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Nutrition. LIU XIAOFANG. FOOD NUTRITION AND SAFETY. protein. A protein is a complex high molecular weight organic compound consists of amino acids joined by peptide bonds. . Figure 2. Structures of Proteins .
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Nutrition LIU XIAOFANG FOOD NUTRITION AND SAFETY
protein A protein is a complex high molecular weight organic compound consists of amino acids joined by peptide bonds.
Figure 2. Structures of Proteins Take away the water about 75 % of the weight is protein. At least 10,000 different proteins in the body.
Proteins form the body's main structural elements are found in every cell and tissue. Body uses proteins for growth and to build and repair bone, muscles, connective tissue, skin, internal organs and blood. Hormones, antibodies and the enzymes are all made of protein. Without the right proteins, blood won't clot properly and cuts won't heal. if carbohydrates and fat can't meet your energy needs, proteins can be broken down and used as a source of emergency energy.
after protein is ingested, digestive enzymes break the protein down into amino acid The amino acids enter the blood stream and travel to the cells where they are incorporated into proteins the body needs. Twenty or so basic building blocks, called amino acids, provide the raw material for all proteins.
Function Proteins are essential to the structure and function of all living cells Many proteins are enzymes or subunits of enzymes. Other proteins play structural or mechanical roles, such as those that form the struts and joints of the cytoskeleton. Still more functions filled by proteins include immune response and the storage and transport of various ligands. In nutrition, proteins serve as the source of amino acids that do not synthesize those amino acids natively.
protein is one of the largest component of the diet. The metabolism of proteins releases ammonia, an extremely toxic substance. converted in the liver into urea, a much less toxic chemical, which is excreted in urine.
In chemistry, an aminoacid is any molecule that contains both amino and carboxylic acid functional groups.
Essential amino acid(EAA) cannot be synthesized from other available resources, and therefore must be supplied as part of the diet. Not all amino acids need to be supplied. 8 amino acids are generally regarded as essential, tryptophan , lysine , methionine , phenylalanine threonine , valine , leucine , isoleucine with two others, histidine and arginine, essential only in children
Foodstuffs that are lacking essential amino acids are poor sources of protein equivalents, as the body will tend to deaminate the amino acids obtained and convert proteins into fats and carbohydrates instead. a balance of essential amino acids is necessary for a high degree of net protein utilization.
In human nutritional needs, proteins come in two forms: complete proteins incomplete proteins complete proteins contain all eight of EAA that humans cannot produce themselves, all meat and other animal products are sources include beef, lamb, pork, poultry, fish, shellfish, eggs, milk, and milk products incomplete proteins lack or contain only a very small proportion of one or more EAA Protein in foods (such as grains, fruits, and vegetables) are either low, are considered incomplete proteins
Humans' bodies can make use of all the amino acids they extract from food for synthesizing new proteins, the inessential ones themselves need not be supplied by the diet, because our cells can make them ourselves. When protein is listed on a nutrition label it only refers to the amount of complete proteins in the food, though the food may be very strong in a subset of the essential amino acids.
Animal-derived foods contain all the EAA while plants are typically stronger in some acids than others. limiting amino acid the EAA found in the smallest quantity in the foodstuff.
Protein deficiency can lead to symptoms such as fatigue, insulin resistance, hair loss, loss of hair pigment, loss of muscle mass, low body temperature, and hormonal irregularities. Severe protein deficiency is fatal.
Protein-energy malnutrition (PEM) contains 3 forms. kwashiorkor (KW) , Marasmus and marasmic KW PEM represent a group of pathologic conditions associated with a nutritional and energy deficit occurring mainly in young children from developing countries at the time of weaning. frequently associated with infections, mainly gastrointestinal infections.
Kwashiorkor occurs in areas of famine, limited food supply and low levels of education lead to inadequate knowledge of proper diet. Early symptoms are fatigue, irritability, and lethargy. As protein deprivation continues, growth failure, loss of muscle mass, generalized swelling (edema), decreased immunity occur. A large, protuberant belly is common. Skin conditions (such as dermatitis, changes in pigmentation, thinning of hair, and vitiligo) are seen frequently. Shock and coma precede death.
6个月大 ，出生时有8斤半。由于母乳少，出生几天就给孩子冲奶粉食用，两个月后，体重是14斤, 现在却仅有12斤。乌黑的头发也渐渐稀疏变黄再变白 。 Skin pigmentation
Marasmus resulting from an insufficient nutritional intake associated with acute conditions (gastroenteritis) or chronic conditions (eg, tuberculosis, HIV infection). Marasmus results from a negative energy balance. a decreased energy intake increased energy expenditure, or both, Children adapt to an energy deficit with a decrease in physical activity, lethargy, a decrease in basal energy metabolism, slowing of growth, and finally weight loss. Pathophysiological changes associated with nutritional and energy deficits can be described as (1) body composition changes, (2) metabolic changes, and (3) anatomic changes.
Body composition Body mass: Body mass is significantly decreased Fat stores can decrease to as low as 5% of the body weight and be macroscopically undetectable. The remaining fat is usually stored in the liver body water: The proportion of water increases proportion of extracellular water also increases resulting in edema. protein mass can decrease up to 30% The muscle fibers are thin , Muscle cells are atrophic
Other organ mass: The brain, skeleton, and kidney are preserved, whereas the liver, heart, pancreas, and digestive tract are first affected.
This is typically a disease of impoverished countries, because of drought or political turmoil. Improving calorie and protein intake will correct it treatment is not started too late. Full height and growth potential will never be achieved in children Severe kwashiorkor may leave a child with permanent mental and physical disabilities.
Side Effects Excess protein can cause problems as well, such as causing the immune system to overreact, liver dysfunction from increased toxic residues, bone loss due to increased acidity in the blood diet high in meat could lead to high cholesterol or other diseases, such as gout. Another potential problem is that may put a strain on the kidneys.
The average person needs 50-65 grams of protein each day. In addition to meat, poultry and fish, significant amounts of protein are found in beans, milk, eggs, dairy foods, seeds, nuts, grains and soy products.
