“Some people think the plant-based, whole foods diet is extreme. Half a million people a year will have their chests opened up and a vein taken from their leg and sewn onto their coronary artery. Some people would call that extreme.”
Caldwell Esselstyn MD
A delicate balance….
Plant-based diets have many beneficial effects on the heart and the cardiovascular system. Let’s start with just one of these – the benefits of eating plants on the very delicate innermost lining of our blood vessels. This lining is called the endothelium and it is the guardian of our circulation system. The endothelium was once thought to be just an inert inner lining for our blood vessels but fairly recent research has revealed the vast extent of its influence on our health. The endothelium is extremely thin, only one cell thick, but it is now considered to be the largest endocrine organ of our bodies. (Endocrine organs are hormone-releasing organs such as the pancreas and the thyroid.) In fact, if laid end to end, the 1.2 trillion endothelial cells from one human being would wrap four times around the world!
The most crucial function of the endothelium is its production of a gas molecule called nitric oxide. Nitric oxide is responsible for relaxing the smooth muscle in blood vessel walls to dilate or open up the blood vessels when nerve and chemical signals from the body call for more blood. Nitric oxide also acts to prevent stickiness between all the different cells that make up the blood in order to keep the blood flowing smoothly (1) and to inhibit inflammation and plaque build-up in blood vessels (3). Nitric oxide is why nitroglycerin works to dilate coronary arteries and relieve angina pain – our body converts the nitroglycerin to nitric oxide. It’s even why Viagra (sildenafil) works. The drug increases blood flow to the penis through the production of nitric oxide, encouraging erection. Dysfunction of the endothelium is directly involved with the development of heart disease as well as peripheral vascular disease, stroke, venous thrombosis (blood clots), tumour growth, diabetes, chronic kidney failure, non-alcoholic liver disease and erectile dysfunction (2).
Injury to the endothelium can occur very quickly. The endothelium reacts to the foods we eat in every meal. A single high-fat meal can hinder endothelial health so greatly that arteries stiffen within hours of the meal, cutting in half their ability to relax and remain dilated (6,11). This effect lasts 4 to 6 hours, just in time to be assaulted by the next unhealthy meal in those eating the standard Western diet. This effect occurs because many of the foods that we eat cause inflammation and the formation of free radicals. In the endothelium, free radicals actually damage the enzyme that is needed for the production of nitric oxide. This oxidative stress appears to be the common underlying mechanism of endothelial dysfunction (15,16). When nitric oxide is lacking, its protective effect on blood vessels is also gone. Plaque blockages are allowed to build up inside the arteries leading to heart disease and strokes. Blood becomes more sticky, encouraging faster plaque build-up on artery walls. Studies show that nitric oxide is crucial in determining whether atherosclerosis will develop or not. Endothelial dysfunction is now recognized as an early, reversible precursor of atherosclerosis (50).
What Can We Do To Improve the Health of our Endothelium?
Eating foods high in antioxidants is very beneficial because antioxidants can tame the oxidizing potential of free radicals. Eating copious amounts of fruit and vegetables brings low nitric oxide levels back to normal (5,49). In fact, each single daily serving of fruits or vegetables is associated with a 6% improvement in endothelial function (17). Once again, it is the whole food that is important here. Studies on micronutrient supplements show no benefit. The whole food package with its myriad of phytonutrients, antioxidants and fiber components working in complex synergy seems to be the key to optimum endothelial health.
Exercise also helps mightily and it does not matter what type of exercise you are doing. Both aerobic exercise and resistance training are good for your endothelium. And tellingly, if you stop your regular exercise, your endothelial function falls quickly (18,19).
One of the most anti-inflammatory foods you can eat is the spice, turmeric. It can improve endothelial function by the same magnitude as that obtained with exercise (19,20).
Tea consumption, both green tea and black tea, substantially enhances endothelial function in arteries (29,30,31,32).
Drinking a glass of purple grape juice or red wine improves artery function (51,33).
Nut consumption is well known to be associated with heart health and it is not surprising that nuts show improvement in endothelial function. Walnuts, hazelnuts, pistachios have all been studied and shown benefits (12,13,14,34,35,36,37,38).
Chocolate has undergone hundreds of randomized controlled trials that illustrate its contribution to significantly improved artery function. Chocolate has even been shown to have the power to open up coronary arteries themselves. (Coronary arteries are the arteries that supply blood to the heart.) These effects only occur with cocoa powder or dark chocolate; milk chocolate does not have any beneficial effect. It appears the negative milk component may cancel out the positive chocolate component (39,40,41,42,43).
The potassium:sodium balance is an additional important factor for the health of our endothelium. Potassium increases the release of nitric oxide while sodium reduces it (52,53,54,55,56,57). We evolved eating ten times more potassium than sodium in our diet; now the ratio is reversed. Eating leafy greens, beans, legumes, sweet potatoes, oranges and bananas, foods that are high in potassium, and avoiding high sodium foods will help the endothelium in its production of nitric oxide.
What Do We Do to Cause Injury to our epithelium?
Examples are legion but here are a few to watch out for.
Studies show that eating a high-fat, refined carbohydrate diet (i.e. one that contains meat, dairy, eggs, oil and/or processed foods) causes damage to endothelial cells and drastically reduces the amount of nitric oxide that the endothelium can produce (4). Both animal fats and isolated plant fats (for example, sunflower oil, canola oil, olive oil) produce the same negative effect on the endothelium (7,8,9,10).
The simple non-action of sitting also has an enormous effect. Studies show that six or more hours of sitting a day can increase mortality rates even if you also exercise an hour a day seven days a week. Endothelial cells can actually sense the shear force (a force perpendicular to the length of a component) of the blood flowing past them and this flow itself helps to maintain the health of the endothelium. If you must sit for long periods it is important to take breaks at least once an hour. The break does not need to be long; two minutes every hour will help. And you don’t need to actually exercise during the breaks – just get up and move around (21,22,23,24,25,26,27). New studies show that even fidgeting while sitting makes a big difference (58,59)!
Smoking introduces inflammatory substances into the blood stream that are significantly detrimental to the endothelium (28).
Eggs, the great controversy….
The subject of eggs deserves a whole paragraph of its own. Studies backed by the Egg Farmers of Canada and the American Egg Board trumpet the findings that eating eggs does not increase blood cholesterol levels and therefore is not detrimental to the vascular endothelium. A close look at these studies will reveal their flaws. The subjects involved were people already eating the standard Western diet and their cholesterol levels ranged from high-normal to extremely high (44,45). Cholesterol has a plateau effect. Once a person’s cholesterol is high, adding more will not result in more problems. It is like throwing a lit match on an already burning fire – nothing happens. On the other hand, studies performed on people whose cholesterol is low to normal show that eating eggs indeed substantially increases cholesterol. With high cholesterol comes the damaging cascade of inflammation, oxidation, free radicals and poor endothelial function (46,47,48).
Eat your fruits and vegetables in abundance, drink tea in place of sugary beverages and enjoy nuts and dark chocolate in moderation. Sprinkle in some turmeric for flavour and colour. Hold back on inflammatory foods like meat, eggs, dairy, oils and processed foods. Bounce your legs while you sit at your computer. Get outdoors and walk whenever you get the chance. Your endothelium will thank you for it.
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Wow! Great article, Deb. Impressive list of footnotes. Very convincing.