Lifestyle and exercise

Does mustard make massive muscles?

“Fitness fanatics should reach for the mustard and not spinach if they want to look like Popeye,” the Daily Mail reported.

This was laboratory research first using rat cells and then live rats. It investigated whether a plant-derived steroid (28-homobrassinolide [HB]) that promotes plant growth could stimulate protein synthesis and muscle growth.

In the laboratory, rat cells exposed to the plant steroid were found to build proteins. Further experiments showed that feeding rats with HB for 24 days caused them to increase their food intake and gain body weight and overall lean muscle mass. The researchers say that these effects did not seem to involve increasing levels of male hormones (androgens) – the effects that illegal anabolic steroids have.

Despite what the Daily Mail reported, this study has no current application to humans. Although this chemical may occur in mustard seeds and other plants, this research used the chemical in its concentrated form and mustard was not used in any part of this experiment. It is not known whether the same effects would be seen in humans and, if they were, how much food containing homobrassinolide we would need to eat to get similar effects. Most importantly, the safety of humans eating high concentrations of plant-derived steroids is completely unknown. 

Where did the story come from?

This research was conducted by scientists from the School of Environmental and Biological Sciences, Rutgers University, New Jersey, in the US. It was supported by grants from the US National Institutes of Health Center for Dietary Supplements Research on Botanicals and Metabolic Syndrome, and the Fogarty International Center of the National Institutes of Health.

The study was published in the scientific journal FASEB .

The actual body of the Daily Mail article is representative of this research in that it does make it clear these were laboratory studies in rats. The headline, though, suggested that the effects of eating mustard have been demonstrated in humans, and this is far from the case. The word ‘mustard’ actually appears nowhere within the research paper.

What kind of research was this?

This was laboratory research using first animal cells and then live animal models. The researchers wanted to see how the application of a chemical called 28-homobrassinolide (HB) to rat cells affected the development of protein. They then trialled the effects of feeding rats with HB on a daily basis.

Brassinosteroids are plant chemicals found in pollen, seeds, leaves and other young vegetation, which are said to have a similar chemical structure to cholesterol-derived animal steroid hormones. Brassinosteroids have no known function in animals, but in plants they help growth and regulate the expression of plant genes.

HB, the variety of brassinosteroid used in this study, is said to be derived from the pollen of Chinese cabbage Brassica campestris var pekinensis and in Japanese cedar trees Cryptomeria japonica. Among its functions, HB is involved in the synthesis of plant proteins, which promotes plant growth.

The researchers said that prior studies have shown that when the chemical is applied to skeletal muscle cells, it may stimulate certain enzyme pathways involved in producing protein in animals.

Anabolic steroids are drugs that mimic the effect of male hormones (such as testosterone) on the body and increase protein synthesis in cells, building up muscle mass. The researchers wanted to see whether plant brassinosteroids worked in a similar way to anabolic steroids and therefore also looked at the effect of HB on the male hormone system.

Experiments such as this one that used animal cells and live animal models can be useful in furthering scientific understanding of the effects that certain chemicals can have on biological tissues, but they have limited application to humans.

What did the research involve?

The initial laboratory tests placed rat muscle cells in a culture with differing concentrations of HB. The researchers used laboratory methods to assess whether the HB was toxic to the cells, and how it affected the production and breakdown of protein in the cells. They also looked at whether HB had bound to androgen receptors in the cell, which would indicate that it was acting in a similar way to anabolic steroids and exerting its actions by mimicking the effects of male hormones.

The researchers then took healthy rats and fed them a normal diet (protein content of 23.9%) supplemented by a daily dose, for 24 days, of either a control substance (1ml of corn oil) or HB (at either 20 or 60mg/kg dose). The rats’ food consumption and body weight were measured every two days until the end of the test period, at which time they were sacrificed and further body measurements taken.

The tests were repeated using the same control and HB supplements but in a group of rats fed on a high-protein diet (protein content of 39.4%).

A final set of tests involved rats that had been castrated, to see whether the effects of HB occurred independently and not through increasing androgen production.

What were the basic results?

The researchers found that when HB was applied to rat muscle cells it stimulated the production of proteins and prevented protein breakdown.

Compared to control rats, rats fed a normal diet and given daily HB increased their food intake, gained body weight, increased lean body mass and increased leg muscle mass. Rats fed a high-protein diet demonstrated a slightly greater effect. HB was also associated with improved physical fitness. A grip test demonstrated that rats given the chemical had a 6.7% increase in lower extremity strength.

The researchers also observed that when HB was given to rats either orally or by subcutaneous injection, it caused a minimal increase in the activity of male hormones (androgens). That HB acted without enhancing androgen activity was also supported by the fact that when applied to cells in the laboratory, HB did not appear to bind to the androgen receptor. Furthermore, when castrated male rats were fed HB, their leg muscles still showed an increase in muscle mass. Overall, the researchers say this suggests that HB triggers protein synthesis and builds up muscles but has no or minimal androgenic side effects.

How did the researchers interpret the results?

The researchers believe that HB may have a muscle-building effect through stimulating protein synthesis and preventing protein breakdown in muscle cells. They say that this stimulatory effect of HB on protein synthesis in muscle cells translates into effects on the whole body, such as increasing lean body mass, muscle mass and physical performance. The researchers also note that HB has its muscle-building effect while having minimal or no androgenic side effects, which makes it different from anabolic steroids.


This study has furthered the understanding of how the plant-derived steroid 28-homobrassinolide has a biological effect on rat muscle tissue. It may be of scientific interest, but has limited current relevance or application to humans.

It is important to point out that the plant steroid that was used in this study was not derived from mustard. Although mustard seeds may contain brassinosteroids, it cannot be assumed that eating mustard will have any effect on muscle growth. Even if this plant steroid does have any effect on muscle growth in humans, it is not known how much plant food containing homobrassinolide would need to be eaten to have any effect. Most importantly, it is unclear whether consuming high amounts of this plant steroid, either through food substances or in the concentrated chemical form, would be safe for humans either in the short or long term.

The researchers’ tests suggests that HB has a different mode of action from anabolic steroids in that it does not seem to have an effect on male hormones. This may suggest to readers that plant-derived steroids could be considered acceptable for use where anabolic steroids are not. However, even if further testing and study did adapt this chemical for use in humans, there would still need to be legal and regulatory issues surrounding its use.

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