Your Gut Bacteria May Be Making You Fat—Even On a Healthy Diet.

A July 2025 study from researchers in Japan found that certain gut bacteria may block weight loss—even when you eat well. People who ate a healthy diet but failed to lose weight had higher levels of Collinsella, a microbe linked to obesity and fat storage.

The study followed 56 middle-aged participants on a calorie-controlled, vegetable-rich diet for 12 weeks. Most lost weight. But about 30% didn’t. Those “non-responders” had gut bacteria that resisted change and kept blood sugar and inflammation high—two major barriers to weight loss. The presence of Collinsella and low microbial diversity seemed to short-circuit the metabolic benefits of healthy eating.

If you’re struggling to lose weight despite eating clean, your gut might be the problem—not your willpower. Prioritize fermented foods, animal-based nutrients, and gut diversity to shift your internal ecosystem.