Some foods and some diet plans are so obviously good for your body that no one questions their ability to keep you healthy or make you feel better when you’re ill. For example, if you’ve ever had abdominal surgery, you know all about liquid diets — the water-gelatin–clear broth regimen your doctor prescribed right after the operation to enable you to take some nourishment by mouth without upsetting your gut.

Or if you have type 1 diabetes (an inherited inability to produce the insulin needed to process carbohydrates), you know that your ability to balance the carbohydrates, fats, and proteins in your daily diet is important to stabilizing your illness. Other proven diet regimens include:

• The low-cholesterol, low-saturated-fat diet: The basic version, known as the Stage 1 Diet, is used as a first step in lowering a person’s cholesterol level. The diet limits cholesterol consumption to no more than 300 milligrams a day and total fat intake to no more than 30 percent of your total daily calories A nifty bonus to this diet is that it’s a relatively painless way of losing weight.

• The high-fiber diet: A high-fiber diet quickens the passage of food through the digestive tract. This diet is used to prevent constipation. If you have diverticula (outpouchings) in the wall of your colon, a highfiber diet may reduce the possibility of an infection. It can also alleviate the discomfort of irritable bowel syndrome (sometimes called a nervous stomach). Extra bonus: A diet high in soluble fiber also lowers cholesterol.

• The sodium-restricted diet: Sodium is hydrophilic (hydro = water; philic = loving). It increases the amount of water held in body tissues. A diet low in salt often lowers water retention, which can be useful in treating high blood pressure, congestive heart failure, and long-term liver disease. By the way, not all the sodium in your diet comes from table salt.

• The extra-potassium diet: People use this diet to counteract the loss of potassium caused by diuretics (drugs that make you urinate more frequently and more copiously, causing you to lose excess amounts of potassium in urine). Some evidence also suggests that the high-potassium diet may lower blood pressure a bit.

• The low-protein diet: This diet is prescribed for people with chronic liver or kidney disease or an inherited inability to metabolize amino acids, the building blocks of proteins. The low-protein regimen reduces the amount of protein waste products in body tissues, thus reducing the possibility of tissue damage.