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 prescribed for those with inherited metabolic disorders, such as Phenylketonuria and Homocystinuria and reduced protein levels have been used by people with kidney or liver disease. Low protein consumption appears to alter the risk of bone breakage, presumably through changes in calcium homeostasis.[1] Consequently, there is no uniform definition of what constitutes low-protein, because the amount and composition of protein for an individual suffering from phenylketonuria would differ substantially from one suffering homocystinuria. The amount used by those with liver disease would still result in individuals being in nitrogen balance.

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, some individuals with damaged livers or kidneys may be advised to eat less protein. Due to the sulphur content of the amino acids methionine and cysteine, excess of these amino acids leads to the production of acid through sulphate ions. These sulphate ions may be neutralized by calcium ions from bone, which may lead to net urinary loss of calcium. This might lead to reduction in bone mineral density over time. 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.[2][3][4][5] Apart from low protein intake, such as in the 80:10:10 diet,[6] other attempts to modulate IIS are through intermittent fasting and the 5:2 diet.

History[edit]

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.[7] Horace Fletcher was an early populariser of low-protein diets, which he advocated along with thorough mastication.

Protein requirement[edit]

The daily requirement for humans to remain in nitrogen balance is relatively small. The median human adult 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.[8] Children require more protein, depending on the growth phase. A 70 kg adult 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 kilocalories in a notional 2,200 kilocalorie ration. William Cumming Rose and his team studied the essential amino acids, helping to define minimum amounts needed for normal health. For adults, 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.[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. Plant protein is often described as incomplete, suggesting that they lack one or more of the essential amino acids. Apart from rare examples, such as Taro,[9][10] each plant provides an amount of all the essential amino acids. However, the relative abundance of the essential amino acids is more variable in plants than that found in animals, which tend to be very similar in essential amino acid abundance, and this has led to the misconception that plant proteins are deficient in some way. However, many plants have low concentrations of protein and so growing individuals may not be able to consume enough plant material to get all the protein that they need.[citation needed]

Low-protein vs calorie restriction[edit]

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.[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 energy 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]

Low-protein and liver disease[edit]

In the past a standard dietary treatment for those suffering from liver disease or damage was a low protein, high carbohydrate, moderate fat and low salt diet. However, more recent research suggests that a high protein diet is required of 1.2–2 g of protein per kg.[clarification needed] Levels of up to 2 g/kg body weight/day have been demonstrated to not worsen encephalopathy. In addition, vitamin supplements especially vitamin B group should be taken. Salt should be restricted to below 5 mg per day.[20][21]

Low-protein and kidney disease[edit]

Low-protein diets to treat kidney disease include the Rice diet, which was started by Walter Kempner at Duke University in 1939. This diet was a daily ration of 2,000 Calories consisting of moderate amounts of boiled rice, sucrose and dextrose, and a restricted range of fruit, supplemented with vitamins. Sodium and chloride where restricted to 150 mg and 200 mg respectively. It showed remarkable effects on control of edema and hypertension.[22][23] Although the Rice diet was designed to treat kidney and vascular disease, the large weight loss associated with the diet led to a vogue in its use for weight loss which lasted for more than 70 years. The Rice Diet program closed in 2013.[24] Other low-protein starch-based diets like John A. McDougall's program continue to be offered for kidney disease and hypertension.[citation needed]

Low-protein and osteoporosis[edit]

