I’ve noticed that anytime I fast and on a ketogenic diet, a hard stool accompanied with blood comes out with lesser bowel movements. When I went back to an unhealthy diet (sugar and high carbs), I had more frequent bowel movements and no blood with stool. Initially, I thought it’s when I immediately ate a heavy meal after a prolonged fast. Now, I haven’t done a 48-hour prolonged fast in the last 2 weeks, so I don’t know what is causing this stool with blood when I’m on a fast and ketogenic diet.
As others have said you should see a doctor. Now Having said that. High fat diets can cause constipation and that causes you to strain while you’re trying to poop. This increases the pressure in the blood vessels in your anus and they can rupture. Additionally not drinking enough water will cause this too. Your body keeps poop in your intestines quit wet to lubricate it. If you’re not hydrated enough Your body can pull water from your poop. Your poop will become dry and hard. You can develop hemorrhoids or anal fissures from this. This would cause bright red blood to be in the poop. Bright red blood generally, (but not all of the time) means it’s from lower in the digestive tract and hasn’t been digested which could indicate hemorrhoids or a fissure. If you ever have dark blood, blood that looks like coffee grounds or a large amount of bright red blood that smells “weird” like iron in the air you need to call for medical aid right away. Depending on your risk factors blood can also be an early signs of colon cancer. Chances are it’s from constipation and staining. If you can afford it/ have the time it’s always best to see a doctor.
If your doctor indicates the blood is not an indication of a larger problem you might consider including magnesium glycinate pills to keep thing moving in a more gentle fashion. Best of luck clearing this up!