Many books are given the epithet ‘groundbreaking’ but The China Study by Dr Colin Campbell and his son Thomas is one that truly deserves the accolade. Based on the biggest survey of the relationship between diet and disease ever done, the book rigorously examines the evidence and reaches several clear, and to many, startling dietary conclusions.
It seems that our high consumption of animal protein is undermining our health more than anything else, especially with regard to cancer, heart disease, obesity and diabetes.
Animal protein, otherwise referred to as first class protein, has been placed on a nutritional pedestal by almost everyone from nutritionists to government health advisors. And for many people protein equates with meat and meat is therefore the most desirable food to have on one’s plate. In this study Campbell knocks animal protein right off its perch.
As an American scientist investigating one of the most carcinogenic substances ever discovered — aflatoxin, a natural poison produced by a mould which grows on peanuts and maize — Campbell chanced upon some research done in India which quite literally changed his life and research focus. Two similar groups of rats were exposed to equal doses of aflatoxin which is strongly linked to liver cancer. One group was fed on a 20% protein diet and the other a 5% protein diet. This was the only difference between the two groups. The results were dramatic and every researcher’s dream for there was an unequivocal, if unexpected, outcome. Every single rat in the 20% protein group developed liver cancer or precursor lesions whereas not one single rat in the 5% protein group developed even the precursor signs of liver cancer.
The protein in question was casein, which is derived from cow’s milk. When he told his colleagues about the research they responded with disbelief. “They must have gotten the numbers on the animal cages reversed. In no way could a high-protein diet increase the development of cancer.” But Campbell could not let go of the intriguing possibility that protein, and in particular animal protein, could be driving the development of cancer in some way.
Research in the Philippines confirmed that aflatoxin was also implicated in the high incidence of human liver cancer, with children being particularly at risk. The consumption of mould-contaminated peanut butter and maize meal was to blame. On further inspection Campbell found that the children who developed liver cancer were also from the best-fed families and consumed more animal protein than anyone else in the country. This again, was not what was expected.
People like to blame chemicals rather than lifestyles or dietary habits for disease, and sometimes with very little real basis. For instance when it was discovered that sodium nitrite (a meat preservative which also imparts a pink colour to canned meats, bacon and hot dogs) might be producing nitrosamines in the body there was widespread panic.
Why? Because ‘low-dose’ nitrosamine consumption in a small group of rats led to a 35% death rate from throat cancer. However, the ‘low-dose’ group received extraordinary amounts of the chemical – the human equivalent of eating 270 000 pounds of bologna every day for over thirty years.
And yet when results showed that a 20% protein intake (well within the range of normal consumption levels in Western societies) experimentally turned on cancer in 100% of test animals given aflatoxin compared with no evidence of cancer in the 5% protein group, there was hardly a ripple in scientific circles.
Campbell decided to repeat the Indian research. He got similar results with all animals dead or nearly dead from liver cancer in the 20% group after two years while all the animals in the 5% protein group were still alive and active. He then switched the groups over midway so that the 5% protein group now got 20% and vice versa. The 5% group, which showed no cancer signs until then, quickly started to develop signs of cancer on the 20% protein diet. The 20% group, which had developed liver precursor cancer signs, showed evidence of reversal on the 5% diet. He then experimented with different amounts of aflatoxin and different types of protein and found that 20% animal protein was the culprit every time – no cancers developed using 5% protein diets or even 20% vegetable protein (from wheat or soya) diets. Then the results were replicated in other animals with different carcinogens and types of cancer, including mammary cancer.
What was going on?
There are three stages to cancer development, which Campbell likens to growing a lawn. First the seeds are planted (initiation), then they start germinating and growing (promotion), and finally they get out of control, invading flowerbeds and paving (progression). During initiation the genetic material in cells is damaged either by chemicals (carcinogens such as aflatoxin and manmade industrial and agricultural pollutants) or radiation leaving the cells, and all subsequent daughter cells, prone to the development of cancer. The damage is almost always irreversible and can happen very quickly – within minutes even.
During promotion the damaged cells start to multiply until they become clinically detectable as cancerous tumours. The promotion stage occurs over a much longer period, which can be many years in humans. The good news is that this stage is reversible in many cases. Like the grass seeds, the right conditions for growth need to be present for promotion and progression to happen, and to continue happening. And this is where dietary factors appear to play a major role, acting either as promoters or anti-promoters. The emerging pattern in this and other research involving other nutrients such as fish and meat protein and different types of dietary fats, Campbell writes, is that “nutrients from animal-based foods increased tumour development while nutrients from plant-based foods decreased tumour development.
