Waking up with an upset stomach or diarrhea may indicate an underlying medical condition such as irritable bowel syndrome, according to Family Doctor.org. Gastritis, ulcers, gastroesophageal reflux disease or gall bladder disease also can cause indigestion and stomach problems in the morning.

Tiny amounts of blood in the stools occur in about 20 percent of marathon runners, according to "Marathon Medicine." This occult -- or hidden -- bleeding is only detectable by laboratory tests. Visible blood in the stools plus cramping are much less common.

If you experience a racing heart and dizziness within one to three hours after eating, you may have a condition called reactive hypoglycemia. Reactive hypoglycemia, also referred to as postprandial hypoglycemia, is characterized by a drop in blood sugar, usually below 70 mg/dL.

Fiber is a recommended part of a healthy diet. Getting the proper amount of fiber per day helps keep your digestion running smoothly and can help prevent constipation. If, however, you consume too much fiber in one sitting or add too much fiber to your diet too quickly, it can cause gas and cramping.

Some medical conditions prevent people from eating enough calories to meet daily-recommended requirements. Other medical conditions require a high number of daily calories that a patient is not able to obtain through oral intake.

Each year, up to one-fifth of people in the United States develop a viral infection called influenza, known more commonly as the flu, FluFacts.com reports.

Oatmeal is the proverbial poster child for a heart-healthy breakfast. It’s an excellent source of satiating complex carbohydrates and a top source of beta-glucan, a highly viscous soluble fiber that helps reduce high cholesterol levels.

The abdomen describes the region of the body that expands from the chest cavity to the pelvis. Because so many organs reside in the abdominal cavity, abdominal pain can occur due to many different conditions.

Acid reflux is known to most as a digestive disorder, with its main symptom being heartburn. But in its chronic form, known as gastroesophageal reflux disease (GERD), its effects can extend well beyond the digestive tract.

Acid reflux disease, also known as gastroesophageal reflux disease, or GERD, occurs when stomach acids leak back into the esophagus, causing irritation and inflammation of the esophageal lining. Protecting the esophagus from acidity allows the lining to heal.

Bloating is an uncomfortable feeling that occurs when gas builds up in the digestive tract. In addition to making your pants feel tighter, bloating can contribute to gas, an embarrassing problem that can lead to social anxiety.

The foods you eat can affect the way you feel, especially if you have a food sensitivity or celiac disease. According to the University of Maryland, up to one in 133 Americans have celiac disease.