Abstract

Cardiovascular diseases (CVDs), obesity, diabetes, cancers and other chronic diseases are becoming main contributors to the global burden of disease, even as nutritional deficiencies are receding as leading contributors to mortality and disability. Diet is closely related to nutrition and health, which has been extensively investigated as risk factors for major chronic diseases. The past two decades have witnessed rapid changes in dietary pattern in China. However, a critical thinking of Chinese diet behind these changes is less emphasized. Given the causal relationship between nutrition and disease, lack of adequate nutrition and unhealthy diet habits might be responsible for the high incidence of chronic diseases in China in recent years. To this end, we will critically review some open problems in current diet compositions and the importance of regular mealtimes. The intake level of dietary supplements in China will also be discussed.

1. Introduction

In recent years, health care or self-management (taking care of your own health) is gaining more and more attention globally because of the baby boom generation and aging population. A publication of the US Public Health Service agenda laid out guidelines that support the realization of a vision of improved health, of which diet changes are one of the most effective approaches to prevent nutrition-related illnesses occurring at any age of life ¹. Food nutrition refers to the general term for the heat energy and nutrients that the human body can obtain from the food. According to the characteristic of nutrients, source of nutrition is classified into 3 categories: (1) fresh food (agricultural products), (2) cooking food and (3) processed food.

China has achieved outstanding economic progress and high levels of education during the past years, and Chinese diet has also evolved rapidly, along with these changes in economy and related social activities ². Traditionally, Chinese diet includes fruits, vegetables and cereals with few animal foods. Many researchers believe that this diet is the most beneficial to health when ingested adequately ³. Nowadays, animal foods including meat, eggs, aquatic products, and milk are becoming very popular in both urban and rural areas. Beyond that, a growing number of people are pursuing a balanced diet that provides all the nutrients in sufficient quantities to meet the nutritional needs of the body. However, it is difficult for a large majority of people to achieve and maintain a balanced diet. For example, the recommended calcium intake for adults over 18 years of age is 800 mg per day according to the Chinese Dietary Reference Intakes Summary ⁴. It was surveyed that the percentage of adults achieving the Chinese dietary reference intake on calcium was only 4.3% ⁵. Eating a well-balanced diet appears to be just a concept for most people and inadequate nutrient intake is still a widespread problem.

It is important to know that a large quantity of nutrients is lost or changed in cooking and processed foods to some extent. Any forms of cooking will destroy some nutrients in the food, but the determinants are the volumes of water used in the cooking process, as well as the cooking time and temperature ⁶. There are some nutrients such as vitamin C, protein and micronutrients that are extremely unstable under high temperature and are readily decomposed or metabolized into other substances ^{7, 8, 9}. Besides that, food processing such as malting, drying, milling, and extrusion is also shown to have major effect on nutrients content ^{10, 11}. These make it difficult to guarantee the intake of necessary and sufficient nutrients from the diet. Moreover, the flavor and taste of the food after cooking or processing have been greatly improved, which may lead to excessive intake of unhealthy ingredients, thereby harming health. A study showed that a number of school students consumed high amounts of sugars, saturated fat and sodium through processed beverages, milk and Ramen in their diet ¹². As a result, some chronic diseases including obesity, diabetes, and cardiovascular diseases (CVDs) resulted from metabolic alterations ^{13, 14}, have dramatically increased in recent years ^{15, 16}.

In the current study, we will provide a critical review of the relationship between Chinese diet and nutrition, as well as dietary factors in increasing incidence of diseases, attempting to show people a positive implication to adjust their diet. Considering the prevalence of health-care food, the intake level of dietary supplement in China and its role in nutritional intervention and health promotion will be discussed.

2. Diet Composition in Relation to Nutrition and Health

Fruits have been considered as an important part of a healthy diet as prolific source of nutrients (vitamins, minerals, folate, and dietary fiber) and bioactive substances (polyphenols, anthocyanins, flavonoids, and essential oils) is present in fruits ^{17, 18}. The consumption of fruits should be encouraged, which may be useful to enhance fruit concentrations of nutrients and bioactive substances. It has been documented that intake of fruits has been associated with lower risks of developing chronic diseases and a wide range of cancer types ^{19, 20}. For example, cranberry can reduce the incidence of urinary tract infections in women ²¹ and grape has favorable effects on cardiovascular risk markers ²². More fruits and their health benefits are described in Table 1.

