Dr. Anthony Gustin is a board-certified sports chiropractor, functional medicine practitioner, entrepreneur, podcast host, and founder of Perfect Keto.
One of the most essential guidelines on the ketogenic diet (or any low carb diet) is to keep carb intake very low, which is necessary for ketosis. This leads to a common question: Can you can eat healthy, low carb grains and stay in ketosis? In other words, do complex carbohydrates have a place (at all) in a ketogenic diet, or should they be eliminated entirely?
This article will help clear things up. Below, you’ll learn the difference between various types of carbohydrates and which ones have a place in a keto diet.
What Are the Different Types of Carbohydrates?
Carbohydrates (along with fat and protein) are a macronutrient. Carbs are broken down by the liver into glucose, your body’s preferred energy source. There are three types of nutrients referred to as carbohydrates: starch, fiber and sugar[*].
Carbohydrates are divided into two categories: simple and complex[*]. Sugar is a simple carb and starch and fiber are complex carbs. Whether a food is classified as a simple or complex carbohydrate depends on how many sugar molecules it contains[*].
Simple carbohydrates are made up of one or two sugar molecules. Monosaccharides, like fructose (the sugar found in fruit) and glucose, are made up of one sugar. Disaccharides, like lactose (the sugar in milk) and sucrose (table sugar) are made up of two sugars[*]. Simple carbs can also be found in soda, candy and refined sugar.
Empty-calorie foods, like soda and candy, give simple carbohydrates a bad reputation, as they should be eliminated from any healthy diet. It’s also found in foods stripped of nutrients — like white rice and white flour. They only contain sugar and no starch or fiber, resulting in a massive blood sugar spike.
Simple carbs are fast-acting; they’re absorbed into the bloodstream almost immediately[*]. Simple carbs come from:
- Added sugars: White sugar, brown sugar, honey, agave nectar, maple syrup, powdered sugar and high fructose corn syrup
- Naturally occurring simple sugars: Found in fruits and milk
When referring to low carb grains like steel-cut oats, whole wheat bread and wild rice, you are referring to complex carbohydrates. Because of their fiber content, they typically have fewer net carbs than simple carbohydrates.
Complex carbohydrates are made up of three or more sugar molecules, called oligosaccharides or polysaccharides. They are more slowly absorbed by your bloodstream than simple carbohydrates[*].
Complex carbs come in the form of:
- Starchy vegetables: Potatoes, corn, parsnips and sweet potatoes
- Legumes: Lentils, black beans and kidney beans
- Whole grains: Bread and breakfast cereals
So, What’s Better: Simple or Complex?
Great question! Frankly, you can’t really label simple or complex carbs as “the best carb.”
Remember, there are three nutrients (sugar, starch and fiber) that make up carbohydrates. These three nutrients can be found in combination within a single food. It is rare to find a food in nature that contains just one of the three. For example, sweet potatoes are a complex carbohydrate commonly referred to as a starchy vegetable, but they also contain fiber and sugar. Likewise, berries are a simple carbohydrate and contain sugar, but they’re also a great source of fiber.
Whether a carbohydrate is classified as simple or complex shouldn’t determine whether that carb is good or bad. Instead, you should look at how much sugar, fiber and starch are in that particular food, and what kind of effect it will have on your blood sugar levels.
How Starch Is Broken Down During Digestion
Starches are a complex carbohydrate, made of many glucose units bonded together[*]. Just like sugar, starch is broken down during digestion into glucose to be used for energy. Starches come from whole foods like brown rice, corn, white potatoes, peas, beans, oats, whole grain breads and whole wheat pasta.
If you’re familiar with your keto food list, you’ll quickly realize none of the above foods are keto-friendly. Why? Even though complex carbs (like starch) have a better reputation in most mainstream health circles, your body processes starch like sugar. Both are transformed into glucose for energy, which inhibits the production of ketones for energy (ketosis).
