What is protein and why it is needed...

Protein is the major functional and structural component of all body cells; all enzymes, membrane carriers, blood transport molecules, intercellular matrices, hair, fingernails, serum albmin, collagen are proteins. In addition, the constituent amino acids of protein act as precursors of many coenzymes, hormones, nucleic acids, and other molecules essential for life. An adequate supply of dietary protein is essential to maintain cellular integrity and function.

Protein is a macronutrient made up of two types of amino acids. Amino acids are the building blocks for new protein to build new tissue and repair old tissue. Non-essential amino acids are synthesized by a healthy body from the foods that we eat each day. Essential amino acids must be obtained daily from our diet.

For more information on protein, see Dietary Reference Intakes for Energy, Carbohydrate, Fiber, Fat, Fatty Acids, Cholesterol, Protein, and Amino Acids, 2002, Chapter 10, pages 465-608, Food and Nutrition Board (FNB), Institute of Medicine (IOM). Also see my Carbohydrates and Fats pages.

Protein deficiency signs?

Sufficient protein must be ingested to maintain body cellular and organ functions. Sufficient carbohydrates must also be consumed to meet energy needs, otherwise the carbon skeletons of amino acids in protein will be used for energy purposes. In addition, amino acids in the right balance must be present in the ingested protein otherwise protein utilization will be affected. Protein-energy malnutrition is quite common in both children and adults and is associated with disease. Protein deficiency has an adverse affect on all body organs and has been shown to have harmful effects on the brain, immune system, digestion, and kidney function. Protein malnutrition can be detected by low levels of albumin and transferrin in the blood. Common physical signs associated with protein deficiency are:

  1. Skin becomes thinner and appears dull
  2. Hair changes color, stops growing, or falls out
  3. Increased secretions from the mouth, nose, and eyes
  4. Edema of the hands and feet
  5. Muscle and/or menstrual cramps
  6. Low tolerance for exercise
  7. Cold hands and feet
  8. Bleeding gums

If you suspect you have a protein deficiency, contact your doctor or healthcare professional immediately.

Non-essential amino acids

  • Alanine (synthesized from pyruvic acid)
  • Arginine (synthesized from glutamic acid)
  • Asparagine (synthesized from aspartic acid)
  • Aspartic Acid (synthesized from oxaloacetic acid)
  • Cysteine
  • Glutamic Acid (synthesized from oxoglutaric acid)
  • Glutamine (synthesized from glutamic acid)
  • Glycine (synthesized from serine and threonine)
  • Proline (synthesized from glutamic acid)
  • Serine (synthesized from glucose)
  • Tryosine (synthesized from phenylalanine)

Essential amino acids

  • Histidine
  • Isoleucine
  • Leucine
  • Lysine
  • Methionine
  • Phenylalanine
  • Threonine
  • Tryptophan
  • Valine

Protein sources

Protein in our diets can come from animal and plant sources. Most animal sources (meat, poultry, fish, eggs, milk, cheese, and yogurt) provide complete protein, meaning that they contain all the essential amino acids. Protein from plants, legumes, grains, nuts, seeds, and vegetables don't contain all the essential amino acids but different sources are deficient in different amino acids; so eating different sources can supply all the essential amino acids. The digestive system, via enzymes, breaks all proteins down into their constituent amino acids so that they can enter the bloodstream. Your body needs protein, it cannot survive on just carbohydrates. Like carbohydrates, one gram of protein provides 4 calories of energy. There is some evidence that the source of protein may be important and that animal protein can cause problems, see Too much protein may cause reduced kidney function and The Effect of Dietary Protein Intake on Kidney Function in Women with Normal or Mildly Abnormal Kidneys which are based on the research article The Impact of Protein Intake on Renal Function Decline in Women with Normal Renal Function or Mild Renal Insufficiency, E.L. Knight, M.J. Stampfer, S.E. Hankinson, D. Spiegelman, and G.C. Curhan, Annals of Internal Medicine, 18 March 2003, Volume 138, Number 6, pages 460–467.

Tissue protein can also be broken down into amino acids and used for energy if there are not enough fats and carbohydrates in the diet. This can result in loss of muscle mass.

How much protein does my body need?

