I’m often asked my opinion about a diet or a disease is. Who cares what my or anyone else’s opinion is? All we should care about is what the science says. What does the best available balance of evidence published in the peer-reviewed medical literature have to say right now?
Welcome to the NutritionFacts Podcast – I’m your host Dr. Michael Greger.
Did you know that a single meal high in saturated fat can impair artery function for hours after consumption? Here’s our first story.
We are only as old as our arteries. What can we do to preserve artery function as we age? A poor diet and sedentary behavior can lead to adverse aging processes, like impairment of the little power plants in our cells, which can result in free radical formation—oxidative stress—and inflammation, which leads to the artery dysfunction that can end in the cardiovascular disease that ends us.
In a series of videos I did about a decade ago, I discussed this landmark research showing that a single high-fat meal could cripple artery function within hours of consumption, compared to no change in the low-fat meal. The high-fat meal that so crippled artery function included Sausage and Egg McMuffins from McDonalds. How do we know the sausage, egg, or cheese was to blame? What about the crappy carbs in the biscuits? Because the low-fat meal that didn’t impair artery function was a sugary mess of carby Frosted Flakes.
And just when your artery function finally starts to recover five or six hours later? Lunchtime! when your arteries may get whacked with another load of meat, eggs, dairy, or oil. Why does it matter so much what happens after a meal within your body? Because most of us spend about 16 hours a day in that after-a-meal state, constantly hammering our arteries. No wonder cardiovascular disease is our #1 killer.
And it doesn’t just inflame the arteries in our heart, but our lungs as well. “A high-fat challenge increases airway inflammation and impairs bronchodilator recovery in asthma.” Have asthmatics cough up sputum from their lungs four hours after the same kind of high-fat meal, and inflammatory cells shoot up in the high-fat meal group. In terms of lung function, give them two hits of their inhalers (containing a drug called albuterol or Ventolin) and their airways open up as they should—after the low-fat meal. But after the high-fat meal, the same inhaler doses don’t work as well, crapping out after a few hours because of all the extra inflammation in their lungs. What you eat can determine how well you breathe.
Okay, but that was asthmatics. But even in nonasthmatic subjects, you get that same spike in inflammatory cells in sputum coughed out of your lungs four hours after eating what was, in this case, a Jimmy Dean Meat Lovers Breakfast Bowl.
And there aren’t only more inflammatory cells; there is a doubling of the amount of pro-inflammatory oxidized LDL cholesterol sucked up by the type of white blood cells that go on to form foam cells. Those are the cells that build up the inflamed pus in your artery wall that leads to heart attacks. And all this happens within just hours of eating pizza, in this case.
The fat in your blood goes up, and so do your endotoxin levels. Endotoxins are the components of bacterial cell walls, and foods like meat can be so contaminated with bacteria—alive and dead—that they accumulate endotoxins. And we’re talking about both red meat and white meat.
But, recent research (published in 2020) suggests the main culprit may not be endotoxins after all, but the fat itself. The saturated fat floating in your blood after an unhealthy meal may be inducing the inflammation more directly. Either way, we are accountable for what we eat, meal-by-meal, for the modification of the risk factors for chronic metabolic disease.
In our next story, we look at the window of time in which sufficient physical activity can help mediate some of the damage caused by eating an unhealthy meal.
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 eithera 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.
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.
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.
Finally today – If you’re going to eat something unhealthy, is there anything you can pair it with to help mediate the damage it may cause?
If you compare the artery function of those who don’t eat meat to those who do, the healthy ability of arteries to dilate and let more blood flow is significantly better among those eating vegetarian––and not just by a little; we’re talking four times better. Well duh, vegetarians tend to be younger, smoke less, be slimmer, and have lower rates of diabetes, high cholesterol, high blood pressure, and heart disease. But, the researchers controlled for all that. They only let healthy nonsmokers into the study, and recruited a group of meat-eaters who were just about as slim, on average, about the same blood pressures, even practically the same cholesterol––a really healthy cohort on omnivores. Yet they still got their arteries handed to them by the vegetarians, and the longer someone was meat-free, the better. The degree of superior artery function correlated with the number of years eating meat-free. Instead of their artery function worsening over time as they aged, it got better the longer they ate that way. This suggests that vegetarian diets, by themselves, have a direct beneficial effect on artery function, and may help to account for the lower incidence of atherosclerosis and cardiovascular mortality.
