The weight loss effects of high protein diets have been extensively studied in the scientific literature. Their satiating and thermogenic effects are well reported and is likely the mechanism by which they are able to cause weight loss in overweight individuals. However, although their general effects are known, the nuances of the metabolic changes caused by higher intakes of protein are not fully understood. To these ends, researchers1 have investigated the effects of protein on the morphology and metabolism of adipocytes in order to better understand their cellular effects. Obese subjects were fed either a restricted calorie high protein diet (1200kcal/d) or a restricted calorie conventional (lower protein) diet (1200kcal/d) for 2 weeks, followed by a washout period of 8 weeks before crossing over to the opposite treatment. The high protein diet was designed to have a low glycaemic load and also contain high amounts of soluble fibre.
Biopsies of adipose tissue revealed that subjects consuming the high protein diet had a significant decrease in adipocyte diameter when compared to subjects consuming the conventional diet. Fasting plasma glucose and plasma C-reactive protein (a biomarker of systemic inflammation) only decreased following the high protein diet, which may reflect the lower glycaemic effects of the food. The possible cardiometabolic risk factors plasminogen activator inhibitor protein-1, vascular endothelial growth factor and interferon-γ inducible protein 10 were significantly lower in the subjects consuming the high protein diets. However, no changes in body composition were reported between the to groups. The researchers also reported that genes associated with inhibiting adipogenesis and angiogensis were correlated with the reduction in adipocyte diameter, suggesting that remodelling at the genetic levels had resulted in the beneficial changes in the high protein diet group.
Although this study contained only 13 subjects it provides evidence that high protein diets may have favourable effects on the remodelling of adipose tissue and a subsequent reduction in metabolic risk factors for cardiovascular disease. Fibre and protein both appear to provide weight loss benefits when incorporated into a healthy diet and this may relate to their effects on the glycaemic load, which may in turn provide beneficial effects on insulin resistance and plasma lipids. No effects on insulin resistance were reported in this study, and this may have been due to the short duration (2 weeks) of the treatment period. This viewpoint is supported by the fact that levels of adiponectin, a marker for insulin resistance, did not change significantly during either treatment. Taken as a whole, these result provide further evidence that high protein diets with a low glycaemic load can provide cardiovascular benefits.
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