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Brain scan looked like early Alzheimer's
The Patient
She had done what everyone told her to do: eat less, exercise more, do cardio, follow the food guide pyramid, and put herself last. She was one of the patients in a study of body composition and brain function at Washington University in St. Louis, where Gabrielle Lyon was a research fellow in geriatrics and nutritional sciences. Lyon's mornings started at 4:00 AM with muscle biopsies, fat biopsies, and brain imaging.
The Insight
The accepted view held that diabetes, Alzheimer's, and cardiovascular disease ride alongside obesity, with body fat as the problem. Looking at the images of this woman's brain and body, Lyon had a flash of insight: the problem was her muscle mass.
The Wider Data
The rest of the data pointed the same direction. Regardless of how much fat someone carried, the more healthy muscle mass they had, the better their survivability, blood markers, glucose regulation, insulin, and fatty acid profiles. Healthy muscle looked like the organ of longevity, and it was the organ system nobody was talking about.
Why does muscle matter so much for blood sugar?
Skeletal muscle is the largest site of insulin-stimulated glucose uptake in the body. In clamp studies led by Ralph DeFronzo in the 1980s, muscle took up roughly 80 percent of the glucose that insulin moved out of the blood. Insulin does this by sending GLUT4 transporters to the surface of muscle cells, where they pull glucose in.
How is Alzheimer's linked to insulin?
In 2005, Suzanne de la Monte and colleagues at Brown University proposed the name type 3 diabetes for Alzheimer's after finding impaired insulin signaling in patients' brains. Insulin receptors are abundant in memory regions such as the hippocampus. Large cohort studies have also found that people with type 2 diabetes develop dementia at higher rates than people without it.
Why did medicine focus on body fat?
Body mass index comes from Adolphe Quetelet, a Belgian statistician who built it in the 1830s to describe populations, not to diagnose individuals. Physiologist Ancel Keys popularized the formula in a 1972 paper, and it spread because it needs only a scale and a tape measure. Neither number can tell fat from muscle, or say where either one sits.
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