The "natty or not" debate is one of the most persistent and polarizing topics in the fitness world. A recent controversy, sparked by a Jeff Nippard video showcasing incredible drug-free physiques, brought the issue to a boiling point. Many viewers cried foul, pointing to a long-held belief: that a Fat-Free Mass Index (FFMI) of 25 represents the absolute limit of natural human potential.
Dr. Mike Israetel dives into this controversy to explain why this supposed "limit" is a misunderstanding of science. He clarifies the difference between likelihood and certainty, and provides a more logical framework for thinking about natural genetic potential.
TL;DR: The Truth About Natural Limits
- The idea of a hard "natural limit" at a 25 Fat-Free Mass Index (FFMI) stems from a misinterpretation of a single 1995 study that had a small, incomplete sample.
- Natural muscle potential exists on a bell curve, and genetic outliers can and do naturally exceed an FFMI of 25. This has been confirmed in other studies on drug-free athletes.
- The biggest mistake in these debates is confusing **likelihood** with **certainty**. It's reasonable to say a high FFMI makes drug use *likely*, but it's a "clown show moment" to claim it makes it *certain*.
- The only true way to discover your personal genetic potential is through 5-10 years of dedicated and intelligent training, nutrition, and recovery.
Why the 25 FFMI "Limit" is a Myth
The belief in a 25 FFMI ceiling comes from a 1995 paper by Kouri et al. However, as Dr. Mike points out, a closer look at the data from that study reveals a major flaw. The graph of the natural lifters does not show a normal bell curve; instead, it cuts off abruptly at an FFMI of 25.
This is not evidence of a hard physiological limit. Rather, it suggests two things:
- Incomplete Sampling: The study was small. By random chance, it likely failed to capture the rare genetic elites who exist at the highest end of the natural bell curve.
- A Self-Selection Problem: Many of the most genetically gifted lifters who reach a high FFMI naturally are also the most likely to transition to using performance-enhancing drugs to compete at higher levels, removing themselves from the "natural" data pool before they even hit their peak.
In fact, other research on drug-free sumo wrestlers and American football players has documented numerous individuals with a natural FFMI well over 25, proving it is indeed possible.
The Crucial Difference: Likelihood vs. Certainty
The core of the issue, according to Dr. Mike, is a failure to distinguish between probability and absolute fact. "The big mistake that so many people make... is in assuming that likely not natural is the same thing as definitely not natural, and it's absolutely not."
Saying someone with a 25+ FFMI is *likely* on performance enhancers is a reasonable probabilistic statement. But saying they are *definitely* enhanced is an overreach that ignores the proven existence of genetic outliers.
A Better Way to Think About FFMI
Instead of a hard cutoff, Dr. Mike proposes a more nuanced, probabilistic approach to interpreting FFMI scores in lean individuals:
- FFMI over 25: It's more likely than not the person is using PEDs.
- FFMI over 27.5: It is very likely they are on gear (85-95% probability).
- FFMI over 30: It is exceedingly likely (97%+ probability), but still not 100% certain.
So, How Big Can You Get Naturally?
While online calculators can give you a rough, evidence-based estimate of your potential, Dr. Mike emphasizes there is only one way to truly find out: you have to put in the work. The only way to know your true natural ceiling is to dedicate **five to ten years** to consistent, intelligent, and intense training, coupled with meticulous nutrition and recovery practices.
Conclusion: Focus on Your Own Journey
While the "natty or not" debate can be entertaining, concluding with certainty that someone is or isn't natural is often a fool's errand. Genetics are real, and rare outliers exist. Instead of spending energy policing others, the best path forward is to focus on your own journey. Put in the years of dedicated work, and you will inevitably discover just how far your own potential can take you.
