What the scale can't see

No one is arguing that body fat is a good thing, but Pennington Biomedical researchers say what matters is where your body stores that fat. And yes, muscle mass is important, but it’s complicated.

Why it matters: The number on the scale tells you your weight, but it reveals little about your body's health—and that goes for the slim as much as the heavy.

Science stuff: Muscle is far from the whole health story. Where your body stores fat is an important chapter.z

• Pennington researchers found this after studying scan and health data from 59,269 UK Biobank participants for a paper in The Journal of Clinical Endocrinology & Metabolism.
• Higher total fat-free mass—a stand-in for muscle that also counts bone and organs—was linked to more cases of metabolic syndrome, a cluster of risk factors tied to heart disease and other chronic illness, and to elevated blood sugar.
• Fat-free mass as a share of body weight pointed the other way.
• The researchers stress that doesn’t make muscle harmful.

Plot twist: Fat packed around internal organs and tucked inside muscle tells the rest of the story.

• X-ray and MRI scans let researchers measure both, and they conclude the muscle-and-health link can’t be understood without accounting for fat distribution.
• Of the factors they tested, fat around the organs had the strongest influence on that link.
• Doctors diagnose metabolic syndrome when someone has three of five markers: a large waist, high triglycerides, low HDL cholesterol, high blood pressure or high blood sugar.

What she said: “Where fat is stored in the body matters,” Dr. Candida Rebello, who directs Pennington’s Nutrition and Chronic Disease Laboratory, said, pointing to fat around organs and inside muscle.

The big picture: Metabolic syndrome isn’t just an obesity problem.

• CDC survey data show more than 1 in 3 U.S. adults had it from 2007 to 2012—and even among adults who weren’t obese, about 1 in 6 did.
• The research came from Pennington’s Baton Rouge campus, in a state where adult obesity rates are higher than in most states.

The catch: The study shows links, not proof that one thing causes another, and its participants were British.

• Pennington says the findings could help guide future research on better ways to measure what’s going on inside the body.

The bottom line: When it comes to your health, fat is a lot like real estate—location, location, location.