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.

In my last video, I discussed studies that show a single meal high in saturated fat can impair artery function in men, as measured in the arm. But what we’re more concerned about is blood flow to the wall of the heart. Researchers randomized men to eat a high-fat meal that was more than 60 percent fat––half of it saturated, with more than an egg’s worth of cholesterol, or a low-fat meal that was mostly carbs––less than 10 percent fat and 50 times less cholesterol.

Here’s a Doppler recording of the left anterior descending coronary artery, known as the widow-maker, before the high-fat meal. Nice strong signal squeezed down within hours after eating. This was taken five hours after the high-fat meal. The coronary flow reserve decreased after a single high-fat meal, but not after a low-fat meal with the same number of calories.

What does “coronary reserve” mean? If a part of a coronary artery is blocked for any reason, the surrounding vessels expand. That extra expansion capacity is called the coronary flow reserve, and it’s clamped down within hours of eating a fatty meal, undermining the heart’s ability to compensate for clogged arteries. That’s how a high-fat meal affects blood flow to the heart.

In extreme cases, you can even witness it in the back of someone’s eye. This is the before—see the sluggish milky-colored vessels—and then after a low-fat diet and drugs to help clear the fat out of the bloodstream. Can you see the difference? Their blood before looked like a milkshake.

What happens if you exercise, though, right after that high-fat meal? After-the-meal inflammation, following the prolonged elevation of fat in the blood that occurs when you eat high-fat meals, provides a likely explanation for increased cardiovascular disease. But substantial evidence has shown that acute exercise is an effective modality for clearing out some of that fat after a meal. However, the benefits of acute exercise for postprandial lipemia, for after-the-meal fatty blood, appear to be relatively short-lived. Going a few days without exercising may completely negate any benefit, no matter how fit you are. The time window appears to be between 18 hours before the meal, up until around 90 minutes after the meal. And how much exercise do we need? About an hour of moderate-intensity exercise should do it.

In this study though, it only took 20 minutes of stair climbing, broken up into five minutes every hour for four hours, after a McDonald’s breakfast of hash browns, eggs, pancakes, muffins, sausage, and a milkshake. Following such a meal, artery function significantly decreased when the subjects just sat around after eating, but not when they did the hourly stair-climbing exercises. In conclusion, hourly exercise may attenuate the negative effects not only of prolonged sitting but also of high-fat meal intake, suggesting that stair climbing should be incorporated as an easily accessible lifestyle strategy to protect artery function. Of course, it goes without saying that the other way you can protect artery-function is to not to eat breakfast at McDonald’s in the first place.

Such a meal would also have more than 2,000 mg of sodium, or more than the 1,500 the American Heart Association recommends you stay under for an entire day. Give someone a meal with even less salt—a third less, and that alone can still impair artery function within an hour of consumption, even independent of the increase in blood pressure.

When it comes to blood pressure, some people are “salt-sensitive,” meaning they suffer a large bump in blood pressure when they eat salt. But others are said to be “salt-resistant.” Their blood pressure doesn’t really depend much on their salt intake. So, for these people is salt okay? No. High dietary sodium intake reduces artery function, regardless of whether your blood pressure is salt-sensitive or salt-resistant. Your artery function is impaired either way, going from a low-salt diet to a high-salt diet. See, there’s an influence of dietary salt beyond blood pressure.

In spite of the seemingly unanimous consensus, some researchers (too often funded by the salt industry) claim that it’s actually not good to cut down on salt, but the evidence is against these dissenters. Like the saturated fat in meat, dairy, and junk, the science indicates that sodium, not sodium reduction, is the real villain.

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