Dr Rajiv Chowdhury, Senior Research Associate in Global Cardiovascular Health at the University of Cambridge in England, is a qualified physician who was trained in Cardiovascular Epidemiology at the University of Cambridge with the support of a prestigious Gates Cambridge scholarship.
Following completion of his PhD in 2013, he embarked on his current position of Senior Research Associate in Global Cardiovascular Health within this department. He was elected a Fellow of the UK Royal Society for Public Health in 2011.
In an interview, he addresses key issues in the debate on saturated fats and nutrition. He also expresses the need for public health practitioners to better inform consumers about the significant health risks associated with consuming trans fats.
- The debate around nutrition is complex, including on saturated fats, sugar and carbohydrates. What do you feel are the key points that need to be addressed?
When it comes to the individual effect of fats, the principal reason why saturated fats have been considered harmful is their detrimental supplement effects on low-density (or bad) lipoprotein cholesterols in blood, observed in the earlier metabolic ward trials.
Nonetheless, these trials also reported that saturated fats tended to enhance high-density (or good) lipoprotein cholesterols and apo-A1, and reduce Lp(a) concentrations – all of which are potentially beneficial circumstances for coronary heart disease (CHD). Therefore, judging the effect of a nutrient on disease risk through its effect on a single intermediate factor may not be optimal.
It is also crucial to appreciate that the traditional crude grouping of fatty acids (such as ‘total’ saturated fats) is less helpful. This is because when specific fatty acid subtypes are examined, associations for these individual fats seem to vary significantly within each broad fatty acid family considered.
For example, recent evidence indicates that while odd-chain saturated fat subtypes (which correlate with dairy products) are beneficial for cardiometabolic health, even-chain saturated fat subtypes (which correlate with refined carbohydrates, sugary drinks and alcohol consumption, among others) tend to raise this risk. This suggests that food sources of specific fatty acid subtypes might be more important to determine subsequent disease susceptibility than any composite fatty acid group alone.
Finally, based on the available evidence from observational studies that assessed substitution effects of various nutrients, a key aspect to consider is what we are replacing the saturated fats with. It is often the case that when food manufacturers take out fats from food products, they replace those with carbohydrates from refined grain or sugar.
These refined carbohydrates get digested in our body rapidly, causing blood sugar and insulin levels to first rise and then dip, leading in turn to hunger, overeating and weight gain. Over time, these can enhance the risk of CHD. Therefore, when foods such as red or processed meats are reduced, they should perhaps be replaced with oily fish, nuts, beans and healthy oils.
- There is an ongoing debate around the world about limiting trans fats. Do you feel there is an adequate understanding of the dangers of trans fats?
One of the key findings that we reported in our Annals of Internal Medicine review was a significant strong positive association of trans (or artificial) fats in diet with CHD risk (meta-analysing data from more than 150,000 participants from five long-term observational studies).
This is in line with the key nutritional guidelines that encourage avoidance of trans fats consumption. Eating trans fats raises bad cholesterols, reduces good cholesterols, and promotes inflammation and loss of optimal endothelial function in humans – all of which are cardiotoxic. Since there are absolutely no known requirements for trans fats for our body functions, the consumption of trans fats should be kept as minimal as possible.
While mandatory inclusion of the trans fats content in food labels has helped Western consumers to identify and avoid products with trans fats content, and encouraged many food manufacturers to reduce inclusion of trans fats in their products, I believe, however, that greater awareness worldwide is needed to inform members of the public and health practitioners about the significant health risks associated with consuming this artificial bad fat.
- Palm oil is well-known as a replacement for trans fats in many foodstuffs. Is replacement of trans fats generally seen as a positive move by the scientific community?
There is little doubt, given the current evidence base, about the significant detrimental effect of trans fats on health, and the fact that this harmful artificial fat in food should be replaced by a healthier, natural alternative. Therefore, complete removal or replacement of trans fats from food products is definitely viewed as the right move forward.
However, when it comes to replacement, the scientific community appears to be somewhat divided on which alternative should be used to replace trans fats optimally. Natural choices such as palm oil are generally higher in even-chain saturated fat content than other plant oils. However, they seem to be less harmful than partially hydrogenated oil high in trans fats.
In dietary intervention studies, comparing a palm oil-rich diet with diets rich in trans fats yields significant higher levels of HDL cholesterol and apolipoprotein A-I, and significantly lower apolipoprotein B, triacylglycerols, and TC/HDL cholesterol.
- Do you plan to conduct further research in this area, and what other questions do you feel need to be looked into?
There should be more research done to better understand individual and substitution effects of specific fat subtypes (and their food sources) on clinical cardiovascular outcomes, since the majority of previous work focused on intermediate factors (such as lipids).
This is also true for palm oil since the majority of studies that looked at palmitic acid (the predominant fatty acid in palm oil) in blood in relation to CHD generally included a few hundred coronary outcomes; were not optimally adjusted for wide range of potential dietary and non-dietary confounding factors; and none were carried out in non-Western populations (where levels of palm oil consumption is high).
Such studies are required to definitively answer which natural and healthier cooking oil is best suited to replace artificial trans fats for coronary disease reduction worldwide. We are currently working on several large-scale observational studies of incident CHD involving both Europeans and South Asians to answer some of these intriguing questions.
- Would you be able to tell us a little more about these new studies, and when you would expect them to be published?
We are presently working on data from a large pan-European cohort and a large South-Asian cohort looking at specific fatty acids in relation to a large number of coronary disease outcomes. We expect preliminary results to be available potentially by middle of 2016.
