News on Cholesterol

2 articles have been published recently in the JAMA adding a little more confusion regarding dietary cholesterol and its association with Cardiovascular disease and mortality. The recent publication of the dietary guidelines for Americans proclaimed that it would no longer include the recommendation to limit dietary cholesterol to <300mg/day, as there was no appreciable relationship between dietary cholesterol and serum cholesterol. Although the guidelines advise to eat as little dietary cholesterol as possible, it sent the opposite message to the public. Recent study pooled individual level data from 29615 participants in 6 prospective cardiovascular disease studies in the US. The authors observed the following:

– The risk of dietary cholesterol affecting cardiovascular outcomes is probably modest only. However, consumption of every additional 300mg of dietary cholesterol was associated with a higher risk of incident cardiovascular disease and total mortality.

– The increased risk ranged from 1 to 4% over a 17.5-year follow-up period.

– The studies done so far also suggest dietary cholesterol could have variable effects on different cardiovascular diseases i.e. strokes, heart attacks and heart failure.

– The risk of adverse events was not seen in those who had a very low cholesterol at base line i.e. those with elevated base line cholesterols (LDL) had a higher risk for adverse cardiovascular events.

– The authors assert that high sodium foods and foods rich in simple carbohydrates (sugars, sweets and polished cereals) and trans fats should be avoided altogether. They also advised that the individual checks his cholesterol levels and adjusts his diet accordingly.

In another study published this month in the JAMA, TMAO (Trimethylamine N-oxide) was identified as a possible culprit in producing cardiovascular disease and increasing all cause mortality. In the previous decades, doctors had pinned the blame for heart disease on saturated fats. The long chain saturated fatty acids in meat steaks, butter and coconut oil which raised the LDL cholesterol was thought to be the culprit for heart disease and death. Recent meta-analysis of dietary recall studies seems to suggest that this relationship was not as tight as previously thought. Researchers are currently homing in on another possible culprit i.e. TMAO which is possibly an additional biological pathway by which red meat increased heart disease risk. The body makes TMAO from foods with choline and L-carnitine which are found abundantly in meat, poultry, fish, dairy and egg yolks. These proteins are broken down by gut bacteria to form trimethylamine (TMA) which is then converted into TMAO in the liver. Red meat is high in L-carnitine and has been shown to raise the TMAO levels more than white meat or non-meat proteins. It also tends to shift the gut microbiome, fuelling more bacteria to produce TMA. The authors conclude that the carnitine-TMAO pathway is a partial reason for the heighted mortality and cardiovascular risk with chronic red meat diet. They conclude that TMAO generation requires the right gut bacteria and this could be another path to reducing cardiovascular events.

Author’s note:

– This may be another reason to take pro-biotic rich foods although we are still unsure as to which bacteria are truly beneficial.

– There are so many different processes that affect what happens inside the body. It is therefore important not to get carried away with every new theory and finding but to adopt moderation in dietary habits and to focus on having adequate plant-based, whole-grain, fibre-enriched and balanced diet.

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