The Personal Fat Threshold
Why do some people who appear normal-weight have diabetes? And why do some people with severe obesity not have diabetes? These observations make the adage “You can’t judge a book by its cover” ring true. While we often associate obesity with metabolic disease, it’s just not that simple. There is far more to the story, and these seeming contradictions are explained by the theory of the Personal Fat Threshold.
There is significant variation in the amount of fat that people are able to store. Some individuals store large amounts of fat easily and do not develop metabolic complications such as diabetes or high blood pressure. For example, I have seen dozens of individuals with severe obesity, with body weights over 500 pounds, who challenge the conventional paradigm.
We have been trained to associate obesity, especially that level of obesity, with diabetes and other related complications. Instead, many of these individuals have had normal glucoses and Hemoglobin A1c’s – about 20% of those with severe obesity do. In fact, they usually also have normal lipid panels and normal blood pressure, as well. For years, I struggled to wrap my head around these observations.
What is the Personal Fat Threshold?
The ability to store fat varies greatly among individuals and ethnicities. Many populations (white, black, Pacific Islander, etc.) can generally accumulate large amounts of body fat, while other populations (Southeast Asian, etc.) generally cannot.
The Personal Fat Threshold is the limit to which one can store excess energy as bodyfat before developing metabolic complications. When fat is accumulating, it initially fills the subcutaneous fat depots, where fat is safely stored. Beyond a certain point, however, excess fat spills over into other fat depots, such as visceral fat and ectopic fat.
In response to the excess energy that overflows from the subcutaneous fat stores, the human body increases insulin levels to drive fat into the cells. The fat then gets shoved into whatever tissue is least resistant to it.
Lipodystrophy: An Illustration of the Importance of Subcutaneous Fat
In order to better understand the concept of the Personal Fat Threshold, it helps to look at an extreme situation where organisms cannot store subcutaneous fat. Lipodystrophy is a condition characterized by the inability to form subcutaneous fat.
Humans with lipodystrophy appear “shredded”, with well-defined muscles due to the lack of overlying fat. The downside of this condition is that individuals with lipodystrophy are prone instead to developing abdominal fat stores – visceral fat – and subsequent insulin resistance, including fatty liver and diabetes.
A study of mice serves as a demonstration that fat tissue essentially serves as a buffer against diabetes. The researchers used a mouse model with lipodystrophy – inability to store subcutaneous fat. In that lipodystrophic mouse model, anything you feed them causes them to create visceral fat and induces diabetes, insulin resistance, etc. Then, they surgically inserted a depot of adipose tissue which was connected to the mouse’s circulation, which reversed their diabetes.
These observations support the notion that subcutaneous fat can be protective against metabolic disease and that visceral fat is pathogenic.
Fat can be a Buffer Against Diabetes
Subcutaneous fat appears to actually buffer against type 2 diabetes and other manifestations of insulin resistance. In one respect, excess energy can be partitioned off into subcutaneous fat stores in a manner that minimizes the negative effects on metabolic health. This buffering effect lasts only until one reaches the capacity for fat storage.
How to Safely Expand Fat Mass
When it comes to accumulating fat mass, there are 2 options: increase the size of the existing fat cells (hypertrophy) or increase the number of fat cells (hyperplasia). As fat cells increase in size, they become more unhealthy. Thus, it is more favorable to increase the number of fat cells, which is what allows some individuals with severe obesity to maintain normal metabolic health.
A notable example of individuals who are obese but are metabolically healthy are sumo wrestlers. Sumo wrestlers are valued for their large body mass, the majority of which is subcutaneous fat. They maintain such a large body mass by eating 5,000-6,000 calories per day. Yet, they maintain a normal amount of visceral fat due to their rigorous training regimens. Upon discontinuation of their vigorous activity, however, they accumulate more visceral fat and develop insulin resistance. Though metabolically healthy during their careers, they tend to die 10 years earlier than the average Japanese individual.
Nature vs Nurture
Genetics certainly play a key role in determining the Personal Fat Threshold, based on the observations above among various populations. It should be noted that human genetics have not changed significantly in thousands of years. Are there other factors?
Seed oils (high omega-6 fatty acid content) have a unique ability to inhibit the formation of new fat cells, instead causing the existing fat cells to grow larger. They are now a ubiquitous ingredient and are likely driving metabolic disease.
Synthetic chemicals are a relatively recent exposure and can damage the mechanisms involved in weight control. Individuals with obesity tend to have higher concentrations of organochlorines than lean individuals. Through many mechanisms, these organic and inorganic substances may be contributing to increased visceral fat and impaired metabolic health.
The Personal Fat Threshold is an important concept that helps understand why there is such dramatic variation in both fat mass and metabolic health among individuals. One can think of it as how fat one can safely get.