The Eugenic History of the Body Type Diet

by Ashley Hamer
July 1, 2025

Getting fit is difficult. Even when you cut out junk food and start working out regularly, it might still take a long time to see results — if you ever do. So it's tempting to think that maybe those boring old rules about eating less and exercising more? They don't make sense for everyone. Maybe you need a custom approach that fits your unique body type.

Here's how Bodybuilding.com describes the three body types, or somatotypes:

An ectomorph tends to be thin, and struggles to gain weight as either body fat or muscle. They can eat piles of food and stay looking the same, even when gaining muscular weight is their biggest goal. Ectomorphs tend to have a lean build, long limbs, and small muscle bellies.

(The muscle belly is just the largest, thickest part of a muscle; it's something bodybuilders obsess over because the shape you're born with affects how much your muscles can visibly "pop.")

The mesomorph has a middle-of-the-road build that includes the best of both worlds. They tend to have wide shoulders, a narrow waist, relatively thin joints, and round muscle bellies. In short, if you're a mesomorph, you have a natural tendency to be fit and relatively muscular.

An endomorph tends to gain weight easily and struggles to lose it. Their build is a little wider than an ectomorph or mesomorph, with a thick rib cage, wide hips, and shorter limbs. If you ever feel like you gain 5 pounds simply walking past a donut shop, you may be an endomorph.

These body types, it's said, mostly come down to genetics. But it's also possible to change them.

According to proponents of body type training, each type needs a different nutritional and exercise approach. For example, according to Phil Cadutal, a celebrity trainer and coauthor of the book Just Your Type: The Ultimate Guide to Eating and Training Right for Your Body Type, skinny ectomorphs should eat more carbs and less fat than stocky endomorphs, while muscular mesomorphs should aim for an even split between carbs, protein, and fat.

Exercise recommendations are similar. Transparentlabs.com recommends that stocky endomorphs incorporate lots of cardio to shed fat, while skinny ectomorphs should avoid cardio and do mostly strength training to bulk up. Mesomorphs can do a bit of both.

Before we start to hack through the dense thicket of nature vs. nurture and correlation vs. causation surrounding this idea, we first need to understand where these categories even came from. After all, just look around — there are way more than three types of bodies out there. Who even decided on such narrow definitions?

His name was William H. Sheldon, and he did it with nude pictures of Ivy League college students.

William Sheldon was an American psychologist and physician born in 1898 who spent his life categorizing human bodies to predict personality traits and behaviors.

He was particularly interested in the work of a German psychiatrist named Ernst Kretschmer, who developed a classification system that associated different body types, or somatotypes, with different psychiatric disorders. While Kretschmer only had three types, Sheldon dreamed of creating a holistic classification system that used multiple measurements to predict temperament in general, rather than just mental illness. But to create this system, he was going to need data — lots of it.

When he was doing his doctoral studies at the University of Chicago in the 1920s, the American posture movement was in full swing: there was a widespread belief that good posture was required for health and that America's youth were slouches. Schools around the country began taking measurements of every student, including photographing them in the nude, to determine who needed special training to straighten back up.

As a result, there were thousands and thousands of photos Sheldon could use to create his classifications. For his early research, he collected 4,000 photographs of white, male students from the University of Chicago and developed a classification system similar to, but more in-depth, than the three somatotypes we know today: rather than slotting everyone into one of three body types, he measured the amount that each body corresponded to each type. The amount of ectomorphy, or thinness, a person had got a score, as did the amount of endomorphy, or fatness and mesomorphy, or muscularity.

Interestingly, although he was using photographs from posture programs, his goals were opposite to theirs. Eugenics was in vogue at the time, and Sheldon and posture educators all believed that a better looking society would be a healthier society, and that certain races just had a more naturally erect posture than their less civilized counterparts.

But posture educators believed bad posture could be improved through training, no matter who you were. Sheldon believed the body you were born with was your destiny. He said that society becoming less beautiful, quote, "was the result of modern medicine's keeping people alive indiscriminately." End quote. Improved exercise wouldn't fix it, in Sheldon's view. Improved breeding would.

