Protein is necessary for Protein Biosynthesis: this is when an animal ingests protein, the protein is digested and broken down into amino acids, and these amino acids are used to build new cells, or substances such as insulin used in cell signalling. Protein can also be converted into carbohydrate and used as fuel through a process called gluconeogenesis - this should only happen during starvation, but some very low-carbohydrate diets promote this.
It used to be thought that vegetal sources of protein are a lower quality than animal sources. This is now widely discredited. However, different proteins have different levels of biological availability to the human body. In general, animal complete proteins that contain all the essential amino acids such as milk, eggs, meat, and the complete vegetable protein soy are of most value to the body. Of course, there are other vegetal sources of protein: it is wise to eat a mixture of these.
Importance of protein regulation
Protein is essential to build and renew cells. Deficiency is rare in the developed world, but can still occur in people who crash-diet, the elderly, and those convalescing from an illness. Protein deficiency can lead to reduced intelligence or Mental retardation. In severe cases of Protein-Energy Malnutrition, white blood cell numbers decline, and the ability of leukocytes to fight infection decreases. In children it is thought to cause Marasmus and Kwashiorkor.
There is evidence to show that large amounts of protein can be harmful in adults and children, but there has been little research into the maximum tolerable intakes and the mechanisms involved. Hence no value for the UL could be identified.
Certain amino acids have been studied extensively, but the potential adverse affects of most amino acids and their dose responses are not well documented. Hence no value for the UL could be identified.
The failure to set UL values should not be taken to imply that it is safe to consume very high amounts of protein or amino acids
Conclusions from "Protein and Amino Acid Requirements," Peter Garlick, Stony Brook University, published on the Institute of Medicine Website: http://www.iom.edu/Object.File/Master/7 ... A%20PG.pdf
Protein poisoning was reported by North American explorers (rabbit starvation). As a general rule, there are adverse effects when >40% of energy intake is protein. In addition, particular amino acids can cause adverse effects in high quantities, such as neurotoxicity (Glutamate, Aspartate, and Glycine), hyperammonemia (Alanine), and hypernatremia (Glycine).
High protein intake can potentially cause brain damage in preterm infants.
Excess protein is broken down into sugars and fatty acids. The liver removes nitrogen from the amino acids, and it is excreted. Usually the body can cope with this, but people with kidney disease may be advised to cut down on protein. Some suspect that Liver dysfunction may be caused due to increased toxic residues, or that it can accelerate the progression of renal disease.
Excessive protein intake may also cause calcium and glutamine to be leached from bone and muscle tissue, to balance increased acid intake from diet. This can cause loss of bone density and frailty of the bones. This effect is not present if intake of alkaline minerals (from fruits and vegetables, cereals are acidic as are proteins, fats are neutral) is high.
Proteins can trigger allergic reactions. Many people are allergic to casein, the protein in milk; gluten, the protein in wheat and other grains; the particular proteins found in peanuts; or those in shellfish or other seafoods.
Recommended Adequate Intake for Protein:
Each person's need for protein differs according to age, gender, climate, pregnancy/lactation and physical activity level. Recommended intake therefore differs quite dramatically between different sources. I've listed three sets of recommendations, and you can use the most appropriate to your lifestyle.
The IOM does not appear to recommend a daily intake, but it does link to a report from the Food and Nutrition Board presenting dietary reference values for the intake of nutrients by Americans and Canadians. According to the FNB (Food and Nutrition Board), the AMDR (Acceptable Macronutrient Distribution Range) for protein is:
- 10 to 35 percent of energy intake for adults
- 5 to 20 percent of energy intake for children 1 to 3 years of age
- 10 to 30 percent of energy intake for children 4 to 18 years of age
The following table is produced by the UK's Department of Health. Since protein from plant sources may be slightly less digestible, they recommend that vegetarians and vegans multiply the figures by a factor of 1.1.
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The UK Reference Nutrient Intakes (RNI*) for protein are as follows:
Type of person Amounts Required (g/day)
0-12 months 12.5-14.9
1-3 yrs 14.50
4-10 yrs 19.7-28.3
11-14 yrs 42.1
15-18 yrs 55.2
11-14 yrs 41.2
19-50 yrs 55.5
50+ yrs 53.3
19-50 yrs 45
50 + yrs 46.5
During pregnancy extra 6g/day
Breast feeding 0-6mths extra 11g/day
Breast feeding 6+ mths extra 8g/day
DISEN (Dieticians in Sport and Exercise Nutrition) publish the following guidelines, and quote some example foods containing protein. I've left the non-vegan ones in for comparison, but you can see that some vegan foods are good protein sources.
