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Low carb diet may increase heart risk: Mouse study

By Jess Halliday , 26-Aug-2009

A new study has concluded that low carb-high protein diet leads to more atherosclerosis in mice, findings that could have implications for diet strategies if they also hold true for humans.

The low carb approach to dieting had its heyday in the 1990s, with the marketing of popular commercial diets such as the Atkins Diet.

While nutrition experts advocate following a balanced diet instead of excluding certain nutrients, the researchers from Beth Israel Medical Center and Harvard Medical School in the US point out that the cardiovascular implications of obesity mean dietary approaches to weight loss are high on the agenda.

Low carb diets also tend to be high in protein and high in fat – but little is known about the cardiovascular implications of such an approach.

To investigate the matter, Anthony Rosenzweig and his team fed mice one of three diets for a 12-week period. Their method and findings are published in the Proceedings of the National Academies of Science.

The low carbohydrate-high protein (LCHP) contained 12 per cent carbohydrate,

43 per cent fat, 45 per cent protein and 0.15 per cent cholesterol. The standard mouse chow diet had for 65 per cent carbs, 15 per cent fat and 20 per cent protein. The ‘typical Western’ diet (WD) 43 had carbohydrate, 42 per cent fat, 15 per cent protein, and 0.15 per cent cholesterol.

The team found that the mice on the LCHP diet had gained less weight than the mice on the standard diet, but they had 15 per cent more aortic atherosclerosis – the thickening of artery walls due to plaque formation – and generated fewer new vessels in response to tissue ischemia. These changes could not be explained by changes in serum cholesterol, inflammatory mediators or infiltrates or oxidative stress.

By contrast, the WD mice group had 9 per cent more atherosclerosis than those on the standard chow.

While they did not settle on an explanation for the increased atherosclerosis, the researchers noted some other interesting factors that could play a part.

The number of bone marrow and peripheral blood endothelial progenitor cells, which indicate capacity for vascular regeneration, was reduced in the LCHP diet mice. These mice also had lower levels of activated Akt, a serine threonine kinase involved in endothelial progenitor cell mobilisation, proliferation and survival.

Rosenzweig said that caution should be taken when extrapolating from animal studies such as this, but added that “these data at least raise concern that low carbohydrate high-protein diets could have adverse vascular effects not adequately reflected in serum risk markers”.

“Moreover, these observations demonstrate important pathophysiological vascular effects of nonlipid macronutrients that are dissociated from weight gain.”

They could have implications for efforts to combat obesity and reduce its complications, he concluded.

Source

Proceedings of the National Academies of Science

Published online ahead of print

“Vascular effects of a low-carbohydrate high-protein diet”

Authors: Shi Yin Foo, Eric Heller, Joanna Wykrzykowska, Christopher Sullivan, Jennifer Manning-Tobin, Kathryn Moore, Robert Gerszten, and Anthony Rosenzweig