UNIT 3 - MACRO NUTRIENTS (Proteins)

Introduction

Protein is the basic material of every living cell. It is the only nutrient that can make new cells and rebuild tissues. Therefore, an adequate amount of protein in the diet is essential for normal growth and development and for the maintenance of health.

Definition

• Proteins are large, complex, organic compounds made up of carbon, hydrogen, oxygen, and nitrogen. The presence of nitrogen distinguishes proteins from carbohydrates and fats. Apart from nitrogen, elements such as sulphur, phosphorus, copper, and iron are also found in some proteins.
• They are composed of one or more chains of amino acids. 
• Proteins are fundamental components of all living cells and include many substances, such as enzymes, hormones, and antibodies that are necessary for the proper functioning of an organism. 
• They are essential in the diet of animals for the growth and repair of tissue and can be obtained from foods such as meat, fish, eggs, milk, and legumes.

Basic Structure of a Protein

Proteins are made up of hundreds or thousands of smaller units called amino acids, which are attached to one another in long chains.
There are 20 different types of amino acids that can be combined to make a protein. 9 are essential and 11 are non essential.
The sequence of amino acids determines each protein’s unique 3-dimensional structure and its specific function.
The bond which unites the two amino acids is called a peptide bond.
 One amino acid has
1 carboxyl group (COOH)
1 amino group or nitrogen group (NH2)
1 hydrogen (H)
And 1 functional group (R)

NH2CHRCOOH.

Amino Acids

Essential amino acids

Those amino acids which cannot be synthesized in sufficient amounts by the body and must be provided by the diet are called essential amino acids. The human adult requires eight essential amino acids, while growing children require ten essential amino acids. Essential amino acids are indispensable to life.

1. Isoleucine
2. Leucine
3. Lysine
4. Methionine
5. Phenylalanine
6. Threonine
7. Tryptophan
8. Valine
9. Histidine (for children)
10. Arginine (for children)

Non essential amino acids

Non-essential amino acids do not mean that these amino acids are not required by the body. They are termed non-essential because they are not dietary essentials. If they are lacking in the diet, they can be synthesized by the body from other amino acids.

1. Alanine
2. Aspargine
3. Aspartic Acid
4. Cysteine
5. Glutamine
6. Glycine
7. Hydroxylysine
8. Hydroxyproline
9. Proline
10. Serine
11. Tyrosine

Classification of protein based on origin

Classification of protein based on characterization

Classification of protein based on function

Dietary Sources of Proteins

Proteins are present in both plant and animal foods.

Animal food sources
Animal food sources provide the highest quality or complete proteins such as eggs, milk and milk products (cheese, paneer, mawa, milk powder, curds, condensed milk),meat, fish, shellfish, poultry, and organ meat.
Plant food sources

• Pulses, especially soya bean (43 per cent protein) and its products such as soya milk textured vegetable proteins: nuts and oilseeds-groundnuts and gingelly seeds are important sources of protein in the Indian diet. 
• Cereals contain 6-12 per cent partially complete proteins and as they form bulk of the diet, they contribute significantly to the protein content.
• Vegetables contain a small percentage of good quality protein (approx 1-3 percent).
• Fruits do not contribute towards protein content of the diet.

Functions of Proteins

Proteins perform three main functions

1. Structural function 
2. Regulatory function 
3. Energy 

Structural function

Growth: The primary function of food protein is the synthesis of body cells. Proteins are the major constituent of muscles, organs, endocrine glands, and collagen. Collagen is the main structural protein of bones, tendons, ligaments, skin, blood vessels, and connective tissue. All enzymes and some hormones, e.g., insulin are made up of proteins. Proteins are required for the formation and growth of all these substances. During periods of rapid growth, additional proteins are needed for synthesis of body components.
Maintenance or wear and tear: Protein is required by all age groups for continuous maintenance of all the cells in the body. Cells have a varying life span and proteins are needed to replace the old or worn out cells.

