When you buy a T-shirt, you usually choose from three sizes: small, medium, or large. There are other options, such as extra-large and XXL, but for this article, we’ll focus on the first three.

Body types also fall into three broad categories:

Ectomorphs – slim, not necessarily short or tall
Endomorphs – more portly, again, not necessarily tall or short
Mesomorphs – somewhere in between

These physiques represent the basic geometry of our bodies and are largely hereditary—there’s not much we can do about that. What we can influence is the weight we add to our natural body shape, particularly the body fat we accumulate, especially around the abdomen. We can give ourselves "this day our daily bread (and breadth)", but unfortunately, what God giveth, He does not always take away!

A Flawed Measure: BMI

Ethicist Arthur L. Caplan, PhD, has suggested that the Body Roundness Index (BRI) should replace the long-standing but flawed Body Mass Index (BMI).

How many of us actually know our BMI? It’s a medical screening tool that has been used for decades to assess obesity. According to the BMI, vast numbers of people around the world are classified as obese. But the tool has serious limitations.

The BMI doesn’t account for racial, ethnic, gender, or age diversity. It was originally developed from a small sample of white men in the armed forces. One of its biggest flaws is that it fails to differentiate between muscle mass and fat. A young Arnold Schwarzenegger, for example, had a 32-inch waist but would’ve been classified as obese under BMI because of his muscle mass.

Given these shortcomings, many experts in metabolism and obesity now favour the Body Roundness Index. Unlike the BMI, which focuses on height and weight, the BRI is concerned with waist size and abdominal fat—a more reliable indicator of long-term health and mortality risk.

Recent studies, including one published in JAMA Network Open, have shown that BRI is a strong predictor of mortality. Simply put: the rounder your midsection, the more health risks you face. Fat stored in the legs or buttocks does not carry the same risks as fat around the abdomen.

The Role of Context in Health Measures

No health test is perfect. Each is a single data point—not infallible, not absolute—and a “pass” doesn’t mean you’ve found the elixir of life. But each test contributes to a bigger picture. And knowledge is power—even literal power, in sport.

When touring with rugby teams, we measured both weight and fat index. Often, the fitter players became, the more their weight increased—especially the tight five, particularly among our Tongan players. Fat percentages dropped, replaced by heavier, stronger muscle, which was exactly what the fitness coach wanted.

As we pursued an aerobic game style to outpace the opposition, our fat percentage ideals were:

Forwards: 21–23%
Backs: 19–21%

For our purposes, 21% was considered optimal. Even a basic bathroom scale can be a useful tool—crude as it may seem—because it can be the first signal that change is needed: more physical output, less caloric input.

A (Possibly Uncomfortable) Truth:

Can an empty bowel improve performance on the field?

Yes, it can. Emptying the bowel may help both physically and mentally by reducing bloating, improving focus, and allowing for better oxygen use—ultimately delaying fatigue and enhancing endurance.

Why?

Improved mental clarity: Reduces discomfort, helping you focus.
Better oxygen utilisation: Removing waste can assist respiratory efficiency.
Reduced bloating: Less abdominal pressure means more comfort and movement.
Enhanced mood: Healthy bowel movements may increase serotonin, improving mental well-being.

Some studies have even found that defecation improved cognitive performance in athletes, with magnesium oxide (a stool softener) further enhancing mental clarity.

A Final Word

In my opinion, there’s a caveat: people can become overly stressed about not being able to "go" on demand. Let’s not lose sight of the mission—winning is more important than perfectly timed toileting. If concerned, consult your primary health provider.

And yes, some of what’s showing up on the scale may not be fat at all—it could just be faecal matter. Good toileting can shape your weight and silhouette more than you think.

But whether you’re looking at body type, BMI, or BRI, the key message remains:

The more you are a-round, the less you’ll be around.