How does this rather radical research apply to humans?
Protein requirements in rats and humans are remarkably similar. Protein should make up roughly 10% of both rat and human energy intake and Campbell found he could increase animal protein intakes to this level without adversely affecting the outcome in his rat experiments. This amounts to around 50-60g of protein per day for humans depending on body weight and total calorie intake. Yet many people in Western societies are consuming much more, with levels approaching 20%. It’s easy to see how with a 300g steak supplying around 75g protein, already more than the daily requirement.
Supportive human evidence was urgently required and this led Campbell on to the impressive China Study. When Chou EnLai, China’s premier in the early 1970s, was dying of cancer he ordered a comprehensive nationwide study of the death rates for twelve different types of cancer throughout China. It was a massive study involving 880 million citizens (96% of the country). In Europe and the US researchers get excited when there is 20% increase in cancer incidence in different areas of the country but in China some of the rates varied by a whopping 10,000%. With such a massive geographical variation in cancer rates in a population which is genetically and ethnically similar (87% Han people), the spotlight moved to environmental and lifestyle factors to account for the differences.
While the cancer variation was huge in China the overall average cancer incidence was far still far less than in Europe and the US, as it was with other so-called diseases of affluence including diabetes, heart disease, obesity and many others. But the core question remained – did diet have anything to do with the dramatic geographical variation in these diseases? Campbell and other researchers therefore took a ‘snapshot’ of the dietary situation in all the different Chinese counties using food intake surveys and blood levels of nutrients and biochemical markers such as cholesterol.
While the Chinese generally eat much less animal foods and more whole plant foods than people in the West, the predominant finding which emerged out of thousands of significant statistical correlations was that as the consumption of plant foods went up so the incidence of all these diseases went down, as well as all important biochemical risk markers such as cholesterol levels. Very few people, including doctors, know that animal protein is much more strongly correlated with blood cholesterol (the bad LDL type) than saturated fat or dietary cholesterol. Or that high cholesterol levels are not only linked to heart disease but also many types of cancer.
Saturated fat, mainly found in animal foods, has been regarded as the biggest nutritional baddie for many years. This has spawned a massive food industry around low-fat animal foods, which encouraged people to continue eating high levels of animal-based food in the belief that they had been rendered harmless.
However, recently released, rather shocking results from the Women’s Health Initiative, which tracked nearly 49,000 women for eight years, have thoroughly refuted this idea. Of the group that reduced their fat consumption to 20% of total calories (typical fat consumption is around 35-40% of calories), absolutely no reduction in health risk was observed. This again supports Campbell’s finding that excessive animal protein may be to blame for much of disease risk in the West.
Fad diets, like the Atkins diet which reduces carbohydrate intake but allows unlimited animal protein and fat, could therefore be doing far greater harm than good. Comparing intakes of the least active Chinese, the equivalent of office workers, Campbell found that while the Chinese had a 30% higher calorie intake their body weight was 20% lower. This could only be partly accounted for by a higher level of physical activity (e.g. cycling to work). The other important finding of the China Study is that diets low in protein and fat encourage more calories to be burned as heat rather than stored as fat. And it is this higher metabolic rate that is largely responsible for keeping obesity at bay, in spite of a much greater calorie consumption.
Campbell concludes that the results of the study were so personally convincing that he and his family have gone from a career of scoffing at vegetarians to eating an almost 100% whole foods, plant-based diet. “A diet that is good for preventing cancer is also good for the prevention of heart disease as well as every other disease of affluence including obesity, diabetes, cataracts, macular degeneration, Alzheimer’s’, cognitive dysfunction, multiple sclerosis, osteoporosis and more. When a whole, plant-based diet is demonstrably beneficial for such a wide variety of disease, is it possible that humans were meant to consume any other diet?”
Michael Pollan, author of the highly influential books, the Omnivore’s Dilemma and In Defence of Food agrees and proposes a new yet very old and simple answer to the question of what humans should be eating to maintain health.
Eat food. Not too much. Mostly plants.
And by food, he means real, unadulterated food as opposed to the many processed and highly adulterated products that masquerade as food, often trumpeting loud health claims. As he drolly comments, shoppers should not be misled by the relative ‘silence of the yams’ and other real foods with respect to their true health value.
Linda Scott has an MSc in Nutritional Medicine and is currently doing doctoral research in this field.