Intermuscular fat is emerging as a new red flag in the debate over ultraprocessed foods. Instead of just padding the waistline, diets dominated by packaged snacks, ready meals and sugary drinks appear to thread fat between muscle fibers themselves.

Researchers using imaging techniques report that people who eat the highest share of ultraprocessed foods show greater intermuscular adipose tissue, even when overall body weight looks similar. This fat infiltrates skeletal muscle, where it can disrupt glucose uptake, promote insulin resistance and lower basal metabolic rate. Unlike subcutaneous fat under the skin, intermuscular fat is closely tied to reduced strength, slower gait and higher cardiometabolic risk.

The mechanism is still being mapped, but scientists point to a mix of excess refined carbohydrates, emulsifiers and low dietary fiber as drivers of chronic low‑grade inflammation and altered mitochondrial function in muscle cells. That biochemical stress seems to encourage lipid storage inside and around muscle fibers, gradually converting active tissue into a less efficient engine. For public health, the finding reframes ultraprocessed foods not only as a weight issue but as a direct threat to the quality and performance of muscle across adult life.