Now people in China may have better access to various fruits harvested in any season because of the development of food technology and prosperity of import trade. It is worth mentioning that citrus fruits have been popular in China for centuries, which is attributed to the fact that they can provide good taste and low cost. Moreover, relatively high content of vitamin C and polyphenols in citrus fruits has attracted intense interest of researchers and consumers during the past years. They can act as antioxidants to protect the body’s tissues against oxidative stress and diseases related to oxidative damage such as CVDs and cancers ⁴⁶. In general, most people in China has realized that intake of fruits in the diet is crucial to long-term health care and it is suggested by Chinese society of nutrition that we should consume fresh fruits of different kinds as possible as we can.

Vegetables in modern Chinese diet likewise provide a significant part of nutrition, as they are important sources of nutrients (minerals and vitamins), dietary fiber, and phytochemicals ⁴⁷. In addition to vitamins, the presence of phytochemicals (polyphenols, glucosinolates, carotenoids, sterols and saponins) in vegetables has been considered to be of vital nutritional value in preventing chronic diseases such as CVDs, diabetes and cancers ^{48, 49}. Previous studies have shown that individuals who eat daily five or more servings of vegetables have approximately half the risk of developing various cancers ⁵⁰.

However, the difference with fruits is that most vegetables need to be cooked before being consumed in order to make them more appetizing or safer to eat. Overall, people enjoy the boiled vegetables in the south of China while people prefer stir-frying vegetables in the north of China. The ingredient content of vegetables prepared with heat may change to varying degrees, particularly the heat-sensitive vitamins and phytochemicals ⁵¹. Miglio et al showed that three common cooking practices (boiling, frying and steaming) have obvious effect on phytochemical contents (polyphenols, glucosinolates, ascorbic acid, and carotenoids) and total antioxidant capacity of selected vegetables, containing carrots, courgettes, and broccoli ⁵². Another study reported that effect of five domestic cooking methods including microwaving, boiling, steaming, stir-frying, and stir-frying/boiling on the nutrients and health-promoting compounds in broccoli, indicating that all cooking treatments, except steaming, led to significant losses of vitamin C and chlorophyll and significant decreases of soluble sugars and total soluble protein ⁵³. Similar reports are shown in the following Table 2. Additionally, in order to make vegetables more appetizing, high consumption of edible salt and sodium glutamate involved high-sodium intake in these cooking methods, especially in the north of China, is linked to the development of hypertension and CVDs ^{54, 55}.

Taken together, it was showed that two popular Chinese cooking methods including stir-frying and boiling could cause great losses of nutrients and bioactive components in vegetables. Therefore, a cooking method for each vegetable must be preferred to preserve the nutritional and physicochemical qualities, and proper use of condiments for a healthy diet is more likely to reduce the risk of CVDs.

Cereals grains including barley, oats, wheat, rice and rye, are staple foods in the diet of many populations, especially in developing countries, as they can provide essential nutrients such as carbohydrate energy, dietary fiber, protein, unsaturated fatty acid and a variety of phytochemicals and micronutrients ^{66, 67}. Rice, is one of the most important staple foods in China, particularly in the southern parts, while wheat and their products have played the role of traditional staple food for thousands of years in the northern China ^{68, 69}.

However, based on previous studies, it has been shown that excessive of intake of white rice was associated with a significantly increased risk of type 2 diabetes, especially in Asian (Chinese and Japanese) regions ^{70, 71}. In addition, for extended shelf life and consumer appeal, rice and wheat have to undergo different degrees of refining and milling process that will cause a reduction in fiber and essential micronutrients content ⁷². Increasing consumption of these highly polished rice and refined grain (wheat) may lead to an extremely high gastrointestinal (GI) value and high prevalence of diabetes and CVDs ^{72, 73, 74}.

