Based on the search results, "lean gut" can refer to different things:

1. Inflated liver due to drinking lean: According to Urban Dictionary, "lean gut" is a term used to describe the condition where someone drinks so much "lean" (a mixture of cough syrup, soda, and candy) that their liver inflates due to the amount of toxin in the drink.

2. Muscular stomach area: On HiNative, "lean gut" is defined as a muscular stomach area with no fat.

3. Bloating due to constipation: A Reddit post suggests that "lean bellies" are not fat but bloated due to constipation.

4. A research topic: A Science article discusses how the broad-nosed caiman, a Brazilian crocodile, adapts to lean times by developing a lean gut.

5. A coaching program: The Lean Gut Mind Method is a 90-day coaching program that aims to help people achieve their health goals, including reducing body fat, managing gut health and hormones, and reducing sugar cravings and emotional eating.

6. A physiological state: A study found that a lean gut environment can protect against severe atopic dermatitis in high-fat diet-fed mice.

In summary, "lean gut" can refer to different things depending on the context. It can mean a muscular stomach area, bloating due to constipation, a research topic, a coaching program, or a physiological state.