Why Changing Your Diet Can Upset Your Stomach

For many people, a diet or healthy eating plan kicks off with a not-so-fun side of stomach pain and discomfort. Sometimes, a transition to more nutritious eating can give you an upset stomach — at least in the beginning. Here's why this happens and how to ease these side effects along the way.

​Read more:​ Keep Salad on the Menu, but Hold the Gas Pain

A less nutritious diet can increase your risk of dying from heart disease, stroke or type 2 diabetes, according to a March 2017 ​JAMA​ study — just to name a few reasons to eat healthier.

But when you first start improving your diet, you might endure an adjustment period of bloating, cramps and pain. "Some people experience an upset stomach when transitioning to a healthier diet because of the new foods they're introducing," says Rocio Salas-Whalen, MD, an endocrinologist with New York Endocrinology and a clinical instructor at NYU Langone Hospital.

"Many veggies and fruits are high in fiber, which can cause side effects like occasional bloating and gas, or frequent bowel movements," says Dr. Salas-Whalen, adding that certain fruits, cruciferous veggies (broccoli, for instance), and high-fiber foods like lentils and legumes can all lead to some discomfort. Despite the stomach discomfort, fruits, veggies and whole grains play an important role in keeping your blood sugar and cholesterol in check as part of a healthy diet, according to the Mayo Clinic.

If your diet involves reducing sugar, pay attention to how your body reacts to any artificial sweeteners you use in its place as they might be the culprit for discomfort, says Dr. Salas-Whalen. Also, be on the lookout for reactions to dairy, which can be potentially difficult to digest, even if you've enjoyed it with no trouble in the past.

Such an adverse dairy reaction can serve as a rude awakening if you're incorporating healthy snacks like yogurt or kefir into your diet. About 75 percent of the world's population eventually loses the ability to digest lactose, the main carbohydrate in milk, according to a 2013 review in the ​European Review for Medical and Pharmacological Sciences​.

Keep in mind that no matter the culprit, these unpleasant reactions are typical for many people. "This is normal, and symptoms typically improve in a few weeks while the body adapts to these new food categories," Dr. Salas-Whalen says. If your upset stomach continues for more than a few weeks, it's worth discussing with your doctor, as you might have a food intolerance or underlying health issue, she says.

For the sake of both your stomach and your diet goals, taking your food transition one step at a time and gradually shifting to healthier eating should ease the transition. Add higher-fiber foods to your diet slowly: Start with one extra serving daily for a week, then gauge how you feel before increasing from there, according to Harvard Health Publishing.

Moreover, "by introducing one type of food at a time, you can mitigate the uncomfortable symptoms while simultaneously making it easier to distinguish which foods are causing certain symptoms," Dr. Salas-Whalen says. "Keeping a food journal to track what food you're consuming each day can also help in this regard."

There's another perk to this slower approach: a hefty dose of mindfulness. Mindful eating may encourage you to have healthier habits, according to an October 2014 study in ​Personality and Individual Differences​. The authors report that being mindful of what you eat is associated with healthier choices, lower calorie intake and improved attitudes toward more nutritious foods. This awareness can potentially have many benefits to help you sustain a pattern of balanced eating.

Being mindful and taking it day by day can help you avoid the pain and pitfalls of an all-or-nothing approach to eating. "Making a gradual transition isn't as drastic as shifting from unhealthy to healthy eating in one day," Dr. Salas-Whalen says. "It enables you to pinpoint what foods your body reacts well to and sets you up for long-term success."

​Read more:​ 40 Foods High in Fiber for Good Gut Health