Protein is one of the three nutrients found in food that the body requires in large amounts. Along with carbohydrates and fat, protein is essential for the human body.

Proteins are made of small compounds called amino acids. There are hundreds of amino acids that exist in nature, but the human body only utilizes 22 of them.

The human body can produce all but nine of the amino acids that it needs. These nine are called essential amino acids and must be consumed through food.

All foods contain differing combinations of amino acids, making a balanced diet essential. In general, animal proteins like meat, dairy, and eggs contain all the essential amino acids.

Plant-based proteins from foods like beans, grains, nuts, and soy are rich in some amino acids but may be lacking in others. This lack underlines the need for a well-balanced diet with variety.

What does protein do?

Protein is the major building block of the human body. Its main job is to build and maintain tissue.

Food sources containing protein.

Many foods are high in protein, including several that are suitable for vegetarians and vegans.

Periods of growth, such as infancy, childhood, and pregnancy, require more protein for this growth to occur. Protein needs are also increased for the following people:

People who have undergone surgery

Active people who are consistently breaking down muscle during exercise

The total amount of protein that is consumed in a day is not nearly as important as how protein intake is spread out over the day.

Many people will consume a small amount of protein at breakfast, a moderate amount at lunch, and a large amount at dinner.

A typical day's eating might involve 10 grams of protein or less at breakfast (cereal), 25 grams at lunch (sandwich), 5 grams for a snack (granola bar), and 40 grams at dinner (chicken or beef).

However, the body can only absorb and use a certain amount protein at one time. The body uses what it can and then what is left over becomes waste. So, it is better for people to spread 60 grams of protein over three or four meals of 15-20 grams each instead of having 60 grams of protein in one meal.

How much protein is needed each day?

There is a certain amount of protein people can aim for to make sure they are they get the most protein use, muscle generation, and recovery every time they eat. This amount depends on the person's body size and how active they are.

Blocks of tofu.

Half a block of tofu contains 18 grams of protein.

A 6-foot, 250-pound man who strength trains five times a week can absorb and utilize more protein than a 5-foot female who does not exercise much. Studies to date have suggested a 20-30 gram per meal protein goal, but more research is needed.

The Recommended Dietary Allowance (RDA) for protein is 0.8 grams per kilogram of body weight per day. The RDA is the minimum amount of protein needed for meeting nutritional requirements, not the maximum.

Endurance athletes need 1.2 to 1.4 grams per kilogram of body weight. Strength training or power athletes require 1.2 to 1.7 grams per kilogram of body weight. The more physically active a person is, the more protein that they will need to consume.

Some research has recommended as much as 2 grams per kilogram of body weight to prevent muscle loss in athletes who want to lose weight and have reduced the amount of calories they consume.

Amount of protein in common food sources

According to the U.S. Department of Agriculture, the following amounts of protein can be found in common sources of food:

Food Amount Grams of protein

Chicken 3 ounces 20

Ground beef 3 ounces 21

Milk 1 cup 9

Egg 1 6

Black beans ¾ cup 11.43

Peanut butter 2 tablespoons 8

Tofu ½ block 18Risks and precautions for consuming protein

Most studies support an intake of up to 2 grams per kilogram of body weight without any negative or adverse effects (including kidney damage). Consuming more than 2.5 grams of protein per kilogram of body weight can increase the risk of the following:

Dehydration

Fatigue

Taking in too many calories

Passing out higher levels of the nutrient calcium in the urine

Eating more than 200 to 400 grams of protein per day can exceed the liver's ability to convert excess nitrogen to a waste product called urea. This can lead to nausea, diarrhea, and other adverse side effects.

Vitamin B12, also called cobalamin, is one of 8 B vitamins. All B vitamins help the body convert food (carbohydrates) into fuel (glucose), which is used to produce energy. These B vitamins, often referred to as B complex vitamins, also help the body use fats and protein. B complex vitamins are needed for healthy skin, hair, eyes, and liver. They also help the nervous system function properly.