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Type of Activity Protein Requirements g / kg / body weight / day
Non Athletes 0.75 - 0.8g
Strength and Speed Athletes 1.4 - 1.8g
Endurance athletes 1.2 - 1.4g
For example if you are a strength athlete weighing 80kg you would require 112 -136g protein /day. This can easily be achieved by diet, protein supplements are not necessary.
Protein requirements are a little higher at the start of a training regime or when you step up the intensity of your training
If you are eating enough food to meet your energy requirements you will be eating enough protein too.
Foods Containing 20g Protein:
75g Lean Beef, Lamb, Pork 2 medium slices
75g Turkey, Chicken 1 small breast
100g Salmon / Tuna 1 small can
100g Grilled Fish 1 small fillet
Eggs 3 medium
75g Cheddar Cheese 2 matchbox size pieces
150g Cottage Cheese 1 small carton
600ml Semi/Skimmed Milk 1 pint
400g Baked Beans 1 can
Foods Containing 10g Protein:
100g Bread 3 - 4 slices
250g Pasta / Noodles 8 tablespoons - cooked
100g Cornflakes 2 large bowls
100g Wheat biscuits 5 biscuits
200g Yoghurt 1½ small pots
50g Nuts or Seeds 4 tablespoons
150g Kidney Beans / Lentils 5 tablespoons - cooked
250g Tofu (soya bean curd) 1 packet
Protein and Weight Loss
There is a lot of talk about high-protein / low-carb diets. In particular, there is a myth that eating a lot of protein will "burn" fat.
The only way you can lose weight is by consuming less colories than you use.
Many of these high-protein/low-carb diets, such as Atkins, can be high in saturated fat and are linked to health problems (link to article)
However, studies indicate that eating a high protein meal makes you feel more satisfied than a low protein meal. You are therefore likely to eat less calories on a high protein diet, without feeling hungry all the time.
In addition, people who do not eat enough protein tend to eat a lot of carbohydrate. Foods containing refined carbohydrate can destabilise your insulin and blood-sugar levels, and leave you feeling hungry shortly after eating. If you find yourself binging on carbohydrates, over a prolonged period of time, you may become more likely to develop yeast and fungal infections, and you risk eventually becoming diabetic (Type II Diabetes). There are also rumoured links to candida and dysmennhorrea (painful periods) for women.
Some diet plans tackle this by defining certain foods as a carbohydrate source or a protein source (for example: Atkins, Banting, Carbohydrate Addicts' Diet, Bodyclock Diet, etc... I've done them all...).
In reality, all foods contain a mixture of protein, carbohydrate and fat. Vegetal protein sources, such as beans and lentils, tend to contain a fair amount of carbohydrate (likewise, brown bread and rice - often classified as carbohydrates - contain protein). These low-carb diets therefore perpetuate the myth that vegan diets are low in protein and high in carbohydrate, by only classifying meat and dairy as protein sources.
The Glycaemic Indix of a food refers to an international ranking of foods that raise blood sugar levels. If you are concerned that your diet is too heavy in carbohydrate, you may find it useful to eat lower GI foods. As a rule, avoiding processed foods with refined sugar, and keeping starchy foods as whole as possible (e.g. eating wholemeal bread instead of white bread) should keep your blood sugar levels stable. There is no need to cut out all carbohydrates (I'm sure we've all heard the stories about actresses only eating burgers and then fainting on set...)
A neat tip I picked up on the EAS Body For Life website: eat six small meals a day (or three meals and three snacks - Recommended by GI Plan). Each meal should combine carbohydrates and protein. Have a portion of high-protein food (e.g. tofu) the size of your open palm, and a portion of high-carbohydrate food (e.g. pasta) the size of your clenched palm. Then go crazy with low-calorie vegetables As I mentioned before, foods like beans and lentils contain protein and carbs, so you can modify your carb portion accordingly (e.g. a bean chilli in a tortilla wrap). You will of course need a little fat each day, and plenty of water too.
Raw Vegan Products Rich in Protein
Protein in Nutrition on Wikipedia
Protein on VeganSociety.com
Protein on DISEN (Dieticians in Sport and Exercise Nutrition)
FNB (Food & Nutrition Board) Guidelines on Macronutrients
Protein and Amino Acid Requirements, Peter Garlick, Stony Brook University, PowerPoint presentation published on the IOM Website
Website of The GI Plan Diet, although you need to buy the book for the GI tables
Free database of foods and their GI values
Nutrition on the EAS "Body For Life Challenge" Website