A ketogenic diet is inherently low glycemic, but it’s not the same thing as a low-glycemic diet. Both approaches lower blood sugar, yet they do it through different mechanisms and allow very different amounts of food. A keto diet caps carbohydrates at roughly 20 to 50 grams per day, which forces your body into ketosis. A low-glycemic diet permits far more carbs, often 40 to 55 percent of total calories, but focuses on choosing carbs that raise blood sugar slowly.
How the Two Diets Differ
The glycemic index (GI) ranks carbohydrate-containing foods on a scale of 0 to 100 based on how quickly they spike blood sugar. A low-glycemic diet uses this ranking to guide food choices: you can eat oatmeal, lentils, sweet potatoes, and whole-grain bread as long as they fall on the lower end of the scale. Daily carbohydrate intake on a standard low-glycemic plan typically lands around 150 grams, roughly 44 to 55 percent of calories.
Keto takes a completely different path. Instead of picking gentler carbs, it nearly eliminates them. Most people on a ketogenic diet average about 50 grams of carbohydrates per day, sometimes less than 20 grams. At that level, nearly every food you eat has a negligible glycemic impact simply because there isn’t enough carbohydrate present to move the needle. In practical terms, keto achieves a low-glycemic outcome by default, but its primary goal is ketosis, not glycemic index management.
Why Keto Foods Score Low on the GI Scale
The staples of a keto diet are fats and proteins: eggs, olive oil, avocado, cheese, nuts, meat, fish, and leafy greens. Most vegetables score below 20 on the glycemic index. Pure fats and proteins don’t have a GI score at all because they contain little to no carbohydrate. When you build a plate from these ingredients, the overall glycemic load of your meal is extremely low.
Even keto-friendly substitutes tend to stay in low-glycemic territory. Almond flour contains just 16 grams of carbs per 100-gram serving, far less than the 76 grams in white flour, giving it a low glycemic index. Coconut flour is higher in fiber and lower in net carbs than regular flour. Common keto sweeteners like stevia and monk fruit both carry a glycemic index of zero. Allulose, another popular option, has a GI of just 1 and contains only 10 percent of the calories in table sugar.
Blood Sugar and Insulin Effects
Both diets improve blood sugar control, but keto tends to produce larger changes. In a 24-week trial comparing the two approaches in people with type 2 diabetes, those on a ketogenic diet (under 20 grams of carbs daily) saw their HbA1c drop from 8.8 percent to 7.3 percent. The low-glycemic group, eating about 55 percent of calories from carbs, went from 8.3 percent to 7.8 percent. HbA1c reflects average blood sugar over roughly three months, so that 1.5-point drop in the keto group represents a meaningful difference in daily glucose levels.
A broader meta-analysis reinforced this pattern. Across multiple randomized trials, ketogenic diets reduced HbA1c by a standardized mean of 1.45 percentage points compared to control diets, while low-carbohydrate diets (which overlap with low-glycemic approaches) achieved a 0.27-point reduction. The keto group’s advantage was statistically significant.
Insulin sensitivity follows a similar trend. One study found that just six days on a ketogenic diet reduced a key marker of insulin resistance (HOMA-IR) by 57 percent, lowered fasting insulin by 53 percent, and cut liver fat by 30 percent. Some of that improvement happens independently of weight loss, likely because drastically reducing carbohydrate intake directly lowers the amount of insulin your body needs to produce throughout the day. Over longer periods, a meta-analysis of randomized trials found that very low-carb ketogenic diets reduced HOMA-IR by 1.36 points more than comparison diets, though these differences sometimes narrowed by the 12-month mark.
Where Keto Can Still Raise Blood Sugar
Being in ketosis doesn’t make you immune to blood sugar spikes. Protein triggers a process called gluconeogenesis, where your liver converts amino acids into glucose. On a high-protein, low-carb diet with a 20:30:50 ratio of carbs to protein to fat, researchers found that average 24-hour blood glucose dropped substantially (from 198 to 126 mg/dl) compared to a standard diet. So protein does raise glucose somewhat, but the net effect is still dramatically lower than eating a typical carb-heavy meal.
The more practical risk is hidden carbs. Keto-labeled snacks, sauces, and processed foods sometimes contain sugar alcohols, starches, or fillers that raise blood sugar more than their labels suggest. If you’re using keto specifically to manage blood sugar, reading ingredient lists matters more than trusting front-of-package claims.
Choosing Between the Two Approaches
A low-glycemic diet is more flexible and easier to sustain long term. You can eat fruit, whole grains, legumes, and starchy vegetables as long as you favor lower-GI options. For people who want modest improvements in blood sugar without overhauling their eating habits, this approach works well, though the improvements in HbA1c tend to be more modest (around 0.5 percentage points in some reviews).
Keto produces faster and often larger metabolic changes, particularly for people with type 2 diabetes or significant insulin resistance. The American Diabetes Association now includes ketogenic diets as a possible therapeutic option in its guidelines, a recent addition. However, the UK’s Scientific Advisory Committee on Nutrition has noted that long-term data on very low-carb ketogenic diets (under 50 grams per day) remains limited, and their 2021 review concluded that low-carb diets are neither clearly superior nor inferior to other dietary patterns for long-term outcomes.
The tradeoff is straightforward: keto is more restrictive but has a bigger impact on blood sugar, while a low-glycemic diet is easier to follow but delivers smaller metabolic shifts. Both are low glycemic in their effect on blood sugar. Only one makes that effect the primary mechanism of the entire diet.