Follistatin vs MK-677: What Are The Differences?

In this article, we will take a close look at the differences between Follistatin and MK-677, two compounds widely used in the field of bodybuilding and muscle growth. We will delve into their unique functions, how they affect the body, and their potential therapeutic applications.
Frederika Malichová

Frederika Malichová

Neuroscientist at the University Of Cambridge.

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Differences Between Follistatin and MK-677

Follistatin and MK-677 are both used in the field of bodybuilding and muscle growth, but they function differently. Follistatin is a protein that inhibits the release of follicle-stimulating hormone, promoting muscle growth. On the other hand, MK-677 is a growth hormone secretagogue, which means it stimulates the production of growth hormone. These differences in function make them unique in their applications and effects on the body.

What is Follistatin?

Follistatin, or FST, is a naturally secreted glycoprotein. It has two major isoforms FST288 and FST315. FST315 is the predominant form of FST [1].

FST belongs to the tissue growth factor β family. It is expressed in various different tissues and its main function is in binding and neutralising transforming growth factor β (TGFβ).

Follistatin is known to antagonise many members of this family for instance activin A, growth differentiation factor 11 and myostatin [2].

Follistatin was discovered in ovarian follicular fluid and functions as a suppressor of pituitary follicle-stimulating hormone (FSH) secretion [3].

The main function of Follistatin is in muscle regeneration. Interestingly, it can increase body weight and lean muscle mass in mice and was found to be a potent inducer of muscle remodelling and regeneration [2, 3].

However, follistatin has been implicated in various diseases, including cancer, where it may contribute to the progression of certain tumours [4, 5].

What is MK-677?

MK-677 is also known as Ibutamoren and it is an orally active growth hormone secretagogue (release-promoting substance). In other words, it promotes the release of growth hormone in the body. It is a similar substance to the naturally present hormone Ghrelin, which is involved in the regulation of hunger, energy use and growth hormone secretion.

MK-677 is believed to have the potential to increase growth hormone and insulin-like growth factor 1 levels, which could potentially help prevent the decline of muscle mass and function in older adults [6]. Surprisingly, in clinical trials, it does not show any serious adverse effects.

In addition, it seems to increase fat-free mass and body cell mass but not the abdominal visceral fat or total fat mass [6].

Potentially MK-677 can be used in reversing diet-induced catabolism ( a condition, in which the body breaks down its own tissue to use for energy) as a treatment for some acute or chronic diseases which involve catabolic processes [7].

What are the differences between Follistatin and MK-677?

Follistatin and MK-677 are different compounds with different roles and effects on the body. Therefore there are differences in almost all aspects.

When comparing the mechanisms of action, Follistatin works by binding and inhibiting the activity of myostatin [8]. MK-667 however works on the principle of mimicking the action of ghrelin, a naturally present hormone that stimulates the release of growth hormone from the pituitary gland [6].

Follistatin is also involved in a wider range of biological functions ranging from anti-inflammatory activities, and wound-healing to muscle-stimulating effects [9]. The role of MK-677 is to mimic the effects of Ghrelin and stimulate the release of growth hormone.

Both Follistatin and MK-677 are used in clinical trials as both have a potential for treating conditions like muscle diseases, conditions with inflammation, fibrosis and GH deficiency and sarcopenia respectively [10, 9]

MK-677 has been used in clinical trials to investigate its potential for treating conditions such as GH deficiency and sarcopenia, a condition characterised by loss of muscle mass and function [11].

Although Follistatin and MK-677 are different in almost all aspects, they both have effects on muscle mass and function and they both have a potential as therapeutic substances related to muscles.

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Frederika Malichová

Frederika Malichová

Frederika is a postgraduate researcher at the University of Cambridge, where she investigates new biomarkers for Frontotemporal Dementia and other tauopathies. Her research has been published at prestigious conferences such as the Alzheimer’s Association International Conference 2023. She obtained her BSc in Biomedical Sciences from UCL, where she worked closely with the UK Dementia Research Institute.