Accordingly, more and more people are inclined to consume the whole grains because all of the nutrients are retained in the form of whole grains and the whole grain foods are believed to improve the quality of the diet. A number of evidences have shown that consumption of whole grains against the risk of many chronic diseases such as type 2 diabetes ^{75, 76} CVDs and some cancers ⁷⁷. The health benefits of whole grains consumption may be due to their unique phytochemicals including carotenoids, phenolics, β-glucan, and γ-oryzanol that are complementary to those in fruits and vegetables when consumed together ⁷⁸. However, it is worth noting that many of the potential beneficial compounds in whole grains become unavailable during the refining process ⁷⁹. Previous studies showed that favorable lipid profiles and glycemic control were closely related to higher intake of whole grains, but not refined grains ^{80, 81}. Thus, we should be prudent to distinguish whole-grain from refined-cereal-grain products for the prevention of chronic diseases.

Meat and processed meat products are regularly consumed in many regions of the word, providing unique eating satisfaction in the lifestyle of the modern society. They also offer high-value proteins and important nutrients such as long chain n-3 fatty acids, vitamin B family, essential trace elements and a number of other micronutrients ^{82, 83, 84}. Although there may be competition between feed and food resources or other environmental problems ⁸⁵, it is estimated that the demand for meat and animal-derived foods in the coming decades will continue to grow strongly in developing countries ⁸⁶. A rich variety of meat and meat products involved in pork, beef, lamb, poultry and fish are produced in China annually. Among them, the consumption of red meat (mostly from mammals) accounts for a larger proportion than white meat (mostly from poultry and fish). However, the red meat is deemed to play a role in both arguments for risks and benefits⁸⁷. The intake of higher amount of red meat than white meat is associated with an increased risk of chronic diseases, but it remains unclear whether the red meat intake is involved in mortality ^{88, 89}.

Influenced by the strong food culture and traditional Chinese cooking techniques, pursuit of gourmet food never seems to be interrupted. Toward this end, meat and meat products have been gone through a series of cooking treatments and processing methods. The cooking operation is a procedure usually applied prior to consumption, especially for meat and meat products, resulting in better aroma and the cooked meat is more tender when compared to the raw one. However, cooking methods also affects the nutritional value of meat due to changes in certain ingredients. Heterocyclic aromatic amines are one of the mutagenic compounds formed naturally during cooking of meat and fish ⁹⁰, which have been positively associated with carcinogenicity in several epidemiological studies ^{91, 92}. Moreover, a previous study showed that different cooking methods (hot plate, boiling, microwave, deep fat frying and oven cooking) caused 10% decrease in the amount of mineral component of beef steaks ^{93, 94}. Yingqiu Li et al reported that pre-frying and extended cooking time significantly increased lipid oxidation and fat loss of stewed pork ⁹⁵. Herein, a traditional concept in Chinese medicine, “Shanghuo” is more akin to inflammation, without specific physiological indicators and varies from person to person, and it will bring about physiological dysfunctions if it is not treated on time ⁹⁶. It is very easy to obtain “Shanghuo” with the use of large number of additives such as cinnamon, star anise, and pepper during the cooking of meat, especially in hot weather. After that, it is necessary to administrate drug and food supplements to regulate the body to a normal state.

In the southwest of China, bacon (salt meat) is quite popular with local residents due to its distinct aroma and taste. Nitrate is added to the meat as an antioxidant to develop flavor and stabilize the red color, but it must be converted to nitrite to play these roles ⁹⁷. Epidemiologic and clinical studies have linked excessive nitrate and nitrite consumption in processed meat with increased risk of thyroid dysfunction and thyroid cancer ⁹⁸, gastrointestinal cancers ⁹⁹, gout ¹⁰⁰, and chronic obstructive pulmonary disease in women ¹⁰¹. Therefore, it should be emphasized to avoid consuming too many preserved foods containing nitrite, as well as other cooking foods with too many additives.

Chinese wine culture is broad and profound. Whether it is a festival, business or entertainment dinner, wine is an indispensable element on the table. Among the different types of wine such as Chinese spirits, red wine, beer, yellow wine, fruit wine and health-care wine, Chinese spirits is the most common and popular one that is fermented from grain and usually has a high alcohol content. Although excessive alcohol consumption is undoubtedly harmful at several levels ¹⁰², consistent studies distinguishing between the consumption of spirits and wine/beer have found that only spirits increase mortality, not wine ¹⁰³ and recent studies have provided further evidence that moderate wine consumption is associated with cardiovascular protection ^{104, 105, 106}. In last two decades, French Paradox described the low CVDs incidence and mortality of the French population despite their high dietary intake of saturated fats, which actually is attributed to wine consumption ^{107, 108}. After that, in order to explain the inverse relationship between moderate wine consumption and the incidence of CVDs ¹⁰⁹, many researchers showed their strong interest in exploring the components of wine ¹¹⁰. It suggested that these effects may be ascribed to polyphenols (especially resveratrol), as well as other bioactive compounds exhibiting anticarcinogenic ¹¹¹, hypotensive ¹¹², antioxidant ¹¹³ and anti-inflammatory activities ¹¹⁴ in wine and beer. Therefore, this review is expected to serve as a reminder to those who might enjoy Chinese spirits or wine that moderate wine consumption, rather than excessive alcohol consumption, is beneficial to health.

