Meat-based Versus Pesco-vegetarian Diet and Colorectal Cancer
Condition: Nutrition Aspect of Cancer; Diet Modification; Cancer of Colon
MeSH terms: Colonic Neoplasms
Study type: Interventional

Summary: 
      Colorectal cancer (CRC) is strongly affected by diet, with red and processed meat increasing
      risk. To understand the role of microbiome in this phenomenon and to identify specific
      microbiome/metabolomics profiles associated with CRC risk, will be studied: 1) healthy
      volunteers fed for 3 months with: a high-CRC risk diet (meat-based MBD), a normalized CRC
      risk diet (MBD plus alpha-tocopherol, MBD-T), a low-CRC risk diet (pesco-vegetarian, PVD). At
      the beginning and at the end of the intervention, gut microbiome profiles (metagenomics and
      metabolomics), and CRC biomarkers (genotoxicity, cytotoxicity, peroxidation in faecal water;
      lipid/glycemic indexes, inflammatory cytokines, oxidative stress), 2) Colon carcinogenesis:
      the same diets will be fed (3 months) to carcinogen-induced rats or to Pirc rats, mutated in
      Apc, the key gene in CRC; faecal microbiome profiles, will be correlated to carcinogenesis
      measuring preneoplastic lesions, colon tumours, and faecal and blood CRC biomarkers as in
      humans; 3) To further elucidate the mechanisms underlying the effect of different microbiomes
      in determining CRC risk, faeces from rats fed the experimental diets will be transplanted
      into carcinogen-induced germ-free rats, measuring how microbiome changes correlate with
      metabolome and disease outcomes. The results will provide fundamental insight in the role of
      microbiome in determining the effect of the diet, in particular red/processed meat intake, on
      CRC risk
    

Detailed description: 
      Colorectal cancer (CRC) is the second leading cause of cancer death in Europe. The
      geographical variation of incidence demonstrates how environmental factors, chiefly dietary
      habits, play a major role in this disease. Convincing evidence suggests that risk of CRC is
      increased by red meat and processed meat consumption (classified, as regard cancer hazard as
      2A and 1, respectively, WHO) and decreased by foods containing dietary fibers. As regarding
      other food groups, like fish, although epidemiological studies suggest a reduction of CRC
      risk associated with its consumption, the evidence for this link is considered limited;
      similarly, for non-starchy vegetables and fruits, although there is suggestive evidence of a
      protective effect, this is considered limited, and thus less convincing than that for red and
      processed meat.

      Several hypotheses are proposed to explain the positive association between red, processed
      meat and CRC: meat-based diets contain mutagens-carcinogens formed during cooking, but also
      lipid peroxidation and N-nitroso compounds whose formation is catalyzed by heme in the colon.
      Accordingly, recent experimental and epidemiological studies on the E3N cohort and on the
      randomized placebo-controlled trial SUVIMAX carried out by our group, demonstrated the
      central role of heme iron in the positive association between meat and CRC. According to
      these studies, this effect is largely explained by the ability of heme iron to catalyze
      peroxidation and induce high luminal polyunsaturated fatty acids (PUFAs) peroxidation,
      forming cytotoxic and genotoxic alkenals which will in turn induce positive selection of
      precancerous cells mutated for Apc, the key gene in CRC. On this basis, it was also
      demonstrated that antioxidants, in particular tocopherol, modulate the risk of cancer
      associated with red meat in experimental animals and humans by controlling heme iron-induced
      peroxidation. Recent data from the investigators demonstrated that microbiota is involved in
      the heme-induced peroxidation and it has been reported that the gut microbiota is required
      for heme-induced epithelial hyperproliferation and hyperplasia because of the capacity to
      reduce mucus barrier function. Notwithstanding these reports, the role of gut microbiome in
      determining cancer risk associated with red and processed meat is not clear.

