Peter Ballerstedt

High insulin can cause insulin resistance, and a healthy person can develop it in just a few days. Insulin resistance is usually described as the starting problem, with high insulin as the body's way of making up for it. That's partly true. When tissues respond poorly to insulin, the pancreas does release more to keep blood glucose in range. The relationship also runs the other way. When researchers gave healthy young people a steady infusion of insulin for about four days, raising it only to levels the body reaches in everyday life while keeping blood glucose normal, they became measurably insulin resistant. Their bodies cleared less glucose in response to insulin, mainly because less of it was stored as glycogen. Their pancreas also responded less to a rise in blood glucose afterward. A similar change showed up when insulin was raised a different way. When the researchers infused glucose for three days so the volunteers' own pancreas released more insulin, the amount of glucose their bodies stored in response to insulin also fell, even though their total glucose uptake didn't change. The researchers concluded that high insulin should be viewed as a cause of insulin resistance that keeps itself going, in addition to being a response to it. This matters because insulin often runs high for years before blood glucose looks abnormal. If high insulin makes cells less responsive, then a way of eating that keeps insulin elevated from morning to night keeps feeding the problem, even while glucose readings look fine. If someone is hoping to restore insulin sensitivity, it's clear that bringing insulin down deserves as much attention as bringing glucose down, and that starts with how much and how often a person eats foods that call for a lot of it.

It’s a reality of aging that we need more dietary protein to keep muscle mass. If you're over 65, the source of your protein may matter as much as the amount. Researchers gave older adults two meals with the same amount of protein and the same calories. One was built around beef, and the other was vegan. After the beef meal, muscle protein synthesis was about 47% higher. After the vegan meal, it barely moved from where it was before eating (PMID 37972895). As we age, muscle gets harder to build and easier to lose. We need to make high-quality animal protein the anchor of every meal.