Over the last decade, the incidence of inflammatory bowel diseases (IBD) has increased worldwide (1).

Symptoms are often painful and include diarrhea, bleeding ulcers and anemia.

Elimination diets, such as the Specific Carbohydrate Diet™ (SCD), have gained traction as potential treatments for IBD and other inflammatory and autoimmune disorders.

While the SCD was introduced in the 1920s by gastroenterologist Sidney Haas, it was expanded and popularized in the 1980s with Elaine Gottschall’s book “Breaking the Vicious Cycle.”

This article explores the SCD, the science behind it and its effectiveness.

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The SCD is an elimination diet that emphasizes the removal of certain types of carbohydrate-containing foods based on their chemical structure.

The governing theory behind the SCD is that complex carbs encourage an overgrowth of unhealthy bacteria in your small intestine if you have IBD.

As these bacteria grow, they produce byproducts that promote inflammation and eventually lead to reduced absorption of nutrients in your digestive tract.

The SCD claims to inhibit the growth of such bacteria and restore digestive function by eliminating all carbohydrate food sources that have two or more linked sugar molecules (di-, oligo- and polysaccharides).

Though many carbs are prohibited, the SCD does permit carb sources that have single, unbound sugar molecules — or monosaccharides — as your digestive tract absorbs them more easily.

Summary The SCD is an elimination diet that restricts certain types of carbs in an effort to treat various autoimmune and inflammatory bowel diseases.

As the name implies, the SCD restricts specific carbs based primarily on their chemical structure.

The diet labels any food or food additive “illegal” that contains two or more chemically linked sugar molecules. The SCD guidebook, “Breaking the Vicious Cycle,” collectively refers to these foods as complex carbs.

In scientific terms, any food with disaccharides, oligosaccharides or polysaccharides will appear on the list of illegal foods.

As you can imagine, the list of banned foods is extensive. Here are a few of the main groups of illegal foods:

  • Potatoes
  • Grains and pseudograins, including rice, wheat, corn, quinoa, millet, etc.
  • Processed meats and meats with additives
  • Dairy, except some cheese, butter and homemade yogurt that has been fermented for at least 24 hours
  • Most legumes, though certain dried beans and lentils are permitted after soaking
  • Most processed sugar, artificial sweeteners and sugar alcohols
  • Processed foods

The general structure of the SCD is very rigid and intended to be followed exactly as outlined in the guidebook — with little to no room for flexibility.

While some people may reintroduce certain illegal foods after symptoms subside, this will vary depending on an individual’s response to the diet.

Summary The SCD restricts any food with two or more linked sugar molecules, such as dairy products, starchy vegetables, table sugar, grains and most legumes. These foods are referred to as “illegal” and are strictly prohibited.

The foods approved by the SCD are collectively referred to as “legal.”

Most of the foods on this list are unprocessed, whole foods that don’t offer many complex carbs.

The main sources of approved or “legal” carbs in the SCD come from the monosaccharides glucose, fructose and galactose.

These are some of the SCD’s legal foods:

  • Fruits: Most unprocessed, fresh or frozen fruits and juices. Canned fruits may be allowed as long as they don’t have added sugar or starch.
  • Vegetables: Most vegetables, except for potatoes, yams, plantains and some other high-starch vegetables.
  • Meat: Most fresh meats, as long as they don’t contain any fillers or additives.
  • Eggs
  • Some dairy: Homemade yogurt fermented for at least 24 hours and some natural cheeses.
  • Certain legumes: Some dried legumes, as long as they’re soaked and prepared according to the directions outlined in the guidebook.
  • Nuts and nut butters: Most nuts, as long as they’re free from added starch or sugar.
  • Herbs and spices: Most dried or fresh herbs and spices. Spice blends are typically discouraged as many of them harbor “illegal” additives.

As it can be difficult to determine which foods are legal, the SCD guidebook recommends eating only the explicitly legal foods to avoid inadvertently ingesting something illegal.

Summary Most unprocessed fruits, vegetables, nuts and meats are permitted on the SCD — with a few exceptions. Some legumes and dairy products are permitted as long as they’re prepared appropriately, as outlined in the guidebook.

