Why Do I Have Gas When Losing Weight?

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Successful weight loss requires dietary changes, and often involves eating more fruits, vegetables and other high-fiber foods. A common side effect of this increased fiber intake is intestinal gas, also called flatulence -- which can lead to discomfort and embarrassment. The good news is this excess bloating and gas is usually temporary as the gut adjusts to more fiber. In some cases, though, food intolerance is the cause and avoidance of certain foods is necessary to prevent this gas.

Increased fiber can cause gas, which can lead to discomfort and embarrassment.
Image Credit: knape/iStock/GettyImages

The Fiber Factor

Foods rich in fiber are a dietary asset when trying to lose weight. Whole grains and legumes, such as dried beans, peas and lentils, are more filling compared to low-fiber bread, cereal or grains, helping to control appetite. Also, eating more fiber-filled whole fruits and vegetables can help replace or reduce portions of higher calorie, less nutritious foods. Because certain fibers move stool more quickly through the intestines, this nutrient also helps prevent constipation and confers other benefits to gut health. Specifically, the health-promoting bacteria that line the colon thrive when feasting on dietary fiber -- a process which produces intestinal gas. While any high-fiber foods can contribute to gas, more common offenders include dried beans and peas, cabbage, Brussels sprouts, broccoli, onions, bran, prunes, peaches, pears and apples.

The Smoothie Factor

If diet changes are significant, and fiber intake is much higher than usual, excess bloating, gas and even diarrhea may follow. While the fullness factor of many high-fiber foods tends to prevent overconsumption, it's easy to pack a lot of fruits and vegetables into smoothies -- a trendy addition to weight loss diets. And it's not uncommon for people to suffer gas and other gastrointestinal side effects after introducing smoothies into their daily diet. The body can adapt to an increased fiber intake over time, but it helps to increase fiber intake gradually, and to start with small amounts of smoothies, assessing tolerance before consuming more.

Food Intolerance

Adding different foods to a weight loss plan can cause gas buildup if food intolerance is present, due to the presence of poorly digested food components in the gut. For instance, if intestinal gas increases after consuming milk or yogurt, this may be related to an intolerance of lactose, a carbohydrate found in milk. Certain carbohydrates in dried beans and peas, some grains and foods high in fructose, a sugar naturally found in fruits and vegetables, can be poorly digested in some people and lead to abnormal gas production. Gas can also be a symptom of celiac disease or gluten intolerance, caused by eating wheat, barley, rye or other gluten-containing foods. If flatulence is caused by food intolerance, the best prevention strategy is to avoid the offending foods.

Sugar Substitutes

If no-sugar-added or sugar-free foods are included in a weight-loss food plan, intolerance of sugar alcohols, a commonly used sweetener, could be the cause. Sugar alcohols, also called polyols, are popular because they do not promote tooth decay, and because their incomplete digestion in the gut means foods sweetened with polyols affect blood sugar less compared to other natural sweeteners. However, this incomplete digestion leads to a laxative-like effect in the gut, and can cause gas, bloating and diarrhea. Most sugar alcohols are synthetically made, and when used as a sweetener, can be identified because their inclusion on the nutrition facts panel of the food label is required. But certain fruits and vegetables -- such as plums, pears, apples, sweet potatoes and mushrooms -- can contain large enough amounts of sugar alcohols to cause gas in sensitive individuals, so in some people, restriction of foods high in polyols is important.


Intestinal gas can be related to increased fiber intake, which can be countered by gradual diet changes, or intolerance of certain foods. Swallowed air, from carbonated beverages, chewing gum or eating too quickly can also lead to gas. But sometimes persistent gas, bloating, diarrhea or unintentional weight loss can be a sign of something more serious, so it's important to have a doctor evaluate this symptom if simple diet changes don't help. In addition, gas caused by food intolerance may take more investigation and diet education to prevent ongoing symptoms, so team up with a doctor and dietitian to learn more about this intolerance and how to manage related gastrointestinal symptoms.

Reviewed by Kay Peck, MPH RD

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