All B vitamins are water soluble, meaning that the body does not store them.

Vitamin B12 is an especially important vitamin for maintaining healthy nerve cells, and it helps in the production of DNA and RNA, the body's genetic material. Vitamin B12 works closely with vitamin B9, also called folate or folic acid, to help make red blood cells and to help iron work better in the body. Folate and B12 work together to produce S-adenosylmethionine (SAMe), a compound involved in immune function and mood.

Vitamins B12, B6, and B9 work together to control blood levels of the amino acid homocysteine. High levels of homocysteine are associated with heart disease. However, researchers are not sure whether homocysteine is a cause of heart disease or just a marker that indicates someone may have heart disease.

It is rare for young people to be deficient in vitamin B12, but it is not uncommon for older people to be mildly deficient. This may be because their diets are not as healthy, or because they have less stomach acid, which the body needs to absorb B12. Low levels of B12 can cause a range of symptoms including:

Fatigue
Shortness of breath
Diarrhea
Nervousness
Numbness
Tingling sensation in the fingers and toes
Severe deficiency of B12 causes nerve damage.

Others at risk for B12 deficiency include:

Vegans and vegetarians who do not eat dairy or eggs, since vitamin B12 is found only in animal products
People with problems absorbing nutrients due to Crohn disease, pancreatic disease, weight loss surgery, or medications
People who are infected with Helicobacter pylori, an organism in the intestines that can cause an ulcer. H. pylori damages stomach cells that make intrinsic factor, a substance the body needs to absorb B12
People with an eating disorder
People with HIV
People with diabetes
The elderly
Folic acid (vitamin B9), especially when taken in high doses, can mask the symptoms of a vitamin B12 deficiency. The danger is that without symptoms, someone with a vitamin B12 deficiency may not know it, and could run the risk of developing nerve damage. You should talk to your doctor first if you plan to take more than 800 mcg of folic acid, to make sure you do not have a B12 deficiency.

Vitamin B12 is used for:

Pernicious anemia

Pernicious anemia is a type of anemia that happens when stomach cells are not able to make intrinsic factor. Without intrinsic factor, your body cannot absorb vitamin B12. Symptoms include:

Weakness
Pale skin
Diarrhea
Weight loss
Fever
Numbness or tingling sensation in the hands and feet
Loss of balance
Confusion, memory loss, and moodiness
Vitamin B12 supplements in high doses, either given as injections or orally, are prescribed to treat pernicious anemia. Pernicious anemia can be a dangerous condition and should always be treated by a doctor.

Heart disease

Many studies suggest that people with high levels of the amino acid homocysteine are almost two times more likely to develop coronary artery disease and 2.5 times more likely to have a stroke than those with normal levels. B complex vitamins, especially vitamins B9, B6, and B12, help lower homocysteine levels. However, researchers do not know whether high homocysteine levels actually cause heart disease.

People who are concerned about heart disease should try to get enough B vitamins from healthy foods. However, in some cases doctors recommend taking B vitamins to lower homocysteine levels. If you are worried about heart disease, ask your doctor whether taking a B vitamin supplement would be right for you.

Age-related macular degeneration (AMD)

One large study found that women who took 1,000 mcg of vitamin B12, along with 2500 mcg of folic acid and 500 mg of vitamin B6 daily, reduced the risk of developing AMD, an eye disease that can cause loss of vision.

Fatigue

Fatigue is one of the symptoms of a vitamin B12 deficiency. One small study suggested that some people who were not deficient in B12 might gain more energy from B12 shots. However, more research is needed. One preliminary study indicated that people with chronic fatigue syndrome might benefit from B12 injections. More research is needed.

Breast cancer

Although there is no evidence that vitamin B12 alone reduces the risk of breast cancer, population studies have shown that women who get more folate in their diet have lower risk of breast cancer. Vitamin B12 works with folate in the body, so it may help reduce breast cancer risk. Another preliminary study suggested that postmenopausal women who had the lowest amounts of B12 in their diet had an increased risk for breast cancer.

