Brain cells, hair, muscle, skin, & nails are just some of the body parts which are protein-based. Estimates suggest which about half dry weight of the human body is made up of protein.
Many of the foods we eat contain it, particularly flesh foods (beef, lamb, chicken, & fish), & legumes like lentils & beans. These are broken down during digestion to release amino acids, that are the building blocks of all proteins. Once inside the body, these amino acids are used to make the new proteins including hormones & enzymes such as adrenalin. It is mostly used as an energy source.
Your protein needs
The amount of protein you need in your diet depends on your age, weight, & health. As a rough guide, the RDI (recommended dietary intake) for it (measured in grams per kilogram of body weight) is:
- 0.75 g/kg for adult women
- 0.84 g/kg for adult men
- Around 1 g/kg for pregnant & breastfeeding women, & for men & women over 70 years.
For example, an adult male, containing 75 kg weight would need 63 g of protein per day. It is recommended that 15 to 25 percent of total energy intake per day is from protein sources. The human body can’t store protein & will excrete any excess. The most effective way of daily requirement and using the daily protein is to eat small amounts at every meal. Using the example of the male having a weight of 75 kg & above, this would require that he eats the approximately 21 g of protein at 3 meals every day.
Sources of protein
Some sources of dietary protein include:
- lean meat, poultry & fish
- dairy products like milk, yogurt & cheese
- seeds & nuts
- beans & legumes (such as lentils & chickpeas)
- soy products like tofu
- some grain & cereal-based products are also sources of protein but are generally not as high in protein as meat & meat alternative products.
The Australian Dietary Guidelines recommend particular serves per day from the lean meat & poultry, fish, eggs, tofu, nuts & seeds & legumes/beans food category, including:
- men aged 19-50 years = 3 serves
- men aged 51 years & over = 2 ½ serves
- women aged 19-50 years = 2½ serves
- women aged 51 years & over = 2 serves
- pregnant women = 3 ½ serves
- breastfeeding women = 2 ½ serves.
A standard serving size is one of:
- 65 g cooked lean meats such as lamb, veal, beef, pork, kangaroo or goat (about 90-100 g raw)
- 80 g cooked lean poultry such as turkey or chicken (100 g raw)
- 100 g fish cooked fillet (about 115 g raw weight) or 1 small can of fish
- 2 large eggs
- 1 cup (150 g) cooked dried beans, lentils, chickpeas, split peas or canned beans (preferably with no added salt)
- 170 g tofu
- 30 g seeds, peanut nuts, or almond butter or tahini or other seed or nut paste (no added salt).
The daily recommendations for adults for foods from the milk, yoghurt, cheese &/or alternatives (mostly reduced fat) group are:
- men aged 19-70 years = 2 ½ serves
- menu aged 70 years & over = 3 ½ serves
- women aged 19-50 years = 2 ½ serves
- women aged 51 years & over = 4 serves.
A serve could include either:
- 250 ml (1 cup) fresh, UHT long life, reconstituted powdered milk or buttermilk
- 120 ml (1/2 cup) evaporated milk
- 200 g (3/4 cup or 1 small carton) yogurt
- 40 g (2 slices) hard cheese such as the cheddar
- 120 g (1/2 cup) ricotta cheese.
Amino acids explained
The Proteins are made up of the chains of smaller building blocks which called amino acids, that are chemically linked to each other. There are more than 20 different amino acids which can be put together in different combinations to make up the millions of proteins that found in nature. A protein can consist of between fifty & tens of thousands of amino acids.
The 2 broad classes of amino acids are those that can be made by the human body (non-essential amino acids) & those that must be supplied to us through our diet (essential amino acids).
Nutritional value of protein
Protein’s nutritional value is measured by the number of essential amino acids which proteins provide.
Different foods contain different amounts of amino acids & Protein. Generally:
- Animal products (such as beef, chicken, or fish) contain all of the essential amino acids.
- Soy products, quinoa & the seed of a leafy green called Amaranth (consumed in Asia & the Mediterranean) also contain all of the essential amino acids.
People following a strict vegan or vegetarian diet need to choose the variety of protein sources from a combination of the plant foods throughout the day to get an adequate mix of the amino acids. For example, a meal containing legumes& cereals, such as baked beans on toast, that provides all the essential amino acids found in a typical meat dish.
Digestion of proteins
A protein-rich food, such as the meat, is broken down into the individual proteins by the gastric juices in the human stomach. Pancreatic enzymes released into the 1st portion of our small intestine (duodenum) split the proteins into their separate amino acids. The amino acids are absorbed by the small finger-like projections (villi) lining the intestine walls, & are taken to the liver via the bloodstream.
Maintaining muscle mass
Beginning at approximately fifty years of age, humans begin to gradually lose the skeletal muscle. This loss is known as the sarcopenia, is common in the elderly, but is also worsened by the chronic poor, illness diet or inactivity. It is likely which protein intake at the upper end of the RDI range that can help maintain muscle strength & mass, that is vital for