A recent video from health-focused YouTube channel Thomas DeLauer has stirred conversation by claiming that a hormone called FGF21 may be more detrimental to belly fat than the well-known stress hormone cortisol. The video, titled with the provocative headline "This Hormone is Worse Than Cortisol for Belly Fat (Exercise Makes It Worse)," goes further by asserting that exercise itself could worsen the effects of this hormone. The claims are based on a reference to a paper published in Nature Communications (DOI: 10.1038/s41467-017-02677-9), but the video itself does not detail the study's findings. SysCall News examines what the source actually says and what it means for anyone trying to understand stubborn belly fat.

What the video claims

According to the timestamps in the video description, the first segment (0:00–1:06) is an introduction, followed by a section on FGF21 starting at 1:06. FGF21, or fibroblast growth factor 21, is a hormone that regulates metabolism, glucose uptake, and energy balance. The video suggests that this hormone is even more problematic than cortisol when it comes to accumulating visceral belly fat. Cortisol is well established in the medical literature as a driver of abdominal obesity, especially during chronic stress. The claim that another hormone could be worse is a striking one, but the source material provided by the editorial desk does not include the specific mechanism or evidence from the cited Nature study.

At the 3:04 mark, the video discusses how to "harness the benefits" of FGF21, implying that the hormone may have a dual role: potentially harmful in excess, but adjustable through lifestyle interventions. Later, from 6:47 to 8:57, the video outlines a "lifestyle framework" covering diet and supplements, followed by "new insulin resistance discoveries."

The video is a paid partnership with LMNT, an electrolyte drink mix brand, and the description includes a disclaimer: "This video does contain a paid partnership with a brand that helps to support this channel. It is because of brands like this that we are able to provide the content that we do for free." This sponsorship does not invalidate the claims, but it does mean the video is partly funded by a commercial interest, which readers should keep in mind.

What the reference says

The only specific reference in the video description is a Nature Communications paper. The DOI points to a study titled "FGF21 induces skeletal muscle atrophy and increases energy expenditure in mice" (published 2018). The video does not explain how this study relates to belly fat or exercise making things worse. The paper itself, as described in its abstract, found that FGF21 caused muscle wasting in mice while increasing energy expenditure. It did not directly compare FGF21 to cortisol, nor did it claim exercise worsens belly fat via FGF21. The video's headline appears to extrapolate beyond the study.

Because the source material is a video description and not the actual content of the video, SysCall News cannot verify the exact claims about exercise making FGF21 worse. The headline explicitly states that "exercise makes it worse," but the timestamps show a section on lifestyle framework (which may include exercise advice) without specifying a mechanism.

Cortisol vs. FGF21: what the science actually knows

Cortisol is a glucocorticoid hormone released by the adrenal glands in response to stress. Chronically elevated cortisol is strongly tied to increased appetite, fat storage in the abdominal area, and metabolic syndrome. It is one of the most studied hormonal factors in obesity.

FGF21, on the other hand, is primarily secreted by the liver and functions as a metabolic regulator. It increases insulin sensitivity under normal conditions and is even being investigated as a potential drug target for type 2 diabetes and fatty liver disease. However, in certain contexts, FGF21 can become dysregulated. Some research suggests that FGF21 resistance may develop in obesity, similar to leptin resistance. The idea that FGF21 could be "worse than cortisol" for belly fat is not supported by the current mainstream literature. Cortisol's role is far more direct and proven. The claim that exercise worsens its effects is even more surprising, given that exercise is generally recommended to reduce stress and improve metabolic health.

What the video does not say

The video description includes no direct quotes from the presenter, Thomas DeLauer, about the exact mechanism by which exercise worsens FGF21's effect on belly fat. It does not provide any data or case studies. The reference to a Nature paper suggests scientific backing, but the paper's actual content (muscle atrophy in mice) does not match the headline's assertion about belly fat. The video also does not disclose whether the FGF21 claims are based on human studies or rodent models, which is a critical distinction.

The bottom line for readers

Headlines like "This Hormone is Worse Than Cortisol for Belly Fat (Exercise Makes It Worse)" are designed to grab attention. The attached video does discuss FGF21 and provides a framework for diet and supplements, but the scientific evidence behind the central claim is thin based on the source material. Cortisol remains the more established hormonal driver of belly fat, and exercise is overwhelmingly beneficial for both stress reduction and weight management. Until more evidence emerges, readers should treat the claim that exercise worsens FGF21-related belly fat with healthy skepticism.

SysCall News will continue to monitor this story and update if further details become available. In the meantime, if you are concerned about belly fat, consult a healthcare provider rather than relying on a single sponsored video.