In fact, some people complain of increased heartburn on a high-protein diet, says Dr. Abdul Jabbar, a gastroenterologist and assistant professor at the University of Louisville in Kentucky. It may be the increased levels of fat, not protein, in these diets that cause heartburn symptoms. Fatty foods can trigger heartburn, possibly because fat slows down the digestive process, allowing food to remain in the stomach longer.

While you may not get heartburn from a high-protein diet, a more likely side effect is constipation. "In prehistoric times, we ate a very high residue [fiber] diet consisting of unrefined roots and vegetables, and berries ≈ foods that had a lot of residue," says Dr. Richard Weisiger, a gastroenterologist and professor of medicine at University of California at San Francisco. "It's been my experience that people on low-residue diets often get very constipated." Studies show that the less fiber you take in, the more likely you are to become constipated; aiming for a fiber intake of at least 25 grams a day and drinking plenty of fluid makes you less likely to suffer from this common condition.

The IBS/stress connection
About 30 million Americans suffer from symptoms of irritable bowel syndrome, which include abdominal bloating, constipation and/or diarrhea. However, the same diet that worsens IBS symptoms in one person may have no effect on another ≈ possibly because some people enjoy eating a high-protein diet. "The main trigger for most irritable bowel syndrome flare-ups is stress," says Weisiger. "Whether or not being on a diet is going to add to your stress depends a lot on how rigidly you stick to it and how stressful the diet is [for you.]"

Research does suggest that a high-fat diet can make IBS symptoms worse. "High-fat diets can make bloating worse because fat slows the intestinal transit time and interferes with the normal clearance mechanism where the bowel cleanses itself of gas," says Weisiger. "That allows more time for gas to accumulate, so in that sense a high-fat diet might be bad." However, he adds that consuming less food on a high-protein diet ≈ or any other plan ≈ can reduce bloating triggered by swallowed air while eating.

As with symptoms of GERD, people with IBS experience different results on high-protein, low-carbohydrate plans. "It's variable," says Jabbar. "Some people with IBS do get worse on high-protein diets compared to others, but there have been no randomized, controlled studies comparing patients with high-protein diets to patients on regular diets as to which ones will get more symptoms." Studies do show that diets high in fiber help ease IBS symptoms, so consuming adequate fiber is still important. Jabbar adds that people who suffer from Crohn's disease, a severe form of IBS, should consume plenty of protein as Crohn's can affect nutrient absorption, but that a high-protein/low-carb diet isn't necessary.

The bottom line
If you notice a change in your heartburn symptoms after switching to a high-protein diet, talk to your doctor. And if you have IBS, severe GERD symptoms, other digestive disorders or liver disease, talk to your doctor before embarking on a high-protein plan or making other significant dietary changes.

By Kelly James-Enger