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Should you go vegetarian or vegan for your heart?
At almost every talk I give, somebody asks me about a vegan diet. Shouldn't we be telling our patients to go vegan, given the evidence against red meat in particular and animal protein in general?
Eating Healthier After a Heart Attack
There is good research to show that once you've had a heart attack, you can reduce your risk of having another heart attack (or a stroke or other cardiovascular event) up to 35% by quitting smoking, exercising regularly, and improving your diet. While quitting smoking and exercising regularly is pretty straightforward, improving your diet, as you probably know, can be confusing.
Diet drinks linked to stroke, heart disease
We know that too much added sugars are bad for you - and in the Western diet these added sugars too often come from sugar-sweetened beverages like sodas and juice drinks. These have fairly convincingly been linked to increased risk of stroke and heart disease, so naturally people turn to sugar-free versions of the same drinks, thinking they're healthier.
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We know that a Mediterranean-style diet can help prevent you from ever developing heart disease. This is known as "primary prevention". But what if you have already had a heart attack or other heart event? Is is too late to reduce your risk of another event?
Researchers in Spain are conducting an ongoing randomized controlled trial in 731 adult men and women recruited between 2009 and 2012 (Stroke doi:10.1161/STROKEAHA.120.033214). The participants have all been diagnosed with coronary heart disease, defined as being diagnosed with a heart attack, unstable angina, or chronic high-risk ischemic heart disease. The participants had to have been stable - with no diagnosed heart events - for 6 months prior to joining the study.
The participants have been randomly assigned to either a Mediterranean-style diet or the diet recommended by Spain's National Cholesterol Education Program (the standard treatment in Spain). Both diets are similar in that they emphasize higher intake of whole grains, fruits and vegetables, and legumes, but the National Cholesterol Education Program's diet recommends <30% of calories from fat, at least 55% of calories from carbohydrates, and 15% of calories from protein.
In contrast, the Mediterranean-style diet the participants were educated in featured at least 35% of calories from fat (<10% saturated fat), 15% of calories from protein, and a maximum of 50% of calories from carbohydrates.
The diets were not designed for weight loss, the participants were not told to change their exercise habits, and there was no limit set on the number of total calories the participants could consume. The participants filled out regular dietary surveys and met with dietitians to help them adhere to their assigned diets.
But how did the researchers know if the diets worked, since both diets were designed to reduce the risk of another coronary event? One of the ways we physicians assess artherosclerosis ("hardening of the arteries") is by measuring the thickness of the two innermost layers on the carotid arteries using ultrasound - what is called the common carotid artery intima-media thickness (CCA-IMT). Thicker layers, to somewhat oversimplify, means greater cardiovascular risk.
All of the participants completed the ultrasound study to measure their CCA-IMT at the start of the study, then again both 5 and 7 years later.
In their analysis the authors took into account age, sex, Body Mass Index, whether the participant had also been diagnosed with type 2 diabetes, and any medications they may have been taking for high blood pressure, diabetes, or to improve cholesterol scores.
Somewhat unsurprisingly, those following a Mediterranean-style diet saw clinically significant reductions in their CCA-IMT as well as the thickness of the cholesterol deposits (this is known as "plaque height").
What's surprising is the effect of the National Cholesterol Education Program diet on CCA-IMT and plaque height: "The low-fat diet did not modify either IMT-CC or carotid plaque ... height after 5 and 7 years of followup."
We've known for some time that a low-fat diet isn't the best diet for your heart - this simply demonstrates the effects at the level of the arteries. The take-home message here is, yes, a Mediterranean-style diet is good for your heart even if you already have heart disease, but just as important is the fact that the participants changed nothing but their diets. They were not instructed to lose weight or change the amount they exercised.
It's not how much you eat - it's what you eat that will keep you healthy (or make you healthier).
First posted: September 1, 2021