Lactose Intolerance

Lactose Intolerance After Bariatric Surgery

June 16, 2021

You have had bariatric surgery and are now rediscovering how and what to eat. After surgery, as you introduce food back in your eating plan or have had surgery years ago, you might notice your body may react differently to foods it had no issue with before surgery. Even if we follow our diet progression and recommendations exactly as written, our body’s anatomy has changed and will now process foods differently. Patients commonly report issues of lactose intolerance after bariatric surgery.

What Causes Lactose Intolerance?

Dairy can be a big part of your diet after surgery because it is an easy way to get in quality protein and nutrition. Cottage cheese, yogurt, and milk can be staples in the liquid and soft diet stages because of their nutrition, soft texture, and availability.

However, to some, the lactose in these products can be irritating to the gut. Lactose is the sugar in dairy products such as milk, cheese, sour cream, ice cream, and yogurt. Your body produces lactase which is the enzyme that breaks down this sugar.

Symptoms Of Lactose Intolerance

The most common symptoms patients experience are belly cramps, pain, nausea, bloating, gas, belching, and diarrhea. These symptoms typically occur within 30 minutes to 2 hours after consumption of dairy products. These symptoms can vary in severity and will last until the lactose passes through the body, which may be up to 48 hours.

Why does this happen after bariatric surgery? As it seems to be more common in the roux en y gastric bypass or modified duodenal switch patients, it can also occur in gastric sleeve patients. It occurs because the dairy product passes through the newly created smaller pouch and into the small intestines at a much higher rate. At this increased rate, lactase is overwhelmed and cannot keep up with the rate of ingestion; therefore, symptoms occur.

Diagnosis Of Lactose Intolerance

It may be challenging to diagnose lactose intolerance after surgery because patients experience various gastrointestinal changes as their body heals from surgery. If you suspect you are lactose intolerant or are experiencing symptoms, the first thing to do is to eliminate dairy products and see how your body responds.

After you have eliminated dairy, you may try to reintroduce it in small amounts and see if your body can process it better. I highly recommend keeping a food journal during this time to keep track of what foods are tolerated and in what amounts.

Some patients have better luck with processed or fermented dairy such as yogurts, low-fat cheese sticks, and kefir. Protein shakes, a staple in post-op diets, contain whey, but the lactose is usually removed as part of the manufacturing process.

There are other tests your physician can perform to diagnose lactose intolerance:

  • Hydrogen breath test: your doctor has you drink a liquid that contains high amounts of lactose and measures the amount of hydrogen in your breath. High amounts of hydrogen show you are not fully digesting lactose.
  • Blood test: two hours after drinking a liquid that contains high amounts of lactose, your doctor will conduct a blood test to measure the glucose in your blood. If your blood glucose level does not rise, it means your body is not digesting or absorbing the lactose properly.

If even small amounts of dairy cause a reaction on their own there are a few things you can do:

  • Pair a small serving of dairy at meals with other foods to slow digestion.
  • Consume lactose-free dairy products such as Fairlife, Lactaid, A2 milk, or others that have had the lactose removed.
  • Use dairy alternative yogurts and kinds of milk from cashew, oat, hemp, soy, coconut, almond, or other sources. Be sure to look at the nutrition facts panel for sugar content and choose unsweetened versions. These dairy alternatives also do not typically have much protein content per serving.
  • Add a lactase enzyme in liquid, powder, or pill form to help process dairy products


If you turn out to be lactose intolerant after bariatric surgery, it would be important to include other calcium-rich foods in your diet, including green leafy vegetables, sardines or anchovies, fortified soy products, broccoli, edamame, acorn squash, and papaya. Supplements may also be beneficial and available from many bariatric vitamin manufacturers.

If you do decide to take a calcium supplement, make sure to take it separately from any iron-containing vitamins or supplements as they compete for absorption.

As always, if you are having issues tolerating foods, such as lactose intolerance, consult with your Registered Dietitian and care team.

Lactose Intolerance
Carla Schuit


Carla Schuit is a Registered Dietitian specializing in adult weight management and performance nutrition at Northwestern Medicine. She holds Level 2 Adult Weight Management certificate as well as a certificate in Food Law. Carla attained her BS in Dietetics from Michigan State University, completed her internship in Dietetics at the State University of New York at Buffalo and received her Master’s in Public Health from Benedictine University.