What a Single Fatty Meal Can Do to Our Arteries

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The phenomenon of postprandial angina was described more than 200 years ago: chest pain that occurs after a meal, even if you're just sitting down and resting. This could be intuitively attributed to redistribution of blood flow away from the heart to the gut during digestion. However, such a mechanism could not be demonstrated experimentally.

The problem appears to be within the coronary arteries themselves. The clue came in 1955 when researchers found they could induce angina in people with heart disease just by having them drink fat. My video Fatty Meals May Impair Artery Function includes a fascinating graph of so-called lactescence, or milkiness, over time. It shows how their blood became increasingly milky with fat over the next five hours, and each of the ten attacks of angina was found to occur about four-and-a-half to five hours after the fatty meal, right when blood milkiness was at or near its peak. After a nonfat meal with the same bulk and calories, but made out of starch, sugar, and protein, no anginal pain was elicited in any of the patients.

To understand how the mere presence of fat in the blood can affect blood flow to the heart, we need to understand the endothelium, the inner lining of all of our blood vessels. Our arteries are not just rigid pipes; they are living, breathing organs that actively dilate or constrict, thinning or thickening the blood and releasing hormones, depending on what's needed. This is all controlled by the single inner layer, the endothelium, which makes it the body's largest endocrine (hormone-secreting) organ. When it's all gathered up, the endothelium weighs a total of three pounds and has a combined surface area of 700 square yards.

We used to think the endothelium was just an inert layer lining our vascular tree, but now we know better:

Researchers found that low-fat meals tend to improve endothelial function, whereas high-fat meals tend to worsen it. This goes for animal fat, as well as isolated plant fats, such as sunflower oil. But, maybe it's just the digestion of fat rather than the fat itself? Our body can detect the presence of fat in the digestive tract and release a special group of hormones and enzymes. Researchers tried feeding people fake fat and found that the real fat deprived the heart of blood while the fake fat didn't. Is our body really smart enough to tell the difference?

A follow-up study settled the issue. Researchers tried infusing fat directly into people's bloodstream through an IV to sneak it past your mouth and brain. Within hours, their arteries stiffened, significantly crippling their ability to relax and dilate normally. So it was the fat after all! This decrease in the ability to vasodilate coronary arteries after a fatty meal, just when you need it, could explain the phenomenon of after-meal angina in patients with known coronary artery disease.


This effect could certainly help explain the findings in Low Carb Diets and Coronary Blood Flow. My video Olive Oil and Artery Function addresses less refined fats like extra virgin olive oil,.

For more on angina, see the beginning of my 2014 annual talk--From Table to Able: Combating Disabling Diseases with Food--and How Not to Die from Heart Disease.

Another consequence of endothelial dysfunction is lack of blood flow to other organs. Check out Survival of the Firmest: Erectile Dysfunction and Death and Atkins Diet: Trouble Keeping It Up.

Fat in the bloodstream can also impair our ability to control blood sugar levels. Learn more with What Causes Insulin Resistance?, The Spillover Effect Links Obesity to Diabetes, and Lipotoxicity: How Saturated Fat Raises Blood Sugar.

Finally, for more on how diet affects our arteries, check out Tea and Artery Function, Vinegar and Artery Function, and Plant-Based Diets and Artery Function.

In health,

Michael Greger, M.D.

PS: If you haven't yet, you can subscribe to my free videos here and watch my live, year-in-review presentations:

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What a Single Fatty Meal Can Do to Our Arteries

Oct12 Fatty Meal copy.jpeg

The phenomenon of postprandial angina was described more than 200 years ago: chest pain that occurs after a meal, even if you're just sitting down and resting. This could be intuitively attributed to redistribution of blood flow away from the heart to the gut during digestion. However, such a mechanism could not be demonstrated experimentally.

