Gluten-Free Diet Side Effects to Expect


When you start the gluten-free diet, side effects can include changes in your weight (either gains or losses), improvements in your energy levels, and boosts to your nutritional status. In many cases, these side effects are beneficial.

However, the gluten-free diet also can cause undesirable side effects. For example, you may find you suffer more from constipation since many gluten-free foods, such as packaged snacks, contain little fiber. You also may also find you are more susceptible gluten cross-contamination.

Wondering what to expect in the way of side effects as you start the gluten-free diet? Here's what you should know.

Your Weight May Change

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If you have celiac disease and experienced malabsorption of nutrients that led to weight loss and/or other health issues, a 2019 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.

But not all people with celiac disease are underweight prior to their medical diagnosis. A 2010 study published in Journal of Clinical Gastroenterology observed the effects of a gluten-free diet on 61% of newly diagnosed celiacs who were considered normal weight, 17% percent who were underweight, 15% percent who were overweight, and 7% who were obese.

The researchers noted that a gluten-free diet helped to regulate body weight to normal levels in the 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


Many newly-diagnosed celiacs cannot digest lactose, the sugar found 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't digest lactose anymore. So 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 very small amounts of milk products at first 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 better to those products.

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

You May React to Trace Gluten


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 single bite of glutenous cake that you just 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 a bit startling once you've gone completely gluten-free. Still, don't be alarmed if you get these recurrent symptoms—and take a look at these tips for recovering from when you get accidentally glutened.

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 very much fiber, and so consuming too little fiber is a common gluten-free diet side effect.

Fortunately more gluten-free bread brands are producing breads made with whole grains. However, getting enough fiber on a gluten-free diet still represents a bit of a challenge, and some people may experience slowed digestion and constipation as a result.

So 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 (as some of us do), you may want to consider grinding your own 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 do, don't add copious amounts of fiber to your diet all at once, since that much fiber 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 about your options.

You May Be Missing Key Nutrients

vitamin-rich fruits in test tubes
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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 obviously are off-limits on the gluten-free diet—and some people don't get enough of those nutrients while eating gluten-free (most gluten-free baked products are not fortified with extra vitamins and minerals).

Pay close attention to your intake of thiamin, riboflavin, niacin, and folic acid (all B vitamins), along with your iron intake, to make sure you're getting the 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 side effect of the gluten-free diet.

A Word From Verywell

weight loss
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Obviously, some of these gluten-free diet side effects are welcome (weight loss when you're overweight, for example). But others may not be welcome at all. It's no fun to become more sensitive to trace gluten, for example.

As you're working your way through the first few months, keep in mind that even though the diet represents a major lifestyle change (and carries a pretty steep learning curve), you likely can expect these side effects to subside eventually.

If you find you're still struggling with constipation or nutrient levels after six months or so on the gluten-free diet, talk to your doctor about a referral to a dietician who specializes in the diet. That person can help you identify problem areas and correct them.

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