The cartoon character Popeye was right to scoff a can of spinach when he wanted his biceps to bulge, according to a study showing why the leafy vegetable makes us stronger.
Researchers at the Karolinska Institute in Stockholm, Sweden, discovered that nitrate, found naturally in spinach and several other vegetables, tones up muscles used for high-intensity activities like sprinting up a steep hill.
For the study, which was released this week and will be published in the Journal of Physiology, scientists gave mice drinking water with nitrate in it and observed a change in their fast-twitch muscles used for strength and high-intensity exercises.
The nitrate, administered in an amount equivalent to a human eating 200 grams of spinach a day, prompted an increase in two proteins that are used for storing and releasing calcium, which is vital to making muscles contract.
In human terms, the nitrate increases the muscle strength available for things like lifting weights or sprinting up a steep hill, the researchers said.
It could also increase endurance, the researchers said, pointing out that when stronger, the fast-twitch muscles, which fatigue faster than other muscles, do not need to contract as frequently.
Other super foods
But spinach isn't the only food that will make you stronger, experts say.
There are hundreds of so-called "super foods" that pack in large amounts of nutrients relative to their weight, says Sydney nutritionist Catherine Saxelby.
"Within every food group there are some foods that stand head and shoulders above the rest," she says.
However, many new "super foods" or "magic ingredients" to prevent cancer, lower our cholesterol or boost the immune system often have to be eaten in huge quantities to see a clinical effect, she says.
Instead, we should be looking for nutrient-rich foods that can be integrated into our diet in small amounts to replace less healthier options.
So what are the top super foods you should be eating? Here are 10 that nutritionists and dietitians rank among the best:
Aside from containing nitrate to tone muscles, spinach is rich in vitamin C, folate and vitamin A. It contains antioxidants to help protect eyes as we age and keep macular degeneration at bay. It also has virtually no fat and few calories.
"This is important in our modern day [diet] because a lot of people are overweight and a lot of people are sedentary," Ms Saxelby says. "You can't tell people to drink cups of coconut oil because it's just too many calories. You have to balance the nutrition aspect with the weight aspect."
LINSEED OR FLAXSEED
Instead of eating white bread, accredited practising dietitian Kellie Bilinski recommends a bread with grains such as linseed.
"Linseed is probably one of the best sources of omega-3 which is something really lacking in people's diets today because we eat a lot of pre-packaged food," Ms Bilinski says.
Omega 3 protects against cardiovascular disease.
Low in saturated fat, rich in zinc, high in protein and a major source of omega-3 fatty acids, there are plenty of reasons to eat salmon and other oily fish. It contains protein and minerals from the sea like iodine, potassium and "prostate-protecting" zinc.
The omega-3 fats are the ultimate anti-ageing nutrient, Ms Saxelby says. "They are an integral part of the structure of your brain and nerve tissues so work to keep you mentally sharp."
One omega-3 fatty acid called DHA is also good for breastfeeding mothers because it plays a key role in the development of babies' brains and eyesight. And fish is a surprise source of calcium too.
Nutritionists recommend eating salmon (fresh, canned or smoked) or other oily fish two to three times a week.
Several recent studies have uncovered the super properties of humble mushrooms. Ms Bilinski, whose area of research is cancer, says there is some indication that mushrooms can reduce the risk of breast cancer. They also contain several different nutrients and antioxidants.
A handful of almonds will help with a healthy heart. The super-nut provides a combination of 28 essential nutrients embracing vitamins, minerals, fatty acids, fibre and protein.
They are rich in monounsaturated fats to help keep levels of bad LDL-cholesterol down and are a good source of magnesium, zinc and potassium, which make blood vessels more elastic and help control blood pressure.
Eating almonds whole (including the skin) is the best way to get the full super food benefit.
Oats are the grain with everything - they are high in beta-glucan, a soluble fibre that will keep your cholesterol down, and have a low Glycemic Index to help keep diabetes at bay and releases carbohydrates into the system slowly, giving you energy for hours after eating. "If you want to live to 100 and be in good shape, start eating more oats," says Ms Saxelby.
Yoghurt has been associated with long lifespan ever since the Russian scientist Dr Ilya Ilyich Mechnikov claimed it was responsible for the longevity of the Bulgarians in the early 1900s. It is packed with calcium, protein and B vitamins (especially riboflavin, a B vitamin needed for healthy skin and eyes). Ms Bilinski says yoghurt is important for a healthy digestive system and immune system and is more concentrated than milk. The calcium in yoghurt can also help prevent osteoporosis.
Chillies have a strong concentration of vitamin C, about two to three times greater than citrus fruits, and are high in fibre, minerals like potassium and some of the B vitamins. But as the quantities of chilli consumed are fairly small, their overall contribution ends up being minor, says Ms Saxelby.
Chillies also raise the metabolic rate and are often promoted to dieters as a food with a "super-speed engine" which burns fuel faster. Red chillies are better than green.
The United States Department of Agriculture's Human Nutrition Centre ranks blueberries as number one for antioxidant activity when compared to other fresh fruits and vegetables. They are the nutrition powerhouses of the fruit world, experts say.
The antioxidants slow down the ageing of the brain. They have been shown to boost memory and brain function as we age, as well as protect the eyes from cataracts and glaucoma. Anthocyanins in blueberries also improve blood circulation and protect the heart.
Half a teaspoon of cinnamon a day may keep the doctor away.
"If you have room for only one spice in your kitchen, cinnamon is it," Ms Saxelby says.
New research has revealed that small amounts of cinnamon taken each day can lower blood sugar levels for those with diabetes. It adds flavour to food without having to use extra sugar or fat.
- with AFP