Fiber Isn’t Broken Down During Digestion
Fiber is a complex carbohydrate found in plant foods. Good sources of fiber include non-starchy vegetables, fruits, nuts and seeds, beans and whole grains. No-carb foods, like cottage cheese, salmon, ground beef and other animal products, do not contain fiber. Fiber is indigestible[*]. Mostly, it passes straight through your intestines and comes out the other end.
Dietary fiber has various health benefits, helping to grow healthy bacteria in your gut, aiding digestion[*]. It’s also been shown to aid weight loss and decrease your risk of colon cancer, weight gain, heart disease and diabetes[*].
There are two kinds of fiber[*]:
- Insoluble: This helps move food quickly through the stomach and intestines, regulating bowel movements and preventing constipation. Examples are bran, seeds, vegetables, brown rice and potato skins.
- Soluble: This helps slow digestion and lower blood glucose and cholesterol levels[*]. Examples are fleshy fruit, oats, broccoli and dried beans.
The Role of Fiber in Low Carb Grains, and Why You Should Focus on Net Carbs (Not Total Carbs)
When considering whether low carb grains have a place in your diet, you need to look at how many net carbs it contains (not total carbs).
The average person needs to stay within 25-30 grams of net carbohydrates to stay in ketosis. Fiber is the differentiating factor between net carbs and total carbs.
Since fiber is indigestible, and not broken down into simple sugars like starch and sugar, it does not affect your blood sugar levels. To calculate how many net carbohydrates are in a certain food, use this formula (in grams):
Total Carbohydrates – Total Fiber = Net Carbohydrates
For example, if a particular food contains 20 grams of total carbohydrates and 12 grams of fiber, the net carb count would be 8 grams.
You Can Only Eat a Low Carb Grain if it Doesn’t Kick You Out of Ketosis
Remember, ketosis is a metabolic state. While this website is filled with food lists, shopping lists and cheat sheets, these are only resources. Ketosis is something that can be tested; and technically, an individual could bite into an apple, eat a piece of candy or chug half a soda and remain in ketosis. Is this highly unlikely? Absolutely, but it’s been known to happen. And for this reason, it is very difficult to label a food (such as simple versus complex carbohydrates) as keto or not keto.
Rather than looking at a particular food and thinking, “This is a simple carb, so I can’t eat it,” or, “This is a complex carb, so I’ll be fine,” you need to dive deeper into the nutritional breakdown of that food. This is where fiber becomes important.
One Final Measure: Where a Carbohydrate Ranks on the Glycemic Index
When determining whether a low carb food will inhibit ketosis, there’s one final measurement you should keep in mind: Where that food ranks on the glycemic index.
The glycemic index (GI) measures how much a particular food raises an individual’s blood sugar (glucose) levels after eating[*]. The index ranks on a scale from 0-100, with 100 spiking blood sugar levels astronomically (high-carb foods), and 0 having no effect (zero carb foods like healthy fats, high-protein foods and low carb vegetables).
For example, refined grains like white bread and white rice hold a ranking of 75 and 73, respectively. A sweet potato holds a ranking of 63[*].
Do Low Carb Foods With High Amounts of Fiber Rank Low on the GI?
Remember, there are two types of fiber: insoluble and soluble. Soluble fiber is the fiber thought to lower blood glucose levels. Since most nutrition labels don’t differentiate between the two, a high-fiber food could be made up of almost all insoluble fiber, thereby ranking higher on the GI[*].
Final Takeaways: Understanding Low Carb Foods
Classifying a carbohydrate as “good” or “bad” would certainly make things easy, wouldn’t it?
Unfortunately, that’s not the case. The defining differentiator between simple and complex carbs is how many sugar molecules it contains. Fiber and starch are complex carbs, while simple sugar is a simple carb. It’s rare that you will find a whole food that contains only one of these.
To understand whether a food will inhibit ketosis, dive a little deeper into the nutritional value of that food. Check the dietary fiber and calculate the net carbs, as individuals can usually consume 25-30 grams of net carbs per day and stay in ketosis. Understanding where a food ranks on the glycemic index is another great indicator.
As always, there is only one sure way to know whether a food will inhibit ketosis, and that’s to test your ketone levels.