Low-protein diet

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A low-protein diet is a diet in which people reduce their intake of protein. A low-protein diet is often prescribed to people with kidney or liver disease, or for those with inherited metabolic disorders, such as Phenylketonuria and Homocystinuria. Consequently, there is no uniform definition of what constitutes low-protein, because the amount of protein for an individual suffering from phenylketonuria would differ substantially from one suffering kidney disease.

Amino acids that are excess to requirement cannot be stored, but must be modified by deamination (removal of the amine group). As this occurs in the liver and kidneys, individuals with damaged livers or kidneys are placed on a low-protein diet. Individuals suffering from phenylketonuria lack the enzyme to convert phenylalanine to tyrosine so low levels of this amino acid need to be provided in the diet. Homocystinuria is an inherited disorder involving the metabolism of the amino acid methionine leading to the accumulation of homocysteine. Treatment includes providing low levels of methionine and high levels of vitamin B6 in the diet.

Low-protein diets are in vogue among some members of the general public because of the impact of protein intake on Insulin/Insulin-like growth factor 1 Signalling (IIS) and the direct sensing of amino acid availability by mammalian target of rapamycin (mTOR), two systems that are implicated in longevity and cancer proliferation.[1][2][3][4] Apart from low protein intake, such as in the 80:10:10 diet,[5] other attempts to modulate IIS are through intermittent fasting and the 5:2 diet.

History

By studying the composition of food in the local population in Germany, Carl von Voit established a standard of 118 grams of protein per day. Russell Henry Chittenden showed that less than half that amount was needed to maintain good health.[6] Horace Fletcher was an early populariser of low-protein diets, which he advocated along with thorough mastication.

Protein Requirement

The daily requirement for humans to remain in nitrogen balance is relatively small. The median human requirement for good quality protein is approximately 0.65 gram per kilogram body weight per day and the 97.5 percentile is 0.83 grams per kilogram body weight per day.[7] A 70 kg human who was in the middle of the range would require approximately 45 grams of protein per day to be in nitrogen balance. This would represent less than 10% of Calories in a notional 2,200 Calorie ration. William Cumming Rose and his team studied the essential amino acids, helping to define minimum amounts needed for normal health. The recommended minimum amounts of each essential amino acid varies from 4 to 39 milligrams per kilogram of body weight per day. To be of good quality, protein only needs to come from a wide variety of foods, there is neither a need to mix animal and plant food together nor a need to complement specific plant foods, such as rice and beans.[8][9] The notion that such specific combinations of plant protein need to be made to give good quality protein stems from the book Diet for a small planet.

Low-protein vs Calorie Restriction

Calorie restriction has been demonstrated to increase the life span and decrease the age-associated morbidity of many experimental animals. Increases in longevity or reductions in age-associated morbidity have also been shown for model systems where protein or specific amino acids have been reduced. In particular, experiments in model systems in rats, mice, and Drosophila fruit flies have shown increases in life-span with reduced protein intake comparable to that for Calorie restriction. The effect appears to be entirely due to restriction of the amino acid methionine, which is required to initiate protein synthesis.[10][11][12][13][14][15][16]

The diets of humans living in some of the Blue Zones, regions of enhanced numbers of centenarians and reduced age-associated morbidity, contain less than 10% of Calories from protein,[17] although reports on all the Blue Zones are not available. None of the diets in these regions is completely based on plants, but plants form the bulk of the food eaten.[18] Although it has been speculated that some of these populations are under Calorie Restriction, this is contentious as their smaller size is consistent with the lower food consumption.[19]

Protein composition of foods

Foods that consist of more than 20% of Calories from protein include meats, eggs, fish, poultry, milk, yogurt, cheese, pulses, peanut butter and nuts. Foods that consist of less than 10% of Calories from protein include vegetables and fruits while cereal products vary around 10% of Calories from protein depending on the constitution of the food. A ration with a large proportion of Calories from vegetables and fruit will therefore tend to be low in protein.

Unprocessed food can also be classified by the amount of protein per 100 grams of weight, values for a wide range of foods and portion sizes can be found here.[20] Most vegetables and fruit contain 1 to 2 grams of protein per 100 grams of weight. Cow's milk contains 3.2 grams of protein per 100 grams. Raw green peas contain 5 grams of protein per 100 grams but dry legumes contain substantially more (see below). Cereals contain around 10 grams of protein per 100 grams, varying from 8 grams (rice) to 13 grams (rolled oats) of protein per 100 grams of uncooked, dry weight. Chicken eggs contain 13 grams of protein per 100 grams of weight, not counting the shell. Fish, poultry and red meat contain 20 or more grams of protein per 100 grams, for example, 20 grams for wild salmon, 21 grams for beef and 22 grams for turkey of protein per 100 grams of flesh. Cheese, a processed form of milk, contains a wide range of values depending upon the method of processing and degree of fat. For example, cream cheese contains 6 grams of protein, brie contains 21 grams of protein, and full fat cheddar cheese contains 25 grams of protein per 100 grams of weight. Dried legumes contain high levels of protein, above 20 grams per 100 grams weight, for example, mung beans contain 24 grams of protein, split dried peas contain 25 grams of protein, lentils contain 26 grams of protein, and soybeans contain 36 grams of protein per 100 grams of weight.

