Transcript: Low Carb Diets and Coronary Blood Flow
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 your cholesterol. You could go on an all-Twinkie diet and lower your cholesterol if you were unable to eat the dozen daily Twinkies necessary to maintain your weight. That’s why a good cocaine habit could end up lowering your cholesterol. Chemotherapy, can drop your cholesterol like a rock. Tuberculosis can work wonders on your waistline. Anything that drops your weight can drop your 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 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 that meta-analysis was published a new study found the same thing. A dietary pattern characterized by high protein and fat, but 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 has 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, 10 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 of 10 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 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 arteries opened right up increasing the blood flow. This person, however, started out with good flow, but after a year on a low carb diet, they significantly clogged down their arterial blood flow.
So this is the best science we have, 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 end-point, death, and low-carb diets were associated with a significantly higher risk of all-cause mortality, meaning low-carbers living a significantly shorter lifespan.
To see any graphs, charts, graphics, images, and quotes to which Dr. Greger may be referring, watch the above video. This is just an approximation of the audio contributed by Ariel Levitsky.
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