The effect of protein on osteoporosis and risk of bone fracture is complex. Calcium loss from bone occurs at protein intake below requirement when individuals are in negative protein balance, suggesting that too little protein is dangerous for bone health.[25] IGF-1, which contributes to muscle growth, also contributes to bone growth, and IGF-1 is modulated by protein intake.[5] However, at high protein levels, a net loss of calcium may occur through the urine in neutralizing the acid formed from the deamination and subsequent metabolism of methionine and cysteine. Large prospective cohort studies have shown a slight increase in risk of bone fracture when the quintile of highest protein consumption is compared to the quintile of lowest protein consumption.[1] In these studies, the trend is also seen for animal protein but not plant protein, but the individuals differ substantially in animal protein intake and very little in plant protein intake. As protein consumption increases, calcium uptake from the gut is enhanced.[25][1] Normal increases in calcium uptake occur with increased protein in the range 0.8 grams to 1.5 grams of protein per kilogram body weight per day. However, calcium uptake from the gut does not compensate for calcium loss in the urine at protein consumption of 2 grams of protein per kilogram of body weight. Calcium is not the only ion that neutralizes the sulphate from protein metabolism, and overall buffering and renal acid load also includes anions such as bicarbonate, organic ions, phosphorus and chloride as well as cations such as ammonium, titrateable acid, magnesium, potassium and sodium.[26] The study of Potential Renal Acid Load (PRAL) suggests that increased consumption of fruits, vegetables and cooked legumes increases the ability of the body to buffer acid from protein metabolism, because they contribute to a base forming potential in the body due to their relative concentrations of proteins and ions. However, not all plant material is base forming, for example, nuts, grains and grain products add to the acid load.[25][27][26]

Protein composition of foods[edit]

Food of different classes differ substantially in the amount of protein and the contribution of protein to Caloric content of the food. This table shows the grams of protein per 100 grams of a representative group of foods, the Calories in that food from protein, fat, and carbohydrate, and the proportion of the Calories due to protein. Refined sugars and oils or fats have not been included because the protein content in those are negligible or zero. Refined protein powders such as isolated soy or whey protein have also been excluded for the opposite reason.

Type Food Protein (g/100 g) Calories (per 100 g) Percent Calories from Protein
Animal Atlantic salmon 19.8 136 59.4
