Nutrients & Diets.pdf

Nutrients & Diet Dr. Maritza Roxana Garcia Modified by Dr. Flores OBJECTIVES 1.- Define diet and nutrients 2.- Know the main classes of nutrients (carbohydrates, proteins and fats) their structures and different types, as well their relevance in human health. 3.- Learn what is the Glycemic index a...

Nutrients & Diet Dr. Maritza Roxana Garcia Modified by Dr. Flores OBJECTIVES 1.- Define diet and nutrients 2.- Know the main classes of nutrients (carbohydrates, proteins and fats) their structures and different types, as well their relevance in human health. 3.- Learn what is the Glycemic index and calculate the Glycemic load. 4. Identify all essential macronutrients, where are they obtained from and the clinical implications. 5.- Understand how food intake is regulated, including all actors that take a role in this mechanisms. 6.- Know the differences between enteral and parenteral nutrition. 2 INTRODUCTION Nutrition is an essential interaction of the organism with the environment. It affects susceptibility to disease. BASIC DEFINITIONS Diet is the total of all the foods and drinks ingested by an individual Nutrients are chemically defined components of food required by the body. NUTRITION • • • To survive, we need oxygen, water, and nutrients. One can exist without oxygen for minutes only, but we can survive without water for 3 days. With these two supplied, a human can survive without food for between 60 and 90 days. FUNCTIONS OF NUTRIENTS • • • Main classes of nutrients can be used to produce energy. The main role of vitamins and other micronutrients is participation in enzymatic reactions as cofactors or components of enzyme prosthetic groups. Minerals are essential for the maintenance of membrane potential, osmotic equilibrium, and bone structure. MAIN CLASS OF NUTRIENTS The main nutrients are carbohydrates (including fiber), fats, proteins, minerals, and vitamins. Carbohydrates, proteins, fat, fiber, and some minerals are macronutrients. Vitamins and trace metals are micronutrients. CARBOHYDRATES Carbohydrates and fats are the main energy sources. Dietary carbohydrates include refined carbohydrates, such as the sucrose in sweets, drinks, and fruit juices, and complex carbohydrates, such as the starch present in grains and potatoes. Fiber is carbohydrate that is indigestible by the human gut, such as cellulose, hemicellulose, lignin, pectin, and β-glucan. There is soluble & insoluble. GLYCEMIC INDEX The glycemic index (GI) is the system of ranking of the carbohydratecontaining foods according to the degree of increase in blood glucose that takes place after their ingestion. The effect of a standard dose (25 or 50 g) of a particular food on plasma glucose concentration is tested and compared with the reference nutrient (e.g. glucose). • • • LOW GIà Slower absorption and digestion. The low-GI foods control postprandial glycemia and insulinemia and are beneficial for people with diabetes and better for weight control. Low-GI foods tend to be high in fat and low in carbohydrate and fiber. The GI is expressed on a scale of 1 to 100 (low GI is 0–55, moderate 56–69, and high >69). • High-GI foods are digested and absorbed rapidly and stimulate the craving/reward areas of the brain. • Metabolically, these carbohydrates are also strong stimulators of hepatic lipogenesis and promote visceral fat deposition through insulin-mediated pathways and SREB1c transcription factor. Thus the idea that eating carbohydrates avoids fat deposition in tissues is a falsity. GLYCEMIC LOAD It translates the qualitative information contained in the GI into data that can be used to calculate the carbohydrate content of a given portion of food. GL = GI x CHO (grams per serving) /100 Example: Carrots (peeled and boiled) have a GI of 47. Let’s say we have 5 g per serving of carrots… what is the GL? PROTEINS Proteins provide cell structure and are responsible for many of the cell's functions, communications, and signaling. • They serve as the “last resort” energy substrate: catabolic states are typically associated with release amino acids from muscle, and thus with muscle wasting. • Due to the different composition of animal and plant proteins, eating no animal products at all may lead to nutrient deficiencies, such as those of essential aminoacid, vitamin B12 , calcium, iron, and zinc. • Protein requirements change during the life cycle. SATURATED FATS palmitic acid (C-16) stearic (C-18) myristic (C-14) lauric (C-12) FAT • Fats are the most important nutrients used for energy storage. • Lipids also provide thermal insulation, are essential components of biological membranes and serve as signaling molecules. Fats are divided into saturated and unsaturated (the latter being either mono- or polyunsaturated). Trans fatty acids are by-products of the hydrogenation process of liquid vegetable oils. Consumption of trans fatty acids are associated with increased risk of coronary disease. FAT Monounsaturated fatty acids are present in all animal and vegetable fats. • Oleic acid (ω-9) is the only significant dietary