Since researchers were able to control for other known risk factors, they figured it must be the food. But what aspect of the food? Is it simply the lack of the deleterious effect of meat? Or could it also be because the vegetarians may simply be eating more whole healthy plant foods––for example, up to a serving a day more vegetables?
When researchers compared two crappy meals, Sausage and Egg McMuffins to Frosted Flakes, and found the fatty meal impaired artery function within hours, but the sugary meal didn’t, they blamed the fat. But it may just be the animal fat, since high-fat whole plant foods like nuts don’t have the same effect. In fact, if you look at a systematic review of all the randomized controlled trials on the effect of nut consumption on artery function, you find that nuts actually make things better over time.
Enough to counter the artery-crippling effects of a salami sandwich? Let’s find out. And the answer is yes for walnuts, but no for almonds. Just like there are some fruits that are better than others––like blueberries over bananas––there are some nuts that are better than others. And walnuts appear to be the blueberries of nuts.
What about the blueberry of berries? Blueberries themselves. A randomized, controlled, crossover trial of cooked blueberries, raw blueberries, or no blueberries at all. If you feed people buns made out of white flour, eggs, butter, and salt, and fill them full of mostly sugar and eggs, you get a gradual drop in artery function over the next six hours. But add the equivalent of a cup of wild blueberries to that same bun, and instead, you get a big boost in artery function––almost as if you had just mixed the blueberries with water.
About the same amount of strawberries failed to rescue artery function from the likes of two cheese blintzes, with whipped cream, a sugary syrup, egg, and bacon. But that is quite the heavy load to bear.
What about açai berries versus a meal with a similar amount of fat? One and a half-frozen smoothie packs with half a small banana in water were able to significantly rehabilitate arterial function, compared to a control smoothie with the same banana and water colored to look like the açai one––though obviously it would have tasted differently. This group of researchers went all out and performed a double-blind randomized controlled trial with raspberries, measuring artery function after two hours and then 24 hours after drinking about ¾ of a cup of frozen red raspberries (about 187g) blended with water (or about a cup and a half), versus a placebo drink meant to match both color and taste. The fake berry drink had no effect on artery function, but the other two did.
Note the ¾ cup dose seemed to work just as well as the cup and a half dose, which is what you see with blueberries: the benefits plateau after about a cup.
The bottom line is that consumption of dietarily achievable amounts of red raspberries acutely improves artery function for up to 24 hours. You say, “Yeah, but by the end of the day, you’re only up like one percent.” Ah, but at a population level, each one percent increase is associated with a 12 percent reduction in risk of a cardiovascular event like a heart attack or stroke. All from just having a berry smoothie.
What about berry juice? Five different concentrations of cranberry juice were used, along with a placebo control evidently indistinguishable in color and taste. The 25 percent cranberry juice drink gave a little bump at two hours; the 50 percent juice was still working eight hours later. The 75 percent juice, the one that was nearly pure juice, and the ultra-concentrated juice also improved artery function within hours of consumption. But this, like that last raspberry study, just involved straight berries without some artery-crushing meal.
Would berry juice be able to stop artery dysfunction caused by a high-fat meal this unhealthy, squeezing down artery function within hours? Researchers created a cocktail of grapes, lingonberry, blueberry, strawberry, and black Aronia berry, and no significant change after the high-fat meal. Of course, if you had just drunk those berries alone, you’d probably get an improvement, but it’s better than nothing.
Well, what about something a little less exotic than black Aronia berries? What about OJ? Participants were provided a high-fat meal of ham and cheese croissants, along with a cup of either water, orange juice, green tea, or red wine. The arteries didn’t much like the croissants, and OJ was useless, as was a cup of green tea and red wine. So, it’s probably best to not eat ham and cheese croissants in the first place.
In fact, drinking orange juice with a fatty meal could actually make things worse. If you give people bacon and cheese muffins with or without orange juice, the OJ can lead to a prolongation of elevated fat in the blood, as your body preferentially burns for energy all the rapidly-absorbed free sugars in the juice––meaning sugars not encased in cells walls as in those in whole fruit.
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