Animal Chicken egg 12.2 142 35.1
Animal Lamb 1/8 inch fat trim 17.8 222 32.8
Animal Lean Chicken 23.1 105 90.0
Animal Lean beef sirlion 21.3 136 63.9
Animal Pork belly 9.3 504 7.6
Dairy Camembert 16.4 297 22.6
Dairy Cheddar cheese 24.8 411 24.7
Dairy Cottage cheese 11.3 104 44.3
Dairy Cow's milk 3.3 64 20.9
Dairy Cream cheese 7.4 339 8.9
Dairy Low fat yoghurt 5.3 55 39.5
Dairy Parmesan cheese 34.7 364 39.0
Dairy Plain yoghurt 5.4 81 27.1
Dairy Triple Brie 12.2 446 11.2
Dairy Vanilla ice cream 1.9 178 4.4
Dry fruit Pitted dates 1.9 338 2.3
Dry fruit Sultanas 3.1 304 4.2
Fruit Apple 0.3 59 2.1
Fruit Avocado 2.0 172 4.8
Fruit Banana 1.1 100 4.5
Fruit Black pitted olives 2.2 182 4.9
Fruit Orange 0.9 52 7.0
Fruit Plum 0.7 52 5.5
Fruit Strawberry 0.7 37 7.7
Grain Jasmine white rice 7.2 361 8.2
Grain Medium grain whole rice 7.6 363 8.6
Grain Pearl barley 8.0 304 10.8
Grain Polenta 8.6 368 9.6
Grain Rolled oats 13.4 360 15.2
Grain Wholemeal flour 11.2 324 14.1
Legume Chickpeas dry 19.3 309 25.6
Legume Split red lentils 24.2 260 38.1
Legume Split yellow peas 23.0 296 31.8
Legume French lentils 23.7 258 37.5
Nuts Almonds 23.2 565 16.8
Nuts Cashews 18.2 584 12.8
Nuts Peanuts 24.7 552 18.3
Nuts Pecan 9.8 692 5.8
Nuts Pine nuts 13.0 687 7.7
Nuts Walnuts 15.2 692 9.0
Processed Bacon 16.0 294 22.3
Processed Beef sausages 12.8 224 23.3
Processed Chicken liver pate 9.1 333 11.2
Processed Chorizo 18.4 287 26.2
Processed Commercial Birchir muesli 12.1 410 12.1
Processed Commercial Hommus 5.4 323 6.8
Processed Commercial jam 0.3 268 0.5
Processed Commercial mustard 7.0 150 19.1
Processed Commercial peanut butter 30.2 597 20.7
Processed Commercial pepperoni 25.3 393 26.4
Processed Commercial salsa 1.6 38 17.0
Processed Commercial sauerkraut 1.3 21 24.4
Processed Corn flakes 7.8 373 8.6
Processed Custard powder 0.5 360 0.6
Processed Dark chocolate 5.0 521 3.9
Processed Desiccated coconut 6.6 645 4.2
Processed Dill pickle 0.8 9 33.1
Processed Fresh pasta sheet 10.9 286 15.6
Processed Gingernut biscuit 4.9 446 4.5
Processed Hazelnut spread 5.4 323 6.8
Processed Italian pasta 12.5 358 14.3
Processed Rice vermicelli 9.6 353 11.1
Processed Salted corn chips 8.2 498 6.7
Processed Salted potato chips 7.6 500 6.2
Processed Tomato sauce 1.8 141 5.2
Processed Vitaweat original 11.2 371 12.4
Processed Wheat bix 12.4 337 15.0
Processed White chocolate 5.0 571 3.6
Processed White flour 10.1 344 12.0
Processed Wholemeal bread 8.3 218 15.5
Seeds Golden linseed 32.4 288 46.0
Seeds Pumpkin kernels (peppitas) 24.4 557 17.9
Seeds Sunflower kernels 22.7 550 16.9
Seeds White quinoa 13.5 358 15.4
Vegetable Cauliflower 2.0 30 26.6
Vegetable Cos lettuce 1.2 21 23.3
Vegetable Cucumber 0.7 18 15.5
Vegetable Potato 2.0 84 9.7
Vegetable Sweet potato 1.6 89 7.3
Vegetable Tomato 0.9 21 17.2

