Take Away Points
In this lesson we learned a lot about proteins. The following video is a great summary.
This lesson should have also demonstrated that proteins are pretty important. Here is a listing of some of their many functions:
- Required for the growth and repair of body tissues.
- Muscles which are ~30% of human bodies are made up of proteins.
- Proteins give structure to the body by providing elasticity, rigidity, and shape to many internal and external organs.
- All enzymes -made up of proteins- are necessary for all biochemical reactions.
- Every cell has a membrane contains different proteins that perform vital functions.
- Many chemical messengers of the body (hormones), are made up of proteins.Â
- 6-8% of human blood plasma is proteins.
- The Hemoglobin of RBCs is protein and is important for carriage of O2 and CO2.
- Proteins like albumin and globulin help to keep fluid in the blood vessels.
- Other blood proteins also help to maintain the correct blood pH.
- Immunoglobulins and complements proteins are critical for immunity.Â
- Proteins like thrombin and fibrin help in blood clotting.
- Proteins also provide the energy required by our body for various functions.
The Recommended Dietary Allowance (RDA) is the estimated average daily nutrient intake sufficient to meet the needs of nearly all (97-98%) of healthy individuals in a particular life stage and sex group.
Acceptable Macronutrient Distribution Ranges (AMDRs) are intakes that are associated with reduced risk of chronic disease. AMDRs apply for carbohydrates, proteins and fats. AMDRs are expressed in percent of calories from total daily calories.
             RDA and AMDR for Protein | ||
Age | RDAGrams/day for average body weight | AMDRGrams/day |
| 0–6 months | 9 g/day (1.5 g/kg) [Adequate Intake] | Not determinable |
| 7–12 months | 11 g/day (1.5 g/kg) | Not determinable |
| 1–3 years | 13 g/day (1.1 g/kg) | 10-50 g/day (5-20% of 1,000 Cal) |
| 4–8 years | 19 g/day (0.95 g/kg) | 30-100 g/day (10-30% of 1,300 Cal)** |
| 9–13 years | 34 g/day (0.95 g/kg) | 40-130 g/day (10-30% of 1,700 Cal)** |
| Boys 14-18 years | 52 g/day (0.8 g/kg) | 55-175 g/day (10-30% of 2,200 Cal)** |
| Girls 14-18 years | 46 g/day (0.8 g/kg) | 45-135 g/day (10-30% of 1,800 Cal) |
This chart was made from data from the Institute Of Medicine, US Department of Agriculture and WebMD.
Lack of protein can lead to different forms of malnutrition, such as Kwashiorkor or Marasmus. Kwashiorkor causes weakness, anemia, failure to grow, and swelling of the belly. Marasmus prevents children from growing properly and causes their fat and muscles to waste away. The figure including the table below highlights the differences.
When proteins are digested amino acids are are released and absorbed into the blood. Amino acids may enter liver, muscle and other body cells, where they can be converted to muscle, other body proteins, glucose or glycogen (a storage form of glucose in the liver and muscles), fatty acids or further to ketones (a source of energy for the brain during low-carb diet) or body fat stores, or can be converted to energy. Clearly there are a lot of different options. What happens to the protein we eat depends on circumstances:
- If we eat more calories than we expend, some protein will be converted to body fat.
- In a low-carbohydrate, high-protein diet, some protein will be used for energy, some will be converted to glucose and some to ketones, both of which can be used as a source of energy for the brain.
- During weight (resistance) training, some protein will be converted to muscle proteins leading to an increase in muscle mass.