While not a common side effect, it is possible for patients to become Lactose Intolerant (LI) after bariatric surgery. Lactose intolerance is a digestive problem caused by the body’s inability to digest the lactose (sugar) found in milk fully.

If you were not lactose intolerant before bariatric surgery, you might be wondering if it can occur after. In short, yes.

Eating or drinking lactose-rich dairy products can trigger uncomfortable side effects like bloating, stomach pain, diarrhea, gas, and loose stools. That is why nutrition management, such as removing or limiting milk and other dairy products from your diet, may be necessary.

Milk and Lactose Intolerance

Reintroduction Lactose after Bariatric SurgeryMilk contains 13 essential nutrients, such as high-quality protein, calcium, and vitamin D. Some health benefits can come from drinking milk, like better bone health, lowered blood pressure, lowered risk of heart disease, and prevention of diabetes. However, it is not recommended for everyone. A dairy allergy, like any food allergy, can induce inflammatory reactions in the body. Milk contains a naturally present sugar called lactose, which some may be intolerant to.

Lactose malaborsption occurs when the body does not have enough lactase enzyme to break down lactose suagr found in dairy products in the gastrointestinal tract and small intestine.

How much lactose is in one 8-ounce glass of milk?

  • Non-fat milk = 12 grams of lactose
  • 1% milk = 13 grams of lactose
  • 2% milk = 12 grams of lactose
  • Whole milk = 12 grams of lactose

WLS-Induced Lactose Intolerance

In some cases, bariatric procedures such as gastric sleeve and gastric bypass can cause LI in patients due to the changes in how the lactose is passed through the digestive system.

You can introduce milk in small increments at about phase 3 of the post-op diet to see whether or not you have developed an intolerance.

For those who do not have an intolerance to lactose before surgery, we may recommend removing milk and other dairy products from your diet. You may also consider taking an enzyme alternative called Lactaid.

What Causes Lactose Intolerance after Bariatric Surgery?

Weight loss patients often experience something called secondary lactose intolerance. That is mostly due to the body adjusting and relearning how to digest foods. This condition could be temporary as the body is healing and inflammation clears.

Secondary lactose intolerance means that it happened because of something else, namely bariatric surgery.

In the case of RNY gastric bypass, dairy passes directly through the gastric pouch into the small bowel at much higher rates. Milk can overpower the available enzyme (lactase), and the body cannot digest the lactose, causing lactose intolerance symptoms.

Recommended Milk Substitutes

Recommended Milk Substitutes-Can Lactose Intolerance Occur After Bariatric Surgery-Mexico Bariatric CenterWhen reintroducing foods and drinks back into your diet after bariatric surgery, it is helpful to recognize the benefits of each meal and drink. Below are some alternatives to milk that patients can include in their diet:


A great milk product we recommend is Fairlife® because it is lactose-free and has a higher protein level. This is a real milk product, but it has been ultrafiltered to provide 50% more protein, 30% more calcium, and half the sugars of regular milk. One 8-ounce glass of 2% Fairlife® milk contains only 6 grams of sugar and 13 grams of protein as opposed to the 12g of sugar and 8 grams of protein found in regular 2% milk.

Other Milk Substitutes

  • Almond Milk (Unsweetened)
  • Coconut Milk
  • Cashew Milk

These 3 milk substitutes are great lactose-free dairy products that patients with lactose intolerance can have. These products are very high in protein but are lactose-free and low in carbs and sugar.  They are great for mixing in your protein shakes in place of water.

lactose intolerance, milk substitutes to avoid.Milk Substitutes to AVOID!

Avoid soymilk or any sweetened flavored milk or milk substitute. These products may be lactose-free but are generally high in added sugar, which is not conducive to a pre-op or post-op diet.

Consult Your Nutritionist and Get Regular Checkups

At Mexico Bariatric Center®, we like to share this information to spread the knowledge further to serve our former and future patients best. We recommend that anyone planning to or has undergone bariatric surgery consult a nutritionist and get regular checkups to help better ensure a healthy recovery.

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