Intro to Proteins

• Biochemistry is the study of nutritional chemistry
• Macronutrients and proteins are key course objectives
• This text will cover protein history, dietary requirements, classification, and links to cardiovascular diseases, cancer, and tooth health

Protein History

• Protein is a complex substance present in all living organisms
• Proteins are nutritionally valuable and essential for life's chemical processes
• In 1838, Jöns Jacob Berzelius coined the term "protein" from the Greek word prōteios, meaning "holding first place"
• Proteins are species-specific, and proteins of one species differ from those of another
• Proteins are also organ-specific; muscle proteins differ from other proteins within a single organism

Protein Basics

• Protein is an essential macronutrient
• Not all protein sources are equal
• Legumes like beans, lentils, and peas are high in protein and essential amino acids
• Plants synthesize all amino acids, but animals cannot
• Animal organs typically have higher protein content than blood plasma
• Muscles contain about 30% protein
• The liver contains 20-30% protein and red blood cells contain 30% protein
• Hair and bones have higher protein percentages because of their low water content
• Ribosomes are critical for protein synthesis in cells
• Serine contains an alcohol group, while cysteine has a mercapto group

Amino Acids

• Phenylalanine, tyrosine, and tryptophan have a benzene ring, which animals cannot synthesize
• Animals can convert phenylalanine to tyrosine

Protein Classification

• Proteins are classified by solubility
• Collagen is a structural protein in bones, tendons, ligaments, and skin once considered insoluble in water
• Keratin is an insoluble protein in epithelial tissues like skin and hair
• Keratin has been isolated from hair, nails, hoofs, and feathers is not attacked by proteolytic enzymes
• Albumins are water-soluble proteins
• Globulins are salted out by half-saturation with ammonium sulfate
• Pseudoglobulins are globulins soluble in salt-free water
• Euglobulins are globulins insoluble in salt-free water
• Prolamins and glutelins are plant proteins insoluble in water but soluble in 50-80% ethanol
• Muscle proteins are abundant in mammals e.g. humans
• Muscle comprises approximately 40% of a healthy adult's body weight of 70 kg which equates to 150 pounds with muscle protein comprising about 20%
• Myogen, an albumin-like fraction, contains enzymes like phosphorylase, aldolase, and glyceraldehyde phosphate dehydrogenase
• Myogen does not appear to be involved in muscle contraction
• Myosin is an example of a contractile protein, that also acts as an ATPase - hydrolyzes adenosine triphosphate

Vital Functions

• Proteins contribute to growth and maintenance
• Bodily functions depend on enzymes
• Digestion, energy production, blood clotting, and muscle contraction are bodily functions that depend on enzymes
• Hormones consist of proteins and peptides made from amino acid chains, hormones like testosterone and estrogen are steroid-based
• Amines, derived from tryptophan or tyrosine, help in the production of hormones related to sleep and metabolism
• Most of the body's hormones are made of proteins and polypeptides
• Insulin signals glucose uptake
• Glucagon signals breakdown of stored liver glucose
• Human growth hormone(hGH) stimulates tissue growth, including bone
• Antidiuretic hormone (ADH) signals the kidneys to reabsorb water
• Adrenocorticotropic hormone (ACTH) stimulates cortisol release, important for metabolism
• Some proteins provide cells and tissues with stiffness and rigidity
• Keratin is in skin, hair, and nails
• Collagen, the most abundant, is in bones, tendons, ligaments, and skin
• Elastin allows tissues to return to their original shape after stretching as it is several hundred times more flexible than collagen
• Proteins help regulate pH
• Hemoglobin is a protein in red blood cells that binds to small amounts of acid
• Maintaining normal blood pH is an important function of hemoglobin
• Other buffer systems are phosphate and bicarbonate
• Albumin and globulin maintain fluid balance by attracting and retaining water
• Lack of protein can cause reduced levels of albumin and globulin
• Reduced protein levels can lead to fluid accumulation in spaces between cells, causing swelling or edema, mainly in the stomach
• Proteins form immunoglobulins, or antibodies, to fight infection
• Antibodies are proteins that protect the body from bacteria and viruses
• Antibodies tag foreign invaders for elimination
• Without antibodies, bacteria and viruses could multiply and overwhelm the body
• Immune cells remember how to make antibodies against particular bacteria or viruses
• Antibodies respond quickly to future invasions
• Proteins transport substances throughout the bloodstream
• Nutrients, vitamins, minerals, blood sugar, cholesterol, and oxygen are substances that proteins transport
• Hemoglobin transports oxygen from lungs to body tissues
• Protein transporters are specific and only bind to particular substances
• Ferritin is a storage protein for iron
• Casein is the major milk protein supporting infant growth

Energy Provision

• Protein provides four calories per gram
• Fats provide nine calories per gram
• The body prefers to use carbohydrates and fats for energy
• The body maintains fuel reserves of carbohydrates and fats
• During fasting (18–48 hours of no food intake), the body breaks down skeletal muscle for energy
• The body uses amino acids from skeletal muscle if carbohydrate storage is low

Summary

• Protein is in muscle, bone, skin, hair, and other body parts/tissues
• Protein makes up enzymes and hemoglobin and at least 10,000 different proteins support the way we are
• Amino acids are building blocks to proteins
• There are 20+ amino acids, nine of which are essential
• Adults need a minimum of 0.8 grams of protein per kilogram of body weight per day
• 10-35% of daily calories should come from protein
• The source of the protein is important to consider

Protein Sources

• A 4-ounce broiled sirloin steak provides about 33 grams of protein and 5 grams of saturated fat
• A 4-ounce ham steak provides 22 grams of protein and 1.6 grams of saturated fat, but contains 1,500 milligrams of sodium
• Four ounces of grilled sockeye salmon provides about 30 grams of protein
• Sockeye salmon is naturally low in sodium and has just over 1 gram of saturated fat
• A cup of cooked lentils provides about 18 grams of protein and 15 grams of fiber with almost no saturated fat or sodium

Health

• Eating even small amounts of red meat regularly increases the risk of heart disease and stroke
• Substituting red and processed red meat with healthy sources, for example beans, soy, nuts, fish, or poultry reduces risk
• Plant sources of protein are more unsaturated vs meat/dairy, which lowers LDL cholesterol
• Red meat intake is associated with higher heart disease risk vs people who get protein from other sources
• Low-carbohydrate diets from plant sources have a 30% lower risk of heart disease
• Eating more red meat predicts a higher risk of type 2 diabetes
• Consuming nuts, legumes, and poultry relate to a lower risk of diabetes
• Each additional serving a day of red/processed red meat increased the risk of diabetes by 12% and 32% respectively.
• Every additional serving of red meat daily was linked to a 10% and 16% rise of cancer death
• A high consumption of red meat carries a risk of breast cancer

Bone and Weight Control

• Research theorizes that eating lots of protein requires more calcium
• Eating red meat, chicken with skin, and cheese is associated with more weight gain
• Yogurt, peanut butter, and nuts have been associated with less weight gain
• Daily consumption of beans, chickpeas, lentils, or peas helps with better weight management
• In those who ate more red and processed meat over the course of the study gained more weight, about one extra pound every four years, while those who ate more nuts over the course of the study gained less weight, about a half pound less every four years.

New Research Highlights

• Eating just two servings of red meat a week may increase the risk of type 2 diabetes
• Eating plant based sources of protein like nuts and legumes or dairy helps reduce the chance of type 2 diabetes