In male C57BL/6 mice (n=8/group) fed a high-fat diet (HFD) for 12 weeks, limiting intake to match low-fat-fed animals erased the weight difference (0.1 g vs low-fat controls) and lowered glucose and cholesterol versus ad libitum HFD. Yet visceral fat as a share of body weight stayed 1.5 to 1.8 percentage points higher, adipose Tnf expression remained elevated in the switch group, and fecal phylogenetic diversity stayed lower (Faith's PD -3.1) in 4 mice per group. The evidence here comes from mice, not humans.
The finding fits a growing view that body weight is a blunt readout of metabolic health. Humans with normal BMI can carry excess visceral fat and its inflammatory signature, the so-called thin-outside-fat-inside phenotype, and this mouse work hints that diet quality may matter beyond calories. Caution is warranted: the microbiome analysis used just four animals per group, many comparisons produced borderline p-values (0.024 to 0.042) with wide confidence intervals, only males were studied, and 12 weeks cannot show long-term consequences. Mouse HFDs are also far more extreme than typical human diets, and the study cannot say whether fat composition, fat source or something else drives the residual effects. This is a preprint that has not been peer reviewed, so results may shift. Treat it as a modest, hypothesis-generating addition: it supports looking past the scale toward waist measurements and food quality, but it offers no direct guidance for people.