Popeye was right, it seems. According to a study published last week in the journal Cell Metabolism, eating spinach can make your muscles stronger.
But it's not the iron in spinach that gives muscles a boost. It's nitrates - natural compounds abundant in vegetables - that appear responsible.
In the study, healthy people took nitrate supplements - the equivalent of 1.5 cups of cooked spinach - for three days. At the beginning and end of the experiment, participants rode an exercise bike while their oxygen intake was measured.
Taking nitrate supplements resulted in more efficient muscles - the amount of oxygen needed to fuel exercise was reduced by as much as five per cent.
It's thought that dietary nitrate helps the mitochondria - the power plant inside every cell - run more smoothly and effectively.
The researchers don't suggest you start popping nitrate supplements before a workout. Rather, they say, the results offer one explanation for the many well-known health benefits of leafy green vegetables.
Nitrates feed into a pathway that produces nitric oxide, a chemical that relaxes blood vessels, lowers blood pressure and improves circulation. In doing so, nitrate-rich leafy greens could increase the flow of oxygen and nutrients to working muscles.
While these findings are interesting, there are plenty of other reasons to eat leafy greens such as spinach, kale, Swiss chard and collards.
When it comes to vitamins, minerals and antioxidants, leafy green vegetables are hard to beat. They offer fibre, vitamins C, A and K, folate, calcium, magnesium, potassium and beta-carotene, and have been linked to a lower risk of heart disease, Type 2 diabetes and certain cancers.
Leafy greens are also an exceptional source of lutein and zeaxanthin, phytochemicals that guard against cataract and macular degeneration. Research also suggests a regular intake of leafy greens can keep your mind sharp as you age.
You'll get more calcium, magnesium, iron, beta-carotene and lutein if you eat your greens cooked rather than raw. That's because cooking breaks down cell walls, increasing the amount of minerals and antioxidants available to your body for absorption.
If you're new to leafy green vegetables, the following tips will help you add them to your diet - aim for one serving each day. (One serving is equivalent to a 1/2 cup cooked or 1 cup raw). These vegetables are readily available in grocery stores. Other leafy greens worth looking for include dandelion greens, beet greens, mustard greens and turnip greens.
To prepare, trim the roots and separate the leaves. Wash thoroughly. Remove the tough stems and ribs from the leaves. Coarsely chop the leaves. Collard greens are most flavourful when sautéed. But you can also add this green to soups and stir-fries.
• Drizzle sautéed collard greens with extra virgin olive oil and freshly squeezed lemon juice. Top with toasted pine nuts.
• Add blanched collard greens to a chicken stir-fry. To blanch, bring water to boil in a large pot. Add greens to boiling water and cook for 1 to 5 minutes, or until greens have wilted. Remove from the heat and drain. Allow greens to cool then squeeze out moisture.
• Sauté collard greens with cubes of firm tofu, minced garlic and a hint of curry paste for a vegetarian meal.
Both leaves and stalks can be eaten, but most recipes call for leaves only. After washing, use a knife to remove the tough stems and ribs. Coarsely chop leaves. Kale leaves are sturdy and hold up well in soups and pasta sauces.
• Add chopped kale leaves to sautéed garlic and red chili flakes; sauté until tender, about 5 minutes. Drizzle with roasted sesame oil just before serving.
• Sauté kale leaves with chopped apple. Before serving, sprinkle with balsamic or apple cider vinegar.
• Add raw kale leaves to any soup and simmer until leaves are tender.
Rapini (broccoli raab)
You can cook and eat the leaves, stalk and flower heads of rapini just as you would regular broccoli. Rapini has a stronger flavour than broccoli. Some people prefer to blanch rapini for one to two minutes before cooking it in order to mellow the flavour. Discard bottom 1/4 inch of stalks.
• Sauté blanched rapini for 3 to 5 minutes with minced garlic. To serve, drizzle with fresh lemon juice and sprinkle with grated Romano or Parmesan cheese.
• Add chopped blanched rapini to a tomato-based pasta sauce with turkey sausage.
• Sauté rapini with minced garlic, red chili flakes and chick peas for a vegetarian dish.
Savoy spinach has crisp, creased, curly leaves. Smooth-leaf spinach has flat, unwrinkled spade-shaped leaves. Baby spinach has a slightly sweeter taste and is great for adding to salads.
• Steam spinach and add a splash of raspberry vinegar just before serving.
• Add layers of steamed spinach to a lasagna recipe.
• Add chopped spinach or baby spinach to pasta sauce at the end of cooking.
This tall leafy green vegetable has a thick, crunchy stalk that comes in white, red or yellow with fan-like green leaves. Discard bottom 1 inch of stems. Then chop the stems and leaves. The stalks will take longer to cook than the leaves; begin cooking them about 2 minutes before adding the leaves.
• Toss cooked Swiss chard with penne pasta, extra virgin olive oil, sautéed garlic, lemon juice, sun-dried tomatoes, chopped black olives and grated Parmesan cheese.
• Add steamed Swiss chard to omelettes, quiches and frittatas.
• For variety, use Swiss chard in place of spinach in recipes.
Leslie Beck, a Toronto-based dietitian at the Medcan Clinic, is on CTV's Canada AM every Wednesday. Her website is lesliebeck.com.