Low-Carb Diets and Coronary Blood Flow

Michael Greger M.D. FACLM · March 21, 2014 · Volume 17

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Blood flow within the hearts of those eating low-carb diets was compared to those eating plant-based diets.

Discuss

Transcript

Below is an approximation of this video’s audio content. To see any graphs, charts, graphics, images, and quotes to which Dr. Greger may be referring, watch the above video.

People going on low-carb diets may not see a rise in their cholesterol levels. How is that possible? Because weight loss by any means can drop our cholesterol. We could go on an all-Twinkie diet and lower our cholesterol if we were unable to eat the dozen daily Twinkies necessary to maintain our weight. That’s why a good cocaine habit can lower cholesterol. Chemotherapy can drop cholesterol like a rock. Tuberculosis can work wonders on one’s waistline. Anything that drops our weight can drop our cholesterol. But, the goal isn’t to fit into a skinnier casket. The reason we care about cardiovascular risk factors like cholesterol is because we care about cardiovascular risk—the health of our arteries.

Well, now we have studies that have measured the impact of low-carb diets on arteries directly, and a review of all the best studies done to date found that low-carb diets impair arterial function, as evidenced by a decrease in flow-mediated dilation—meaning low-carb diets effectively cripple people’s arteries. And, since the meta-analysis was published, another study found the same thing. A dietary pattern characterized by high protein and fat, low carbohydrate, was “associated with poorer peripheral small artery function”—again measuring blood flow into people’s limbs. Peripheral circulation is great, but what about circulation in the coronary arteries that feed our heart?

There’s only been one study ever done measuring actual blood flow to the heart muscles of people eating low-carb diets, and this is it. Dr. Richard Fleming, an accomplished nuclear cardiologist, enrolled 26 people into a comprehensive study of the effects of diet on cardiac function using the latest in nuclear imaging technology—so-called SPECT scans—enabling him to actually directly measure the blood flow within the coronary arteries.

He then put them all on a healthy vegetarian diet, and a year later, the scans were repeated. By that time, however, ten of the patients had jumped ship onto the low-carb bandwagon. At first, I bet he was upset, but surely soon realized he had an unparalleled research opportunity dropped into his lap. Here, he had extensive imaging on ten people following a low-carb diet, and 16 following a healthy high-carb diet. What would their hearts look like at the end of the year? We can talk about risk factors all we want, but compared to the veg group, did the coronary heart disease of the patients following the Atkins-like diets improve, worsen, or stay the same?

Those sticking to the vegetarian diet showed a reversal of their heart disease, as expected. Their partially clogged arteries literally got cleaned out. They had 20% less atherosclerotic plaque in their arteries at the end of the year than at the beginning. What happened to those who abandoned the treatment diet, and switched over to the low-carb diet? Their condition significantly worsened. 40 to 50% more artery clogging at the end of the year. Thanks to the kind generosity of Dr. Fleming, we can actually see the changes in blood flow for ourselves.

Here are some representative heart scans. The yellow, and particularly red, represent blood flow through the coronary arteries to the heart muscle. This patient went on a plant-based diet, and their coronary arteries opened right up, increasing blood flow. This person, however, started out with good flow, but after a year on a low-carb diet, significantly clogged down their arterial blood flow.

This is the best science to date demonstrating the threat of low-carb diets, not just measuring risk factors, but actual blood flow in people’s hearts on different diets. Of course, the reason we care about cardiac blood flow is we don’t want to die. And, a meta-analysis was recently published that finally went ahead and measured the ultimate endpoint, death, and “low-[carb] diets were associated with a significantly higher risk of all-cause mortality”—meaning low-carbers living a significantly shorter lifespan.

Please consider volunteering to help out on the site.

Sources

Acknowledgements

Images thanks to C-Monster, seagers, and Mykl Roventine via flickr; Veronidae and Linda Bartlett via Wikimedia, and the World Lung Foundation.

Below is an approximation of this video’s audio content. To see any graphs, charts, graphics, images, and quotes to which Dr. Greger may be referring, watch the above video.