The problem appears to be within the coronary arteries themselves. The clue came in 1955 when researchers found they could induce angina in people with heart disease just by having them drink fat. My video Fatty Meals May Impair Artery Function includes a fascinating graph of so-called lactescence, or milkiness, over time. It shows how their blood became increasingly milky with fat over the next five hours, and each of the ten attacks of angina was found to occur about four-and-a-half to five hours after the fatty meal, right when blood milkiness was at or near its peak. After a nonfat meal with the same bulk and calories, but made out of starch, sugar, and protein, no anginal pain was elicited in any of the patients.

To understand how the mere presence of fat in the blood can affect blood flow to the heart, we need to understand the endothelium, the inner lining of all of our blood vessels. Our arteries are not just rigid pipes; they are living, breathing organs that actively dilate or constrict, thinning or thickening the blood and releasing hormones, depending on what's needed. This is all controlled by the single inner layer, the endothelium, which makes it the body's largest endocrine (hormone-secreting) organ. When it's all gathered up, the endothelium weighs a total of three pounds and has a combined surface area of 700 square yards.

We used to think the endothelium was just an inert layer lining our vascular tree, but now we know better:

Researchers found that low-fat meals tend to improve endothelial function, whereas high-fat meals tend to worsen it. This goes for animal fat, as well as isolated plant fats, such as sunflower oil. But, maybe it's just the digestion of fat rather than the fat itself? Our body can detect the presence of fat in the digestive tract and release a special group of hormones and enzymes. Researchers tried feeding people fake fat and found that the real fat deprived the heart of blood while the fake fat didn't. Is our body really smart enough to tell the difference?

A follow-up study settled the issue. Researchers tried infusing fat directly into people's bloodstream through an IV to sneak it past your mouth and brain. Within hours, their arteries stiffened, significantly crippling their ability to relax and dilate normally. So it was the fat after all! This decrease in the ability to vasodilate coronary arteries after a fatty meal, just when you need it, could explain the phenomenon of after-meal angina in patients with known coronary artery disease.


This effect could certainly help explain the findings in Low Carb Diets and Coronary Blood Flow. My video Olive Oil and Artery Function addresses less refined fats like extra virgin olive oil,.

For more on angina, see the beginning of my 2014 annual talk--From Table to Able: Combating Disabling Diseases with Food--and How Not to Die from Heart Disease.

Another consequence of endothelial dysfunction is lack of blood flow to other organs. Check out Survival of the Firmest: Erectile Dysfunction and Death and Atkins Diet: Trouble Keeping It Up.

Fat in the bloodstream can also impair our ability to control blood sugar levels. Learn more with What Causes Insulin Resistance?, The Spillover Effect Links Obesity to Diabetes, and Lipotoxicity: How Saturated Fat Raises Blood Sugar.

Finally, for more on how diet affects our arteries, check out Tea and Artery Function, Vinegar and Artery Function, and Plant-Based Diets and Artery Function.

In health,

Michael Greger, M.D.

PS: If you haven't yet, you can subscribe to my free videos here and watch my live, year-in-review presentations:

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Inhibiting Platelet Activation with Tomato Seeds

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In the prevention of cardiovascular disease, the consumption of fruits and vegetables is crucial. Preventing the oxidation of cholesterol may be one of the mechanisms by which fruits and vegetables reduce the risk of heart attacks and strokes. However, hyperactivity of platelets is also critically important in the pathogenesis of cardiovascular disease, as I've covered before (See Inhibiting Platelet Aggregation with Berries).

In recent years, it has been shown that platelets are not only involved in the arterial clotting process, but also that they play an active role in the inflammatory process of atherosclerosis from childhood. By the end of our teens, atherosclerotic lesions are present in most people living in industrialized societies, and so suppressing the over-activity of platelets may be beneficial not only for heart disease, but for cancer, allergies, and diseases for which inflammation plays a major role.

The antioxidant properties of fruits and veggies are well known. However, their anti-clotting effects on platelets are less known. Preliminary studies have demonstrated the platelet activation suppressing activity of a variety of fruits and vegetables. They suppress platelet activation so well that they can actually mess up platelet function tests. And, the effects are so long-lasting that fasting the morning of your blood test may not be sufficient.

