Eating more foods rich in certain amino acids – the building blocks of protein – may be as good for your heart health as cutting sodium, getting more exercise and quitting smoking, rang headlines about a study published this month in the Journal of Nutrition.
Previous studies have linked higher protein intakes with lower blood pressure. However, it is not clear whether animal proteins (meat, poultry, fish, eggs, dairy) or plant proteins (beans, lentils, soy) are more cardio-protective. Nor is it known whether eating foods high in certain amino acids is more beneficial than other protein-rich foods.
Long chains of amino acids are found in protein-rich foods and, once consumed, these amino acids are used to make proteins in the body such as muscle tissue, hormones, enzymes and immune compounds.
Evidence suggests certain amino acids may benefit heart health. Some have been shown to influence levels of nitric oxide, a molecule that regulates blood pressure by relaxing blood vessels. Others may help the body use insulin properly and increase glucose (blood sugar) uptake. And a higher intake of certain amino acids has also been tied to a lower risk of stroke.
For the study, researchers from the University of East Anglia in Norwich, England, investigated the effect of seven amino acids (arginine, cysteine, glutamic acid, glycine, histidine, leucine and tyrosine) with potential cardio-protective effects in 1,900 woman, ages 18 to 75 years. Their diets were analyzed and compared with measures of blood pressure and arterial stiffness.
Having stiffer arteries increases the risk of high blood pressure, heart attack and stroke, even among people who do not have symptoms of cardiovascular problems. Stiffer arteries, measured in studies by pulse wave velocity (PWV), mean the heart has to work harder to push blood through them. (PWV is the time it takes a pulse to travel between two points; the greater the velocity, the stiffer the arteries. PWV is a strong predictor of future heart problems and cardiovascular death.)
After accounting for established heart risk factors, including family history, sodium intake, body weight and physical activity, all seven amino acids – especially those from plant protein sources – were tied to lower blood pressure to a magnitude similar to that previously reported for lifestyle risk factors for hypertension.
Plant protein foods high in the amino acids analyzed include edamame, soy milk, tempeh, firm tofu, black beans, chickpeas, kidney beans, lentils, almonds, cashews, pistachio and pumpkin seeds. Amaranth, oats, quinoa and seitan (a vegetarian protein food made from wheat gluten) are also good sources.
A higher intake of glutamic acid, leucine and tyrosine – abundant in animal proteins – was associated with lower levels of arterial stiffness. The difference was similar to the effect of not smoking.
These findings do not mean you should load up on steak, cheese, eggs or even tofu. Consuming too much saturated fat, found in higher-fat meats and dairy products, can raise the level of LDL (bad) cholesterol, damage blood vessels and contribute to high blood pressure.
What the findings do suggest, however, is that having an adequate intake of protein plays a role in cardiovascular health. If your diet is heavy on carbohydrates such as bread, pasta and cereals and light on protein, tweaking your diet to include more lean meat, fish, dairy, legumes and soy may help to keep your arteries smooth and flexible and your blood pressure in check.
And it doesn't take much protein. According to this study – the first to investigate the relationship between these seven amino acids and arterial function – eating 2.5 ounces of steak, 3.5 ounces of salmon or two cups of skim milk each day had beneficial effects on blood pressure.
Keep in mind, however, this study was not a randomized controlled trial and, as such, it did not prove that eating more foods plentiful in certain amino acids reduced blood pressure or arterial stiffness. Even so, it adds to a growing body of evidence connecting protein to cardiovascular health.
Of course, there is more to healthy arteries and blood pressure than protein. Besides limiting your intake of foods high in sodium, saturated fat and refined carbohydrates, avoiding trans fats and controlling your weight – very important messages you have no doubt heard over and over – the following dietary strategies can also help keep your arteries youthful and maintain healthy blood pressure.
Increase potassium
This mineral, abundant in fruits and vegetables, helps blood vessels relax. A higher intake of potassium also causes the kidneys to excrete more sodium, preventing blood pressure from rising. Excellent sources include bananas, apricots, prune juice, cantaloupe, honeydew, spinach, Swiss chard, lentils, black beans, kidney beans, milk and yogurt.
Boost vitamin C
Studies have found that higher intakes of vitamin C from foods and supplements (500 milligrams per day) have modest blood-pressure-lowering effects. Top sources of vitamin C include red and green bell peppers, citrus fruit, kiwi fruit, strawberries, cantaloupe, broccoli, Brussels sprouts, cabbage and cauliflower.
Drink tea
Research has shown that antioxidants in black and green tea, called flavonoids, reduce artery stiffness by increasing the production of artery-dilating nitric oxide. A higher intake of flavonoids has also been associated with a lower risk of dying from cardiovascular disease. Other flavonoid-packed foods include berries, apples, citrus fruit, kale, onions, green peppers, garlic, soybeans and dark chocolate.
Get more omega-3s
Long-term fish-oil supplementation – equivalent to eating 12 ounces of salmon per week – has consistently been shown to reduce artery stiffness. Omega-3 fatty acids in fish oil called DHA (docosahexaenoic acid) and EPA (eicosapentaenoic acid) are thought to improve artery flexibility by reducing inflammation, blood clotting and blood-vessel constriction. Fish oil capsules provide 300 milligrams to 600 milligrams of EPA and DHA. Liquid fish oil can deliver as much as 1,300 milligrams of EPA and DHA per teaspoon.
Leslie Beck, a registered dietitian, is based at the Medisys clinic in Toronto.
Leslie Beck