The primary difference between simple and complex carbohydrates lies in their chemical structure and how quickly your body digests them and converts them into glucose (blood sugar). The GAPS diet excludes all grain because they are hard to digest and increase the breakdown of the tight junctions in the gut wall that lead to arterial damage. By severely restricting carbohydrates, the diet minimises glucose and insulin spikes. This reduces the chronic demand on the pancreas, allowing the body’s cells to become more sensitive to insulin again, thus reversing insulin resistance. Other leading doctors share the same fundamental principle for recommending the elimination of refined sugar and grains, but do not focus their attention on a diet for gut health as much as Dr Natasha Campbell-McBride does.

The Carbohydrate-Insulin Model

Both refined sugar and grains (complex carbohydrates) break down into glucose, causing spikes in blood sugar(glucose), which in turn triggers the release of high amounts of insulin. The doctors argue that this chronic overstimulation of insulin is the root cause of insulin resistance and metabolic dysfunction, leading to type 2 diabetes and contributing to high blood pressure (hypertension).

Their shared goal is to:

1. Lower Blood Glucose: Stop feeding the system the fuel (carbohydrates) that causes toxic blood sugar levels.
2. Lower Insulin: Allow insulin levels to drop, reversing insulin resistance and enabling the body to burn stored fat.

1. Difference in the Body’s Processing

Feature	Simple Carbohydrates (Sugars)	Complex Carbohydrates (Starches & Fibre)
Chemical Structure	Shorter chains of sugar molecules (one or two sugars)	Longer, complex chains of three or more sugar molecules
Digestion Speed	Very Fast	Slow
Glucose Release	Quick release, causing a rapid spike in blood sugar and insulin levels.	Gradual release, causing a slower, more sustained rise in blood sugar.
Energy	Provides a quick burst of energy, often followed by a rapid “crash.”	Provides longer-lasting, sustained energy.
Satiety/Fiber	Typically low in fiber, leading to less satiety (you feel hungry sooner).	High in fiber (which the body cannot digest) and starches, keeping you feeling fuller for longer.
Nutrients	Often contain “empty calories” with little to no nutritional value (especially added sugars).	Generally nutrient-dense, providing essential vitamins, minerals, and antioxidants.

2. Food Sources

The healthiest diets favour foods rich in complex carbohydrates and naturally occurring simple sugars (like those in whole fruit), while limiting foods high in added simple sugars.

Type of Carbohydrate	Food Sources	Note
Simple Carbs (Added Sugars)	Candy, table sugar, syrups (maple, corn), regular soda/soft drinks, cookies, cakes, fruit juice concentrates, refined breakfast cereals, jams, and many processed foods.	These are best consumed in moderation as they provide fast energy with few nutrients.
Simple Carbs (Naturally Occurring)	Whole fruits, milk, and dairy products.	Although they contain simple sugars (like fructose and lactose), these foods also provide fibre, vitamins, and minerals, making them a healthier choice than added sugars.
Complex Carbs (Starches & Fibre)	Italic signifies not in a GAPS diet. Whole Grains: Whole-wheat bread/pasta, brown rice, oatmeal, quinoa, barley, farro, millet.	These are the preferred source of carbohydrates for long-term health and stable energy.
	Legumes: Beans (black, kidney, pinto), lentils, chickpeas, peas.
	Starchy Vegetables: Sweet potatoes, white potatoes (especially with the skin), corn, butternut squash, peas.
	Fibre-Rich Vegetables: Broccoli, leafy greens (kale, spinach), carrots.
	Fibre-Rich Fruits: Apples, berries, bananas.