Tea culture is also an important part of Chinese traditional culture. Tea is one of the most widely consumed beverages in China and there are a variety of teas such as green tea, white tea, black tea, oolong tea in the present market ¹¹⁵. Among them, green tea accounts for the largest share of tea production in China ¹¹⁶, which is considered to have potential health benefits by traditional medicine in Asian regions ^{117, 118}. In particular, it has been demonstrated that phenolic compounds in tea possess the bioactivity to influence the pathogenesis of many chronic diseases such as CVDs and cancers ^{117, 119, 120}.

However, it was reported that tea had a remarkable effect on non-heme iron absorption in human body, which is attributed to the flavonoids present in tea ¹²¹. Meanwhile, polyphenols in tea also has the ability to inhibit non-heme iron absorption in man, suggested by several studies in vivo ^{122, 123} and in vitro ¹²⁴. For subjects at risk of iron deficiency, it is recommended to increase heme-iron intake (mainly present in fish and poultry) and to consume tea between meals instead of during the meals ¹²⁵.

Unhealthy dietary patterns including those that are high in total sodium, fat, and refined sugar have been linked to mid- and late-life diabetes ¹²⁶, CVDs ¹²⁷, obesity ¹²⁸ and cancers ¹²⁹. The snack foods are frequently considered unhealthy and recommendations are often made to limit their consumption, mainly as part of an effort to control body weight but also to avoid intake of saturated and trans fats ¹³⁰. In recent years, processed snack foods such as French fries, candy, ice cream, popcorn, and soft drinks, make up a large proportion of the average diet and have been increasingly consumed by children and adolescents in China ^{131, 132}. These unhealthy snack foods may lead to chronic disease in adulthood begin early in life, and diet-related chronic disease risk factors ¹³³. Consequently, children and adolescents are suggested to eat less snacks with high energy and sweetener content; investigators should develop healthier snack foods including these high in fruits, vegetables and whole grains.

3. Association between Mealtimes and Health Promotion

A number of evidences have documented eating disorders in frequency and timing of meals, occurring across the globe in both developed and developing countries ¹³⁴, increasing rates of eating disorder symptoms and behaviors in both children and adults with high mortality rates and high treatment costs ^{135, 136}. Fundamentally, the circadian clock system programs daily rhythms and coordinates multiple behavioral and physiological processes, including sleep and eating ¹³⁷. Once the chronic disruption of the synchronous relationship between endogenous and exogenous circadian time may lead to the development of obesity and metabolic diseases ¹³⁸, implying the frequency and timing of meals are associated with cardiovascular health outcomes ¹³⁹.

In particular, the mealtimes play an important role in eating behavior. The food was usually eaten in three meals per day in China, consisting of breakfast, lunch and dinner, where lunch was the main meal ¹⁴⁰. Not eating at the right time or eating too much at a meal would result in the extension of the next meal time and a greater sense of satiety. Then, when you feel hungry, you have already missed the meal time. As a result, two forms of disordered eating including binge eating and night eating will appear ¹⁴¹, which is very common among young people in China. These unhealthy eating habits are often affected by social factors and are closely linked to metabolic diseases such as obesity ¹⁴², aging ¹⁴³ and other chronic diseases ¹⁴⁴. Remarkably, breakfast plays a crucial role in energy balance and health-related quality of life. It was reported that regular breakfast had a significant effect on satiety over the entire morning and aspects of cognitive performance in adolescents ¹⁴⁵. Therefore, it is suggested to establish and adhere to a regular and healthy diet, especially for children and adolescents.