People going on low-carb diets may not see a rise in their cholesterol levels. How is that possible? Because weight loss by any means can drop our cholesterol. We could go on an all-Twinkie diet and lower our cholesterol if we were unable to eat the dozen daily Twinkies necessary to maintain our weight. That’s why a good cocaine habit can lower cholesterol. Chemotherapy can drop cholesterol like a rock. Tuberculosis can work wonders on one’s waistline. Anything that drops our weight can drop our cholesterol. But, the goal isn’t to fit into a skinnier casket. The reason we care about cardiovascular risk factors like cholesterol is because we care about cardiovascular risk—the health of our arteries.

Well, now we have studies that have measured the impact of low-carb diets on arteries directly, and a review of all the best studies done to date found that low-carb diets impair arterial function, as evidenced by a decrease in flow-mediated dilation—meaning low-carb diets effectively cripple people’s arteries. And, since the meta-analysis was published, another study found the same thing. A dietary pattern characterized by high protein and fat, low carbohydrate, was “associated with poorer peripheral small artery function”—again measuring blood flow into people’s limbs. Peripheral circulation is great, but what about circulation in the coronary arteries that feed our heart?

There’s only been one study ever done measuring actual blood flow to the heart muscles of people eating low-carb diets, and this is it. Dr. Richard Fleming, an accomplished nuclear cardiologist, enrolled 26 people into a comprehensive study of the effects of diet on cardiac function using the latest in nuclear imaging technology—so-called SPECT scans—enabling him to actually directly measure the blood flow within the coronary arteries.

He then put them all on a healthy vegetarian diet, and a year later, the scans were repeated. By that time, however, ten of the patients had jumped ship onto the low-carb bandwagon. At first, I bet he was upset, but surely soon realized he had an unparalleled research opportunity dropped into his lap. Here, he had extensive imaging on ten people following a low-carb diet, and 16 following a healthy high-carb diet. What would their hearts look like at the end of the year? We can talk about risk factors all we want, but compared to the veg group, did the coronary heart disease of the patients following the Atkins-like diets improve, worsen, or stay the same?

Those sticking to the vegetarian diet showed a reversal of their heart disease, as expected. Their partially clogged arteries literally got cleaned out. They had 20% less atherosclerotic plaque in their arteries at the end of the year than at the beginning. What happened to those who abandoned the treatment diet, and switched over to the low-carb diet? Their condition significantly worsened. 40 to 50% more artery clogging at the end of the year. Thanks to the kind generosity of Dr. Fleming, we can actually see the changes in blood flow for ourselves.

Here are some representative heart scans. The yellow, and particularly red, represent blood flow through the coronary arteries to the heart muscle. This patient went on a plant-based diet, and their coronary arteries opened right up, increasing blood flow. This person, however, started out with good flow, but after a year on a low-carb diet, significantly clogged down their arterial blood flow.

This is the best science to date demonstrating the threat of low-carb diets, not just measuring risk factors, but actual blood flow in people’s hearts on different diets. Of course, the reason we care about cardiac blood flow is we don’t want to die. And, a meta-analysis was recently published that finally went ahead and measured the ultimate endpoint, death, and “low-[carb] diets were associated with a significantly higher risk of all-cause mortality”—meaning low-carbers living a significantly shorter lifespan.

Please consider volunteering to help out on the site.

Images thanks to C-Monster, seagers, and Mykl Roventine via flickr; Veronidae and Linda Bartlett via Wikimedia, and the World Lung Foundation.

Doctor's Note

The reason I have so few videos about low carb diets is that I already wrote a whole book about it! Carbophobia is now available free online full-text at AtkinsFacts.org. Atkins’ lawyers threatened to sue, leading to a heated exchange I reprint on the site.

I did touch on low-carb diets in my video Atkins Diet: Trouble Keeping It Up, though they don’t have to necessarily be that unhealthy (see Plant-Based Atkins Diet).

Here are some recent videos I’ve done on conquering our #1 killer:

What about the keto diet? In 2019 I did a 7-video series on that. Check it out here.

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