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The preventability estimate for colorectal cancer (CRC) is approximately 50%, highlighting the huge potential for altering modifiable lifestyle factors (including diet and body fatness) in order to reduce risk of this common malignancy. There is strong evidence that dietary factors (including intake of wholegrains, fibre, red and processed meat and alcohol) affect CRC risk. The lack of positive intervention trials and limited mechanistic understanding likely explain limited public health impact of epidemiological observations, to date. An alternative strategy for nutritional prevention of CRC is use of supplements that provide higher individual nutrient exposure than obtained through the diet (chemoprevention). There are positive data for calcium and/or vitamin D and the n-3 fatty acid EPA from polyp prevention trials using colorectal adenoma as a CRC risk biomarker. Although CRC is an obesity-related malignancy, there remains a paucity of observational data supporting intentional weight loss for CRC risk reduction. Some types of obesity surgeries (Roux-en-Y gastric bypass) might actually increase subsequent CRC risk due to alteration of local intestinal factors. There is intense interest in nutritional therapy of patients after diagnosis of CRC, in order to impact on recurrence and overall survival (now often termed cancer interception). In conclusion, nutritional prevention of CRC continues to hold much promise. Increased mechanistic understanding of the role of individual nutrients (linked to intestinal microbiota), as well as a precision medicine approach to CRC chemoprevention and interception based on both tumour and host factors, should enable translation of nutritional interventions into effective CRC risk reduction measures.
Symposium 4: GI Cancers, the role of nutrition in prevention, pathology and management
Nutrition and gastrointestinal cancer are inextricably linked. The metabolic effects of cancer along with changes in dietary intake, the development of cancer cachexia and the presence of sarcopenia can influence changes in body composition. These have a negative impact on quality of life and tolerance to cancer treatment. Treatment for cancer presents some significant nutritional challenges as nutrition impact symptoms may develop, be exacerbated by treatment and may contribute to a worsening in nutritional status. Nutrition screening and assessment should be an integral part of holistic patient care. The provision of appropriate, evidence-based dietary advice should occur before, during and after cancer treatment. Appropriate and timely methods of nutritional support across the spectrum of gastrointestinal cancer are needed to ensure that people are adequately supported during courses of treatment that can span weeks and months. These can range from standard approaches of supplementing oral intake to complex interventions such as managing high output intestinal stomas. The gastrointestinal tract is particularly susceptible to impact from systemic anti-cancer treatments and radiotherapy. Gastrointestinal late effects of cancer treatment are now recognised to present particular challenges in terms of both medical and nutritional management. These late effects have a significant impact on the individual and their quality of life in addition to implications for the health service. Dietary intake following cancer treatment has an impact on quality of life and future research may demonstrate its influence on the risk of recurrence of gastrointestinal cancer.
Nutrition support involves the use of oral supplements, enteral tube feeding or parenteral nutrition. These interventions are considered when oral intake alone fails to meet nutritional requirements. Special diets and oral supplements are usually the first approach to managing malnutrition; however, their role becomes limited when oral intake is restricted or if swallowing is unsafe. Enteral tube feeding or parenteral nutrition are alternative means of providing nutrition support for this select group of patients. Percutaneous endoscopic gastrostomy (PEG) feeding was introduced into clinical practice in 1980. It describes a feeding tube placed directly into the stomach under endoscopic guidance. It is an established means of providing enteral nutrition to those who have functionally normal gastrointestinal tracts, but who cannot meet their nutritional requirements due to inadequate oral intake. The intervention is usually reserved when nutritional intake is likely to be inadequate for more than 4–6 weeks. Although the benefits of PEG have been shown for a select group of patients, there currently exists concerns about the increasing frequency of this intervention, and also uncertainty about the long-term benefits for certain patients. The 2004 UK National Confidential Enquiry into Patient Outcome and Death report emphasised this concern, with almost a fifth of PEG being undertaken for futile indications that negatively influenced morbidity and mortality. The present review paper discusses the indications for, controversies surrounding and complications of gastrostomy feeding and provides practical advice on optimising patient selection for this intervention.