Countries

In the United Kingdom, low-protein products and substitutes are prescribed through the health service.

Claims

Low protein, vegetarian diets have been hypothesized to be linked to longer life.[21]

See also

References

  1. ↑ Alayev A and Holz MK (2013) mTOR signaling for biological control and cancer. Journal of Cell Physiology vol 228 pages 1658-1664
  2. ↑ Jewell JL and Guan K-L (2013) Nutrient signaling to mTOR and cell growth. Trends in Biochemical Sciences vol 38 pages 233-242
  3. ↑ Pollak MN, Schernhammer ES and Hankinson SE (2004) Insulin-like growth factors and neoplasia. Nature Reviews Cancer vol 4 pages 505-518
  4. ↑ Thissen J-P, Ketelslegers J-M and Underwood LE (1994) Nutritional regulation of the Insulin-like growth factors. Endocrine Reviews vol 15 pages 80-101
  5. ↑ http://www.dailymail.co.uk/femail/article-2149362/Fruit-meals-cooking-allowed-Is-80-10-10-raw-vegan-diet-secret-Olympic-athletes-body.html
  6. ↑ Lewis HB (1944) Russell Henry Chittenden. Journal of Biological Chemistry vol 153 pages 339-342
  7. ↑ Rand WM, Pellett PL, Young VR (2003) Meta-analysis of nitrogen balance studies for estimating protein requirements in healthy adults. American Journal of Clinical Nutrition vol 77 pages 109-127
  8. ↑ McDougall J (2002) Plant foods have a complete amino acid composition. Circulation vol 105 page e197
  9. ↑ Howard BV (2002) Response to plant foods have a complete amino acid composition. Circulation vol 105 page e197
  10. ↑ Ooka H, Segall PE, Timiras PS (1988) Histology and survival in age-delayed low-tryptophan-fed rats. Mechanisms of Ageing and Development vol 43 pages 79-98
  11. ↑ Orentreich N, Matias JR, DeFelice A and Zimmerman JA (1993) Low methionine ingestion by rats extends life span. Journal of Nutrition vol 123 pages 269-274
  12. ↑ Miller RA, Buehner G, Chang Y, Harper JM, Sigler R, Smith-Wheelock M (2005) Methionine-deficient diet extends mouse lifespan, slows immune and lens aging, alters glucose, T4, IGF-I and insulin levels and increases hepatocyte MIF levels and stress resistance. Aging Cell vol 4 pages 119-125
  13. ↑ Grandison RC, Piper MDW and Partridge L (2009) Amino-acid imbalance explains extension of lifespan by dietary restriction in Drosophila. Nature vol 462 pages 1061-1064
  14. ↑ Flatt T (2009) Diet and longevity in the balance. Nature vol 462 pages 989-990
  15. ↑ Caro P, Gomez J, Sanchez I, Naudi A, Ayala V, Lopez-Torres M, Pamplona R and Barja G (2009) Forty percent methionine restriction decreases mitochondrial oxygen radical production and leak at complex I during forward electron flow and lowers oxidative damage to proteins and mitochondial DNA in rat kidney and brain mitochondria. Rejuvenation Research vol 12 pages 421-434
  16. ↑ Brind J, Malloy V, Augie I, Caliendo N, Vogelman JH, Zimmerman JA, Orentreich N (2011) Dietary glycine supplementation mimics lifespan extension by dietary methionine restriction in Fisher 344 rats. The FASEB Journal vol 25 page 528.2
  17. ↑ Willcox BJ, Willcox DC, Todoriki H, Fujiyoshi A, Yano K, He Q, Curb JD, and Suzuki M (2007) Caloric restriction, the traditional Okinawan diet, and healthy aging. Annals of the New York Academy of Science vol 1114 pages 434-455
  18. ↑ Pes GM, Tolu F, Poulain M, Errigo A, Masala S, Pietrobelli A, Battistini NC, and Maioli M (2013) Lifestyle and nutrition related to male longevity in Sardinia: An ecological study. Nutrition, Metabolism and Cardiovascular Diseases vol 23 pages 212-219
  19. ↑ Keys A and Kimura N (1970) Diets of middle aged farmers in Japan. American Journal of Clinical Nutrition vol 23 pages 212-223
  20. ↑ http://nutritiondata.self.com/
  21. ↑ "Vegetarian low protein diet could be key to long life." Telegraph.co.uk.
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