Regulatory function

• All amino acids from food protein are used for growth and maintenance. Certain amino acids and proteins have highly specialized functions in the regulation of body process and protection against disease. Some of the regulatory functions are as follows.
• Haemoglobin, an iron containing protein in the red blood cells, performs an important role by transporting oxygen to the tissue cells. 
• Plasma proteins maintain water balance and regulate the osmotic pressure in the body. 
• Antibodies that are protein in nature perform a protective function by increasing the body’s resistance to disease. 
• All enzymes and some hormones, e.g. insulin are made up of protein. The hormone insulin regulates blood sugar levels. Enzymes act as specific catalysts to metabolic process in the body.  
• Some amino acids have specific functions, e.g. tryptophan serves as a precursor for niacin, a complex vitamin. The amino acid tyrosine in combination with iodine forms the hormone thyroxine. 

Energy

• Like carbohydrates, proteins too provide 4 kcal/g when broken down in the body. If the diet does not supply adequate calories from carbohydrates and fats, the proteins from the diet will be oxidized to meet the energy needs of the body. Protein is used by the body as a source of energy only when no other source of energy is available.

Methods of improving protein quality

• Animal protein contains all essential amino acids in correct proportions and amounts and is good quality proteins. Four essential amino acids are in short supply in plant proteins. They are lysine, methionine, threonine, and tryptophan. Proteins in plant foods are generally deficient in one or two essential amino acids. Cereals are poor in lysine and pulses are poor in methionine.
• Protein will be synthesized only when all amino acids, which form the protein, are present simultaneously. Vegetable proteins are partially complete proteins. These two points should be kept in mind while improving the protein quality of a meal.

The protein quality of a mainly vegetarian diet can be improved in the following ways.

1. By including a small quantity of complete protein food in every meal. Complete protein foods such as milk, curds, paneer, cheese, buttermilk, and eggs could be used in small quantities in various preparations instead of including it in one meal only, e.g. cereal and milk, egg or cheese sandwiches, french toast, raitha, curd rice, or buttermilk at all meals in place of bowl of curd in one meal. 
2. Correct mixtures of plant foods could provide all essential amino acids in suitable proportions and amounts. Cereal and pulse combinations will complement each other as cereals provide methionine, which is lacking in pulses, and pulses provide lysine, which is lacking in cereals, when cereal and pulses are consumed together in the same meal, e.g. missie roti, thalipeeth, puran poli, idli, and rajma chawal. This is possible because the same amino acids are not missing from all plant foods. 
3. Synthetic amino acids may be added to processed foods to compensate for the amino acid deficient in them, e.g., lysine enriched bread. Textured  vegetable proteins are used successfully to improve the protein quality and reduce the cost of protein rich foods.
4. When plant proteins are consumed with a small quantity of animal protein, the quality of the mixture is likely to be as effective as if only animal protein has been consumed. A good rule while planning menus would be to include some animal proteins at each meal instead of concentrating it all in one meal.

Whey Protein

• Whey protein is a mixture of proteins isolated from whey, which is the liquid part of milk that separates during cheese production.
• Milk actually contains two main types of protein: casein (80%) and whey (20%).
• Whey is found in the watery portion of milk. When cheese is produced, the fatty parts of the milk coagulate and the whey is separated from it as a byproduct.
• If you've ever opened a yogurt container to see liquid floating on top — that’s whey. Cheesemakers used to discard it before they discovered its commercial value.
• After being separated during cheese production, whey goes through various processing steps to become what people generally recognize as whey protein — a powder that is added to shakes, meal replacements and protein bars .
• Whey protein doesn't taste very good on its own, which is why it’s usually flavored. Chocolate-, vanilla- and strawberry-flavored powders are popular.
• It's important to read the ingredients list, as some products may have unhealthy additives like refined sugar.
• Taking whey protein is a convenient way to add 25–50 grams of protein on top of your daily intake.
• This can be important for bodybuilders and gym enthusiasts, as well as people who need to lose weight or are simply lacking protein in their diet.

