Some facts Consumptions and Metabolism

Digestion & Absorption 

The oral cavity, or mouth, is where food is initially broken up. Salivary enzymes, such as amylases and microbiota, aid this process by breaking down some starches into maltose and dextrin, and thereby starting the digestion process. In the stomach, a very low pH further degrades foods, and microbial populations are maintained at relatively low levels. Gastric juice in the stomach starts protein digestion. The small intestine is a very narrow tube with a large surface area and is the major site of absorption in humans – in fact, 95% of absorption of nutrients occurs here. Pancreatic enzymes and bile aid the digestive process and microbial numbers begin to rise. Finally, the transit time of the large intestine is very slow, with around 200 g of dietary contents entering per day in an adult. The dietary contents are a mixture of undigested carbohydrates, proteins, vitamins, and lipids. These help to fortify an intensively colonized microbiota, which contributes to digestion by metabolizing these substrates into organic acids, gases and nitrogenous compounds like ammonia, amines and phenols. Each of these may exert varying influences upon health

Metabolism     

Metabolism can be defined as the chemical processes by which organisms convert food into energy to maintain life, growth and to reproduce. These processes  occur inside and outside of cells in the body  and can be ‘destructive’ (catabolic) processes, which release energy by breaking down large molecules into their constituent parts (dietary fats, carbohydrates and protein) to provide  the fuel for ‘constructive’ (anabolic) processes, which involve building large complex molecules for structural and functional roles in living organisms (proteins, fats and nucleic acids). These processes occur in a series of energy-dependent steps, whereby one molecule such as glucose is broken down into smaller molecules to release energy, or, conversely, molecules are built-up to make larger molecules. These series of transformative steps are called ‘metabolic pathways’ and are regulated by enzymes (proteins that act as chemical catalysts) that promote reactions to convert substrates into products, which would not happen spontaneously. The activity of enzymes can be controlled in many different ways to regulate metabolism (rate or flux of molecule transformations through the pathway). The rate of metabolism can be estimated by measuring the rate at which energy is used by an organism.

Gut Microbiome   

   

The gut microbiome is a vast ecosystem of organisms such as bacteria, yeasts, fungi and viruses that live in our digestive pipes. Many of these organisms are vital – breaking down food and toxins, making vitamins and training our immune systems. Gut transit time and pH maintain gut microbiota populations in the stomach and small intestine at lower levels than in the large intestine, where the vast majority of microbiota reside. Metabolic capacity of the microbiota is vast, with many different end products being formed, including short-chain fatty acids (SCFA). These are thought to exert energy generation, satiety and colonocyte regulation. Fermentable carbohydrates like starch and fibers are the main substrates for SCFA generation. On the contrary, protein and lipids can be metabolized by the microbiota, but these produce toxic compounds such as ammonia and certain amines. Through the formation of metabolites, microbiota end products can onset intolerance symptoms.  The indigenous microbiome can influence the immune response both positively and negatively. More positive components of gut microbiota can be fortified: a prebiotic (such as bifidobacteria and lactobacilli) is a substrate that beneficially affects the host by targeting indigenous components thought to be positive

Nutrient–Gene Interactions  

Nutrigenetics is the science of how nutritional components in our diet interact with variations in our genes. People respond in different ways to eating certain kinds of foods, and this is because we all possess versions and combinations of genes. Sometimes copies of genes don’t function or are damaged, which can lead to obesity, metabolic diseases, or even cancer. Versions of genes (or polymorphisms) involved with regulating our body weight, for example, can lead to some people gaining weight or becoming obese. Research has shown that individuals with a lower body mass index tend to eat more legumes, fruit and fish; and it is not so much how many calories a person consumes, but rather where those calories are coming from. Vitamins and minerals also play a key role in regulating our body’s development and growth. Having enough B vitamins and folic acid within the diet can determine aspects of our overall health, as well as affect our risks of developing metabolic diseases. Consumption of certain foods can, however, decrease our risk of developing some diseases and improve our long-term health. Consuming polyphenols (found in fruits, vegetables, and nuts) alters the expression of genes related to blood pressure, improving cardiovascular function, for instance.

Personalized versus Public Health Advice    

Poor diet choices and lack of physical activity are some of the key causes of obesity, heart disease, diabetes and some cancers. Over the years, public health strategies have attempted to improve diet through campaigns, which are typically delivered on a population basis, using a ‘one size fits all’ approach. Guidelines may differ according to gender, age, weight or specific conditions such as pregnancy, and are unlikely to suit everybody. In contrast, personalized nutrition seeks to tailor dietary information according to individuals’ characteristics, including diet intake and physical health. The completion of the Human Genome Project in 2003 made it possible to tailor advice based on genetic makeup. For example, research has shown that people with specific variants of the APOE gene respond better to a diet low in saturated fat. Motivating individuals to change their dietary behaviour is arguably one of the greatest challenges in nutrition interventions, and evidence suggests that an individualized approach – through a registered nutritionist/ dietitian – helps people to follow a healthy diet more than ‘one size fits all’ public health guidance. However, public health guidance remains a vital means of raising awareness of important health issues in the population.     

Dietary Assessment

Scientists, healthcare professionals and, increasingly, members of the public are seeking new and innovative ways of assessing dietary intake. Accurate dietary assessment is vital and forms an integral part of studies that focus on exploring the relationship between diet and health. Traditional methods of assessment include: food frequency questionnaires and diet recalls, whereby individuals are required to remember the foods they have eaten over the past 24 hours to one year; and food diaries, whereby individuals are asked to record what they eat in ‘real-time’. These traditional methods are often burdensome on both the individual and the researcher. Furthermore, individuals may under-report their food intake or change their dietary behaviour, because they are aware of being assessed. Several web-based tools have been developed to improve the accuracy of traditional assessment methods. In parallel, scientists are looking towards the use of biological markers in hair, urine, blood and faeces to assess dietary exposure. Commercial smartphone applications can help consumers to track their own dietary intake; however, further research is needed to assess the accuracy of these applications and their effectiveness for weight management.