Dear Alice,

What are the consequences to having a diet too low in protein?


Dear SMS,

Beans, seafood, poultry, meat, and eggs. These are just a few sources for protein. Our bodies need protein for numerous functions. Hemoglobin, which carries oxygen, is an essential protein that gives blood its red color when oxygenated. Antibodies, which act as defenders against disease, are composed of proteins. Hormones, some of which are made from amino acids (the building blocks of protein), regulate many systems in our bodies. These include the regulation of metabolism, digestion, and nutrient absorption, and the concentration of blood glucose. Proteins are also used by our cells to regulate the distribution of water and the movement of nutrients in and out of cells, particularly since proteins are one of the components of cell membranes. Furthermore, proteins are involved in blood clotting, acid-base balance, and visual pigmentation.

Considering we need protein to help our bodies carry out and sustain essential physiological functions, a diet very low in protein is obviously not a good idea. The good news is that it is not difficult to obtain sufficient protein from our diet and most Americans have no trouble doing so. Dietary protein can be obtained from animal and vegetable sources. If your diet is insufficient in protein, you could also be deficient in many important vitamins and minerals found in protein-rich foods. Deficiencies could occur in niacin, thiamin, riboflavin, B-12, B-6, iron, zinc, and calcium, among others, depending on what foods are missing from your diet. The effects of prolonged low protein in the diet would eventually manifest themselves as impaired immune function, and irregularities in other bodily functions and systems described above.

The Recommended Dietary Allowances (RDA) for protein are as follows:

Recommended Dietary Allowance for Protein
  Grams of protein needed each day
Children ages 1 - 3 13
Children ages 4 - 8 19
Children ages 9 - 13 34
Girls ages 14 - 18 46
Boys ages 14 - 18 52
Women ages 19 - 70+ 46
Men ages 19 - 70+ 56

Table via the Centers for Disease Control and Prevention

Protein recommendations vary from individual to individual depending on her/his amount of lean body mass.

As you can see, proteins are an integral and necessary part of our functioning.  Animal sources, such as meat, fish, poultry, eggs, and dairy products, contain complete proteins — all the amino acids our bodies require to form the proteins we need. Vegetable sources, such as nuts, seeds, legumes (beans, peas, lentils, and soy products), grains (breads and cereals), and green leafy vegetables, contain incomplete proteins. This means that not all of the amino acids are found in one food. Mother Nature is tricky — the amino acids absent in some foods are present in others. Rice and beans, which together have all the essential amino acids, form a complete protein. This is an example of a way vegetarians can make sure they get complete proteins from their diet; however, according to research, it's not necessary to get complete proteins for every meal. Having some amino acids during breakfast and the others during lunch will have the same effect as consuming them together, during the same meal. Your body has the ability to combine complementary proteins as long as their eaten on the same day.

The following is a broad overview of the protein content in different food groups:

1 cup dairy or soy milk 6-8 g
3 oz. lean beef, fish, or poultry 21 g
1/2 cup beans 7 g
1 slice of bread 3 g
1/2 cup cooked vegetables 2 g

Dietary protein adds up rather quickly, and, as mentioned earlier, without too much effort. In the US, it is rare to find protein deficiencies among the general population. Ours is more a problem of excess than deficiency.

If you have special dietary needs and/or would like some nutrition counseling to help you eat enough protein from your diet, talking with a nutritionist can be a big help.


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