Lactose intolerance – the NET Effect

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 When I cast my mind back to my very first surgery, I remember asking my Oncologist what I could do to put on weight.  He said to drink full-fat milk.  I was compliant in those days without reverting to Dr Google.   Anyway, I did put on weight but perhaps the milk played a small part in that, and I eventually returned to semi-skimmed which I continue to use today (12 years on).   

My breakfast regime in the last 12 years since that surgery contains regular semi-skimmed milk and my many cups of tea have the same milk added.  I guess there is milk in many other things such as dairy products which I happily consume.  I don’t believe I have any lactose intolerance to worry about.  Given the facts above, I think I would know about it.

A lot of people mention milk and try to avoid regular milk due to lactose intolerance and I set about researching to be able to document it in this blog.  I found some linkages to NET treatment. 

What is Lactose Intolerance and what causes it?

People with lactose intolerance are unable to fully digest the sugar (lactose) in milk. The condition, which is also called lactose malabsorption, is usually harmless, but its symptoms can be uncomfortable. 


Normally, lactase turns milk sugar into two simple sugars — glucose and galactose — which are absorbed into the bloodstream through the intestinal lining.  If you’re lactase deficient, lactose in your food moves into the colon instead of being processed and absorbed. In the colon, normal bacteria interact with undigested lactose, causing the signs and symptoms of lactose intolerance.  Symptoms usually begin from 30 minutes to two hours after eating or drinking foods that contain lactose.

Common signs and symptoms include:

  • Diarrhea
  • Nausea, and sometimes, vomiting
  • Stomach cramps
  • Bloating
  • Gas (wind)

Now, those symptoms look like something we see attached to many ailments and alleged drug side effects we see daily in NET patient groups. I’m not suggesting lactose intolerance is the cause, I’m suggesting it’s one of several potential differentials. 

Types of Lactose Intolerance

Primary lactose intolerance.  In primary lactose intolerance, lactase production falls off sharply by adulthood, making milk products difficult to digest.

Secondary lactose intolerance

This form of lactose intolerance occurs when your small intestine decreases lactase production after an illness, injury or surgery involving your small intestine. Diseases associated with secondary lactose intolerance include intestinal infection (including small intestine bacterial overgrowth (SIBO), celiac disease, bacterial overgrowth and Crohn’s disease.  Treatment of the underlying disorder might restore lactase levels and improve signs and symptoms, though it can take time. 

Congenital.  It’s possible, but rare, for babies to be born with lactose intolerance caused by a lack of lactase. This disorder is passed from generation to generation in a pattern of inheritance called autosomal recessive, meaning that both the mother and the father must pass on the same gene variant for a child to be affected. Premature infants can also have lactose intolerance because of an insufficient lactase level.

Risk factors also include cancer treatment such as chemotherapy and radiotherapy. If you’ve had radiation therapy for cancer in your stomach or you have intestinal complications from chemotherapy, your risk of developing lactose intolerance increases.

The NET Effect

Given the above, there are some risks of developing secondary lactose intolerance in NET patients who have had small intestine surgery, chemotherapy or radiotherapy (and I suspect Peptide Receptor Radionuclide Therapy (PRRT) probably needs to be included in the overarching umbrella term of radiotherapy).

Sorting out the Symptoms

Although lactose elimination diets can give clues, a firmer diagnosis can be made via one or more of the following tests:

  • Hydrogen breath test. After you drink a liquid that contains high levels of lactose, your doctor measures the amount of hydrogen in your breath at regular intervals. Breathing out too much hydrogen indicates that you aren’t fully digesting and absorbing lactose.  The same test is used separately for Fructose Intolerance, and they are normally tested in one investigation due to close similarly of symptoms. 
  • Lactose tolerance test. Two hours after drinking a liquid that contains high levels of lactose, you’ll undergo blood tests to measure the amount of glucose in your bloodstream. If your glucose level doesn’t rise, it means your body isn’t properly digesting and absorbing the lactose-filled drink.

