5 common facts about medical science that are actually not true: The 3rd one might shock you

There are things in medical science that have been passed around so often that they’ve started sounding like absolute truths. These so-called “facts” are believed widely, seen in everyday advice, online health tips, and even casual conversations. But the reality is that not everything heard or read is accurate. Some of these ideas are either outdated or misunderstood.

Here are five commonly believed medical facts that are either half-truths or completely misunderstood. Each one carries a twist worth knowing and one in particular may catch most people off guard.

It’s okay to measure waist size around the belt line
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The given fact: Waist size can be measured around wherever the belt sits.
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The truth: For an accurate reading of abdominal fat, waist circumference should be measured at the level of the navel, not the belt line or hip.

The belt rests lower than the actual waist, especially in men, which underestimates the fat around internal organs (visceral fat). This type of fat is closely linked to heart disease, insulin resistance, and fatty liver disease.

Medical guidelines suggest ideal waist measurements should be under 37 inches for men and under 31.5 inches for women. Anything above that calls for attention, regardless of what the weighing scale says.

The given fact: Liver enzyme levels (like AST) are normal if they fall within the lab reference range.
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The truth: This is where things get tricky. Even within the lab-defined “normal” range, certain values can point toward early signs of health issues.
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For example, AST (aspartate aminotransferase) is a liver enzyme which is tested in liver function panels. Many labs consider up to 40 U/L as acceptable. But newer insights suggest aiming for less than 25 U/L for optimal liver health, especially to rule out fatty liver disease, which can go unnoticed for years.

So, a reading of 35 U/L might look “fine” on paper, but it could actually be a subtle warning sign. This gap in understanding has left many early cases of liver dysfunction undiagnosed.

The given fact: A normal BMI means a healthy body.
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The truth: BMI is not a reliable indicator of true health. It only calculates weight in relation to height and doesn't consider body fat percentage, muscle mass, or even fat distribution.
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For example, athletes with high muscle mass often fall into the “overweight” category based on BMI, despite being very fit. On the other hand, someone with a normal BMI could still have high visceral fat, which is dangerous. Medical science now understands that relying solely on BMI gives an incomplete and often misleading picture of health. It’s just one piece of the puzzle—certainly not the full story.

The given fact: Triglyceride levels under 200 mg/dL are fine.
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The truth: That bar is set too high. In reality, health experts now recommend fasting triglycerides to be below 150 mg/dL, and ideally closer to 100 mg/dL or lower.
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​Triglycerides are a type of fat found in the blood, and high levels are linked to heart disease, insulin resistance, and even pancreatic issues. They usually rise after meals, but fasting levels give a clearer picture of underlying metabolic health.

Maintaining a low-carb, balanced diet and increasing physical activity are practical ways to bring triglycerides into a healthier range. Overlooking this marker just because it’s “under 200” can be a missed opportunity for early prevention.

The given fact: Being slim automatically means being healthy.
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The truth: This is one of the biggest myths in everyday thinking. Many lean individuals may still have high levels of visceral fat, insulin resistance, or abnormal blood markers, a condition sometimes referred to as TOFI (Thin Outside, Fat Inside).

This makes it clear that metabolic health isn’t about dress size or body weight—it’s about what’s going on inside.