By Runtian Wu
As the ageing of populations occurs in many nations worldwide, people are increasingly looking for health-oriented diets to avoid diseases and increase the life span.1 Various health claims are circulating in the daily communications, such as the benefit of vegetarian, tea, restricted food intake, and organic food. Although many of these claims are partially substantiated by scientific literature, they should be treated cautiously. Nevertheless, there is growing evidence that certain kinds and amounts of diet have great potential of increasing human lifespan. This paper will examine popular health claims and recent research to present the possibilities that how food can impact human life expectancy and health conditions.
Low meat intake
Many vegetarians would argue the benefit of low meat intake. Although the benefits are not conclusive, current research showed that low meat intake correlates positively with longer life expectancy. A study2 that involved 6000 vegetarians (never eat meat and fish) and 5000 nonvegetarians that have similar lifestyle, social class, and health conditions found that vegetarians have significantly lower total cholesterol (often involved in heart disease) concentrations. An 11-year follow-up of 1,904 vegetarians in Germany3 also showed that mortality from all causes (such as cardiovascular and cerebrovascular diseases) was cut in half compared with the general population. However, as many critics pointed out, the improved health conditions in vegetarians are likely to do with their lifestyles. According to the report from Fraser4, most vegetarians never smoke cigarettes, seldom drink alcohol, and do not have chronic diseases. A 6-year study based on data collected from 34,198 members of a church5 explicitly excluded participants that ever smoked, drank alcohol, or had coronaryartery disease, stroke, and cancer. The study showed that fatal ischemic heart disease was reduced by 37% in male vegetarians compared with nonvegetarians. A review in 20036 also found that long-term vegetarians (no meat intake for 17 years) have higher life expectancy than short-term vegetarians (no meat intake < 17 years). It is worth attention that all the research mentioned here was conducted in affluent countries where meatless diets are rare6, so it is hard to conclude whether low meat intake in some underdeveloped countries where populations can hardly have meat diets will have the same positive effect.
Compared with lowering meat intake, perhaps a more “extreme” claim would be the dietary restriction. Dietary restriction restricts nutrient intake without causing malnutrition.7 There is evidence that such removal of food will trigger an increase in stress resistance and autophagy and a decrease in translation and ribosome biogenesis, thereby contributing to longevity.8 Dietary restriction in Caenorhabditis elegans (C. elegans) showed a remarkable extension of life as well as an increase in thermotolerance.7
The mechanism of how Dietary restriction increases lifespan remains unclear; however, growing evidence suggested that at least some mechanisms may be conserved across species. For example, under dietary restriction, a loss of function mutations in daf-2 increased the lifespan of C. elegans by 49% compared with those without the mutation.7 Gene mutation increases lifespan additively with dietary restriction is also seen in other species. A study in Ames dwarf mice showed that although dietary restriction increased the life span of both wild-type mice and mutants with the gene Prop1df, the mutants live about 50% longer than the wild type.9 It’s still unclear whether dietary restriction will have a similar effect on the longevity of humans, and arbitrary dietary restriction may come with health hazards. For example, there are suggestions that the increase of lifespan under dietary restriction is correlated with the loss of fecundity10, and experiments in flies have demonstrated that a reduction in female reproduction can lead to life extension under dietary restriction.11 However, a direct causal link is yet to be established,12 and subsequent research has shown that dietary restriction can increase lifespan in both male flies and sterile female flies.12,13
Instead of generally restricting food intake, a more advisable way toward a healthy life is carefully selecting the food. Reviews based on past research found that mortality of all-cause can be decreased by increasing intake of whole grains, vegetables, fruits, nuts, and fish and reducing intake of red and processed meat.14,15,16 Consumption of certain food groups such as nuts, fruit, vegetables, and legumes was found to reduce the mortality of cardiovascular diseases and cancer.17.18 There is also a significant effect of food on lifespan. A 13-year study using data from 1548 counties in the United States showed that populations with healthy diets have around 20 years longer life expectancy than those without healthy diets.19 Five healthy foods (whole grains, fresh fruits & vegetables, nuts, dairy, seafood) and three unhealthy foods (refined grains, red & processed meats, sugar-sweetened beverages) were used to construct a diet score with 1 average point given to a county if the average expenditure on a healthy food of the county was above the average; otherwise, the county received a 0 point.16 The total diet scores were then compared with the life expectancy in the county.
Flavonoids, tea, and organic food
The health effects of food such as tea and fruit are further substantiated with the understanding of an important substance called flavonoids. Flavonoids are a group of important plant pigments that can display colours in flowers. They are present in all plant parts and can be in any food with natural flavours and colourings or made from plants (20). Humans and other animals cannot synthesise flavonoids. It has been found that flavonoids have considerable effects on human health with their antiallergic, anti-inflammatory, antiviral, antiproliferative, and anticarcinogenic activities.21 The protective role of flavonoids against heart disease may also be explained by the ability to prevent lipoproteins from oxidation to an atherogenic form.20 Tea, which is rich in flavonoids, showed positive effects against cancer, diabetes, cardiovascular and neurological diseases22, although further investigation is needed.
The popularity of organic food is driven by the perception that organic food is healthier, has greater nutritional value and fewer toxic chemicals.23 Although such claims lack substantial scientific support, there is growing evidence that organic food is different from non-organic food in many aspects. For example, a review in 2010 analysed the data collected by French Agency for Food Safety (AFSSA) and concluded that organic food contained more dry matters and minerals (Fe, Mg), antioxidants such as phenols and salicylic acid, less nitrite in 50% of organic products and 94-100% without pesticide residues.24 An animal study25 found that rats fed with organic food exhibit a greater level of stimulated lymphocyte proliferation, while another study in the Netherlands26 found that chicken fed with organic food had lower body weights and a more active immune system. However, these studies are insufficient to prove the benefits of organic food. Apart from the ongoing debate on the impact of the nutritional content of food on the health27, the content of organic food is also subject to multiple factors such as fertiliser, weather and earth conditions.28,29,30
This paper reviewed the research on impact of food on health, particularly on life expectancy. Low-meat intake and dietary restriction both showed a positive effect on life expectancy, although the arbitrary practice of dietary restriction is not recommended. Food choice can significantly impact human health, but the exact effect of many types of food remains unclear. Increasing evidence has pointed to the role of flavonoids in supporting critical functions in the human body. The benefits of organic food remain controversial, although there is some evidence suggesting the increased nutritional content in organic food. Current research on the health claims is still ongoing, so the interpretations in this paper should be taken cautiously as they are subject to change as new evidence are discovered.
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