monounsaturated fatty acid • α-linolenic (ω-3), eicosapentaenoic (ω -3), and docosahexaenoic (ω-3) acids are present primarily in fish, shellfish, and phytoplankton, and also in some vegetable oils such as olive, safflower, corn, sunflower, and soybean oil, as well as in leafy vegetables. Arachidonic acid (ω-6) and its precursor, linoleic acid (ω-6) are present in soybean and canola oils and in fish oils. • Olive oil is a particularly rich source of monounsaturated fats. Polyunsaturated FA ESSENTIAL NUTRIENTS Essential (limiting) nutrients are these that cannot be synthesized in the human body. Essential nutrients include essential amino acids, essential fatty acids (EFA), and some vitamins and trace elements. *Note that carbohydrates are not essential nutrients. Vitamins and trace metals are important for the catalysis of chemical reactions, acting as coenzymes and forming functionally important prosthetic groups of enzymes. ESSENTIAL AMINOACIDS & FATS Eg. PYRUVATE DEHYDROGENASE COMPLEX Five coenzymes are required for PDC activity: thiamine pyrophosphate, lipoamide (lipoic acid bound in amide linkage to protein), CoA, FAD, and NAD+. Four vitamins are required for their synthesis: thiamine, lipoic acid, pantothenic acid, riboflavin, and nicotinamide. REGULATION OF signals are mediated FOOD INTAKE by2. These the adipokine leptin and by insulin. Food intake is controlled by hunger (a desire to eat) and appetite (a desire for a particular food). • • 3. In response, the brain sends signals through a complex network of neuropeptides that regulate appetite and hunger. Main centers regulating appetite are in the hypothalamic arcuate and paraventricular nuclei in the central nervous system (CNS). The brain regulates energy homeostasis and is also the primary regulator of body weight. 1. Regulation of food intake is accomplished by signals generated in the adipose tissue, pancreas, stomach, and brain. REGULATION OF FOOD INTAKE Leptin • • • • Its secretion is linked to the adipose tissue mass and to the size of adipocytes. Acting in the CNS, it decreases food intake. It affects metabolism by stimulating fatty acid oxidation and by decreasing lipogenesis. Importantly, it also decreases ectopic deposition of fat in liver or muscle. Adiponectin • Stimulates glucose utilization in muscle and increases fatty acid oxidation in muscle and the liver. • It also decreases hepatic glucose production. • Adiponectin increases insulin sensitivity; LOW concentrations leads to insulin resistance and hepatic steatosis. REGULATION OF FOOD INTAKE • Physical training increases adiponectin expression and upregulates its receptors in the skeletal muscle. Conversely, its concentration decreases in obesity and in type 2 diabetes. • Low levels of adiponectin are also associated with lowgrade inflammation, oxidative stress, and endothelial dysfunction. Adiponectin receptors activate the PPARα, which in turn regulates fatty acid metabolism. NUTRITIONAL SUPPORT • • • • Patients unable to eat would need nutritional support if they have been (or will be) unable to take food for more than 7 days. Ranges from simple assistance with meals, to enriched or special-consistency diets, to enteral nutrition and total parenteral nutrition. The optimal route is oral intake. If the GI tract is nonfunctional, nutritional support can be provided by the intravenous route. ENTERAL NUTRITION • If oral intake is impossible, but the gastrointestinal (GI) tract is functional, enteral feeding is considered. • This could be provided through the nasogastric or nasojejunal route. • The alternative is using the percutaneous endoscopic gastrectomy (PEG), which provides direct access to the stomach. Standard enteral feeds contain carbohydrate, protein, fat, water, electrolytes, vitamins, and minerals, including trace elements. Predigested feeds contain short peptides or free amino acids. PARENTERAL NUTRITION • Total parenteral nutrition is appropriate when the gastrointestinal tract does not function. • • • • Exampleà intestinal obstruction or when large parts of it have been surgically removed Consists of intravenous feeding that covers all the nutritional requirements Contain fluids, glucose (dextrose), amino acids, and fats given as lipid emulsion. Vitamins, minerals, and electrolytes are also included. EXAM LIKE QUESTION Mary was recently diagnosed with insulin resistance (prediabetes). Her doctor explained to her that high glycemic index (GI) foods are bad, and that there is a difference between carbohydrates, especially in regards of the degree they increase glucose levels after digestion. She should be eating low glycemic index (GI) foods. The following are effects of high glycemic index foods in the body, EXCEPT…. A. B. C. D. E. Stimulate of hepatic lipogenesis. Reduce visceral fat deposition via insulin Activate SREB1c transcription factor Increase post prandial peaks of insulin Stimulate the craving/reward areas of the brain QUESTIONS? REFERENCES Baynes, J., & Dominiczak, M. H. (2019). Medical biochemistry. Elsevier Health Sciences. CHAPTER 32, 471-487