Interestingly, some medical sites suggest similar tests for SIBO and IBS as the symptoms of SIBO, IBS and Lactose Intolerance are also very similar. 

What can you do about it?

This is something to be discussed with your doctors and if you have one, your registered dietitian. I suspect they see a lot of lactose-related issues daily.    Most sites seem to point to a reduction/elimination strategy, i.e. cut down on lactose-related foods, with some suggesting the use of probiotics if bacterial overgrowth is suspected as the cause.

I know from many comments in my support group, that many try lactose-free milk or alternative (non-diary) milk products such as soy, almond, rice, oat, and coconut. The evidence of any of them vs other strategies is weak as far as I can tell from online checks. I did find this summary from a Canadian Society of Intestinal Research – click here.   Healthline is a site I look at a lot as its articles are always authored by a relevant healthcare professional – click here.

If milk is not the cause of your lactose intolerance or indeed the cause of the symptoms above, then it might be better to stick to cows’ milk as it’s a good source of high-quality protein (something NET dietitians will say is important for NET patients).  It’s naturally rich in calcium, B vitamins, and many minerals. It’s also often fortified with vitamins A and D, making it a very nutritious food for both children and adults, and many NET patients may be dealing with several vitamin deficiencies as a result of their cancer type and side effects of treatment.

It’s not just about milk as a standalone item though. Dairy products also include:

  • butter
  • cheese
  • cream
  • yoghurt
  • ice cream

Many processed foods can also contain lactose, including:

  • cereals
  • baked foods like bread, crackers, cakes, biscuits, and pastry
  • sauces and salad dressings
  • diet and protein shakes.

Thus, why a diary and trial and error make sense to help work out the causal source. This is something to be discussed with your doctors and if you have one, your registered dietitian

Supplementary reading - click the picture to read more
Supplementary reading - click the picture to read more


I am not a doctor or any form of medical professional, practitioner or counsellor. None of the information on my website, or linked to my website(s), or conveyed by me on any social media or presentation, should be interpreted as medical advice given or advised by me. 

Neither should any post or comment made by a follower or member of my private group be assumed to be medical advice, even if that person is a healthcare professional.   

Please also note that mention of a clinical service, trial/study or therapy does not constitute an endorsement of that service, trial/study or therapy by Ronny Allan, the information is provided for education and awareness purposes and/or related to Ronny Allan’s own patient experience. This element of the disclaimer includes any complementary medicine, non-prescription over the counter drugs and supplements such as vitamins and minerals.

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3 thoughts on “Lactose intolerance – the NET Effect

  • Cheryl Mogar

    Milk has been my body’s downfall forever
    A scoop of ice cream is what I believe brought on my idiopathic acute and chronic pancreatitis and tumor on tail of my pancreas
    But no one listens because it’s idiopathic

  • Pipp Alliss

    I have never liked milk much. When my brother suggested over 10 years ago that not drinking it would help with the chronic sinus and ear pain I had endured for several years, I gladly moved to Soya milk and yoghurts. I have read since that doing this can cause your body to become more lactose intolerant and this is certainly my experience, though I can’t discount the NET effect since the increasing episodes of gut pain was what led to my diagnosis. I don’t avoid milk totally when out and certainly indulge in a bit of ice cream on occasions with no ill effects. However, I find that too much in a short period, usually ingested via milk chocolate, evap milk or cream in desserts, creamy savoury sauces, too much ice cream etc. does not have the quick effect expected from intolerance as you quote, but causes spasmodic large bowel pains the following day. Interestingly, the effect is the same from too much apple (fructose) or bread/pastry (gluten), both of which I have generally limited consumption of after being taken through the FODMAP diet by an NHS dietician in 2017.

    • thanks for your comment. This is a real minefield area and we will probably never get to the bottom it. There are just too many variables and differential reasons. People do need to use trial and error and take advantage of any testing available. I’m fairly certain in my own mind that many problems I see in my patient group are unrelated to syndrome issues and more related to either side effects of treatment or other illnesses unrelated to NET. Really large meals and bowel surgery never go well together.

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