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March 24, 2015 - September 8, 2018
A metanalysis tabulates the combined data from multiple studies and analyzes them as one data set. By accumulating and analyzing a large body of combined data, the result can have considerably more weight. Metanalysis findings are therefore more substantial than the findings of single research studies,
After obtaining the results from a variety of studies, we can then begin to use these tools and concepts to assess the weight of the evidence. Through this effort, we can begin to understand what is most likely to be true, and we can behave accordingly. Alternative hypotheses no longer seem plausible, and we can be very confident in the result. Absolute proof, in the technical sense, is unattainable and unimportant. But common sense proof (99% certainty) is attainable and critical. For example, it was through this process of interpreting research that we formed our beliefs regarding smoking
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In the Indian study, when all the rats had been predisposed to get liver cancer after being given aflatoxin, only the animals fed 20% protein got the cancer while those fed 5% got none.
Anything less would not have convinced anyone, especially my peers who would review my future request for renewed funding! In hindsight, we must have succeeded. The NIH funding for this study continued for the next nineteen years and led to additional funding from other research agencies (American Cancer Society the American Institute for Cancer Research and the Cancer Research Foundation of America). On these experimental animal findings alone, this project gave rise to more than 100 scientific papers published in some of the best journals, many public presentations and several invitations to
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the sidewalk. So what is the process that successfully “implants” the grass seed in the soil in the first place, i.e., initiates cancer-prone cells? Chemicals that do this are called carcinogens. These chemicals are most often the byproducts of industrial processes, although small amounts may be formed in nature, as is the case with aflatoxin. These carcinogens genetically transform, or mutate, normal cells into cancer-prone cells. A mutation involves permanent alteration of the genes of the cell, with damage to its DNA.
Promotion is reversible, depending on whether the early cancer growth is given the right conditions in which to grow. This is where certain dietary factors become so important. These dietary factors, called promoters, feed cancer growth. Other dietary factors, called anti-promoters, slow cancer growth. Cancer growth flourishes when there are more promoters than anti-promoters; when anti-promoters prevail cancer growth slows or stops. It is a push-pull process. The profound importance of this reversibility cannot be overemphasized.
We initially determined whether the amount of protein that we eat could change this enzyme activity. After a series of experiments (Chart 3.218), the answer was clear. Enzyme activity could be easily modified simply by changing the level of protein intake.18–21 Decreasing protein intake like that done in the original research in India (20% to 5%) not only greatly decreased enzyme activity but did so very quickly.22 What does this mean? Decreasing enzyme activity via low-protein diets implied that less aflatoxin was being transformed into the dangerous aflatoxin metabolite that had the
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We now had impressive evidence that low protein intake could markedly decrease enzyme activity and prevent dangerous carcinogen binding to DNA. These were very impressive findings, to be sure. It might even be enough information to “explain” how consuming less protein leads to less cancer. But we wanted to know more and be doubly assured of this effect, so we continued to look for other explanations. As time passed, we were to learn something really quite remarkable. Almost every time we searched for a way, or mechanism, by which protein works to produce its effects, we found one! For example,
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From our extensive research, one idea seemed to be clear: lower protein intake dramatically decreased tumor initiation. This finding, even though well substantiated, would be enormously provocative for many people.
A principle was being established. Foci development, initially determined by the amount of the carcinogen exposure, is actually controlled far more by dietary protein consumed during promotion. Protein during promotion trumps the carcinogen, regardless of initial exposure.
Foci did not develop with up to about 10% dietary protein. Beyond 10%, foci development increased dramatically with increases in dietary protein.
foci developed only when the animals met or exceeded the amount of dietary protein (12%) needed to satisfy their body growth rate.39 That is, when the animals met and surpassed their requirement for protein, disease onset began.
According to the recommended daily allowance (RDA) for protein consumption, we humans should be getting about 10% of our energy from protein. This is considerably more than the actual amount required. But because requirements may vary from individual to individual, 10% dietary protein is recommended to insure adequate intake for virtually all people. What do most of us routinely consume? Remarkably, it is considerably more than the recommended 10%. The average American consumes 15-16% protein. Does this place us at risk for getting cancer? These animal studies hint that it does.
In the animals fed the 20% level of protein, foci increased in number and size, as expected, as the aflatoxin dose was increased. The dose-response relationship was strong and clear. However, in the animals fed 5% protein, the dose-response curve completely disappeared. There was no foci response, even when animals were given the maximum tolerated aflatoxin dose. This was yet another result demonstrating that a low-protein diet could override the cancer-causing effect of a very powerful carcinogen, aflatoxin.
Is it possible that chemical carcinogens, in general, do not cause cancer unless the nutritional conditions are “right”? Is it possible that, for much of our lives, we are being exposed to small amounts of cancer-causing chemicals, but cancer does not occur unless we consume foods that promote and nurture tumor development? Can we control cancer through nutrition?