Male infertility

Studies suggest that vitamin B12 supplements may improve sperm counts and sperm's ability to swim. More research is needed.

Dietary Sources

Vitamin B12 is found only in animal foods. Good dietary sources include:

Fish
Shellfish
Dairy products
Organ meats, particularly liver and kidney
Eggs
Beef
Pork
Available Forms

Vitamin B12 can be found in multivitamins (including children's chewable and liquid drops), B complex vitamins, and individual supplements. Vitamin B12 is available in intranasal forms (administered through the nose), as well as oral tablets, capsules, soft gels, and lozenges. Vitamin B12 is also sold under the names cobalamin and cyanocobalamin.

How to Take It

If your diet includes meat, fish or shellfish, milk, and other dairy products, you should be able to meet the recommended daily requirements without taking a vitamin B12 supplement. Vegetarians who do not eat any animal products should take a vitamin B12 supplement with water, preferably after eating. Elderly people may need larger amounts of vitamin B12 than younger people because the body's ability to absorb vitamin B12 from the diet declines with age.

If you are considering taking a B12 supplement, ask your health care provider to help you determine the right dose for you.

Daily recommendations for dietary vitamin B12 are listed below.

Pediatric

Newborns to 6 months: 0.4 mcg (adequate intake)
Infants 6 months to 1 year: 0.5 mcg (adequate intake)
Children 1 to 3 years: 0.9 mcg (RDA)
Children 4 to 8 years: 1.2 mcg (RDA)
Children 9 to 13 years: 1.8 mcg (RDA)
Teens 14 to 18 years: 2.4 mcg (RDA)
Adult

19 years and older: 2.4 mcg (RDA)*
Pregnant women: 2.6 mcg (RDA)
Breastfeeding women: 2.8 mcg (RDA)
*Because 10 to 30% of older people may not absorb B12 from food very well, people over 50 should meet their daily requirement through either foods fortified with vitamin B12 or a supplement containing B12.

Precautions

Because of the potential for side effects and interactions with medications, you should take dietary supplements only under the supervision of a knowledgeable health care provider.

Vitamin B12 is considered safe and nontoxic, however taking any one of the B vitamins for a long period of time can result in an imbalance of other important B vitamins. For this reason, you may want to take a B complex vitamin that includes all B vitamins. Taking folic acid at high doses can hide a vitamin B12 deficiency. So these vitamins are often taken together. Talk to your doctor before taking more than 800 mcg of folic acid.

People with abnormal levels of red blood cells, or abnormalities in their red blood cells, should work with a doctor to determine whether B12 is appropriate for them. In some instances, B12 can be beneficial. But it can be harmful with other health conditions. For instance, B12 supplements can cause serious damage to the optic nerve in people with Leber's disease (a disease of the eye). Again, be sure to work with your doctor.

Possible Interactions

If you are currently being treated with any of the following medications, you should not use vitamin B12 supplements without first talking to your health care provider.

Medications that reduce levels of B12 in the body include:

Anti-seizure medications -- including phenytoin (Dilantin), phenobarbital, primidone (Mysoline)
Chemotherapy medications -- particularly methotrexate
Colchicine -- used to treat gout
Bile acid sequestrants -- used to lower cholesterol; include colestipol (Colestid), cholestyramine (Questran), and colsevelam (Welchol)
H2 blockers -- used to reduce stomach acid; include cimetidine (Tagamet), famotidine (Pepcid AC), ranitidine (Zantac)
Metformin (Glucophage) -- medication taken for diabetes
Proton pump inhibitors -- used to reduce stomach acid; include esomeprazole (Nexium), lansprazole (Prevacid), omeprazole (Prilosec), rabeprazole (Aciphex)
Antibiotics, Tetracycline: Vitamin B12 should not be taken at the same time as

This section looks at the potential health benefits of vitamin D, from assisting good bone health to possible cancer prevention.