4. Intake Level of Dietary Supplements in China

A dietary supplement, also called health-care product in China, is any supplement taken orally that contains a dietary ingredient, involving products such as minerals, vitamins, herbs or botanicals, and amino acids. On one hand, many people cannot achieve adequate nutrients from the diet, so they expect to strengthen nutrition from dietary supplements. In recent years, there has been an increasing need for dietary supplements, which reflects contemporary people’s growing attention to health care. On the other hand, the over-saturated dietary supplement market in developed counties such as the US also drives the need for foreign market expansion, and Chinese market is a viable market for dietary supplement. Numerous literatures on dietary supplements reported that it could be used to improve overall health and well-being of an individual as well as reduce the prevalence of nutrition-related diseases. For example, vitamins and minerals have been identified as playing a potential role in prevention of bone diseases such as osteoporosis ¹⁴⁶. Milan Holecek reviewed that branched-chain amino acid (BCAA: valine, leucine and isoleucine) supplementation exhibited a favorable effect on the prognosis and treatment of hepatic disease ¹⁴⁷. Another study suggested that a low dietary intake of antioxidant vitamins increased the incidence rate of CVDs and cancers ¹⁴⁸. However, there are still some open issues to be discussed about the intake of dietary supplements in China.

First, health-care products are rarely popularized in rural areas while the intake level of health-care products by urban residents is relatively optimistic, but there are still some unscientific and blind worship phenomena, and some people even exaggerate the efficacy of health-care products. Thus, in order to obtain additional nutrients, people in both rural and urban areas should be educated about the safety and effectiveness of dietary supplements ¹⁴⁹. Second, at present, there are many varieties of health-care products with different functions on the market, and it is very challenging for consumers who lack relevant professional knowledge to find the right product for themselves ¹⁵⁰. In this regard, consumers should attempt to read the labels that provide important information such as ingredients, content, and shelf life of a specific product. Third, most of the main components in health-care products are synthesized and extracted, leading to their poor bioavailability in human body. For instance, commercial coenzyme Q10 (CoQ10) formulations available in the market are often of poor intestinal absorption ¹⁵¹. The low oral bioavailability was mainly caused by the poor aqueous solubility in the GI tract ¹⁵². Many investigators try to introduce novel delivery systems in order to improve the absorption rate in the body ^{153, 154}, but this also bring in more chemicals, which may cause adverse reactions to the human body ¹⁵⁵. Therefore, for a balanced nutrition, it is recommended that we should scientifically and rationally deal with dietary supplements at all times.

5. Challenges of the Status Quo

Since the rapid development of China's economy, along with the continuous development of urbanization and industrialization and the accelerated pace of life, Chinese diet has also undergone major changes. On the whole, the quality of Chinese people's meals has been significantly improved, and the malnutrition of children and adolescents has basically been solved. However, some health problems still exist. For example, the diet structure varies in different regions, accompanied with some nutritional deficiencies, and the incidence rate of chronic diseases such as diabetes and obesity are on the rise. The reason is that blindly pursuing a good taste and stimulation on the tip of the tongue often overlooks some of the adverse effects caused by cooking methods and food processing. Moreover, given the China's historical and cultural background, it is estimated that some eating habits are difficult to change. Hence, only by constant education and promotion of healthy diets, combined with physical exercise, can improve the overall physical fitness of the Chinese.

6. Conclusion

Diet can be an important factor affecting not only health but also risks of diseases. A balanced and broadly varied dietary intake plays a critical role in human general health. This will require active collaborations between government, industry and academy; each of which possesses a concept of health promotion that can contribute to the realization of healthy diet for people in both rural and urban communities. Unfortunately, both Chinese traditional and modern diet composition have certain shortcomings, and it needs to be adjusted in order to achieve sufficient nutrients for the normal operation of the body. Meanwhile, proper mealtime behavior is also a guarantee of health, especially for children and adolescents. In addition, consumers should be scientifically educated about the safety and effectiveness of health-care products and investigators are definitely required to develop health-care products with relatively high bioavailability.

Acknowledgements

We would like to thank co-authors and their team members for technical support in each part of this work. We would also like to thank Professor Cao Yong of the School of Food Science of South China Agricultural University for his views on the development trend of functional food in China.

Conflict of Interest

The authors have declared that no competing interests exist.

References