Out of 16 different fruits tested, tomatoes came out number one. The anti-platelet activation components in tomatoes are water soluble, so we don't have to eat them with fat; heat stable, meaning we can cook tomatoes without losing the benefits; and concentrated in the yellow fluid around the seeds. This is why tomato pomace beat out tomato juice, sauce, or ketchup. Pomace is basically the seeds and the peel, which the industry throws away, and it may be the healthiest part. And the more tomato seeds the better. But this study was measuring platelet activation in a petri dish. Grapefruit came in number two here, and grapefruit juice at least didn't appear to help when people actually drank it. Would drinking tomato juice actually help?

Platelets of patients with diabetes are characterized by intensified activation, so 20 diabetics were asked to drink a daily cup of tomato juice for three weeks or a tomato-flavored placebo beverage, and there was a significant drop in platelet activation.

A study done by the Rowett Research Institute, highlighted in my video, Inhibiting Platelet Activation with Tomato Seeds, found this works in healthy people as well. Within three hours of consumption, two tomatoes lowered platelet activation, and six tomatoes worked even better. Also, the effects were more wide-ranging than those of aspirin in that the tomatoes targeted multiple pathways of platelet activation.

About one in four people are aspirin resistant, meaning aspirin doesn't work to calm down their platelets, whereas only 3% of study subjects were found to be tomato resistant.

This finding indicates an advantage of the tomato extract's broad antiplatelet activity profile over single-target drugs such as aspirin. Also, when researchers stuck tubes into people while they were eating tomatoes, they found no changes in blood clotting times, implying that supplementation with tomatoes should not result in a prolonged bleeding times, so one might get the best of both worlds: less platelet activation without the bleeding risk. But if tomatoes don't thin our blood, do they work?

Researchers out of North Carolina State University report that, "consumption of tomato products has been found to be protectively correlated with a lower incidence of acute coronary events, less development of early atherosclerosis, and lower mortality from heart disease."

If you don't like tomatoes, kiwifruit recently beat them out in a test tube study of platelet activation. Strawberries may help too, but we have data showing kiwis may actually work in people, and two kiwis appeared to work just as well as three kiwis. It appears to work for green-on-the-inside kiwifruit; and for yellow-on-the-inside kiwifruit. In this case, though, one a day seemed to help whereas two-a-day did not, which seems a little strange. And there haven't been any studies to see if kiwifruit eaters actually have fewer strokes and heart attacks, so the best evidence for a dietary intervention to decrease platelet activation currently rests with tomatoes.

One of my favorite videos, The Tomato Effect, is actually not about tomatoes at all, but talks about the power of a diet composed entirely of plants to combat the heart disease epidemic. After all, Heart Disease Starts in Childhood.

I do have some others that really do touch on tomatoes, though:

More on kiwis here:

In health,
Michael Greger, M.D.

PS: If you haven't yet, you can subscribe to my free videos here and watch my live year-in-review presentations Uprooting the Leading Causes of Death, More Than an Apple a Day, From Table to Able, and Food as Medicine.

Image Credit: Rusty Clark / Flickr

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Preventing Breast Cancer with Flax Seeds

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I've previously discussed the role of dietary lignans in the reduction of breast cancer risk and improvement in breast cancer survival, based on studies that showed that women with breast cancer who ate the most lignans appeared to live longer (Flaxseeds & Breast Cancer Survival: Epidemiological Evidence and Flaxseeds & Breast Cancer Survival: Clinical Evidence). However, lignans are found throughout the plant kingdom--in seeds, whole grains, vegetables, fruits, berries--so how do we know lignans aren't merely a marker for the intake of unrefined plant foods? For example, those who eat lots of plants--vegetarians--have about eight times the lignan intake than omnivores.

