Food can work either to treat a disease or feed one. The simple idea that food could be used as preventive medication is an antiquated yet underrated one. In 431 BC, Hippocrates, known as the founder of medicine, is recorded as having said: “Let food be thy medicine and medicine be thy food.”

Hippocrates was conceptually ahead of his time in believing illness to have a physical and rational explanation, stemming from functional foods. These types of foods, particularly fruits, herbs, and spices, exert positive health effects beyond the body’s basic dietary needs. They fight off a myriad of physiological problems, including infection, alleviate pain, boost the immune system, lower stress levels, and diminish digestive problems.

Over the centuries, diets have been designed, altered, and adjusted as the medical field has come to more intimately understand the human body’s relationship with food. In many cases, doctors discover a diet plan to treat and alleviate symptoms of a disease or condition when they fail to uncover a curative approach.

Here are 5 Diets Prescribed For Diseases:

1. Mediterranean Diet: Heart Disease

Heart disease is the number one cause of death among both men and women, killing nearly 800,000 people every year. The heart is the engine of the body, which requires clean fuel in order to run properly. According to the American Heart Association (AHA), a healthy diet and lifestyle are the best weapons against heart disease risk.

In 2015, a group of cardiologists from the Cleveland Clinic created a wellness plan designed to address the pitfalls in America’s diet. Central to their recommendations were wholesome foods that most closely align with the Mediterranean diet, including olive oil, fatty fish high in omega fatty acids, and cultured yogurt. The AHA’s current recommendations also follow the basis for the Mediterranean diet, which is the elimination or minimization of processed foods, sugars, salts, and an emphasis on healthy, whole foods.

The Mediterranean diet is based on the typical meal found on Crete, one of the small Greek islands in the Mediterranean Sea. Its people have the lowest death rate from diseases ranging from heart disease to cancer. They eat off the land, which provides them plenty of fruits, vegetables, unrefined whole grains, nuts, and legumes. The small portion of protein they consume is typically fish or lamb cooked in olive oil and served with greens and fibrous whole grains.

2. DASH Diet: High Blood Pressure

According to the Mayo Clinic, high blood pressure can quietly cause damage to your body for years before symptoms present themselves. Your heart pumps blood throughout your entire body by means of arteries and veins. Healthy arteries are flexible, strong, and elastic in order to efficiently pump blood to the necessary organs, and to your brain and extremities. High blood pressure increases the pressure of blood flowing through the arteries, which can damage the inner lining or cause a bulge (aneurysm), which can ultimately lead to heart attack, heart failure, kidney failure, stroke, arterial disease, eye damage, and life-threatening internal bleeding.

Turning to the DASH (Dietary Approach to Stop Hypertension) diet can help prevent damage before it occurs or stop it from worsening. The 2,000-calorie diet plan includes daily 7 to 8 servings of whole grains and unrefined breads, 4 to 5 servings of vegetables, 4 to 5 servings of fruits, 2 to 3 servings of low-fat or nonfat dairy, 6-ounces or less of meat, poultry or fish, and 4 to 5 servings of nuts, seeds, and dry beans a week. According to the National Heart, Lung, and Blood Institute, when participants with high blood pressure followed the Dash diet it led to a reduction in blood pressure regardless of age, gender, or race.

3. Ketogenic Diet: Epilepsy

In the 1920s, a team of researchers from Johns Hopkins Medicine recruited hundreds of children to undergo a radical diet overhaul called the ketogenic diet. The diet, which is very high in fat and low in carbohydrates, was designed to treat childhood epilepsy. When the body is in a fasting state, the brain triggers the body to convert sugar into fat by-products called ketones. According to the Harvard Gazette, the ketones activate a potassium channel in the brain cells that provide enough activity to maintain normal function in the brain.

Epilepsy causes seizures, which are essentially an electrical misfiring of the brain. When the brain is on the cusp of triggering a seizure, the potassium shuts the malfunction down and acts as a neurological surge protector. Researchers found 50 percent of patients stopped seizing permanently after 2 years on the dietary treatment.

4. Gluten-Free Diet: Autoimmune Diseases

Autoimmune diseases affect up to 50 million Americans and have as many as 80 different types of autoimmune diseases with similar symptoms that are often difficult to diagnose. It occurs when your immune system incorrectly defends the body against healthy cells, and as a result causes damage or abnormal tissue growth. Currently, there are no cure-all treatments for autoimmune disease, however there are treatments that focus on relieving symptoms and staving off their adverse and often painful effects.

One of the most well-known autoimmune diseases has been spotlighted recently because of the gluten-free fad. Celiac disease is an immune disorder in which people cannot tolerate gluten because it damages the inner lining of their small intestine and prevents their body from absorbing nutrients. Gluten, which is a protein found in many breads and other grain-based products, is often avoided by those who suffer from Celiac disease in order for them to maintain a healthy inner lining and avoid malnourishment.

Gluten is also a major trigger for Hashimoto’s hypothyroidism because the thyroid hormone receptors are nearly identical to gluten. When the body recognizes gluten as an allergy, the thyroid becomes confused and produces antibodies to attack. Roughly 30 percent of those with Celiac disease also have this autoimmune condition named after the Japanese specialist Hakaru Hashimoto who first wrote about it.

Sales of gluten-free products are projected to grow nearly 20 percent through 2019 and reach billions, reflecting the growing demand. Celiac disease varies in severity, so while some sufferers cannot stomach any gluten without experiencing damage, others can do so in moderation. Although avoiding gluten isn’t a cure to the Celiac disease, doctors increasingly recommend cutting gluten out to prevent flare-ups, which makes the disease easier and nearly symptom-free to live with.

5. High-Fiber Diet: Diverticulitis

The condition of diverticulitis is a painful inflammatory reaction that occurs in the colon or large intestine. Small pouches bulge outward along the line of the digestive tract to cause cramps, bloating, and constipation, and in serious cases, bleeding, tears, and blockages. Doctors aren’t sure what causes diverticulitis, however bacteria is found to grow inside the pouches, which accounts for the tears and infection within the intestinal walls. Treatment may include antibiotics and pain relievers; however doctors recommend a high-fiber diet to prevent reoccurrence.

Fiber is found in plant material, which helps the stool move smoothly through the colon. A lack of fiber can cause constipation, which makes stools harder and more difficult to pass, ultimately putting stress on the muscles of the colon. The domino effect increases the risk of diverticulitis, and can wind up sending the person into surgery.

Experts recommend including 20 to 35 grams of fiber a day into their diet to keep things moving nicely. Foods include cereals like shredded wheat, grains like whole wheat pasta, oatmeal, brown rice, black beans, lentils, broccoli, Brussel sprouts, carrots, raspberries, blackberries, avocados, prunes, and raisins.