MD PhD Walter Willett - Red meat & Cancer скачать в хорошем качестве

MD PhD Walter Willett - Red meat & Cancer

The importance of proteins in the diet has been increasingly acknowledged over the last two decades as a result of new scientific findings in the field of nutrition. The value of proteins as an essential source of amino acids is well documented, but recently it has been recognized that dietary proteins exert many other functionalities in vivo by means of biologically active peptides. Inactive within the sequence of the parent protein, such peptides can be released by digestive enzymes during gastrointestinal transit (Bhat 2015). Defined as “a food component that can affect biological processes or substrates and, hence, have an impact on body function or condition and ultimately health”, a bioactive dietary substance should give a measurable biological effect in the range of doses it is usually assumed in the food and this bioactivity should be measured at a physiologically realistic level. Following this definition, milk, meat, fish and egg-derived bioactive peptides are their respective components that are able to influence some physiological functions, finally acting on body health condition. (Bhat 2015). By 1900, the surgeon William Banks had suggested that the increased incidence of cancer in his lifetime was related to the consumption of “butcher's meat” (Haddon 1900). More than 115 y later, a vast number of large-scale epidemiological studies have consistently shown a positive association between high red and/or processed meat consumption and a range of chronic diseases, including colorectal cancer, coronary heart disease and type 2 diabetes (Hecke 2017). High intakes of red meat and poor digestion of meat are positively associated with elevated risk of colonic cancer. This may in part be mediated by the production of the carcinogenic N-Nitroso Compounds (NOCs) and heterocyclic amines as a result of cooking at high temperatures; however, the additional possibility remains that proteins which are incompletely digested may enable the generation of carcinogenic by-products in the large intestine (Patel 2013). Dietary differences in the world likely contribute to global variations in cancer cases. Meat is an important source of proteins and provides essential amino acids. It is one of the largest dietary sources of heme. Epidemiological and experimental studies have suggested that the high heme content in red meat is associated with several diseases, including heart diseases, diabetes and cancer. Red meat (beef, lamb and pork) has 10-fold high heme content as compared to white meat (chicken). Studies have shown that an increased risk of several types of cancer is associated with diets high in red meat. On the contrary, consumption of substantial amounts of green vegetables is associated with decreased risk of colon cancer, likely because vegetables contain low levels of heme iron. Below we provide an overview of recent epidemiological data showing the association of increased risk of cancer with high heme iron intake (Hooda 2014). A number of studies have demonstrated a positive association between high intake of red meat and colorectal cancer (CRC). However, the association between red meat intake and other cancer types such as gastrointestinal, lung cancer, pancreatic, breast and esophageal are understudied and less consistent (Hooda 2014). Colorectal cancer is the third leading cause of death around the world and accounts for more than 1 million cases and 600,000 deaths each year. CRC is most commonly associated with dietary preferences high in red meat, suggesting that the risk of CRC can be reduced by controlling dietary intake (Hooda 2014). In 2011 a meta-analysis of prospective cohort studies of colon cancer reported heme intake of 566,607 individuals and 4734 cases of colon cancer. The study compared the RR of subjects with highest category of heme intake with those in lowest category. In their analysis of experimental studies in rats with hemically induced colon cancer, they showed that dietary hemoglobin and red meat promote a putative cancer lesion, an aberrant cryptic foci (Hooda 2014). Low pH of stomach releases heme-containing proteins hemoglobin and myoglobin from dietary meat (Hooda 2014). Several potential mechanisms have been suggested to explain the association between high intake of red meat and the risk of colorectal cancer. It has been shown that under anaerobic conditions, hemoproteins, hemoglobin and myoglobin in meat can react with nitric oxide to form nitrosating agents (Hooda 2014). Soon after transglutaminase was discovered, it was noted that some proteins might serve as amine acceptors, whereas others incorporated insignificant quantities of amine. It was later found that native hemoglobin was not a transglutaminase substrate, but that heat denaturation of hemoglobin made it a good substrate, at least at certain glutamine positions (Toone 2011).