In a petri dish, lignans have been shown to both have direct anticancer growth activity against human breast cancer cells and to prevent cancer cell migration. But it wasn't until 2005 that it was put to the test in people. Researchers from the University of Toronto conducted a randomized double-blind placebo-controlled clinical trial (as seen in my video, Can Flax Seeds Help Prevent Breast Cancer?) of flaxseeds, the world's most concentrated source of lignans in breast cancer patients. The researchers found that flax appears to have the potential to reduce human breast tumor growth in just a matter of weeks. Therefore, I started recommending ground flax seeds to breast cancer patients.

Can lignans also help prevent breast cancer in the first place? High lignan intake is associated with reduced breast cancer risk, but again lignan intake may just be saying an indicator of high plant food intake in general. So researchers from the University of Kansas gave women at high risk for breast cancer a teaspoon of ground flaxseeds a day for a year, and found on average a drop in precancerous changes in the breast.

What about women who regularly eat flax seeds? Outside of an experimental setting, there just weren't a lot of women eating flax seeds regularly to study--until now. Matching 3,000 women with breast cancer to 3,000 women without, a study published in Cancer Causes and Control found that consumption of flaxseed (and of flax bread) was associated with a 20-30 percent reduction in breast cancer risk. The researchers note that, as flaxseeds are packed with lignans, only a small daily serving of flaxseed is required to attain the level of lignan intake associated with a reduction in breast cancer risk. Researchers concluded: "As it appears that most women do not consume flaxseed and that small amounts may be associated with reduced breast cancer risk, interventions to increase the prevalence of flaxseed consumption might be considered."

The latest review summarizes the association between flax and decreased risk of breast cancer, better mental health, and lower mortality among breast cancer patients. The only other study of flax and brain health I'm aware of was an exploration of 100 commonly used drugs and supplements on cognition in older adults, which found that flax is one of the few things that appears to help.

How else may flaxseeds aid in preventing and treating breast cancer? There's an inflammatory molecule called interleukin-1, which may help tumors feed, grow, and invade. Our bodies therefore produce an interkeukin-1 receptor antagonist, binding to the IL-1 receptor and blocking the action of IL-1. The activity of this protective inhibitor can be boosted with the drug tamoxifen--or by eating flax seed. In premenopausal women, the proinflammatory profile of interleukin-1 can be counteracted by a dietary addition of a few spoonfuls of ground flax. One month of flax may be able to increase the anti-inflammatory inhibitor levels by over 50 percent, better even than the drug.

Yes, having one's ovaries removed may reduce breast cancer risk as much as 60 percent, but at the cost of severe side-effects. The drug tamoxifen may reduce the incidence of breast cancer by more than 40 percent, but may induce other severe side effects such as uterine cancer and blood clots. That's why less toxic (even safe!) breast cancer preventive strategies such as dietary modifications need to be developed. These lignan phytoestrogens in flaxseeds may be one successful route given the data showing reduced breast cancer risk and improved overall survival.

Lignans are not a magic bullet to prevent breast cancer--we can't just sprinkle some flax on your bacon cheeseburger--but as a part of a healthy diet and life-style, they might help to reduce breast cancer risk in the general population.

Flaxseeds may also help fight hormone-mediated cancers in men. See Flaxseed vs. Prostate Cancer and Was It the Flaxseed, Fat Restriction, or Both?

What else can these puppies do? See:

I have another 100+ videos on breast cancer if you want to become an expert and help take care of yourself and/or the women in your life. Here's a few recent ones to get you started:

In health,
Michael Greger, M.D.

PS: If you haven't yet, you can subscribe to my free videos here and watch my live year-in-review presentations Uprooting the Leading Causes of Death, More Than an Apple a Day, From Table to Able, and Food as Medicine.

Image Credit: Alisha Vargas / Flickr

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The #1 Dietary Risk Factor is Not Eating Enough Fruit

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The Global Burden of Disease Study published in 2012, is the most comprehensive and systematic analysis of causes of death undertaken to date, involving nearly 500 researchers from more than 300 institutions in 50 countries, and starting with almost 100,000 data sources. What did the researchers find? Here in the U.S., they determined that our biggest killer was our diet. Number 1 on their list of the most important dietary risks was not eating enough fruit, responsible for an estimated 4.9 million deaths a year around the world.

