Gluten-Free Diets: Are There Negative Side Effects?

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Abiding by a gluten-free diet can produce side effects like weight fluctuations, increased energy levels, and nutrition improvements.

However, a gluten-free diet also can cause negative side effects like increased constipation from processed snacks that contain little fiber. You also may find you are more susceptible to gluten cross-contamination.

Wondering what to expect from gluten-free diet side effects? Here's what you should know.

Your Weight May Change

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One review published in BMC Medicine found that a gluten-free diet can lead to weight gain since many gluten-free foods tend to be higher in vegetable fats.

However, not everyone with celiac disease is underweight before their medical diagnosis. A study published in the Journal of Clinical Gastroenterology observed the effects of a gluten-free diet on 61% of newly diagnosed celiacs who were considered normal weight, 17% who were underweight, 15% who were overweight, and 7% who were obese.

Researchers noted that a gluten-free diet helped regulate body weight to normal levels in subjects who were either underweight or overweight.

Therefore, your weight could normalize as a side effect of the gluten-free diet. Many people also mistakenly believe a gluten-free diet will automatically lead to weight loss. If you indulge in too many gluten-free snack foods (which tend to be high in calories and low in nutrition, just like their conventional counterparts), you could find yourself packing on a few extra pounds.

Your Lactose Intolerance May Improve

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Many newly diagnosed celiacs cannot digest lactose, the sugar in milk and milk products, such as ice cream and yogurt. That's because of the intestinal damage caused by celiac disease. Intestinal villi are responsible for digesting lactose, and when they're destroyed by the reaction to gluten in our diets, we can no longer digest lactose. You may find yourself going dairy-free as well as gluten-free.

However, as your intestinal damage—known as duodenal villous atrophy (DVA)—begins to heal, you may begin to tolerate lactose-containing foods again as a side effect of your gluten-free diet. Expect this change to be gradual, especially if your lactose intolerance has been severe—try small amounts of milk products to see how your body reacts.

Symptoms of lactose intolerance include:

  • Abdominal bloating
  • Diarrhea
  • Gas

If you experience these after a large serving of a milk product, back off for a while before trying again. You also can try reduced-lactose or lactose-free milk to see if your body reacts more favorably to those products.

If you're not eating dairy, ensure you're getting enough calcium in other ways, such as by taking a gluten-free vitamin supplement.

You May React to Trace Gluten

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When you were eating gluten every day, you may not have had reactions to individual instances of accidental gluten ingestion. However, once you remove it from your diet, you may find your body is more sensitive to trace amounts of gluten found in cross-contamination in your food.

You could also find that you're more sensitive to that bite of glutenous cake you couldn't resist. Sensitivity to trace gluten and cross-contamination is a common side effect of the gluten-free diet, and the level and severity of sensitivity can vary from person to person.

A reaction to gluten in your food may come quickly within an hour or less in some cases, or may not appear until the next day or even later.

Your digestive symptoms may come in the form of the following:

  • Abdominal pain
  • Constipation
  • Diarrhea
  • Gas
  • Reflux
  • Vomiting

You may also experience other symptoms, including:

  • Brain fog
  • Bouts of depression
  • Fatigue
  • Joint pain

All this from a tiny crumb? Yes. The body's adverse reactions to gluten-containing foods can be startling once you are gluten-free. Still, don't be alarmed if you get these recurrent symptoms—and follow these tips for recovering if you accidentally eat or drink gluten.

Once you can function again, scrutinize your diet to see where you may be getting hidden gluten.

Remember to always play it safe and cook gluten-free recipes.

You May Need More Fiber in Your Diet

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Whole grains, including bread products, provide a substantial source of fiber in most people's diets. But when you give up gluten, you're left with fewer whole-grain products from which to choose—unfortunately, many gluten-free breads and other baked goods don't contain much fiber, and consuming too little fiber is a common gluten-free diet side effect.

Fortunately, more gluten-free bread brands are producing bread made with whole grains. However, getting enough fiber on a gluten-free diet still represents a challenge, and some may experience slow digestion and constipation.

What can you do? You can try adding sources of fiber to your diet, including:

  • Beans and legumes
  • Fresh fruits and vegetables
  • Nuts and seeds
  • Whole-grain, gluten-free bread

If you bake your own bread, consider grinding your flour from whole gluten-free grains. Here's a list of five interesting gluten-free grains to try, many of which are high in fiber. You also can take a gluten-free fiber supplement.

Whatever you choose, don't add copious amounts of fiber to your diet all at once, since it can upset your digestive tract and cause bloating.

If you're still struggling with constipation or are concerned that you're not getting enough fiber, talk to your doctor.

You Can Miss Key Nutrients

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Prior to going gluten-free, many of us got some of our iron and B vitamins from enriched wheat flour products. Because those products are off-limits on the gluten-free diet, some won't ingest enough of those nutrients while eating gluten-free.

Pay attention to your intake of thiamin, riboflavin, niacin, and folic acid (all B vitamins), along with iron to ensure you're getting recommended daily allowances.

Load up on fresh fruits and vegetables (many contain high levels of B vitamins), try gluten-free cereals (many of which are fortified), or consider taking a supplement to make up for any nutritional shortfalls that may occur as a negative side effect of a gluten-free diet.

A Word From Verywell

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The negative side effects of a gluten-free diet are no fun as you're more sensitive to trace gluten.

While working your way through the first few months, remember that even though a gluten-free diet represents a major lifestyle change (and carries a pretty steep learning curve), you likely can expect these side effects to subside eventually.

Speak to a dietician if you're struggling with negative side effects like constipation or deficient nutrient levels after six months on a gluten-free diet.

12 Sources
Verywell Fit uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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Jane Anderson

By Jane Anderson
Jane Anderson is a medical journalist and an expert in celiac disease, gluten sensitivity, and the gluten-free diet.