Lactose Intolerance and Weight Gain: Are They Linked?

If you are lactose intolerant, you likely avoid lactose-containing foods. But if you've gained weight since making those adjustments, you might wonder if those extra pounds are due to your diet modifications.

Lactose is a naturally occurring sugar in milk. According to the Mayo Clinic, for those who are lactose intolerant, symptoms when lactose is consumed can include bloating, diarrhea and gas. But can it affect the number on the scale?

According to Matthew Ciorba, MD, a gastroenterologist and professor at Washington University School of Medicine in St. Louis, there's no direct cause-and-effect relationship between having a sensitivity to lactose and weight. "Lactose intolerance itself is not a cause of weight gain," says Dr. Ciorba.

That said, the doctor does acknowledge how a person's reaction to their food sensitivities can indirectly affect their weight. "It is possible that individuals may substitute healthy milk- or lactose-containing foods for unhealthy foods and then could gain weight," he says. "But the medical state of lactose intolerance itself should not cause weight gain."

Ojai, California-based dietitian Sharon Palmer, RDN, agrees. "There is a myth that food allergies or intolerances may lead to weight gain," she says. "I don't believe there is enough evidence on this concept, which runs along the idea that food sensitivities lead to insulin resistance, which leads to weight gain. There is not enough understanding to directly link all of those things together at this time."

"We do know that if you have a food sensitivity and you eat that food, it raises inflammation levels, and that inflammation is also present in obesity," says Palmer. "But that doesn't mean that we have an understanding of a direct link that inflammation causes obesity."

People with lactose intolerance may be avoiding milk, but they still need to pay attention to their diet in order to prevent weight gain. A March 2017 study in ​Cancer Causes & Control​ reiterates that taking in more calories than you burn off "is the main driver of weight gain."

Moreover, a diet high in ultra-processed foods makes you more likely to cause obesity, according to a February 2019 study in the ​Canadian Journal of Public Health​, as does a diet high in sugar, per a February 2018 study in ​Obesity Facts​.

​Read more:​ How to Avoid Dairy in Your Diet and What to Eat Instead

According to a 2018 report by the National Institute of Diabetes and Digestive and Kidney Diseases, not everyone who is lactose intolerant has to practice utter lactose avoidance. It noted that "people with lactose intolerance can handle different amounts of lactose" and that milk products could potentially be tolerated in small doses, or when consumed with meals or with the aid of products designed to help digest lactose.

Such lactase supplements can make it possible to digest dairy and lactose-containing foods with less severe symptoms, if any. The diet's affect on symptom reduction, in fact, is one of the main considerations when developing a diet or eating plan if you're lactose intolerant.

Another key consideration is to ensure that you'll receive adequate nutrition, especially nutrients such as calcium and vitamin D, which are abundant in dairy products. An April 2017 study in the ​Journal of Nutrition​ found that people with lactose intolerance have lower blood levels of vitamin D than the general population.

Several studies have linked adequate levels of vitamin D with healthy weight, including a May 2014 study in the ​American Journal of Clinical Nutrition​ that acknowledges the association between vitamin D deficiency and obesity.

Also needing consideration, of course, is your diet's affect on your weight. Because it's not the state of being lactose intolerant as much as your food selections that can produce weight gain, making healthy choices takes center stage.

If you have lactose intolerance and are putting on pounds, consider working with a nutritionist on developing an individualized eating plan for proper weight management.

​Read more:​ Do 'Lactose-Free' and 'Dairy-Free' Mean the Same Thing?