"Eat to Live, Not Live to Eat"
John H Weisburger, 2000
At one level of analysis, the long-term health benefits of food can be divided into three broad categories. The most basic level is where there's a focus on individual chemical components, eg riboflavin or glucose. At the next higher level it can concern the properties of individual foods, eg apples or olive oil, and at the highest level it can shift to dietry patterns where the makeup of the whole diet is the focus, eg the Mediterranean diet, which inlcudes mainly vegetables, fruits, whole grains, legumes, nuts and olive oil, some sea foods, poultry and dairy, optional red wine and limited red meats.
The first level is obviously the longer term goal in nutrition science, with the example of pure chemical drugs being enormously successful in controlling diseases and also through their development, leading to increased understanding of how they exert their effects in the body. But we're still generations away from understanding how hundreds of individual components in single foods interact and are treated in the body, let alone with normal meals when there is the added complexity of interactions across various foods. Even if eaten in isolation, individual food constituents will still interact with others at various stages of processing and distribution throughout the body before being stored, metabolised or eliminated. Plus, individual chemicals or foods can't supply all the necessary nutrients for long term well-being. So, we're mainly left, for the present, with studying the health effects of particular food patterns. Given the alarming negative trends such as the ever-increasing prevalence of obesity and diabetes in all developed countries, government agencies, health societies and individuals are all looking for direction to improve matters. As a result we have a continuing stream of new diet fads being promoted with full hyperbole, very often without adequate supporting scientific evidence. Consequently they inevitably fail at some stage and the public is sold the next marketing story.
Scientific evidence supporting a particular dietry pattern can be gained in various ways, with controlled human clinical trials being the gold standard. But these are difficult to set up with willing or suitable subjects, very expensive, sometimes have serious ethical limitations and usually take many years to complete. Then depending on the criteria for inclusion in the study they may have to be broadened or extended to cover different scenarios. Another common approach in seeking evidence is to design epidemiological studies where groups of subjects are examined for particular patterns. These are notorious for confounding factors affecting interpretation and they only show associations, but over time can provide valuable insight on promising future directions. The following is a summary of a large epidemiological study (Epidemiology 2007;18: 393-401) examining the impact of different dietry patterns on mortality of Chinese women.
Many foods and nutrients have been suggested to influence life expectancy. However, previous studies have not examined the relationship between dietary patterns and cause-specific mortality. This study prospectively examines the relationship of dietary patterns with total mortality and cause-specific mortality in a population-based cohort study of Chinese women. The Shanghai Women's Health Study is a population-based cohort study of 74,942 women aged 40 to 70 years at the time of recruitment (September 1996 to May 2000). Detailed dietary information was collected using a validated, quantitative food frequency questionnaire. The cohort has been followed using a combination of in-person interviews and record linkage with various registries. Dietary patterns, derived from principal component analysis, were examined for their relation to total mortality and cause-specific mortality using Cox regression models. After an average of 5.7 years of follow-up (423,717 person-years of observation), there were 1565 deaths. We derived three major dietary patterns that these women followed, vegetable-rich, fruit-rich, and meat-rich. The significant adjusted hazard ratios for the fruit-rich diet were 0.94 for all causes of death and 0.89, 0.79 and 0.51 for death caused by cardiovascular disease, stroke, and diabetes respectively. There were non-significant trends for the meat-rich diet pattern, with increased risk of diabetes and a slightly elevated risk of total mortality. There were no significant trends seen with the vegetable-rich diet. In general, a fruit-rich diet was related to lower mortality, whereas a meat-rich diet appeared to increase the probability of death.
It's interesting that the one pattern that was beneficial in a number of chronic diseases was a fruit-rich diet. Although vegetables are normally recommended together with fruit in a healthy diet, a major problem with the former is that usually they are cooked or processed in some way and this can result in major degradation of favourable nutrient properties of the fresh food. Of course many vegetables are not particularly palatable or flavoursome in the fresh state and need some cooking, but the goal in these cases should be to minimise negative outcomes. With a large cohort of more than 70,000 women, it's not surprising to find that the major fruits consumed were the staples of citrus, apples, pears, bananas, watermelon, peaches and grapes. Major vegetables were beans, rice stems, eggplant, celery, cucumber, cauliflower and cabbage. In the meat-rich diet pattern major foods were chicken, animal parts (heart, brain, tongue, tripe and intestines), liver, rice, pig's feet and pork chops. The biggest effect of fruit on specific disease mortality was with diabetes, where women in the top 25% of those conforming to the fruit-rich diet were 81% less likely to die than those in the bottom 25%.