Macronutrients.pdf

Macronutrients: Protein Carbohydrates Fats Pr. Roberta FORESTI Professor of Biochemistry, Faculty of Health, UPEC [email protected] Protein Protein is a unique macronutrient in nutrition as it is a major component of all livi...

Macronutrients: Protein Carbohydrates Fats Pr. Roberta FORESTI Professor of Biochemistry, Faculty of Health, UPEC [email protected] Protein Protein is a unique macronutrient in nutrition as it is a major component of all living cells and the human body. Protein performs vital functions in the body, there are ~30 000 50 000 different proteins. Proteins are made of aminoacids (aa), which all have the same basic structure: an amino group (NH3+) and a carboxilic acid group (COO-) 21 aa are involved in the synthesis of proteins glycine aspartate histidine  Protein is vital, we cannot live without it! In growing individual protein is needed to make up new tissue. In a non-growing adult, protein is needed to replace proteins lost by ‘wear and tear’. The need of protein was demonstrated in the early nineteenth century: animals that were only fed fats, CHO and minerals were unable to maintain their body weight and showed severe wasting of muscle and other tissues.  FUNCTIONS OF PROTEINS IN THE BODY Enzymes. They perform metabolic reactions Transport proteins. They carry other substances around the body or across cell membranes Contractile proteins. They are responsible Structural proteins. They ‘hold up’ the body and provide a for muscle contraction (heart, smooth barrier, ex. bone and skin muscle)  IMPORTANT CHARACTERSTIC OF PROTEINS-NITROGEN (N) CONTENT Different proteins contain different proportion of the different aa. However, they all contain C H O and N, and in some cases also S. The most useful feature for us is the N content. glycine aspartate histidine In fact, this distinguishes protein from all the other components of both foods and tissues- H2O, fat and CHO do not contain N. Thus, if we want to measure the protein content of food or a tissue sample, all we have to do is to measure the N content. N content is also important in metabolism. Once protein enters the body it is metabolized in a variety of substances and excreted in a variety of forms. Again, N content is the feature that distinguishes protein. So, N metabolism becomes synonymous with protein metabolism! How do we measure protein content in a sample? The Kjendahl method. C and H are oxidized to CO2 and H2O 1. Sample is digested with strong sulfuric acid and heating in the presence of catalist 2. N is reduced to ammonia (ammonium sulfate) 3. Sample is neutralized with alkaline solution (NaOH), + distillation in weak acid (ex. boric acid) to form ammonium borate 4. Titrate the ammonium borate with strong acid (ex. HCl) Now we know the N content in the sample. But what is the protein content? We use the knowledge that the AVERAGE N content of protein is 16% So we divide the N content by 0.16 or………. 16 : 100=N : X (total protein) X (total protein) = N x 100/16 X (total protein) = N x 6.25 ……… multiply N x 6.25 This is an average but for some foods we can be more precise because we know that the N content is more or less than 16% Food Conversion factor Egg or meat 6.25 Dairy products 6.38 Wheat 5.70 Almonds 5.18 Peanuts 5.46 Digestion and absorption of protein Once the aa are in the body, how are they utilized? 1) Protein synthesis Biggest process for use of aa. An adult synthesises 300-400 g of protein each day 2) Oxidation aa are oxidized to urea, H2O, CO2 and energy 3) aa used in other metabolic pathways Ex. Hormones, nucleic acids aa are divided into ESSENTIAL (8/9 in man) and NON-ESSENTIAL This was discovered in rats using diets where each aa was removed and observing growth. In men it was done using nitrogen balance (intake (from diet) – output (in feces and urine)) ISOLEUCINE, LEUCINE, VALINE, THREONINE, TRYPTOPHAN, METHIONINE, PHENYLALANINE, LYSINE/HISTIDINE CYSTEINE, TYROSINE, ALANINE, ASPARTATE, GLUTAMATE, ARGININE, ASPARAGINE, GLUTAMINE, GLYCINE, PROLINE, SERINE  PROTEIN INTAKE-RECOMMENDATIONS (from EFSA) Abstract This opinion of the EFSA Panel on Dietetic Products, Nutrition and Allergies (NDA) deals with the setting of Dietary Reference Values (DRVs) for protein. The Panel concludes that a Population Reference Intake (PRI) can be derived from nitrogen balance studies. Several health outcomes possibly associated with protein intake were also considered but data were found to be insufficient to establish DRVs. For healthy adults of both sexes, the average requirement (AR) is 0.66 g protein/kg body weight per day based on nitrogen balance data. Considering the 97.5th percentile of the distribution of the requirement and assuming an efficiency of utilisation of dietary protein for maintenance of 47 %, the PRI for adults of all ages was estimated to be 0.83 g protein/kg body weight per day and is applicable both to high quality protein and to protein in mixed diets. For children from six months onwards, age-dependent requirements for growth estimated from average daily rates of protein deposition and adjusted by a protein efficiency for growth of 58 % were added to the requirement for maintenance of 0.66 g/kg body weight per day. The PRI was estimated based on the average requirement plus 1.96 SD using a combined SD for growth and maintenance. For pregnancy, an intake of 1, 9 and 28 g/d in the first, second and third trimesters, respectively, is proposed in addition to the PRI for non- pregnant women. For lactation, a protein intake of 19 g/d during the first six months, and of 13 g/d after six months, is proposed in addition to the PRI for non-lactating women. Data are insufficient to establish a Tolerable Upper Intake Level (UL) for protein. Intakes up to twice the PRI are regularly consumed from mixed diets by some physically active and healthy adults in Europe and are considered safe. 70 kg man= 0.83 g/kg x 70 kg= 58 g protein 55 kg woman= 0.83 g/kg x 55 kg= 47 g protein More for young children to support growth More during pregnancy More during lactation (Anses) Carbohydrates Carbohydrate (CHO) is a source of energy and it is the most important on a worldwide basis. CHO include 1) sugars (glucose, fructose, sucrose-disaccharide made of glucose and fructose) 2) polysaccharides (starch, glycogen, non-starch polysaccharides-dietary fibre) Table. Effect of national wealth on source of energy (from FAO Food Balance Sheets) Countries Mean Energy Intake % energy from (kcal/person/d) protein fat CHO Richest 3300 12 36 52 Intermediate 2600 11 22 67 Poorest 2000 10 15 75  SUGARS Glucose Fructose (6 carbons) (6 carbons) Little free glucose found in food Free monosaccharide in the diet Free sugar transported in blood and is the fuel Found mainly in fruit (fruit sugar) for cells and tissues (glycolysis) Used in food industry, with glucose, e.g; invert Basic unit for glycogen (storage polysaccharide sugar/fructose rich syrups in animals) and starch (storage polysaccharide in plants) It is half of the common dietary sugars lactose and sucrose  SUGARS Sucrose Lactose (glucose+fructose (glucose+galactose) Major sugar in our diet, e.g. table sugar, Occurs naturally only in milk and is the only manufactured products natural sugar in the newborn infant Consumption rises as people become more Present in products made with milk affluent Present in the water fraction that is discarded Recommended to limit intake to