For all of these experiments, we were using casein, which makes up 87% of cow’s milk protein. So the next logical question was whether plant protein, tested in the same way, has the same effect on cancer promotion as casein. The answer is an astonishing “NO.” In these experiments, plant protein did not promote cancer growth, even at the higher levels of intake.
Gluten, the protein of wheat, did not produce the same result as casein, even when fed at the same 20% level.
Rats fed 20% soy protein diets did not form early foci, just like the 20% wheat protein diets. Suddenly protein, milk protein in this case, wasn’t looking so good. We had discovered that low protein intake reduces cancer initiation and works in multiple synchronous ways.
The effects of protein feeding on tumor development were nothing less than spectacular. Rats generally live for about two years, thus the study was 100 weeks in length. All animals that were administered aflatoxin and fed the regular 20% levels of casein either were dead or near death from liver tumors at 100 weeks.36, 43 All animals administered the same level of aflatoxin but fed the low 5% protein diet were alive, active and thrifty, with sleek hair coats at 100 weeks. This was a virtual 100 to 0 score, something almost never seen in research and almost identical to the original research in
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Let there be no doubt: cow’s milk protein is an exceptionally potent cancer promoter in rats dosed with aflatoxin. The fact that this promotion effect occurs at dietary protein levels (10-20%) commonly used both in rodents and humans makes it especially tantalizing—and provocative.
nutritional effect on a virus-induced cancer,
Studying animal protein effect on hepatitis B
By this time, we had more than enough information to conclude that casein, that sacred protein of cow’s milk, dramatically promotes liver cancer in: rats dosed with aflatoxin mice infected with HBV
This research showed that increasing intakes of casein promoted the development of mammary (breast) cancer. They found that higher casein intake: promotes breast cancer in rats dosed with two experimental carcinogens (7,12-dimethybenz(a)anthracene (DBMA) and N-nitroso-methylurea (NMU)) operates through a network of reactions that combine to increase cancer operates through the same female hormone system that operates in humans
casein affects the way cells interact with carcinogens, the way DNA reacts with carcinogens and the way cancerous cells grow.
The results of these, and many other studies, showed nutrition to be far more important in controlling cancer promotion than the dose of the initiating carcinogen.
The Journal of the National Cancer Institute, which is the official publication of the U.S. National Cancer Institute, took note of these studies and featured some of our findings on its cover.52
nutrients from animal-based foods increased tumor development while nutrients from plant-based foods decreased tumor development.
the early 1970s, the premier of China, Chou EnLai, was dying of cancer. In the grips of this terminal disease, Premier Chou initiated a nationwide survey to collect information about a disease that was not well understood. It was to be a monumental survey of death rates for twelve different kinds of cancer for more than 2,400 Chinese counties and 880 million (96%) of their citizens. The survey was remarkable in many ways. It involved 650,000 workers, the most ambitious biomedical research project ever undertaken. The end result of the survey was a beautiful, color-coded atlas showing where
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This atlas made it clear that in China cancer was geographically localized. Some cancers were much more common in some places than in others.
In effect, we are comparing, within the Chinese range, diets rich in plant-based foods to diets very rich in plant-based foods. In almost all other studies, all of which are Western, scientists are comparing diets rich in animal-based foods to diets very rich in animal-based foods.
I have never pursued health hoping for immortality. Good health is about being able to fully enjoy the time we do have. It is about being as functional as possible throughout our entire lives and avoiding crippling, painful and lengthy battles with disease. There are many better ways to die, and to live.
Because the China Cancer Atlas had mortality rates for more than four dozen different kinds of disease, we had a rare opportunity to study the many ways that people die. We wondered: do certain diseases tend to group together in certain areas of the country? For example, did colon cancer occur in the same regions as diabetes? If this proved to be the case, we could assume that diabetes and colon cancer (or other diseases that grouped together) shared common causes. These causes could include a variety of possibilities, ranging from the geographic and environmental to the biological. However,
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The disease that kills most Westerners, coronary heart disease, is more common in areas where breast cancer also is more common. Coronary heart disease, by the way, is relatively uncommon in many developing societies of the world. This is not because people die at a younger age, thus avoiding these Western diseases. These comparisons are age-standardized rates, meaning that people of the same age are being compared. Disease associations of this kind have been known for quite some time. What the China Study added, however, was an unsurpassed amount of data on death rates for many different
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A 95% certainty means a 19 in 20 probability that the observation is real; a 99% certainty means a 99 in 100 probability that the observation is real; and a 99.9% certainty means a 999 in 1,000 probability that the observation is real.
