Protein and Amino Acids
Rowden January 2015
Protein and Amino Acids
Large amounts of protein are contained in:
• Fish and seafood
• Dairy products
Fair amounts are also found in:
• Seeds and nuts
• Beans and lentils
Other foods contain only small amounts of protein:
• Grains and their derivatives (pasta, rice, whole grain bread)
• Green vegetables
During digestion proteins are broken down into simple substances called amino acids. The food you eat MUST provide you with 9 essential amino acids as the body itself is not capable of synthesising these 9 on its own (However see Histidine).
Getting all 9 amino acids is doubly important for the following reason; if only one is missing, the others may be assimilated badly, or not at all!
Most foods, except eggs, do not contain all 9 essential amino acids. They may contain one or even a few, but the absence of the others (or even their presence in too small amounts) can inhibit the assimilation of the amino acids they do contain. Meat and cow’s milk lack methionin; fish lacks tryptophan. This means that the only way to provide the body with all the essential nutrients in precisely the right amounts is to eat a BALANCED diet.
If for example you eat mainly fish and avoid meats and dairy products (a fairly common diet nowadays) you will lack tryptophan. At certain times too your body will need more of certain amino acids because your cells have to regenerate faster. This is true of children, teenagers, pregnant or breast feeding women and persons fighting disease or convalescing.
Proteins should make up 15% of your daily food intake. The amount generally recommended is one gram of protein to each kilogram of body weight. Growing adolescents or persons participating in sport or carrying out demanding physical work, can increase their protein intake to 1.5 or even 2.0 grams per kilogram of body weight.
How does this translate into actual food? 100 grams of meat contains between 15 and 20 grams of protein as does:
• 100 grams of fish
• 2 eggs
• Half a litre of milk
• 60 grams of hard cheese (medium strength)
However vegetables, grains and nuts etc all contain some protein, these are the vegetal proteins. Although easy to assimilate, they do not have the same biological value as protein obtained from non-vegetal sources, primarily because they lack one or a number of essential amino acids. Vegetal proteins obtained from grains generally lack isoleucine and lysine. On the other hand it’s easy to compensate for this lack by combining a grain from another source of vegetal protein (in the same meal). Eating a grain like rice with beans, lentils, soya-bean, peas etc provides you with all essential amino acids. On the other hand you could also combine a grain with meat or a dairy product (cheese, eggs, chicken etc).
Let us look at the amino acids in more detail, what they are , what they do and which foods apply.
WHAT ARE AMINO ACIDS?
Amino acids are the building blocks of proteins, which are necessary for the body for repairing and maintaining muscles, bones, body organs and blood. Therefore, when you eat foods with protein, you are also ingesting amino acids. As the proteins you eat are broken down and digested in the body, amino acids are left over. The amino acids are then used by the body for a variety of important functions, including breaking down food, promoting healthy growth, repairing body tissues and other needs of the body. In addition, the amino acids can be reused to make proteins so that they can carry out their aforementioned roles within the body.
ESSENTIAL AND NONESSENTIAL AMINO ACIDS
Though there are many various types of amino acids in existence, there are 22 specific amino acids that your body needs regularly. Of those 22, your body can make 13 on its own, even if you aren’t getting them in your diet. These 13 compounds are called nonessential amino acids because you don’t have to make sure that you are eating proteins which contain those particular amino acids.
The remaining nine amino acids that your body needs are called essential amino acids. Your body is not capable of making these particular amino acids on its own (see however Histidine), so it’s critical that you eat foods that contain these compounds. The nine essential amino acids are:
WHERE TO FIND ESSENTIAL AMINO ACIDS
Individuals should try to get each of the nine essential amino acids in their diet each day. These amino acids can be found in a variety of different foods which contain protein. The following is a list of the best sources for the nine essential amino acids:
1. Histidine: This is found in the highest concentration in various types of game meat. Deer, boar and antelope are each a top source of histidine. Pork is also a good source, regardless of the way it is prepared. You can also get histidine from fish like cod, pike, haddock, sardines and tuna. Other sources of histidine include chicken, turkey and kidney beans, eggs, dairy products, some grains, rice, wheat, rye, beans, mushrooms, citrus fruits and bananas. Histidine is the one amino acid vital to children (adults can synthesise most of their needs through the liver, children can’t and must obtain the amino acid through the food intake).
2. Isoleucine: If you want to get isoleucine in your diet, your best option is to eat egg whites, which contain by far the most of this amino acid per serving. Turkey is your next best option, following by soy, chicken, lamb and crab. Many types of fish also contain isoleucine, including pike, cod and tuna as do cottage cheese and legumes.
3. Leucine: Leucine can be found in some interesting foods, including soy, seaweed and elk. However, egg whites are also an excellent source of this amino acid, as is chicken. Tuna is another great option if you are looking for ways to add leucine to your diet. Cottage cheese, cheeses, milk, nuts and sesame seeds are also sources.
4. Lysine: Lysine is found in the highest concentration in chicken breast meat and turkey breast meat. However, fish is your next best option, with ling, pike, tuna, cod and dolphin all being excellent sources of lysine as well. Though not as high in concentration, watercress, seaweed and parsley also contain significant amounts of lysine, as do soya bean, lentils, peas, beans and semi-skimmed milk.
5. Methionine: As with many other essential amino acids, egg whites are the best source for methionine. However, fish like pike and tuna aren’t far behind. You can also eat meats like elk, turkey and chicken to get this amino acid in your diet. Lobster and crab are also among the top foods for methionine. Other sources are spinach, broccoli, zucchini, brazil nuts and sesame seeds.
6. Phenylalanine: Meat is the way to go for phenylalanine, which is found in the highest concentration in pork, beef, turkey, veal and lamb. Salmon is also a solid source of this amino acid, as are other sea-foods, cod, crab, oysters, mussels, tuna and sardines. Liver, chicken, cheese, milk, walnuts, eggs, soy products, lentils and chickpeas also have some content.
7. Threonine: Threonine marks a refreshing break from meats and fish since the top source of this amino acid are raw watercress and spinach. However, you can still get this compound from moose, turkey or tilapia if you so choose. Egg whites and soy are also significant sources of threonine. Other sources are lentils, walnuts, milk and seaweed.
8. Tryptophan: Though it is commonly associated with turkey, especially at Thanksgiving, tryptophan is actually found in the highest concentration in elk and sea lion meats. Other top sources for this amino acid include seaweed, soy, egg whites and spinach.
9. Valine: Once again, egg whites come in first when it comes to getting valine in your diet. However, watercress, spinach, seaweed, elk and turkey are also great options for this amino acid. Other sources are soy derived products, beans, lentils (good volume), peanuts and peanut butter: also chicken, tuna, cheeses and dairy products.
For athletes what are known as the branched-chain amino acids are particularly important as these significantly aid muscle recovery. These 3 are valine, leucine and isoleucine and all young people involved in sport should ensure they prioritise foods containing these amino acids.
Regarding meat substitutes such as quorn it should be noted that although mycoprotein (vegetable in origin) contains all the 9 amino acids these are not present to quite the same value as animal protein sources. Children or young persons on strict vegetarian or vegan diets should therefore be careful as to the levels of histidine in their total intake. Another aspect can be the lack of iron (abundant in red meats for example) not so readily available in meat substitutes. In the case of an unbalanced diet one must also consider the lack of other trace elements.