The amount of protein needed by your body depends on your activity level with a minimum of 0.36g/lb (0.8g/kg) and a maximum of 0.91g/lb (2.0g/kg) of body weight. The recommended maximum percentage of protein in our diet is 30% of total calories.

How much protein is converted to glucose?

It is generally believed that about 55% of protein is converted to glucose within 3-4 hours of being eaten and that fat has little effect on blood glucose levels. However, according to recent studies, very little protein or fat is converted to glucose. In addition, protein does not slow down the absorption or glucose response of a carbohydrate-dense meal. Fat delays the peak but not the total glucose response. So increasing the amount of protein and fat in our diet looks like a viable means of controlling postprandial glucose responses; however, this doesn't mean that a high-fat or high-protein diet is warranted.

The same studies alluded to above also indicate that, over the long term, high-fat and high-protein diets may induce insulin resistance! Another study indicates that monounsaturated fatty acids (found mostly in vegetable and nut oils such as olive, peanut, and canola) can improve insulin resistance (when calories from fat are less than 37% of total calories). See Protein Controversies in Diabetes, Marion J Franz, Diabetes Spectrum, Vol. 13, No. 3, 2000, pages 132-141; Effect of Protein Ingestion on the Glucose Appearance Rate in People with Type 2 Diabetes, MC Gannon, JA Nuttall, G Damberg, V Gupta, FQ Nuttall, The Journal of Clinical Endocrinology & Metabolism, Vol. 86, March 2001, pages 1040-1047; and Substituting dietary saturated for monounsaturated fat impairs insulin sensitivity in healthy men and women: The KANWU study, B Vessby, M Uusitupa, et al, Diabetologia, Vol. 44, Issue 3, 2001, pages 312-319.

I think there may be a connection with the effect of high levels of protein and possible calcium depletion (for example, see Dietary protein intake and urinary excretion of calcium: a cross- sectional study in a healthy Japanese population, R Itoh, N Nishiyama and Y Suyama, AJCN, Vol 67, 438-444, 1998; and Dietary protein and phosphorus do not affect calcium absorption, Robert P Heaney, AJCN, Vol. 72, No. 3, 758-761, September 2000). I also find myself asking about the use of calcium in bones and the production of red blood cells by bone marrow. Overall, it would seem prudent to take a calcium supplement and limit protein intake to 0.4g/lb of body weight with a maximum of 100g/day. In addition, it would also seem prudent to limit fat intake to a maximum of 30% of total calories with less than 10% saturated fat with the rest made of monounsaturated and polyunsaturated fats. Essential fatty acids (polyunsaturated fats) also improve protein and amino acid utilization, so a balanced EFA supplement seems warranted, I take 1 tbsp/day of Udo's Choice Ultimate Oil Blend (1tbsp=15mL: 135cals/ 14.5g fat/ 0.2g protein/ 0g carb).

Whey protein

Diabetes may deplete Glutathione (GSH) levels and a low GSH level may even be a contributing factor to the onset of diabetes, ongoing difficulty in controlling blood glucose levels, and in the development of diabetic complications. Whey protein stimulates GSH synthesis and enhances the body's immune system and there is some evidence that it also reduces hypertension, the leading causes of heart disease and stroke. It seems prudent to supplement our diet with about 30g/day of whey protein; I currently use and recommend GNC Pro Performance Elite Series Whey ISO Burst, Banana Berry Burst or French Vanilla, sucralose sweetened (45g: 160cal, 0.5g fat, 40g protein, 1.5g carb).

Whey is a high quality complete protein, second only to eggs, that contains all the essential amino acids required by the body. Typical whey protein quality measure values: PDCAAS=1.0; Amino Acid Score=1.14; PER=3.2; BV=100.

Whey protein is obtained from milk. Milk consists of 87% water and 13% solids; it contains two primary proteins (which make up 27% of the milk solids) casein (80% of milk protein) and whey (20% of milk protein). When cheese is produced, liquid whey separates from the casein (curd). The whey protein is then separated from the liquid whey and purified to various protein concentrations. To ensure maximum assimulation, use only products based on Whey Protein Isolate or Hydrolyzed Whey Protein Isolate which both have >90% protein, 0.5-1.0% lactose, and 0.5-1.0% fat.

For more information on whey protein, see the Whey Protein Institute.

Updated: October 28, 2005