F or millions of Americans, troubling digestive symptoms are a part of daily life.

Yet for most digestive ills, relief is simply a matter of adhering to a few basic eating principles.

The same high-fiber, low-fat diet that protects you against heart disease and cancer 20 years down the road will also relieve heartburn, constipation, etc. -- within 24 hours. Here are the basics...

EAT MORE FIBER

Dietary fiber is the indigestible part of grains, fruits and vegetables. Fiber...

... reduces risk of cancer by pushing food through the gastrointestinal tract quickly, limiting the body’s exposure to carcinogens.

... relieves constipation by adding bulk to the stool.

... prevents diarrhea by absorbing water from the stool.

... prevents stomach ulcers by speeding excretion of bile acids (secreted by the gallbladder).

The average American eats 10 g of fiber a day. That’s only one-third of what you need for optimum health.

To boost fiber intake: Eat bran cereal and whole-grain bread... have five servings of fruits and vegetables each day.

If you do not eat enough fruits and vegetables, ask your doctor about taking Metamucil, Citrucel or another fiber supplement.

Important: Make these dietary changes gradually. Too much extra fiber too soon can cause gas and cramps.

EAT LESS FAT

The average American gets a whopping 35% of his/her calories in the form of fat -- even though nutritionists have been clamoring for years that we should limit fat consumption to no more than 25%.

Besides promoting cancer and heart disease, too much dietary fat exacerbates pancreatitis, an inflammation of the pancreas marked by pain in the upper abdomen.

Fat also aggravates gallstones... and promotes heartburn by loosening the muscular valve between the esophagus and stomach, allowing stomach acid to splash back into the throat.

To cut fat consumption: Substitute skim milk and fat-free yogurt for whole-milk products... build your meals around vegetables... and avoid red meat.

If you insist on eating red meat, take smaller portions and trim away all visible fat.

Better: Substitute fish and skinless chicken.

WATCH OUT FOR LACTOSE

If you have gas, cramps or diarrhea, you may be suffering from lactose intolerance. This hereditary condition is caused by a lack of lactase, the enzyme needed to digest lactose (milk sugar).

Self-test: Avoid milk products for three days. See if your symptoms dissipate.

If you are lactose-intolerant, avoid all dairy products... or take a lactase tablet each time you have dairy. Lactase tablets (Lactaid) are available at drugstores and health-food stores.

CUT DOWN ON SPICES

Spicy foods don’t cause ulcers, heartburn or diarrhea. But if your digestive tract is inflamed, spices can make matters worse.

Usual culprits: Pepper, garlic, chili, mustard seed, cloves, nutmeg and curry.

AVOID GAS

Beans are rich in fiber, protein, vitamins and minerals. But if they cause discomfort (physical or social), avoid them.

Helpful: Beano. This nonprescription remedy contains an enzyme that digests the carbohydrates beans contain.

AVOID OVEREATING

Overeating promotes gallstone formation, exacerbates heartburn and causes gas, cramps, nausea and diarrhea.

QUICK-FIX TIPS

When diet alone fails to relieve gastrointestinal complaints, over-the-counter (OTC) drugs -- along with simple lifestyle changes -- usually do the trick.

Heartburn. Antacids such as Tums or Maalox provide quick relief. H2 blockers (Zantac, Pepcid and Tagamet) take a little longer to kick in -- but keep working for hours.

Additional help: Elevate the head of your bed on six-inch blocks. Avoid eating just before bedtime.

Constipation. Fiber supplements like Metamucil promote normal bowel movement by adding bulk. Stool softeners like Colace allow stool to pass more easily.

The colon naturally starts contracting for a bowel movement 20 to 30 minutes after breakfast. If you fail to heed this urge to defecate, the urge will pass. This leads to constipation.

Solution: Get up earlier -- to give yourself time to defecate.

Intestinal gas. To avoid gas, eat slowly and chew your food thoroughly... avoid eating when tense or upset... eat small meals... avoid carbonated beverages... and get plenty of exercise.

If gas persists, try Mylanta Gas Relief or another remedy containing simethicone. For gas accompanied by heartburn, take Extra Strength Maalox Antacid/Anti-Gas or another remedy containing simethicone and an antacid.

Flatulence. Try activated charcoal tablets. Don’t take other drugs within one hour.

Diarrhea. Imodium A-D is best for quick relief. But don’t use any diarrhea remedy for more than two days without consulting your doctor.

WHEN TO SEE A DOCTOR

If gastrointestinal symptoms persist for five days despite your self-help efforts, see a doctor. See a doctor immediately if you experience “alarm” symptoms.

Examples: Trouble swallowing... bloody stool... sudden weight loss... change in bowel habits... feeling full right after you start eating... severe abdominal pain.