The SCD was originally designed as a therapy for people with IBD, an umbrella term which includes ulcerative colitis, celiac disease and Crohn’s disease.

These diseases can hamper your ability to digest and absorb nutrients from food. Thus, the SCD aims to heal intestinal tissue in order to restore its functions.

The SCD’s promoters claim that some people are less adept at digesting foods — such as grains, legumes, refined sugar and high-starch food additives — that result from settled agricultural practices and the modern food industry.

Supporters assert that continued ingestion of these carbs leads to an overgrowth of unhealthy bacteria in your gut which promotes inflammation, eventually diminishing your ability to digest.

Strict adherence to the SCD is supposed to eventually starve these bacteria by depriving them of food, allowing your gut tissue to heal.

To this day, the SCD is primarily used to treat intestinal disorders — but with varied success.

One of the major criticisms of this diet is its lack of concrete scientific evidence.

The bulk of the available data is weak and limited to very small studies or anecdotal evidence, which isn’t enough to definitively state whether or not the SCD works (2).

Ultimately, more research is needed to determine whether the SCD is truly an effective treatment for IBD.

Summary Though the SCD is often promoted for people with IBD, there are very few studies that support its effectiveness.

Although primarily used to treat IBD, the SCD is also marketed for people with other medical conditions, including autism spectrum disorder (ASD) and cystic fibrosis (CF).

Early research suggests that gut bacteria may be crucial in treating some behavioral and autoimmune conditions, such as CF and ASD (3, 4).

Because the Specific Carbohydrate Diet is designed to balance your digestive tract, its proponents theorize that it may be an effective therapy for these conditions, too.

However, the scientific understanding of these disorders is limited. Beyond anecdotal reports, there is no research to suggest that the SCD treats diseases outside of IBD — if that.

In fact, it’s still unclear whether the SCD impacts gut bacteria at all.

More research is needed to understand if the SCD affects autism spectrum disorder and cystic fibrosis.

Summary While proponents of the SCD claim that it treats autism spectrum disorder and cystic fibrosis, there isn’t any scientific research to support this notion.

A diet as restrictive as the SCD doesn’t come without risks.

When well planned, the SCD can be balanced, complete and healthy.

However, the SCD eliminates large groups of nutrient-dense foods that are beneficial for most people, including whole grains, some legumes and most dairy.

Eliminating these foods without replacing their key nutrients could result in poor diet quality and subsequent nutritional deficiencies.

Maintaining good nutrition may already prove difficult if you have IBD. Adopting an extremely restrictive diet like the SCD could increase your risk of malnutrition and associated complications (5, 6).

Ensuring that the SCD is safe and wholesome takes effort but isn’t impossible.

If you’re considering this diet, consult with your dietitian or another qualified health professional to make sure you’re meeting your needs.

Summary Because the SCD is so restrictive, you could be at risk of malnutrition if the diet isn’t appropriately planned.

While anecdotal evidence indicates that the SCD improved IBD symptoms in some people, there is no guarantee that it will work for everyone. Medical conditions like IBD are complex and specific interventions may pan out differently for different people.

With current evidence, it remains unclear if the diet plays any role in IBD treatment — beyond a placebo effect (2).

That said, a well-planned elimination diet may be worthwhile, especially if you want to avoid the more serious risks associated with certain long-term medications and surgeries (2).

While dieting is a personal decision, you should discuss the SCD with a qualified health professional prior to making any major lifestyle changes.

Summary There is very little substantial evidence to support the SCD. While it may be less risky than other medical therapies, you should still consult your healthcare provider before diving in.

The SCD is an elimination diet designed to treat symptoms of IBD and restore digestive function by purging many carb-containing foods, due to the notion that they harm your gut.

While some people may notice improvements in their IBD symptoms, very little research supports its effectiveness beyond a placebo effect.

Due to the restrictive nature of the diet, it could increase your risk of malnutrition.

If you’re considering the SCD, discuss it with your healthcare provider and dietitian first to reduce possible risks and ensure a balanced diet.