If you’ve spent time researching nutrition—especially in your quest to say keto—you’ll have undoubtedly come across the concept of “good” and “bad” carbs and how important it is to understand them in the context of your diet.
In this article, we’re going dive into the world of carbs and review what healthy carbs are versus unhealthy carbs, and how they relate to staying keto.
What are Carbohydrates?
Let’s start by recapping what carbohydrates are, and why we need to avoid them to achieve ketosis.
Chemically, carbohydrates are molecules consisting of carbon, oxygen, and hydrogen that, in biological terms, can be divided into four categories.
Monosaccharides are the most basic units of carbohydrates and include glucose and fructose, while disaccharides are made up of two monosaccharide molecules, and include sucrose and lactose. These are what we usually mean when we say “sugars.”
Polysaccharides are formed of long chains of these smaller molecules and include what we call “starch.” Cellulose, an essential form of dietary fiber, is also part of the polysaccharide family.
Lastly, we have oligosaccharides, which are smaller chains and helpful for feeding our friendly gut bacteria and aiding digestion.
Simple vs Complex Carbs
Nutritionists tend to take a more straightforward view of things when looking at carbs and differentiate them as “simple” or “complex.”
So which is good, and which is bad?
Generally speaking, complex carbs are seen as better, as it takes longer for the body to break them down and digest them.
This means we get a steadier flow of energy, leading to a more stable blood sugar level, and we tend to find complex carbs in legumes, whole grains, and starchy vegetables.
Simple carbohydrates take a lot less time to break down—giving us an instant energy boost—but they’re not inherently bad; we have to take their source into account.
Natural, unrefined sugars, like those found in fruit, milk, and honey, are generally considered “good,” while those that have been refined, like the sugars in white bread, candy, and pasta, are “bad.”
This is because refining carbohydrates remove most of the vitamins, minerals, fiber, and antioxidants, so you’re only left with calories.
“Good” and “Bad” Carbs and the Keto Diet
The keto diet isn’t your standard “healthy” diet, so the rules that dictate what carbs are good and bad don’t necessarily apply when aiming for ketosis.
On keto, carbs shouldn’t be making up more than 5-10% of your daily caloric intake which, on average, would be no more than 50g per day. Because this can alter with each individual, we recommend using a ketogenic macro calculator which can be found in under 1 minute.
To limit carb intake, we have to stick to low-calorie food, regardless of their complexity. Even things that are generally considered to be a source of good carbs, like most fruit, grains, and starchy vegetables need to be avoided as their carb count is just too high to achieve or maintain ketosis.
The best carbs to go for on keto are complex, low-starch, high-fiber greens, and vegetables, like broccoli, cabbage, lettuce, and cucumber. Nuts and seeds can be great as they’re low in carbs, but high in fat and fiber, although they are calorie-dense so it’s important to pay close attention to how many you’re introducing into your diet.
In short, it’s better to eat unrefined, complex carbs while on the keto diet as they’ll keep your glucose levels at a low, steady level while ensuring you still have enough energy to stay healthy.
If you find that you’re not getting as much fiber as you’d like when you cut out carbs, you can always introduce fiber supplements like acacia fiber or psyllium husk into your diet to boost your intake.
This is always something worth thinking about, as fiber isn’t just crucial for good digestive health, but also for regulating our blood sugar levels1 and supporting our immune system.
Does the Glycemic Index (GI) Matter?
The glycemic index measures how carbs raise the glucose levels in our blood two hours after ingestion2. We can rank food on a scale of 0-100, whereby 100 is the GI of pure glucose. For our purposes, we want to take into account the amount of carbs eaten, so we look at the glycemic load (GL).
We want to be aiming for foods lower down on GL index, ideally with a GL of less than 10, whereby anything over 20 can be considered far too high.
Calculating the GL of a particular food is actually easier than you might expect; just take the GI number of the food, multiply it by its carb count in grams and divide by 100. The exception to this rule might be for keto dieters who are highly-active, as their targeted ketogenic diet allows for higher carb intake, meaning they can sparingly use high-GI foods for their workouts and recovery.
The truth is, while it’s important to know about the role carbs play in nutrition—whether a carb is viewed as “good” or “bad”—doesn’t have a significant impact on keto dieters.
Considering the first step of the diet is reducing your carb intake dramatically by swapping high-carb foods for low-carb foods, your consumption will generally be low enough that the type of carb doesn’t matter.
On the whole, unrefined and complex carbs will be better for you, but the foods you’ll be naturally introducing to your diet will likely fall into those categories in the first place. In the long run, it’s probably best to just to focus on the carb content of what you’re eating and to make sure you’re meeting your keto macros.
 Weickert MO1, Pfeiffer AF. Metabolic effects of dietary fiber consumption and prevention of diabetes. J Nutr. 2008 Mar;138(3):439-42.
 David S. Ludwig, Joseph A. Majzoub, Ahmad Al-Zahrani, Gerard E. Dallal, Isaac Blanco, Susan B. Roberts. High Glycemic Index Foods, Overeating, and Obesity. Pediatrics; March 1999, VOLUME 103 / ISSUE 3. ELECTRONIC ARTICLE.