      Microbial fermentation of plant-based foods, associated with a low CRC risk increases
      intestinal Short Chain Fatty Acids (SCFAs), among which butyrate, endowed with antineoplastic
      activity through its inhibition of histone deacetylase and promotion of apoptosis and
      microbial activated phytochemicals, such as polyphenols with anti-inflammatory and
      antioxidant activities. Accordingly, it is also known that the process of fermenting fibers
      to SCFAs needs intestinal bacteria because germ-free mice produce almost no SCFAs. These data
      clearly indicate that, at least part of the effect of the diet on colon carcinogenesis is
      mediated by the intestinal microbiome. Accordingly, it is well know that diet shapes gut
      microbiome composition, as described in a human rural population study and emerging evidences
      implicate an involvement of the gut microbiota in CRC. Microorganisms and their metabolites
      have been proposed to promote carcinogenesis by several mechanisms, including induction of
      inflammatory signaling pathways, genetic mutations, and epigenetic dysregulation. Recently, a
      review conducted on 31 studies (human and animal models) has shown that certain bacterial
      groups are increased (eg. Fusobacterium spp, Alistipes, Staphylococcaceae, Akkermansia spp.
      and Methanobacteriales), while others (eg. Bifidobacterium, Lactobacillus, Faecalibacterium
      spp) are consistently diminished in CRC, with consequent increase of potentially carcinogenic
      metabolites (nitrogen compounds, bile acids) and decrease of SCFAs (eg. butyrate). However,
      it is still not clear whether dysbiosis (imbalanced microbiota) is the cause or consequence
      of CRC. Tumorigenesis can indeed produce inflammation, ulceration and necrosis of the mucosa,
      by changing the microenvironment and growth conditions for different microorganisms, thus it
      is difficult to understand what comes first. And furthermore, how dietary risk is mediated by
      the interaction with the gut microbiome? How can the modulation of the microbiome promote or
      prevent the development of a microenvironment containing pro-inflammatory and carcinogenic
      metabolites that favour the neoplastic initiation process? Cohort studies with subjects
      consuming various types of diets (i.e omnivores, vegetarians, vegans) suggest that diet
      alters the intestinal microbiome as well as the cytotoxic and genotoxic activities of the
      luminal colonic content. In a study on ten volunteers following for 5 days a strictly
      vegetarian diet and then moving to a strictly carnivorous diet, it was demonstrated that the
      intestinal bacteria react very quickly (24-48 hours). In particular, bacterial species
      capable of digesting complex carbohydrates prevailed during the vegetarian diet period while
      during the animal proteins based diet, specific bacterial species were selected, such as
      Bilophila wadsworthia, which are able to metabolize proteins and produce toxic compounds like
      secondary bile acids (BA, promoters of carcinogenesis) and with great pro-inflammatory
      potential. Feeding a high-fibre low-fat African-style diet to African Americans at high risk
      of colon cancer and, vice versa, feeding a high-fat, low-fiber western style diet to rural
      Africans at low risk of cancer, causes variation in microbiome and in parameters associated
      with CRC risk. Preliminary data in humans also demonstrate that when an animal-based diet
      rich in fat and simple sugars is introduced into a traditional African diet, composed of
      cereals, legumes and vegetables, the gut microbiome shifts, leading to progressive loss of
      biochemical functions associated with SCFAs production, suggesting indeed that faecal
      microbiome may act as determinant of colon cancer risk related to the diet. Regarding heme
      iron, the investigators recently demonstrated that after a short term exposure (14 days), the
      gut microbiota of heme-fed rats was enriched with Enterobacteriaceae and B. fragilis whereas
      Roseburia spp. and Lactobacillus spp. were underrepresented. Notably, Enterobacteriaceae
      expansion is also found in Inflammatory Bowel Disease (IBD) patients at high risk for CRC and
      can induce inflammation in the host gut epithelium. Moreover, B. fragilis has been associated
      with inflammation-induced colon cancer. It has also been shown that Lactobacilli can inhibit
      iron-induced lipoperoxidation. Remarkably, the gut microbiota modulations observed after heme
      iron intake present similarities with that observed comparing colorectal cancer patients and
      healthy volunteers. However, although the association between gut microbiota and CRC is
      conceptually interesting, these outcomes do not help to explain the mechanism behind the
      modulations of the gut microbiota by the diet and the consequent impact on CRC risk. In
      addition, while many studies have been conducted for bacteria, fungi have been virtually
      unexplored by metagenomic studies, yet they are emerging as key players involved in
      autoimmune or inflammatory disorders, as recently demonstrated. Their relative
      under-representation in number compared to bacteria, results in their underestimation, since
      fungal DNA often cannot be purified using standard approaches. Preliminary results revealed a
      higher frequency of S. cerevisiae in IBD, a group pathologies associated with increased risk
      of CRC.
    

Intervention name(s): Meat-based diet; Meat-based diet supplemented with alpha-tocopherol (MBD-T); Pesco-vegetarian diet
Intervention type(s): Behavioral; Dietary Supplement; Behavioral
Intervention description(s): Diet including 4 servings per week of red meat (1 serving = 150 g), 3 servings per week of processed meat (1 serving = 50 g), and 1 servings per week of poultry (1 serving = 150 g), for a total amount of 900 g per week of meat.; Dietary intervention like the MBD with supplementation of alpha-tocopherol at a dosage of 100 mg/die. Available evidence suggests that alpha-tocopherol may help prevent colon cancer by decreasing the formation of mutagens arising from the oxidation of faecal lipids, by decreasing oxidative stress in the epithelial cells of the colon and by molecular mechanisms that influence cell death, cell cycle and transcriptional events (Pierre 2013, Bastide 2016, Bastide 2017, Diallo 2016). It is important to note that 200 mg/day of tocopherol was administered to 20,000 women for 10 years without side effects (Lee et al.,2005).; Diet excluding fresh and processed meat, poultry but including 3 servings per week of any type of fish, excluding shellfish (1 serving = 150 g), for a total amount of 450 g per week. Diet will contain other sources of proteins (e.g. eggs, dairy, legumes/beans). There is suggestive evidence that fish and vegetable consumption has protective effects against CRC (Vieira et al., 2017).
Other intervention name(s): MBD; MBD-T; PVD
Intervention MeSH terms: Tocopherols; Vitamin E; Tocotrienols; alpha-Tocopherol
Allocation: Randomized
Intervention model: Parallel Assignment
Intervention model description: Randomized parallel open dietary intervention study with 3 arms of intervention
Masking: None (Open Label)
Primary purpose: Prevention
Keywords: vegetarian; meat; fish