| In the age of widespread obesity, booming weight-loss drugs, and New Year’s resolutions set on weight-loss, it may sound unbelievable that there is a small portion of the population that struggles to gain or maintain a healthy weight. More than just an anomaly, this small demographic could offer important clues for understanding metabolism and weight regulation that scientists still haven’t fully unlocked. However, being in this group comes with a different set of challenges compared to the more commonly studied overweight population. These are people who may intentionally overeat or purposefully eat more junk foods in an effort to appear more “normal.” They are often misunderstood, suspected of disordered eating, and may struggle to build or maintain muscle mass. This condition is estimated to affect only about 1–2% of the population, but these outliers challenge much of what we think we know about weight gain. It may seem obvious that eating a fast-food burger every day will lead to weight gain — but that’s not always the case for this select group, or the amount of weight they gain is far smaller than expected compared to the average person. Deep Dive: The Other End Of The Weight Spectrum |
| It’s become more widely understood that people have different metabolisms. What remains largely unexplained is why. Some factors are genetic, but it’s difficult to connect metabolic function to any single gene. Gender, hormones, stress, and age all influence how the body stores fat, but this group of naturally very thin individuals doesn’t appear to fit neatly into those categories, and the usual “rules” of weight gain don’t seem to apply. One study in the 1990s overfed pairs of identical twins for several months, and the wide variation in how different twin sets gained weight suggested that metabolism is far more complex than genetics alone. Because the “constitutionally thin” make up such a small percentage of the population, very few studies have been conducted compared with the vast body of research on weight gain and obesity. Even though this small group could serve as a “mirror model” for weight-gain studies, only about 50 or so studies have examined weight-resistance so far. Researchers suspect that this group’s metabolism may convert fewer calories into muscle mass than most people do. And while constitutionally thin individuals can sometimes eat more than the average person without gaining much weight, many of them don’t naturally have large appetites, which makes intentional weight gain feel like work. Related: How Pop Culture Got Obsessed With One Macro Related: Top 5 Protein Myths Debunked Another confusing finding emerged from research on fat distribution. Constitutionally thin people may weigh as little as 70 pounds at a height of five feet, yet their body-fat levels can still fall within a normal range. Unfortunately, this points to an issue with building lean muscle and bone mass, which limits how useful this group may be for people seeking weight-loss insights and it also means they may face their own health risks, similar in seriousness to those associated with excess weight. This “skinny-fat” composition where individuals struggle to build typical amounts of muscle and bone despite being very thin has researchers puzzled and increasingly turning back to genetics for answers. While genetics can’t be the only factor shaping metabolism, studies suggest that around 74% of constitutionally thin individuals have a close relative with a similar build. Ultimately, constitutional thinness reminds us that bodies exist along a wide biological spectrum and that weight is more than a matter of discipline, diet, or willpower. It’s more complicated than “calories in, calories out”. As researchers continue studying this small but important group, we may gain a deeper understanding of how metabolism really works and on the many different ways healthy bodies can look and function. |