Values taken from labels on commercial items and from a nutritional database.[28]

Methionine and Cysteine content of foods[edit]

It is often claimed that methionine and cysteine are more likely to be encountered in animal foods than in plant foods. This is often found in arguments for selective consumption of plant foods to combat osteoporosis, and in arguments to choose plant foods in diets restricting methionine. However, this is not strictly true, as the following table shows. Animal protein shows a range of approximately 3% to 4% methionine plus cysteine for meat as well as for milk and dairy. Eggs have higher values in a 4% to 7% range. While many fruit and vegetables have values below 3%, values for grains, seeds, and nuts fall in the 3% to 4% range, and many exceed 4%. Dry or mature legumes have values in the range 2% to 3%, but sprouted legumes exceed 4%. The highest value is for Brazil nuts. This table shows that unless large classes of plant food are avoided, a plant-based diet is unlikely to be significantly lower in methionine and cysteine than an omnivorous diet if the same level of protein is consumed.

Type Item Methionine (g/100g) Cysteine (g/100g) Protein (g/100g) Percent Methionine plus Cysteine in Protein
Animal Abalone, mixed 0.386 0.244 17.1 3.7
Animal Chicken, breast 0.563 0.274 20.8 4.0
Animal Lamb 1/8 inch fat trim 0.457 0.214 17.8 3.8
Animal Lobster, northern 0.529 0.211 18.8 3.9
Animal Pork, mixed cuts 0.347 0.169 13.9 3.7
Animal Salmon, Atlantic 0.626 0.219 20.4 4.1
Animal Sea bass, mixed 0.546 0.198 18.4 4.0
Dairy Camembert 0.565 0.109 19.8 3.4
Dairy Goat, soft 0.494 0.084 18.5 3.1
Dairy Parmesan 0.958 0.235 35.8 3.3
Dairy Ricotta 0.281 0.099 11.3 3.4
Dairy Roquefort 0.558 0.126 21.5 3.2
Dairy Yoghurt, plain, whole 0.102 0.032 3.5 3.8
Milk Buffalo, Indian 0.097 0.048 3.7 3.9
Milk Cow 0.082 0.030 3.3 3.4
Milk Goat 0.080 0.046 3.6 3.5
Milk Human 0.021 0.019 1.0 4.0
Milk Sheep 0.155 0.035 6.0 3.2
Egg Caviar 0.646 0.449 24.6 4.5
Egg Chicken 0.380 0.272 12.6 5.2
Egg Duck 0.576 0.285 12.8 6.7
Egg Goose 0.624 0.309 13.9 6.7
Fruit Apple 0.001 0.001 0.3 0.7
Fruit Avocado 0.038 0.027 2.0 3.2
Fruit Banana 0.008 0.009 1.1 1.5
Fruit Mango 0.005 0.000 0.5 1.0
Fruit Orange 0.020 0.010 0.9 3.3
Fruit Peach 0.010 0.012 0.9 2.4
Fruit Pear 0.002 0.002 0.4 1.0
Fruit Pineapple 0.012 0.014 0.5 5.2
Grain Barley, hulled 0.240 0.276 12.5 4.1
Grain Brown long-grain rice 0.179 0.096 7.9 3.5
Grain Durum wheat 0.221 0.286 13.7 3.7
Grain Maize, white 0.197 0.170 9.4 3.9
Grain Oats 0.312 0.408 16.9 4.3
Grain Rye 0.248 0.329 14.8 3.9
Legume Black beans 0.325 0.235 21.6 2.6
Legume Chickpeas 0.253 0.259 19.3 2.7
Legume Fava beans 0.213 0.334 26.1 2.1
Legume Kidney beans 0.355 0.256 23.6 2.6
Legume Lima beans 0.271 0.237 21.5 2.4
Legume Mung beans 0.286 0.210 23.9 2.1
Legume Pink lentils 0.212 0.327 24.9 2.2
Legume Soybeans 0.534 0.638 39.6 3.0
Legume Sprouted lentils 0.105 0.334 9.0 4.9
Nut Almonds 0.196 0.293 22.1 2.2
Nut Brazilnuts 1.008 0.367 14.3 9.6
Nut Cashews 0.362 0.393 18.2 4.1
Nut Hazelnuts 0.221 0.277 15.0 3.3
Nut Pecans 0.183 0.152 9.2 3.6
Nut Pistachio 0.338 0.357 20.6 3.4
Nut Walnuts 0.236 0.208 15.2 2.9
Seed Chia 0.090 0.361 15.6 2.9
Seed Flaxseed 0.370 0.340 18.3 3.9
Seed Pumpkin, pepitas 0.551 0.301 24.5 3.5
Seed Sesame 0.586 0.358 17.7 5.3
Seed Sunflower 0.494 0.451 20.8 4.5
Seed Watermelon 0.834 0.438 28.3 4.5
Soy Milk, unfortified 0.027 0.000 3.3 0.8
Soy Miso 0.129 0.000 11.7 1.1
Soy Tempeh 0.175 0.193 18.5 2.0
Soy Tofu, raw, firm 0.202 0.218 15.8 2.7
Vegetable Breadfruit 0.010 0.009 1.1 1.7
Vegetable Cabbage 0.012 0.011 1.3 1.8
Vegetable Capsicum, Hungarian 0.010 0.015 0.8 3.1
Vegetable Carrot, baby 0.006 0.007 0.6 2.2
Vegetable Cauliflower 0.028 0.023 2.0 2.6
Vegetable Celery 0.005 0.004 0.7 1.3
Vegetable Cucumber 0.006 0.004 0.7 1.4
Vegetable Lettuce, Cos 0.015 0.006 1.2 1.7
Vegetable Potato 0.033 0.026 2.0 2.9
Vegetable Sweet potato 0.029 0.022 1.6 3.2
Vegetable Taro 0.020 0.032 1.5 3.5
Vegetable Tomato 0.006 0.009 0.9 1.7
Vegetable Yam 0.021 0.019 1.5 2.7

The values in the table show only weak correlations between pairs of methionine, cysteine and total protein content.[original research?] Methionine and cysteine are treated together because they are interconverted via homocysteine and because both amino acids contain sulphur, and so both contribute to the acid load when they are broken down. All values for methionine, cysteine, and protein content of foods were taken from a nutritional database.[29]

Countries[edit]

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

Claims[edit]

Low protein, vegetarian diets have been hypothesized to be linked to longer life.[30]

See also[edit]

References[edit]

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