Has the Rapid Dietary Transition in China Affected Cancer Risks in the Population?
by Junshi Chen, Institute of Nutrition and Food Safety, Chinese Center for Disease Control and Prevention, Beijing

The status of diet and nutrition among both urban and rural Chinese populations has improved significantly in the last two decades, and the prevalence of malnutrition and nutritional deficiency has continually declined. Meanwhile, the prevalence of non-communicable chronic diseases, including cancer, has rapidly increased.

Are recent changes in Chinese diet and nutrition related to this surge in chronic disease, and specifically in cancer mortality?

Changes in Diet Affect Body Weight
During the past 20 years, the dietary changes among the Chinese people include increased consumption of animal products and fat/oil, and decreased intake of cereal grains, coupled with a rise in the use of highly refined rice and wheat flour (Table). Between 1982 and 2002 (the most recent year for available national exposure data), fat intake increased from 68.3 to 85.6 g/person/day in urban populations and from 39.6 to 72.6 g/person/day in rural populations. As a consequence, the contribution of fat to the total energy intake rose from 25 to 35 percent in urban populations and from 14 to 28 percent in rural populations. During the same period, the contribution of cereal to the total dietary energy decreased from 70 to 47 percent in urban populations and from 80 to 61 percent in rural populations. While the average Chinese diet remains plant food-based, with cereals as a staple (366 and 415 g/person/day in urban and rural populations, respectively) and vegetable and fruit intake high (330 and 332 g/person/day in urban and rural populations, respectively), Westernization of the dietary pattern is clear.

One of the most striking and obvious health outcomes of these dietary changes is the increase in overweight and obese people in China. The percentages of overweight (BMI ≥24) and obesity (BMI ≥28) in the total population increased from 12.8 and 3.1 percent, respectively, in 1992, to 17.5 and 5.7 percent in 2002. Although these BMIs are lower than those in Western countries, if one considers only adults in large Chinese cities, the prevalence of overweight and obesity has reached 30.0 and 12.3 percent, respectively. And the numbers are continuing to increase steadily. Meanwhile, obesity is known to adversely affect the risk for several chronic diseases, including several forms of cancer.

Dietary Changes Have Shifted the National Disease Burden
Along with these changes in dietary patterns and other lifestyle factors, such as increased rates of smoking and decreased physical activity precipitated by the explosion of the automobile and urban work methods, the disease pattern of the Chinese people is in transition, moving from communicable to non-communicable diseases, including cancer, at breakneck pace.

At present, non-communicable diseases account for about 70 percent of total deaths in China. Meanwhile, according to the most recent nationwide disease surveillance data collected from 145 sites, from 1991-2000, the age-adjusted mortality for total cancer in China increased by 24 to 26 percent, from 114 to 144 per 100,000 population in males and 67 to 83 in females. A 50 percent increase in lung cancer mortality (from 22.7 to 33.9 per 100,000 persons) during this time was due mainly to the delayed effects of cigarette smoking. (Both number of smokers and cigarette usage among smokers were up.)

Mortality from several diet-related cancers also increased. For example, the age-adjusted death rate for colon cancer rose 15 percent in males (from 5.4 to 6.2 per 100,000 persons) and 10 percent in females (from 4.4 to 4.8 per 100,000 persons), and that of breast cancer in females climbed 29 percent, from 3.1 to 4.0 per 100,000 persons from 1991-2000. It is hypothesized that these increases in colon and breast cancer are related to the dietary changes and weight gains noted above.

Esophageal and stomach cancers continue to be the major cancers in China, accounting for about half of total cancer deaths. However, studies in high-risk areas for esophageal cancer (e.g. Linzhou, Henan province) have shown that, although overall esophageal cancer mortality did not change significantly over the last decade, it decreased among younger age groups. Experts hypothesize that this change was related to improvements in local diet as part of the rapid economic development and corresponding transition from a monotonous, deficient diet to a more varied, micronutrient-rich one that affected younger people in particular. This is supported by the observation that esophageal cancer mortality in older age groups in the same area has stabilized. In contrast, mortality for stomach cancer has remained stable or showed a slight increase, presumably because the major risk factors for this cancer, including a high infection rate with the stomach/intestinal bacterium Helicobacter pylori and a high salt intake, did not change.

Commitment to Cancer Control Unclear
Although improvements in cancer diagnosis may have contributed to the increase in cancer mortality in China during this past decade, it is unlikely that this alone would account for the 24 to 26 percent rise in total cancer mortality within the 10-year period. Dietary changes represented by the increased consumption of animal foods and oils, and decreased consumption of cereals are likely to have played a major role in the striking overall upsurge.

With this in mind, in 2004, the Ministry of Health promulgated a Five-Year Plan for the Control of Cancer in China, emphasizing balanced diet, moderate drinking and tobacco control as major preventive measures. Since no national death registration system exists in China, another national retrospective survey on cancer mortality is planned, and will commence later this year. Nevertheless, an overall commitment to combat this public health problem is lacking, as compared with the control of infectious diseases, which still receives the lion’s share of government attention and resources.