Low carbohydrate, high protein diets are popular because both anecdotal and research evidence suggests that they cause weight loss. This appears to be particularly true for those individuals with large amounts of abdominal adipose tissue who find it difficult to lose weight by calorie restriction or exercise. Protein is though to cause weight loss because it can stimulate the release of satiety hormones from the gut (such as peptide YY), increases gastrointestinal transit time, and is less efficiently stored as energy compared to carbohydrate. However, some concern surrounds low carbohydrate high protein diets when the red and processed meat content is increased disproportionately to other protein sources. This is because epidemiological evidence suggests that diets high in red and processed meats may be detrimental to heath, primarily because they increase systemic inflammation. Protein from vegetable sources should therefore also be included in any high protein diet.
Researchers1 have assessed the impact of proteins from animal and vegetable sources on the risk of developing type 2 diabetes in a prospective study of 40,475 men (age 40-75) initially free of diabetes, cancer and cardiovascular disease. The subjects were followed for up to 20 years and their diets assessed via a frequent food questionnaires every 4 years. From the study 2689 cases of type 2 diabetes were identified at follow up. Analysis of the diets of these individuals showed that following adjustments for confounding variables, a low carbohydrate diet, when accompanied by high amounts of animal protein and fat was positively associated with type 2 diabetes. This association was mainly due to consumption of red and processed meat. However, a low carbohydrate diet high in vegetable protein and fat was not significantly associated with type 2 diabetes.
The association between diets high in red meat and processed meat is not surprising because these foods are known to cause systemic inflammation. Red meat is high in arachidonic acid (AA, C20:4 (n-6)) which can accumulate in cell membranes where it is converted to the pro-inflammatory series 2 and series 4 eicosanoids. Metabolic syndrome, cardiovascular disease, obesity and type 2 diabetes are increasingly being though of as inflammatory conditions, and high intakes of red meat may therefore contribute to the disease process. Vegetable protein is not associated with inflammation, but it is difficult to attain high amounts of protein from vegetables without also ingesting carbohydrates. Supplemental whey protein is a good way to increase protein levels, because it is low in carbohydrate and fat and is high in sulphur containing amino acids that have been shown to increase immunity.
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