The health benefits of fruit, vegetables and dietary fibre have been promoted for many years. Much of the supporting evidence is circumstantial or even contradictory and mechanisms underlying health benefits of specific foods are poorly understood. Colorectal cancer shows marked geographical differences in incidence, probably linked with diet, and explanations for this require knowledge of the complex interactions between diet, microbiota and the gut epithelium. Dietary fibres can act as prebiotics, encouraging growth of saccharolytic bacteria, but other mechanisms are also important. Some but not all soluble fibres have a ‘contrabiotic’ effect inhibiting bacterial adherence to the epithelium. This is particularly a property of pectins (galacturonans) whereas dietary fructans, previously regarded as beneficial prebiotics, can have a proinflammatory effect mediated via toxic effects of high butyrate concentrations. This also suggests that ulcerative colitis could in part result from potentially toxic faecal butyrate concentrations in the presence of a damaged mucus layer. Epithelial adherence of lectins, either dietary lectins as found in legumes, or bacterial lectins such as the galactose-binding lectin expressed by colon cancer-associated Fusobacterium nucleatum, may also be important and could be inhibitable by specific dietary glycans. Conversely, emulsifiers in processed foods may increase bacterial translocation and alter the microbiota thus promoting inflammation or cancer. Focusing on one condition is of limited value although in developing public health messages and growing evidence for impacts of dietary components on all-cause mortality is gaining more attention. We are only just starting to understand the complex interactions between food, the microbiota and health.
Symposium 1: Nutrition, inflammation and pathobiology
Dietary restriction of fermentable oligosaccharides, disaccharides, monosaccharides and polyols (FODMAP) is clinically effective and a commonly utilised approach in the management of functional symptoms in irritable bowel syndrome. Despite this, the low FODMAP diet has a number of challenges: it can alter the gut microbiota; impact nutrient intake and diet quality; is complex to understand; requires the patient to be adequately supported to follow the diet accurately and safely; and lastly, not all patients respond to the diet. The current review highlights the evidence for the clinical effectiveness of the low FODMAP diet, but focusses on the challenges associated with the diet to the patient, health professionals and the wider healthcare service. Finally, the review discusses research findings and practical guidance for how these challenges can be minimised and mitigated. The low FODMAP diet is a useful management strategy for irritable bowel syndrome, with data from clinical trials suggesting a 50–80% response rate, and when administered appropriately, the challenges to implementing the diet can be overcome so that these outcomes can be realised effectively and safely in clinical practice.
Symposium 2: Sensing and signalling of the gut environment
In recent years, the importance of the gut microbiota in human health has been revealed and many publications have highlighted its role as a key component of human physiology. Owing to the use of modern sequencing approaches, the characterisation of the microbiome in healthy individuals and in disease has demonstrated a disturbance of the microbiota, or dysbiosis, associated with pathological conditions. The microbiota establishes a symbiotic crosstalk with their host: commensal microbes benefit from the nutrient-rich environment provided by the gut and the microbiota produces hundreds of proteins and metabolites that modulate key functions of the host, including nutrient processing, maintenance of energy homoeostasis and immune system development. Many bacteria-derived metabolites originate from dietary sources. Among them, an important role has been attributed to the metabolites derived from the bacterial fermentation of dietary fibres, namely SCFA linking host nutrition to intestinal homoeostasis maintenance. SCFA are important fuels for intestinal epithelial cells (IEC) and regulate IEC functions through different mechanisms to modulate their proliferation, differentiation as well as functions of subpopulations such as enteroendocrine cells, to impact gut motility and to strengthen the gut barrier functions as well as host metabolism. Recent findings show that SCFA, and in particular butyrate, also have important intestinal and immuno-modulatory functions. In this review, we discuss the mechanisms and the impact of SCFA on gut functions and host immunity and consequently on human health.