Bloating, food sensitivities, stomach ache, constipation, diarrhea, etc. aside.
Skin irritation and acne: This can result from gut dysbiosis (an imbalance of bacteria) and leaky gut (or increased intestinal permeability) - which is where holes in the lining of the gut break or increase in size allowing bacterial endotoxin to seep through which causes an inflammatory response. (Source: 1, 2, 3)
Intense sugar cravings: The way I like to visualise this to keep it simple... bad bacteria feed on sugar, so when they "overthrow" your digestive system, they influence your hunger and cravings to support themselves. Which is crazy to think!
"Gut microbes may manipulate host eating behavior in ways that promote their fitness at the expense of host fitness." (Source)
Loss of hunger: Something I experienced (complete loss in my case), here's a full review on how the gut can affect your appetite and hunger.
Mental issues including anxiety, depression, fatigue, brain fog, and an inability to articulate yourself (like a disconnect in your brain, again, something I suffered from): We've discussed the gut-brain axis in the past, and here's a great medically reviewed summary of the link between the gut and fatigue.
Abdominal weight gain: This was a tough pill to swallow for me... gut issues can lead to you holding more visceral fat in your abdominal region. I clearly found my body to change in this way when I had IBS, and many clients of mine have shared this experience.
Thyroid issues: Gut dysbiosis (an imbalance of good and bad bacteria) can lower the levels of thyroid hormones T3 and T4, which can lead to what's called hypothyroidism (where your thyroid gland doesn't produce enough hormones). Symptoms include "tiredness, weight gain, dry skin, cold intolerance, constipation, muscle weakness, puffiness around the eyes, hoarse voice, and poor memory.". (Source)
Insomnia or poor sleep: Although research is yet to clearly define which came first, the poor sleep or the gut issues. (Source)
(Weak support) Eye floaters: The best way to describe eye floaters is type it into google images. These can be caused by a broad range of issues including inflammation. I myself suffered from eye floaters to the point that I couldn't see, which went away as I overcame IBS, and have shared this experience with others (of course, not scientific support).