Dietary fat and coronary artery disease- Have we been fooled? Dr. Sundeep Mishra writes
M3 India Newsdesk Jun 23, 2019
In the Suday Series here is an article from Prof. Dr. Sundeep Mishra where he discusses role of fat in coronary artery disease based on clinical trials.
From time immemorial there has been a myth that consuming high cholesterol and saturated fat diet can contribute to the development of CAD.
Are dietary fats bad for the heart?
At Cardiology Society of India (CSI) 2018 meeting, Dr. D Prabhakaran introduced the delegates to two raging controversies:
Can high consumption of dietary cholesterol lead to CAD?
Can high consumption of saturated fats lead to CAD?
He revealed that while there is a definite and a strong association of excess carbohydrate intake (>60% of total caloric intake) which was found to be associated with higher total and non-cardiovascular disease mortality, there was no such relation with dietary fats.
As a matter of fact, higher fat intake, including saturated fats, had no association to major cardiovascular disease events, myocardial infarction or cardiovascular disease mortality. The fact has been brought out by several follow-up studies which show no association between dietary cholesterol (egg consumption) and serum cholesterol, all-cause death, total coronary heart disease, or other heart disease problems such as angina pectoris or myocardial infarction.
Furthermore, several meta-analysis and recent studies ( PURE, Malmo diet Cancer study, Predimed) have shown that saturated fats may be neutral or protective. Unfortunately in day-to-day practice carbohydrates still account for a large proportion of total energy intake (~70% in some Indian populations).
Changing dietary habits are further worsening the whole problem:
- Coarse grains (millet, barley, sorghum, and maize) are being replaced with refined grains (wheat and rice)
- Increased processed foods (salted snacks and prepared sweets), edible oils, and animal products (milk, egg, chicken, and fish)
- Mustard and Groundnut oil are being replaced with palm and soybean oil
Dr. D Prabhakaran's advice to delegates was:
- Eat in moderation
- Eat plenty of fruits and vegetables
- Overcome your destiny by eating right
- Cook your food the right way
- Reduce deep fried foods
- Reduce salt
- Others: Avoid tobacco in all forms and alcohol as much as possible, moderate exercise
Are dairy fats good for the heart?
In another presentation on this issue “Are dairy fats good for the heart?”, by Dr Arun K Chopra from Fortis, Amritsar discussed the validity of the current dietary guidelines by AHA and USDA restricting dairy fats as part of their recommendation to curtail saturated fats (despite removing the upper limits on dietary cholesterol and total fat intake).
- He opined that the AHA, AAP, and USDA have recommended the intake of low-fat or no-fat dairy for lowering LDL cholesterol and preventing CVD, but these guidelines have been questioned in view of several recent studies suggesting benefits of dairy fat with regard to CHD, stroke, and type 2 diabetes.
- He questioned the wisdom of lumping together all dairy as one when it includes a large variety of foods with very different properties, like milk (whole and low-fat), yogurt, several types of cheese, cream, butter, ghee (clarified butter) and desserts.
The only evidence against dairy appears to be its saturated fat content (3.5% total fat in milk, accounts for over half of its calories and 51% of its fat content), while about 25% of dairy fat is MUFA and 15% are classic dairy fats (medium-chain, odd-chain and ruminant trans fatty acids).
- He further discussed several meta-analyses demonstrating the neutral association of saturated fats with CHD, and borderline negative association with strokes suggesting an overall neutral impact on CVD (Siri-Tarino et al 2010, Chowdhary et al 2014).
- While there is little data supporting the US guidelines recommending 3 daily servings of low-fat milk for adults and at least 2 for children for promoting bone health, there is none showing any harm as well.
The only study showing benefits with restricting saturated fats from 6 months of age is the STRIP study from Finland; here too, it is a comprehensive lifestyle change (cessation of smoking, exercise, reduced salt, and increased fibre, fruits, and vegetables) that is rewarding, rather than simple restriction of dairy fats.
- This stresses the need to focus on sources of saturated fats, rather than saturated fats in general; meat, for instance, is associated with increased risk of CVD and diabetes, while dairy appears largely negatively associated with these diseases.
- Discussing specific studies on risk factors, dairy appears to have little long-term impact on body weight in adults, as they tend to compensate for their carbohydrate intake according to their intake of dairy products.
If at all, a study on American children (age 9-14 years, followed for 3 years) suggested that weight gain in children depended on the total number of servings of dairy consumed daily, and that low-fat milk rather than whole milk was associated with weight gain.
This is apparently due to increased hunger in kids consuming low-fat milk, especially when it is flavoured (flavoured milks have similar sugar content as colas, and are thus to be discouraged). On the other hand, there is reasonable data that other dairy products (except excessive butter or ghee) are associated with weight maintenance rather than gain.
Dairy appears to be strongly negatively associated with diabetes; the strongest data is for unsweetened yogurt, followed by cheese and butter.
- Several large meta-analysis support this conclusion; the mechanisms appear to be its MUFA, branch chain, and odd-chain fatty acids, probiotic bacteria, fermentation leading to the formation of vitamin K2.
- A recent meta-analysis by the FORCE Consortium provides further evidence of a 29% reduction in incident diabetes over 20 years follow-up with specific biomarkers of dairy fat.
- An earlier systematic review and meta-analysis performed by Mozaffarian et al in lakhs of subjects further upholds the benefits of dairy by confirming neutral association with CAD and reduction in strokes and diabetes.
However, milk unlike popular perception, is not a perfect food and has many problems such as:
- lactose intolerance in 2/3rd of the adult population (increased by pasteurisation of milk)
- presence of hormones, antibiotics, and inflammatory substances that are associated with a variety of allergies, eczema and acne,
- IGF-1, which increases lean mass growth in athletes but is also linked with increased risk of cancers
However, these problems are not due its fat content, but due to other MSNF (milk solids-not-fat) and injections given to cows and buffaloes for improved milk output.
Dairy fat is not associated with any increase in CAD risk, and appears beneficial for stroke and diabetes, and is not associated with any increase in CVD or total mortality; hence, dairy fat is good for the heart.
Disclaimer- The views and opinions expressed in this article are those of the author's and do not necessarily reflect the official policy or position of M3 India.
The writer, Dr. Sundeep Mishra is a Professor of Cardiology.
This article was originally published on 28.11.18
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