1) Vitamin D for healthy bones
Vitamin D plays a substantial role in the regulation of calcium and maintenance of phosphorus levels in the blood, two factors that are extremely important for maintaining healthy bones. We need vitamin D to absorb calcium in the intestines and to reclaim calcium that would otherwise be excreted through the kidneys.

Vitamin D deficiency in children can cause rickets, a disease characterized by a severely bow-legged appearance triggered by impaired mineralization and softening of the bones.

In adults, vitamin D deficiency manifests as osteomalacia or osteoporosis. Osteomalacia results in poor bone density, muscular weakness and often causes small pseudo fractures of the spine, femur and humerus. Osteoporosis is the most common bone disease among post-menopausal women and older men.

2) Reduced risk of flu
Children given 1,200 IU of vitamin D per day for 4 months during the winter reduced their risk of influenza A infection by over 40%.2

3) Reduced risk of diabetes
Several observational studies have shown an inverse relationship between blood concentrations of vitamin D in the body and risk of type 2 diabetes. In type 2 diabetics, insufficient vitamin D levels may have an adverse effect on insulin secretion and glucose tolerance.3 In one particular study, infants who received 2,000 IU/day of vitamin D had an 88% lower risk of developing type 1 diabetes by the age of 32.

4) Healthy infants
Children with normal blood pressure who were given 2,000 IU/day had significantly lower arterial wall stiffness after 16 weeks compared with children who were given only 400 IU/day.

Low vitamin D status has also been associated with a higher risk and severity of atopic childhood diseases and allergic diseases, including asthma, atopic dermatitis and eczema. Vitamin D may enhance the anti-inflammatory effects of glucocorticoids, making it potentially useful as a supportive therapy for people with steroid-resistant asthma.5,8

5) Healthy pregnancy
Pregnant women who are deficient in vitamin D seem to be at greater risk of developing preeclampsia and needing a cesarean section. Poor vitamin D status is also associated with gestational diabetes mellitus and bacterial vaginosis in pregnant women. It is also important to note that vitamin D levels that were too high during pregnancy were associated with an increase in food allergy of the child during the first two years of life.

6) Cancer prevention
Vitamin D is extremely important for regulating cell growth and for cell-to-cell communication. Some studies have suggested that calcitriol (the hormonally active form of vitamin D) can reduce cancer progression by slowing the growth and development of new blood vessels in cancerous tissue, increasing cancer cell death and by reducing cell proliferation and metastases. Vitamin D has an influence on more than 200 human genes, which can be impaired when D status is suboptimal.3

Vitamin D deficiency has also been associated with an increased risk of cardiovascular disease, hypertension, multiple sclerosis, autism, Alzheimer's disease, rheumatoid arthritis, asthma severity and swine flu, however more reliable studies are needed before these associations can be proven.

Flaxseed is one of the most important oilseed crops for industrial as well as food, feed, and fiber purposes. Almost every part of the flaxseed plant is utilized commercially, either directly or after processing. The stem yields good quality fiber having high strength and durability. The seed provides oil rich in omega-3, digestible proteins, and lignans. In addition to being one of the richest sources of α-linolenic acid oil and lignans, flaxseed is an essential source of high quality protein and soluble fiber and has considerable potential as a source of phenolic compounds. Flaxseed is emerging as an important functional food ingredient because of its rich contents of α-linolenic acid (ALA), lignans, and fiber. Lignans appear to be anti-carcinogenic compounds. The omega-3s and lignan phytoestrogens of flaxseed are in focus for their benefits for a wide range of health conditions and may possess chemo-protective properties in animals and humans. This paper presents a review of literature on the nutritional composition of flaxseed, its health benefits, and disease-prevention qualities, utilization of flaxseed for food, feed, and fiber, and processing of flaxseed.