Soy Protein

• Soybeans are among the best sources of plant-based protein.
• The protein content of soybeans ranges from 36 to 56% of the dry weight .
• One cup of boiled soybeans (172 g) contains around 29 grams of protein .
• The nutritional value of soy protein is good, although the quality is not quite as high as animal protein .
• The main types of protein in soybeans are glycinin and conglycinin, which make up approximately 80% of the total protein content. These proteins may trigger allergic reactions in some people.
• Consumption of soy protein has been linked with a modest decrease in cholesterol levels.

UNIT 4 - MICRO NUTRIENTS (Vitamins)

What are Vitamins?

• Organic molecules with a wide variety of functions
• Cofactors for enzymatic reactions
• Essential, supplied in the diet
• Two distinct types: Fat soluble (A, D, E, K)
• Water soluble (B – complex, C)

Vitamins are organic molecules that are essential for normal  health and growth. They are required in trace amounts and must  be obtained from the diet because they are not synthesized in the  body. Before vitamins were discovered, it was known that lime  juice prevented the disease scurvy in sailors and that cod liver oil  could prevent rickets. In 1912, scientists found that, in addition to  carbohydrates, fats, and proteins, certain other factors called  vitamins must be obtained from the diet.

Source: https://www.slideshare.net/syed_ismail/vitamins-29442747

Author : Dr. Syed Ismail Ibrahim, Professor

Published on: Dec 23, 2013

UNIT 3 - Macro Nutrients (Lipids)

Introduction

• The basic use of fats and oils in cookery is to add richness and flavor to food and as a cooking medium to fry or cook food. They improve the texture of various preparations such as cakes, pastries and biscuits.
• Fats and oils are found in plants, animals and marine foods.
• They are organic compounds composed of C, H and O
• Collectively known as LIPIDS
• Immiscible in water but soluble in organic solvent. (Ether, Chloroform, Benzene and Acetone)
• Unlike carbohydrates – contains small proportion of O and larger proportion of H and C
• Provide more energy per gram than carbohydrates.

Healthy Lipids

Lipids important to health are

• Fatty acids
• Fats
• Oils
• Phospholipids
• Lipoproteins
• Sterols 

Classification of Lipids

Saturated Fatty Acids

• Fats that are tightly packed are called saturated fats. There are some exceptions, but most are solid at room temperature.
• These are found in animal foods such as meat, butter, cheese, and egg yolk and in plant foods such as coconut oil, palm oil, and cocoa butter. 
• Hydrogenated fats used in bakery products and confections have a high percentage of saturated fatty acids. 
• Stearic acid, palmitic acid, myristic acid, and butyric acid are some of the saturated fatty acid. 
• A maximum of 10% of our total calories should come from saturated fats.

Sources of saturated fat include:

• Red meat
• Some pork and chicken products
• Dairy products including butter, shortening and cheese
• A diet high in saturated fat may raise your low-density lipoprotein (LDL)cholesterol levels. This will raise your risk of heart disease and type 2 diabetes.

Saturated Fatty Acids present in some food items

Unsaturated Fatty Acids

• Unsaturated fats are loosely packed. They tend to be liquid at room temperature.
• Replacing saturated fat with unsaturated fat can improve your health. Unsaturated fat comes from plants. It’s found in:
•     vegetable oils, olives, nuts and seeds, some fish
• There are two main types of unsaturated fat:
• Monounsaturated fats
• Monounsaturated fats can help improve your cholesterol levels and lower your risk of cardiovascular disease. It may also help you control your insulin levels and blood sugar.