According to the Union of Concerned Scientists: "If Americans ate just one more serving of fruits or vegetables per day, this would save more than 30,000 lives and $5 billion in medical costs each year." One antidote for individuals is easy, painless, and even pleasurable: exploit the multiple nutritional and protective benefits of fruits and vegetables.

One way plants protect us may be their antiplatelet effects. Platelets are what trigger the blood clots that cause heart attacks and most strokes. And beyond their obvious function in blood clotting, platelets are now considered to play a pivotal inflammatory role in the hardening of the arteries in the first place, and in allergies, rheumatoid arthritis, and even cancer.

Normally, under healthy conditions, platelets circulate in a quiescent, inactive state. But once they become activated, they can emerge as culprits in inflammation. Platelets transport a vast amount of inflammatory chemicals, and upon activation they release these chemicals, which can recruit the inflammatory cells that form the pus pockets within our arterial walls that can eventually burst and kill us.

This involvement of platelet activation in atherosclerosis development is well established. We've long recognized the platelets' role in the final stages; however, a growing body of data indicates that platelets may also play an important role in the initiation and propagation of atherosclerosis in the first place. How can we prevent the excessive activation of platelets? It's generally recognized that platelet hyper-reactivity is associated with high levels of cholesterol circulating in the blood; so we can cut down on foods that have trans fats, saturated fats, and dietary cholesterol.

We can also eat more fruits and vegetables. For example, different varieties of strawberries have shown a significant antiplatelet effect in a petri dish and in people. How did researchers figure it out? In my video, Inhibiting Platelet Aggregation with Berries, you can see a platelet in a resting state, packed with little round granule grenades of inflammatory chemicals, which fuse together and are released when the platelet gets activated. Because resting and activated platelets look so different, we can just take blood from people and count how many are resting and how many are activated before and after people eat more than a pint of strawberries every day for a month. From just adding strawberries to people's diets, there's a small but significant drop in the percentage of activated platelets circulating throughout their bodies.

Other berries had a similar effect, even at a more modest two servings a day. Drinking orange or grapefruit juice doesn't seem to help, but purple grape juice successfully reduces platelet activity on the same order that aspirin does.

Studies have shown that daily aspirin can reduce heart attacks and strokes; however, aspirin can also cause severe gastrointestinal disturbances and bleeding problems, and so should not be used for the primary prevention of heart attacks and stroke as the benefits don't clearly outweigh the serious risks. It's nice to have safe, side-effect free alternatives.


One of the ways plants help keep platelets in their place may actually be their aspirin content! See Aspirin Levels in Plant Foods. Why would a plant make a human drug? It's so cool, check out Appropriating Plant Defenses.

Is the Standard American Diet really so bad that we could save 100,000 people by just getting up to minimum fruit and veggie recommendations? Even cynics might be surprised: Nation's Diet in Crisis. Even more plants may cut deaths even more, though. See One in a Thousand: Ending the Heart Disease Epidemic.

For more on lowering cholesterol see my video Trans Fat, Saturated Fat, and Cholesterol: Tolerable Upper Intake of Zero. And it's never too early to start eating healthier. Check out: Heart Disease Starts in Childhood. Heart disease may be a choice. See: Cavities and Coronaries: Our Choice.

Berries are the healthiest fruits, shown to maintain our brain power (How to Slow Brain Aging By Two Years) and improve our immune function (Boosting Natural Killer Cell Activity). That's one of the reasons we want to eat Antioxidant Rich Foods With Every Meal.

In health,
Michael Greger, M.D.

PS: If you haven't yet, you can subscribe to my free videos here and watch my live year-in-review presentations Uprooting the Leading Causes of Death, More Than an Apple a Day, From Table to Able, and Food as Medicine.

