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Low-carb diets may clog up arteries
A low-carb diet may not raise cholesterol but it may contribute towards a build-up of plaque in your artery walls, which is a risk factor for heart attack and stroke, according to US researchers
Diets that allow you to eat cheese and meat - as long as you cut the carbs - and still lose weight, were always going to be popular. Even better, the usual signs of stress on the heart and blood vessels, such as raised cholesterol, appeared to be absent in people following such diets.
However, Dr Shi Yin Foo, a clinical cardiologist in the Rosenzweig laboratory at by the Beth Israel Deaconess Medical Center (BIDMC) at Harvard University, started to investigate the effects of a low-carb diet on heart health after seeing heart attack patients who were on these diets.
"It's very difficult to know in clinical studies how diets affect vascular (blood vessel) health," explains senior author Dr Anthony Rosenzweig, Director of Cardiovascular Research in BIDMC's CardioVascular Institute and Professor of Medicine at Harvard Medical School.
"We, therefore, tend to rely on easily measured serum markers (such as cholesterol), which have been surprisingly reassuring in individuals on low-carbohydrate/high-protein diets, who do typically lose weight. But our research suggests that, at least in animals, these diets could be having adverse cardiovascular effects that are not reflected in simple serum markers."
According to the Proceedings of the National Academy of Sciences (PNAS), their study showed that mice placed on a 12-week low-carbohydrate/high-protein diet showed a significant increase in atherosclerosis (a build-up of plaque in the heart's arteries).
Worryingly, their findings also showed that the diet damaged the body's ability to form new blood vessels in tissues deprived of blood flow – this is required for recuperation after a heart attack.
The mice were divided into three groups and fed the equivalents of a low-carb/high-protein diet, a typical 'western diet' and a high-carb diet. The scientists then observed the mice after six weeks, and again at 12 weeks.
Just as in humans, the mice fed the low-carbohydrate diet gained 28 percent less weight than the mice fed the Western diet.
However, further investigation revealed that the low-carb diet animals had double the thickness of plaque in their blood vessels - 15.3 percent compared with 8.8 percent among the Western diet group. As expected, the mice on the high-carbohydrate diet showed minimal evidence of plaque build-up compared with either of the other two groups.
Searching for an explanation that might account for these findings, the team tested the mice for all the usual indications of vascular disease, including cholesterol, triglyceride levels, oxidative stress, insulin and glucose, as well as levels of some inflammatory cytokines. However, in each case there were no differences between the low-carb mice and the Western diet mice. If anything, the results were slightly in favour of the low-carb diet.
Dr Foo wondered whether the restorative capacity of the animals might be contributing to the difference. The investigators, therefore, looked at the animals' blood vessel lining cell (EPC) counts. Derived from bone marrow, the EPC cells may play a role in vessel re-growth and repair following injury.
"Examinations of the animals' bone marrow and peripheral blood showed that the measures of EPC cells dropped fully 40 percent among the mice on the low-carb diet – after only two weeks," commented Rosenzweig.
“For now, it appears that a moderate and balanced diet, coupled with regular exercise, is probably best for most people," says Rosenzweig, who, following these results, abandoned the low-carb diet he had been following.
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