Researchers have finally caught up with the wisdom of mothers, who, for decades have been coaxing their children to eat spinach.

We know this leafy green is a good source of folate, a very important B vitamin involved in cell division. Spinach is also rich in iron, making it a potentially important source of this mineral for vegetarians.

Now, researchers in Sweden have uncovered another reason to eat spinach. They appear to have provided an explanation for why Popeye, the cartoon character, had such large muscles and superhuman strength.

There’s a growing body of recent research demonstrating that the inorganic nitrate found in certain vegetables might have important biological functions.

Previously nitrate in food was seen as a potential hazard because a small percentage of it could be converted to nitrite in our bodies. Nitrites can react with other dietary constituents to form nitrosamines, which are suspected stomach carcinogens.

But researchers have now demonstrated that nitrate can be converted back to nitric oxide, a compound important for dilating blood vessels and preventing hypoxia (inadequate blood supply). During exercise, nitric oxide reduces oxygen consumption allowing muscles to exercise more efficiently.

The Swedish researchers, who published the findings of a research project that involved adding nitrate to the drinking water of mice. They gave one group of mice drinking water with added nitrate and a control group water without nitrate for a period of seven days.

The authors suggest the amount of nitrate fed to the mice is equivalent to what an adult might obtain from 200 grams to 300 grams of fresh spinach. The standard serving size for fresh spinach is about 30 grams, and for cooked spinach, it’s about 180 grams.

So to consume the same amount as the mice, you’d have to eat one to two serves of spinach every day for a week. We can’t determine what effect smaller amounts of nitrate over a prolonged period might produce.

After one week, the mice were sacrificed for knowledge and their muscles dissected for experiments. The extensor digitorum longus muscle that extends down the front of the leg and contains fast twitch muscle fibres and the soleus muscle (which has slow-twitch muscle fibres) were tested. Fast-twitch fibres generate short bursts of strength or speed as in sprinting while slow-twitch fibres involve prolonged contraction as might be used in a marathon.

The isolated muscles were stimulated and the contractions measured. Researchers found that the mice that had consumed nitrate had increased contractile force in the fast-twitch muscle, that is, they had stronger muscles.

Further studies indicated that nitrate-fed mice had higher concentrations of two different proteins in their muscles; calsequestrin 1 (CASQ) and dihydropyridine receptor (DHPR). These proteins allow increased calcium storage and subsequent release in the muscle for contraction.

The researchers now plan to look for applications of nitrate supplementation not only in exercise performance but for a therapeutic role in diseases with or causing muscle weakness.

Now that science has shown that spinach makes you stronger, there’s no longer a reason to not eat it and excuses won’t do. But if you still can’t be convinced, you will be pleased to know that beetroot, celery, rocket, lettuce and bok choy are also rich in nitrate.