Image Credit: Michael Stern / Flickr

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How Grapefruit Affects Prescription Drugs

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Does grapefruit in particular help people lose weight?

If someone eats half of a grapefruit three times a day before each meal for a couple months, they may lose about two pounds -- but that's no more than if they ate three apples or pears a day. In one study, the grapefruit eaters not only saw their weight go down, but their waist got slimmer, and their body fat melted away. If, however, we repeat the experiment and instead ask people to drink a half cup of water before each meal, we get the same result. So this belief that grapefruit has some special fat-burning quality appears to be just a long-held myth.

The researchers reported that grapefruit consumers had a drop in weight, a significant drop in cholesterol, and a significant drop in blood pressure. They concluded that consumption of grapefruit daily for six weeks does not significantly decrease body weight, cholesterol, or blood pressure, though. That made me do a little double take, but again, it's because the grapefruit didn't do any better than placebo.

Other studies have found a legitimate cholesterol-lowering benefit of grapefruit, and even a little dip in triglycerides, especially eating red as opposed to white . For example, one study showed a decrease in cholesterol, but only from one life-threatening cholesterol level to another life-threatening cholesterol level. To prevent heart disease, we really have to get down to a total cholesterol of around 150, which is the average cholesterol of those eating diets composed exclusively of plant foods, not just grapefruits (See, for example, One in a Thousand: Ending the Heart Disease Epidemic).

Even though grapefruits alone don't do much, the researchers suggest that people might be more likely to stick with them than cholesterol lowering drugs, noting that most people with heart disease stop taking their statin drugs within a couple years because of the adverse side effects (see Statin Muscle Toxicity). While grapefruits alone don't have any side effects, ironically, combining grapefruits and drugs can make drug side effects even worse.

If we eat lots of fruits and vegetables, we hopefully won't need a lot of drugs (Say No to Drugs by Saying Yes to More Plants), but certain phytochemicals in plants can affect the metabolism of drugs in the body. Grapefruit is the poster child, described as a "pharmacologist's nightmare." Natural phytochemicals in grapefruit suppress the enzymes that help clear more than half of commonly prescribed drugs, and less drug clearance means higher drug levels in the body. This may actually be good if we want a better caffeine buzz from our morning coffee, or our doctors want to help us save thousands of dollars by boosting the effects of expensive drugs instead of just peeing them away.

But higher drug levels may mean higher risk of side effects. Women taking the Pill are normally at a higher risk of blood clots, but even more so, perhaps, if they have been consuming grapefruit. Taking the Pill with grapefruit juice may increase blood drug concentrations by 137 percent.

If suppressing our drug clearance enzymes with grapefruit juice elevates levels of ingested estrogen, what might it be doing to our own estrogen levels? A study associating grapefruit consumption with breast cancer freaked out the medical community, but subsequent studies on even larger groups of women found no evidence of a link. The Harvard Nurses' Study even found a decreased risk of the scariest breast cancer type, so it doesn't look like we have to worry about grapefruit affecting our natural chemistry.

For those prescribed unnatural chemistries, it may be a good idea to discontinue grapefruit consumption for 72 hours before use of a drug that may interact with it. If you don't want to give up your grapefruit, you can ask your doctor about switching from a grapefruit-affected drug like Lipitor to one of the citrus-proof alternatives (the replacement drug chart can be seen in my video, Tell Your Doctor If You Eat Grapefruit).

Other videos on citrus include:

And another video on the risks associated with taking estrogens: Plant-Based Bioidentical Hormones.

Can't eat grapefruit without sprinkling sugar on top? Try erythritol instead to avoid so many empty calories: Erythritol May Be a Sweet Antioxidant.

-Michael Greger, M.D.

PS: If you haven't yet, you can subscribe to my free videos here and watch my live year-in-review presentations Uprooting the Leading Causes of Death and More Than an Apple a Day.

Image Credit: Liz West / Flickr

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