During his career, Sheldon collected tens of thousands of photographs and climbed the academic ladder. He befriended psychiatric greats like Carl Jung and Sigmund Freud, along with authors like Aldous Huxley, who wrote about his somatotypes in the magazine Harper's Weekly to make them household names.

But as World War II exposed the horrors of eugenics, Sheldon and his ideas faced mounting criticism. His views were overtly racist: his master's thesis compared the intelligence of Mexican and White children, and he called Jews and Italians "vermin" in his books. He was also just difficult to work with and rarely finished any of the projects he started.

The final blow came from his own assistant, Barbara Honeyman Heath. She exposed his fraudulent methods to his funders by revealing that Sheldon cherry-picked the photographs he included in his research to "prove" somatotypes didn't change throughout life. He would trim photos based on subjects' memories of their height and weight at 18, not their actual measurements.

Combined with parent complaints over nude photos of students, especially young women, this led to Sheldon's professional downfall. Heath went on to lead a successful career by modifying his techniques, but his original system was discredited.

It might surprise you that after all that, someone could still build a career on Sheldon's methods — and it might surprise you further that there's still a whole active field of anthropometry, the study of measurements and proportions of the human body. The truth is that a person's outward appearance can tell you something about them — just not their temperament, personality, or mental health status.

For example, BMI is an anthropometric measurement: the ratio of your height to your weight can give some indication of body fat, which can gauge your risk for things like heart disease and diabetes. When you take a baby to the pediatrician, measurements of their height, weight, and head circumference let the doctor know how well they're growing. Anthropometric measurements in athletes can help them refine their training and performance.

Which brings us back to somatotype, a term that appears in thousands of academic papers even from the last five years. Scientists still use the three somatotypes as a handy shorthand, especially in exercise science.

Studies have found that a person's somatotype correlates with lots of different things, some more obvious than others. For example, it should surprise no one that endomorphs tend to consume more calories, while ectomorphs tend to have more nutritional deficiencies.

And there are plenty of studies that simply describe the somatotypes of top performers. For instance, one study found that the best elite female volleyball players in Spain were taller with more ectomorphy than lower level players. Another found that elite Italian gymnasts tended to be more mesomorphic and less endomorphic than other elite athletes, and another study found the same thing to be true of Croatian track-and-field athletes at the national level. Studies like this suggest that an athlete's body type can be a contributing factor toward reaching elite status.

And there are a few studies that suggest different somatotypes respond to exercise differently. Research suggests that in an activity like weight lifting, about a third of strength performance comes down to your somatotype, with different somatotypes doing better with different lifts. There's also some evidence that aerobic training has a greater effect in mesomorphs than in other somatotypes.

So does this mean that you should train according to your body type? Not in the way these books and websites suggest.

First of all, eating a diverse diet of whole foods in moderate portions and exercising regularly will benefit most people regardless of body type. The differences these studies have found between somatotypes are tiny, and more relevant for a professional athlete with Olympic goals than an office worker who wants to fit into their old jeans.

But here's the biggest logical flaw in body type training: The science suggests that there are certain body types that do better in certain sports, yet these programs push everyone to become mesomorphs by doing exactly what their body type supposedly isn't suited for.

For example, elite marathoners tend to be ectomorphs, which suggests a lean frame is better for endurance running. But the body type training approach would suggest that ectomorphs avoid cardio and instead hit the weights to increase their muscle mass.

And elite weightlifters tend to have some endomorphy, which suggests extra weight on your frame is good for generating power. But this approach would tell them to do more cardio and avoid carbs to shed excess fat.

Instead, it's better to assess your own goals and go from there. If you're skinny and you want more muscle, by all means, pound the protein and lift heavy weights. If you've got fat you want to lose, focus on diet and exercise plans designed to help you lose it. If you know you do better with one exercise routine than another, do that routine. Very little of this depends on the body type you were born with.

Your body type might have a small influence on how you respond to training, but it doesn't dictate your destiny. Unlike Sheldon's eugenic vision, modern fitness is about working with what you have, not being limited by it.

Remember: The most effective workout plan is the one you'll actually stick to, regardless of whether you're an ectomorph, mesomorph, or endomorph. Your genetics might be the hand you're dealt, but how you play that hand is entirely up to you.

By Ashley Hamer