How much dietary cholesterol you consume is not something your doctor can know when he or she checks your cholesterol levels. The doctor can’t measure dietary cholesterol any more than he or she can measure how many hot dogs and chicken breasts you’ve been eating. Instead, the doctor measures the amount of cholesterol present in your blood. This second type of cholesterol, blood cholesterol, is made in the liver. Blood cholesterol and dietary cholesterol, although chemically identical, do not represent the same thing. A similar situation occurs with fat. Dietary fat is the stuff you eat: the
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Lower blood cholesterol levels are linked to lower rates of heart disease, cancer and other Western diseases, even at levels far below those considered “safe” in the West.
Most Americans know that if you have high cholesterol, you should worry about your heart, but they don’t know that you might want to worry about cancer as well.
In the China Study higher levels of the bad LDL cholesterol also were associated with Western diseases.
Blood cholesterol is clearly an important indicator of disease risk. The big question is: how will food affect blood cholesterol? In brief, animal-based foods were correlated with increasing blood cholesterol (Chart 4.5). With almost no exceptions, nutrients from plant-based foods were associated with decreasing levels of blood cholesterol.
In rural China, animal protein intake (for the same individual) averages only 7.1 g/day whereas Americans average a whopping 70 g/day. To put this into perspective, seven grams of animal protein is found in about three chicken nuggets from McDonald’s. We expected that when animal protein consumption and blood cholesterol levels were as low as they are in rural China, there would be no further association with the Western diseases. But we were wrong. Even these small amounts of animal-based food in rural China raised the risk for Western diseases.
These studies showed that people who migrated from one area to another and who started eating the typical diet of their new residency assumed the disease risk of the area to which they moved. This strongly implied that diet and lifestyle were the principle causes of these diseases.
Findings from rural China showed that reducing dietary fat from 24% to 6% was associated with lower breast cancer risk. However, lower dietary fat in rural China meant less consumption not only of fat but, more importantly, of animal-based food.
This connection of breast cancer with dietary fat, thus with animal-based foods, brought into consideration other factors that also place a woman at risk for breast cancer: Early age of menarche (age of first menstruation) High blood cholesterol Late menopause High exposure to female hormones
The much later age of menarche in rural China is remarkable. Twenty-five women in each of the 130 villages in the survey were asked when they had their first menstrual period. The range of village averages was fifteen to nineteen years, with an average of seventeen years. The U.S. average is roughly eleven years!
higher levels of blood hormones such as estrogen. These hormone levels remain high throughout the reproductive years if consumption of a diet rich in animal-based food is maintained. Under these conditions, age of menopause is deferred by three to four years,I thus extending the reproductive life from beginning to end by about nine to ten years and greatly increasing lifetime exposure to female hormones. Other studies have shown that an increase in years of reproductive life is associated with increased breast cancer risk.35, 36 This network of relationships becomes still more impressive.
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Nonetheless, when hormone levels among Chinese women were compared with those of British women,38 Chinese estrogen levels were only about one-half those of the British women, who have an equivalent hormone profile to that of American women. Because the length of the reproductive life of a Chinese woman is only about 75% of that of the British (or American) woman, this means that with lower estrogen levels, the Chinese woman only experiences about 35-40% of the lifetime estrogen exposure of British (and American) women. This corresponds to Chinese breast cancer rates that are only one-fifth of
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The strong association of a high-animal protein, high-fat diet with reproductive hormones and early age of menarche, both of which raise the risk of breast cancer, is an important observation. It makes clear that we should not have our children consume diets high in animal-based foods. If you are a woman, would you ever have imagined that eating diets higher in animal-based foods would expand your reproductive life by about nine to ten years? As an aside, an interesting implication of this observation, as noted by Ms. magazine founder Gloria Steinem, is that eating the right foods could reduce
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Diet and disease factors such as animal protein consumption or breast cancer incidence lead to changes in the concentrations of certain chemicals in our blood. These chemicals are called biomarkers. As an example, blood cholesterol is a biomarker for heart disease. We measured six blood biomarkers that are associated with animal protein intake.39 Do they confirm the finding that animal protein intake is associated with cancer in families? Absolutely. Every single animal protein-related blood biomarker is significantly associated with the amount of cancer in a family.II–III
If we don’t consume enough fiber, we are susceptible to constipation-based diseases. According to Burkitt, these include large bowel cancer, diverticulosis, hemorrhoids and varicose veins.
Dietary fiber is exclusively found in plant-based foods. This material, which gives rigidity to the cell walls of plants, comes in thousands of different chemical variations. It is mostly made of highly complex carbohydrate molecules. We digest very little or no fiber. Nonetheless, fiber, having few or no calories itself, helps dilute the caloric density of our diets, creates a sense of fullness and helps to shut down appetite, among other things. In doing so, it satisfies our hunger and minimizes the overconsumption of calories.
