes after the kill, as part of their hunting ritual. The skins were prepared and used to cover the tepee. The tepee was made of log poles with the skin draped over it. It remained warm in the winter and cool in the summer, and a great shield against the wind.[9] With further preparation of tanning and softening, the women made special clothing from the skins: robes and moccasins. They rendered bison fat to make soap. Both men and women made utensils, sewing needles and tools from the bones, using tendon for fastening and binding. The stomach and bladder were cleaned and prepared for use as containers for storing liquids. Dried bison dung was fuel for fires. the fires. The Niitsitapi used almost every part of the buffalo and considered it a sacred animal, integral to their lives.[10]”

From this D’Adamo would predict that they had primarily O-type blood.  Wrong again. states that 82% of Blackfoot people have A-type blood, and only 17% have O-type. 

Looking from the other side, D’Adamo’s hypothesis would predict that Cantonese Chinese would have a higher incidence of A-type and lower incidence of O-type because they have lived for millennia on a rice-based agricultural diet. states that Cantonese Chinese have 46% O- and 23% A- types, the reverse of the D’Adamo prediction. 

Meanwhile, the northern Chinese (Peking) have 29% O, 27% A, and 32% B, a distribution which according to D’Adamo’s hypothesis would predict that the population has a long history of living on dairy products.  Unfortunately for D’Adamo, the pastoral lifestyle is not common in China at all, only practiced by Chinese in the western, mountainous provinces.

Just as one black swan is sufficient to disprove the claim that all swans are white, these few counter examples are sufficient to disprove the claims that hunting-based subsistence favors the O-type blood, while an agricultural subsistence favors the A type blood.  D’Adamo is just wrong when he asserts that dietary differences drive differences in distribution of blood types among humans. 

No Anatomical Evidence

All humans, regardless of blood type, cultural background, or  diet histories have the same basic gut design, dentition (number and type of teeth, type of enamel), type of saliva and digestive enzymes.  This is why we call them humans.  

For example, scientists have found no nutritionally relevant anatomical, physiological, or biochemical differences between Chinese and Eskimos. 

Nor are there any such differences between people with A-type and O-type blood.  

Medical Evidence?

D’Adamo claims that O-type people get ulcers more frequently than people with A-type because O-type individuals, according to him, produce more stomach acid than people with A-type blood.  He says that O-types produce this greater amount of acid as an adaptation to a high meat diet; A-types have less acid because they are adapted to a low protein, low meat diet. 

Apparently he missed the memo when research discovered that gastric ulcers arise from infection with H. pylori bacteria, not excessive stomach acid production.  While it is true that group O individuals have approximately 35% greater risk of gastrointestinal ulcer when compared to group A individuals, this is not because O-types produce more acid that A-types.   The ulcer-causing bacterium, H. pylori, can more easily attach to the G.I. lining of Group O, because it has a protein structure that mimics the Group O host (which confuses the host’s immune system).  In contrast, the immune system of A-type individuals more easily recognizes the bacterium as a foreign invader, making them more resistant to this infection.

D’Adamo correctly states that group A individuals have a higher risk of cancer than group O individuals.  Relative to Group O individuals, Group A individuals have higher risks of cancers of stomach , colon, ovary, uterus, cervix, and salivary glands (relative risks 1.2, 1.11, 1.28, 1.15, 1.33, and 1.64).  D’Adamo implies that this difference arises due to influence of dietary lectins. Presumably, the more vegetarian diet  he prescribes for A-types will protect them from cancer by reducing their exposure to harmful lectins.

First of all, if dietary lectins are the cause of cancers in anyone, it is very hard to understand how a vegetarian diet based on grains and beans will help prevent cancer.  Lectins are carbohydrate-binding proteins found in the highest concentrations in carbohydrate-rich foods like gains, legumes, and potatoes, not meat.  From Wikipedia entry on lectins:

“The toxicity of lectins has been identified by consumption of food with high content of lectins, which can lead to diarrhoea, nausea, bloating, vomiting, even death (as from ricin). Many legume seeds have been proven to contain high lectin activity, termed as hemagglutinating activity. Soybean is the most important grain legume crop, the seeds of which contain high activity of soybean lectins (soybean agglutinin or SBA). SBA is able to disrupt small intestinal metabolism and damage small intestinal villi via the ability of lectins to bind with brush border surfaces in the distal part of small intestine. Heat processing can reduce the toxicity of lectins, but low temperature or insufficient cooking may not completely eliminate their toxicity, as some plant lectins are resistant to heat.”

Therefore, the diet he apparently prescibes to A-types to reduce their risk of cancer actually provides MORE potentially hazardous dietary lectins than the diet he prescribes to O-types.

Secondly, D’Adamo doesn’t appear to know that the reason for increased risk of cancers in individuals with A-type blood is similar to the reason for the increased risk of ulcers in individuals with O-type blood.  Tumors often express an A-like antigen that the immune system of an A group individual will accept as “self” while the immune system of an O or B group individual will attack any cell with an A antigen. 

Note also that group O- and B- individuals still get these tumors. For example, the relative risk of stomach cancer is only 20% greater among A-type individuals compared to O-type.  This means that if 5 of 100 individuals having blood type O get stomach cancer, 6 of 100 individuals having blood type A get the same cancer; if 50 type Os get the cancer, 60 type As will get it.  In absolute numbers, the difference between these groups is not significant. 

Do Lectins Cause Selective Agglutination?

A lynch pin of D’Adamo’s hypothesis is the claim that lectins selectively cause agglutination in different blood types.  For example, according to D’Adamo, people with B-type blood should avoid chicken because it contains lectins that will agglutinate blood in these individuals, but not in people with other blood types.

We don’t have any evidence for this.  In fact, published data indicates that any individual lectin will affect all blood types in essentially the same way. 

Wikipedia discusses this topic:

“D'Adamo claims there are many ABO specific lectins in foods.[14] This claim is unsubstantiated by established biochemical research, which has not found differences in how the lectins react with a given human ABO type. In fact, research shows that lectins which are specific for a particular ABO type are not found in foods (except for one or two rare exceptions, e.g. lima bean), and that lectins with ABO specificity are more frequently found in non-food plants or animals.[15][16]

The Nachbar Study[17] has been cited in support of D'Adamo's theories, because it reports that the edible parts of 29 of 88 foods tested, including common salad ingredients, fresh fruits, roasted nuts, and processed cereals were found to possess significant lectin-like activity (as assessed by hemagglutination and bacterial agglutination assays). However, almost all of the 29 foods agglutinated all ABO blood types, and were not ABO blood type specific. Since D'Adamo's theory has to do with lectins in food that are "specific for a certain ABO blood type", this study does not support his claim that there are many ABO specific lectins in foods.”

Reference 15 in this excerpt refers to The Handbook of Plant Lectins

So Why Do People Feel Better?
D’Adamo advises the avoidance of wheat to O, A, and B blood types. Collectively, these comprise 96% of all people in the U.S..  Therefore, most people who read the book will get advice to avoid wheat, and they may try it.  This alone will improve health for some people who are wheat sensitive. 

Besides this, most people adopting the blood type diet will simply make general improvements to their diets, like reducing sugar intake, eating less processed and more unprocessed foods. D’Adamo suggests these steps to all blood types.  The general steps will help most people feel significantly better and perhaps lose some body fat. 

Bottom Line

The blood type diet does not have a solid leg on which to stand.  The hypothesis is riddled with errors. 

Addendum 10/28/11

Michael Klaper, M.D.: Challenges to the Blood Type Diet