High protein diets are popular as they may have weight loss effects. The weight loss effects of protein are not fully understood, but may result from a number of factors including increased satiety, increase nitrogen retention leading to anti-catabolic skeletal muscle effects, as well as other unidentified factors. High protein diets are generally healthy in the short term and no studies have conclusively proven damaging effects for healthy individuals consuming high protein diets. Long term consumption of high protein diets may also be safe, however a number of issues can arise from their long term use. In particular, calcium excretion can increase as protein intake increases. For example, metabolic studies have investigated the effects of high protein diets on the calcium excretion in urine in healthy young male adults. Increases in nitrogen intake from 0 to 90 grams per day increased the excretion of calcium by 800 %, something that was independent of the calcium intake of the subjects1.
Protein metabolism results in the formation of sulphuric and phosphoric acid, because proteins is high in phosphorus and sulphur. Sulphur is contained in the sulphur containing amino acids methionine and cysteine, and phosphorus is present in genetic material and other cellular component. One gram of protein for example, contains 13 to 15 mg of phosphorus, and around half of this is absorbed. An intake of 90 grams of protein therefore result in the absorption of around 600 to 700 mg of phosphorus, and this increases the production of phosphoric acid considerably2. Protein also contains around 100 to 300 mg per 100 grams sulphur. The acid load from protein acidifies the blood and in response the calcium is released from its store in bone to act as a buffer to maintain the blood pH at around 7.2 to 7.4. This calcium is then excreted, and long term this can result in significant bone loss. High protein diets may therefore have detrimental effects on bone health in the long term, particularly in at risk groups.
Dr Robert Barrington’s Recommendation: the negative effects of high protein diets can be annulled by increasing the plant material content of the diet. Plant foods are high in potassium, and this increases production of potassium salts which in turn increases the buffering capacity of the blood. The acid load from protein is therefore not problematic if high amounts of plant foods are eaten concomitantly. Problems however do occur if the typical Western diet is consumed, because not only is it high in protein it is also low in plant foods. Long term consumption of the Western diet is now considered a risk factor for the development of osteoporosis. Weight bearing exercise also helps calcium retention in bone because it increases the structural strength of the bone and this requires the addition of calcium. A sedentary lifestyle in combination with a high protein Western diet is therefore a considerable health risk for detrimental bone diseases including osteoporosis.
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