Foods that contain monounsaturated fats include:
olive oil
peanut oil
canola oil
avocados
most nuts
most seeds

Polyunsaturated fats

• Your body needs polyunsaturated fats to function. This type of fat helps with muscle movement and blood clotting. Since your body doesn’t make it, you have to get it in your diet.
• Polyunsaturated fats can be further divided into two types: omega-3 and omega-6 fatty acids.
• Omega-3 fatty acids may be beneficial to the heart. 
• Omega-3 fatty acids can be found in:
• fatty fish, such as sardines, tuna, salmon, trout, mackerel, and herring
• ground flax and flaxseed oil
• non-hydrogenated soybean oil
• safflower oil
• sunflower oil
• canola oil
• walnuts
• sunflower seeds
• chia seeds
• hemp seeds

Unsaturated Fatty Acids

Polyunsaturated fats can be further divided into two types: omega-3 and omega-6 fatty acids.
Omega-6 fatty acids may also help protect against cardiovascular disease. But there’s debate about the inflammatory role of omega-6’s
Omega-6 fatty acids can be found in:
safflower oil
soybean oil
sunflower oil
walnut oil
corn oil
Research has found that repeatedly heating oils can decrease their antioxidant activity and increase free radical production, which may lead to poor health effects. Avoid overheating or burning of oils to keep their nutrient content.

Essential Fatty Acids

• EFAs are a special type of “good fat”. They are also essential nutrients; sometimes called vitamin F. 
• Essential nutrients are necessary for life, but must be obtained through diet because the body cannot make them. 
• EFAs are required for the proper structure and function of every cell in the body, and are important for optimal health. 
• EFAs increase the absorption of vitamins and minerals; nourish the skin, hair and nails; promote proper nerve functioning; help produce hormones; ensure normal growth and development; and prevent and treat disease.
• The two primary EFAs are known as linoleic acid (omega-6) and alpha-linolenic acid (omega-3).

Classification of saturated fats and unsaturated fats:

The following are the kinds of fats, their dietary sources and effects:

Dietary Sources of Lipids

• Most foods except the bread cereal group and the vegetable fruit group (except olives and avocado) contain varying percentages of lipids. 
• Some fats are visible such as fats and oils added to food or used for frying. 
• Many sources are hidden or invisible such as the fats and oils naturally present in the food, e.g., milk, egg yolk, oily fish, and meat. 
• Both visible and invisible sources must be taken into account while calculating the fat content of a meal.

Plant sources

• All oils and oilseeds like groundnut, sesame, soya bean, rice bran, coconut, almond, cashew nut, corn, safflower, sunflower, and all hydrogenated fats and margarine are sources of lipids.

Animal sources

• Mutton, pork, fish, poultry, milk, and milk products such as butter, cream, yoghurt, cheese, eggs and organ meats.

Invisible sources

• Invisible sources of fats are nuts, salad dressings, flesh food, desserts, cookies, cakes, milk, eggs, milk based sweetmeats, etc., which are rich in fat, but the fat is not visible.

Functions of Lipids

 1. Provide Energy

• Although the main source of energy for our bodies is carbohydrates, fat is used as a source of backup energy in cases when carbohydrates are not available. 
• This is a concentrated energy source but it is important to remember that each gram of fat has nine calories (over double the calories from protein and carbohydrates) so you should avoid having more than 20 to 35% of your daily calories from fat. 
• In a 1,800 calorie diet, you should only consume 40-70 grams of fat.

2.   Absorb Vitamins

• Certain vitamins, which are known as fat-soluble, need fat in order to be absorbed and stored. Some examples include vitamin A, vitamin D, vitamin E and vitamin K, all of which are an essential part of anyone’s daily diet. 
• Vitamin A is responsible for promoting good vision and keeping our eyes healthy; vitamin D helps us absorb calcium; vitamin E neutralized free radicals, protecting cells in the process; and vitamin K is essential for blood clotting.
•  If you don’t have enough fat in your body, you become deficient in one or more of these vitamins.

