Food and diet

Stick with the gym Popeye

“Popeye the cartoon sailor may have been right to claim that spinach builds muscles,” reports The  Daily Telegraph today. It said that researchers tested the effect of chemicals extracted from spinach (phytoecdysteroids) on samples of human muscle in the laboratory and found that “they sped growth by up to 20 per cent”. They say that the researchers also found that rats injected with the extract for a month were stronger and had increased grip strength. However, the newspaper also reports that the researchers estimated that people would have to “eat more than 2.2lb (1kg) of spinach every day” to see these effects.

This report is based on a study looking at the effects of different phytoecdysteroids, including one found in spinach, on mouse and human cells grown in the lab, and on live rats. The researchers did find that the compounds, which are actually a form of steroid, had an effect on human cells and rats. However, there is no guarantee that the compounds will have the same effect on live humans.

The researchers say that unfeasibly large amounts of spinach would need to be consumed for any effect (if there is one in humans). As such, there is no need to worry that eating spinach will cause alarming muscle growth. Those seeking to enhance their physique purely by eating spinach may find that they are disappointed.  Spinach can be eaten as part of a healthy diet.

Where did the story come from?

Dr Jonathan Gorelick-Feldman and colleagues from Rutgers University, Brown Medical School and the University of Illinois in the US carried out the research. The study was funded by the Fogarty International Center of the National Institutes of Health (NIH), the NIH Center for Dietary Supplements Research on Botanicals and Metabolic Syndrome, and Phytomedics Inc (a company developing new drugs from plant sources).

The study was published in the peer-reviewed: Journal of Agricultural and Food Chemistry.

What kind of scientific study was this?

In this experimental laboratory study, the researchers investigated what effect a type of plant steroid (phytoecydysteroids) has on human and mouse muscle cells, and live rats. They were particularly interested in whether the phytoecydysteroids made muscle cells produce more protein, and whether this translated to greater grip strength in rats. Phytoecydysteroids are thought to be involved in plant defences against insects, and are found in particularly high concentration in plants such Ajuga turkestanica , a herb from the basil family and native to Uzbekistan, and at considerable levels in some edible plants such as spinach.

In the first part of their study, the researchers tested several different purified plant steroids, including the main one found in spinach, one from Ajuga turkestanica , and one chemically produced (synthetic) anabolic steroid, Methandrostenolone. 

To do this, mouse muscle cells were grown in the laboratory and exposed for four hours to increasing concentrations of the different steroids or a control solution containing no steroids. The researchers then looked at how much protein the cells were making by measuring how much of a radioactively labelled (traceable) amino acid (a building block for proteins) the cells were taking up. They repeated these experiments with extracts from both spinach and Ajuga turkestanica.  The experiment was then repeated, but this time exposing human muscle cells to the purified spinach phytoecydysteroid for 24 hours.

In the second part of their experiment, 40 rats (10 per group) were given purified spinach phytoecydysteroid, spinach extract, the synthetic steroid, or none of these (control). This was given in addition to their normal diet for 28 days and the strength of the rat’s grip with their front limbs was tested at the end of this period.

The researchers also tested whether the purified spinach phytoecydysteroid would bind to a rat androgen receptor when they were mixed together under appropriate conditions in the laboratory. These receptors naturally bind to the steroid testosterone, but other steroids can also bind to them. This leads to the muscle enhancing effects of these steroids, but also side effects such as the deepening of the voice, acne and excess hair in women, as well as growth of breast tissue and impairment of sperm production in men.

What were the results of the study?

The researchers found that all of the different phytoecydysteroids increased protein synthesis in the mouse muscle cells, and the higher the dose the greater the increase. The spinach and Ajuga phytoecydysteroids had the greatest effect, while the synthetic steroid did not increase protein synthesis. The spinach phytoecydysteroid had a similar effect on human muscle cells.

Rats given the purified spinach phytoecydysteroid had a stronger grip than the control rats, as did rats given the spinach extract and the synthetic steroid. The researchers found that although the synthetic steroid bound to the rat androgen receptor, the purified spinach phytoecydysteroid did not.

What interpretations did the researchers draw from these results?

The researchers concluded that the phytoecydysteroids used in their experiments increased protein production in mouse and human muscle cells and increased muscle strength in live rats. They say that these results suggest that both of the plant extracts tested may stimulate muscle growth and strength in live animals.

What does the NHS Knowledge Service make of this study?

The effects of the phytoecydysteroids on muscle are not surprising as other members of the steroid family of compounds are known to produce muscle growth and strengthening effects. It is not possible to be certain that the effects seen in cells grown in the laboratory or in rats will necessarily be the same in humans. If these phytoecydysteroids are to have a role in medicine, they will need to undergo thorough testing in the laboratory and in animals before testing in humans.

It is also clear that the effects seen in this study occurred with purified spinach phytoecydysteroid and specially prepared and concentrated spinach extracts. Attempting to recreate the effects with ordinary spinach, where these compounds are much less concentrated, will not produce the same results. Spinach should be eaten as part of a balanced diet.

Sir Muir Gray adds...

Spinach is good for you.

NHS Attribution