Can a Food Intolerance Cause Weight Gain?

Last Updated: 20th December 2022 · Written by Dr. Kristen Poe

Mystery weight gain can be one of the most baffling – and frustrating – symptoms someone can experience. Sometimes the explanation is outside of what is considered traditional as it pertains to weight gain.  Typically, when someone has unexplained weight gain, they have already gone to their general practitioners and had lab work and testing done to rule out more serious causes.   When a patient falls into this category of otherwise normal exams, labs, and testing, it makes sense to look at unexplained weight gain through a different lens.  Sometimes it is not as complicated as it may seem.

Up to 30% of people in the UK suspect they might have a food intolerance/sensitivity of some kind. Food intolerances are a subset of all adverse food reactions and are reported by 15 to 20 percent of the population in the United States as well. Food intolerances/sensitivities are even more common among patients with irritable bowel syndrome and other functional gastrointestinal disorders, with 50 to 80 percent reporting consistent problems with certain foods [1].  The most common symptoms of food intolerances include digestive problems (bloating, nausea, diarrhea, constipation, discomfort etc), and many people have also discovered that their sensitivities may also be contributing to weight gain.

What exactly is a food intolerance?

There is a lot of confusion regarding intolerances vs. allergies.  Intolerances/sensitivities and allergies are often terms that are used interchangeably.  However, they are clinically different, and should not be used as synonyms.  As I tell my patients, an allergy is cut and dry.  If you’re allergic, your immune system is heavily involved, they can be life threatening, and you avoid it.  Food allergy is due to an abnormal immunologic response following exposure (usually ingestion) to a food [1,2]. There are multiple types of food allergies, each with distinct clinical and pathophysiologic features.  Food allergies are broadly categorized into either immunoglobulin E (IgE) mediated or non-IgE-mediated processes.  IgE-mediated food allergic reactions are rapid in onset, typically beginning within minutes to two hours from the time of ingestion.  They can be life-threatening and cause anaphylaxis.

Food intolerances/sensitivities often have “a grey area” that is not as easily understood. Unlike an allergy, food intolerances aren’t usually life-threatening – but they can be life-limiting. Food intolerances are not immunologic allergies and do not carry the same risk as an immune system reaction from allergies. A simple way to explain the difference is that food intolerances/sensitivities generally involve the digestive system (although sometimes other body systems and symptoms occur), the amount of food ingested is directly related to the severity of symptoms, and the food causes similar symptoms with each exposure.  A food sensitivity occurs when your body is unable to digest certain compounds, such as the proteins found milk, eggs, wheat, or soy etc.  After you consume a food that contains these compounds, you may later experience uncomfortable symptoms. 

The tricky part is that these symptoms can be delayed by up to 48 hours.  They can also occur due to imbalances in gastrointestinal pH, gut microbiome, and intestinal integrity.  More and more research from some of the top medical schools, hospitals and institutions in the world are continuing extensive research on the immune system and gut connection. 

Dr. David Heber, MD, PhD, from UCLA School of Medicine [4] states, “70% of the immune system is located in the gut, where diverse bacteria is best.  You likely know that what you eat can affect your weight and energy level throughout the day.  But you might not realize the extent to which diet affects the immune system.”

How can food intolerances cause weight gain?

Our Complete Intolerance Test Box.

When you eat something you’re intolerant to, it can cause your digestive tract to become inflamed, often resulting in symptoms like those of IBS (irritable bowel syndrome).  Chronic inflammation can impact weight gain. To control inflammation, the body naturally produces cortisol, an anti-inflammatory hormone that comes from the adrenal glands, which are located above the kidneys. In addition to reducing inflammation, however, cortisol increases insulin levels, and can cause blood sugar levels to fluctuate. As the body produces more insulin to control blood sugar, it can eventually cause insulin-resistance.

When there is a lot of excess insulin and blood sugar in our blood stream, it signals our body to put that excess sugar in storage. We can store some sugar in our liver and muscles, but when these are full, our body starts to store the extra sugar as fat. This of course starts to cause weight gain. Insulin resistance can interfere with your body’s ability to metabolize the foods you eat, which can ultimately lead to weight gain.  These changes encourage the body to store fat rather than processing calories efficiently.  Therefore, unidentified intolerances and sensitivities that cause chronic inflammation can sometimes contribute to unexplained weight gain over time. Food intolerance testing can serve as an additional health optimization tool to help you feel your best. 


  1. Lomer MC. Review article: the aetiology, diagnosis, mechanisms and clinical evidence for food intolerance. Aliment Pharmacol Ther. 2015 Feb;41(3):262-75. doi: 10.1111/apt.13041. Epub 2014 Dec 3. PMID: 25471897.
  2. NIAID-Sponsored Expert Panel, Boyce JA, Assa’ad A, Burks AW, Jones SM, Sampson HA, Wood RA, Plaut M, Cooper SF, Fenton MJ, Arshad SH, Bahna SL, Beck LA, Byrd-Bredbenner C, Camargo CA Jr, Eichenfield L, Furuta GT, Hanifin JM, Jones C, Kraft M, Levy BD, Lieberman P, Luccioli S, McCall KM, Schneider LC, Simon RA, Simons FE, Teach SJ, Yawn BP, Schwaninger JM. Guidelines for the diagnosis and management of food allergy in the United States: report of the NIAID-sponsored expert panel. J Allergy Clin Immunol. 2010 Dec;126(6 Suppl):S1-58. doi: 10.1016/j.jaci.2010.10.007. PMID: 21134576; PMCID: PMC4241964.
  3. Sampson HA, Aceves S, Bock SA, James J, Jones S, Lang D, Nadeau K, Nowak-Wegrzyn A, Oppenheimer J, Perry TT, Randolph C, Sicherer SH, Simon RA, Vickery BP, Wood R; Joint Task Force on Practice Parameters, Bernstein D, Blessing-Moore J, Khan D, Lang D, Nicklas R, Oppenheimer J, Portnoy J, Randolph C, Schuller D, Spector S, Tilles SA, Wallace D; Practice Parameter Workgroup, Sampson HA, Aceves S, Bock SA, James J, Jones S, Lang D, Nadeau K, Nowak-Wegrzyn A, Oppenheimer J, Perry TT, Randolph C, Sicherer SH, Simon RA, Vickery BP, Wood R. Food allergy: a practice parameter update-2014. J Allergy Clin Immunol. 2014 Nov;134(5):1016-25.e43. doi: 10.1016/j.jaci.2014.05.013. Epub 2014 Aug 28. PMID: 25174862.
  4. David Heber M.D., Ph.D., FACP, FASN – Chairman, Herbalife Nutrition Institute

Buy with confidence

We're proud of our team and are established members of the scientific community

UKCA logo
C.E logo
Trusted Shops logo
Winner of Derbyshire Business Awards 2019
GDPR Compliant logo
Medilink Midlands logo