3. Store Fat for Subsequent Use

Our bodies can also store fats to be used later on. If you consume food that includes more energy than the body needs to perform its normal functions, any excess food is stored as subcutaneous fat under the skin. Sometimes this adipose tissue will be stored in the thighs and stomach, causing lumpy patches. The body also stores fats around our vital organs to help protect them from outside impacts or any sudden movements.

4. Maintain Proper Body Temperature

You can also find a thin fat layer located right underneath the skin. This layer of fat is designed to insulate the body, keeping heat inside and therefore helping us maintain the proper body temperature. In addition to insulating, this layer of fat can also protect the inner core from extreme temperature changes. That is because when our skin temperatures significantly drop, our fat deposits will generate and then release heat which helps increase the temperature.

5. Protect Your Body

The body also has a layer of fat that is surrounding major organs (including the brain and heart), nerves, tissues and bones and this is designed to act like a protective cushion. If for some reason you experience a sudden impact or even severe trauma, this layer of fat will absorb as much of the shock as it can so it can protect these essential organs and structures from being significantly damaged.

6. Hair and Skin

Fat also helps maintain healthy hair and skin. That is because it helps our bodies absorb increased amounts of vitamin A, vitamin D, vitamin E and vitamin K through the bloodstream. That is why dry, flaky skin is a symptom of a deficiency in fatty acids. Subcutaneous fat (which is found just under the skin) not only helps round the skin, but also helps insulate the body, regulating body temperature in the process.

Cholesterol

• It is a fat like substance present in food. 
• It is different in structure from triglycerides, as it has a ring structure. It is present in all cells of the body and in large amounts in brain and nerve tissue. 
• Cholesterol if consumed in excess is responsible for diseases of the cardiovascular system. 
• The normal blood cholesterol level for adults should be below 200mg/100ml blood. 

The human body gets cholesterol from two sources:

• Synthesis in the liver 
• Food rich in cholesterol (meat, poultry and full-fat dairy products)

There are two main forms, LDL (low density lipoprotein) and HDL (high density lipoprotein).
 LDL cholesterol is often referred to as "bad cholesterol" because too much is unhealthy.
HDL is often referred to as “good cholesterol” because it is protective.

Dietary Cholesterol

Dietary cholesterol is found in animal-based products including meat, fish, eggs, as well as poultry and dairy. Red meat will have more cholesterol than chicken and fish, but shrimp and eggs have been known to be the worst cholesterol culprits of the group.
 Blood cholesterol - Lipoproteins carry cholesterol in the blood. The two main types that carry cholesterol to and from cells are called low density lipoproteins (LDL-C) and high density lipoproteins (HDL-C).
The lower the density of the lipoproteins the more fats it contains. High density lipoprotein (HDL cholesterol) is called the ‘good cholesterol’ because it helps to keep cholesterol from building up in the arteries. Low density lipoprotein (LDL cholesterol) is called the ‘bad cholesterol’ because it is the main source of cholesterol build-up and blockage in the arteries. Statin medication work to reduce this LDL-C.

Deficiency and Excess of Fats

Deficiency of fats

• Leads to deficiency of essential fatty acids (linoleic and linolenic)
• EFA are required for cell membrane permeability
• Dryness of skin
• May lead to fat soluble vitamin deficiency

Excessive intake

• Causes obesity
• Excess fat is stored in adipose tissue
• Saturated fat – blood cholesterol 
• Cardiovascular diseases 

RDA
Fat should not contribute more than 30% Kcal
Saturated fat – not more than 10%

Significance of fatty acids in maintaining health

Monounsaturated fatty acid (MUFA) and polyunsaturated fatty acid (PUFA) fats are healthy to eat as they increase the good cholesterol and lower the bad cholesterol in our body.
The saturated fatty acid (SFA) fats on the other hand increase the level of bad cholesterol and decreased the level of good cholesterol, thereby causing the risk of coronary heart ailments. 

Tips to consume healthy forms of fat