Both low-carb and ketogenic eating can lower A1C, because carbohydrate is the nutrient that raises blood sugar the most, and cutting it reduces the glucose your body has to handle. Keto is essentially a stricter version of low-carb, restrictive enough to shift your metabolism into ketosis, and it often produces larger and faster improvements in blood sugar and weight in the short term. The catch is that keto is harder to sustain, and over the long run the approach you can actually stick with usually wins. Just as important, cutting carbs while taking insulin or certain diabetes pills can cause dangerously low blood sugar, so either approach should be started with a clinician who can adjust your medication. The best choice is the one that fits your health, your preferences, and your ability to maintain it.
What separates low-carb from keto
The two approaches sit on the same spectrum of carbohydrate restriction, and the main difference is how far they go.
Low-carb eating has no single official definition, but it generally means getting somewhere around 26 to 45 percent of your calories from carbohydrate, often translating to under roughly 130 grams a day. That still leaves room for some fruit, legumes, dairy, and modest portions of whole grains. A ketogenic diet is far stricter, typically limiting carbohydrate to about 20 to 50 grams a day, or under roughly 10 percent of calories, with most calories coming from fat and a moderate amount from protein. That degree of restriction is low enough to push the body into nutritional ketosis, a state in which it burns fat for fuel and produces ketones because carbohydrate is scarce.
| Feature | Low-carb | Ketogenic (keto) |
| Typical carbohydrate | Around 130 g/day or less (about 26 to 45% of calories) | About 20 to 50 g/day (under ~10% of calories) |
| Induces ketosis | Usually not | Yes, by design |
| Food flexibility | More: some fruit, legumes, whole grains | Less: very limited carbohydrate foods |
| Fat intake | Moderate to higher | High |
Why cutting carbs lowers A1C
The reason carbohydrate restriction works is straightforward. Of the three macronutrients, carbohydrate has by far the biggest and most direct effect on blood glucose, because it breaks down into sugar that enters the bloodstream after a meal. Protein and fat have much smaller effects.
When you eat less carbohydrate, you blunt the after-meal glucose spikes that drive a large share of your A1C, and you lower the overall glucose load your body must clear. Over time that shows up as a lower average and a lower A1C. Carb restriction also frequently leads to weight loss, which improves insulin sensitivity, and it can reduce the amount of insulin or medication a person needs. This is why reducing carbohydrate is among the most reliable dietary levers for blood sugar and a central theme in the broader strategies that lower A1C naturally.
What the research shows
The evidence for carbohydrate restriction in type 2 diabetes is among the strongest for any dietary pattern, and the American Diabetes Association explicitly recognizes both low-carbohydrate and very-low-carbohydrate eating as viable options.
Studies consistently show that both approaches lower A1C, with the largest effects appearing in the first three to six months. A recurring finding is that the advantage tends to shrink over 12 to 24 months, largely because sticking to strict carbohydrate limits gets harder with time, not because the biology stops working. Very-low-carbohydrate and ketogenic approaches often produce bigger early reductions in A1C and weight, and greater cuts in medication, than moderate low-carb. A notable supervised program studied by Hallberg and colleagues, published in 2018, reported meaningful A1C improvements and substantial reductions in diabetes medication in people with type 2 diabetes following a very-low-carbohydrate plan with close medical support. The consistent thread across the research is that results track with how much carbohydrate you actually cut, how well you stick with it, and how much weight you lose, which is exactly why sustainability matters as much as the initial numbers. For people also exploring meal timing, our look at intermittent fasting and A1C covers a different but complementary approach.
How they compare for A1C
Put side by side, the two approaches trade off speed and intensity against livability.
| Consideration | Low-carb | Keto |
| Short-term A1C reduction | Meaningful | Often larger and faster |
| Medication reduction | Common | Often greater |
| Long-term adherence | Generally easier | Harder for many people |
| Restrictiveness | Moderate | High |
| Side effects | Fewer | More (keto flu, lipid changes, others) |
| Monitoring needs | Moderate | Closer, especially early |
The honest takeaway is that keto can deliver more dramatic early results, but low-carb is often easier to maintain, and a moderate plan followed for years may do more for your A1C than a strict one abandoned after a few months. Neither is universally better; the right level of restriction is the one that gives you a real benefit you can sustain safely.
Safety and medical cautions
This is where careful attention matters most, because cutting carbohydrate changes how your body and your medications behave.
The biggest immediate risk is hypoglycemia. If you take insulin or an insulin secretagogue such as a sulfonylurea, sharply reducing carbohydrate while keeping the same medication doses can drive your blood sugar dangerously low. Doses often need to be reduced at the start, which is a change to make with your clinician rather than on your own. A second serious caution applies to SGLT2 inhibitors, a class of diabetes medication: the U.S. Food and Drug Administration has warned that these drugs can cause ketoacidosis, and combining them with a very-low-carbohydrate or ketogenic diet appears to raise that risk, sometimes even when blood glucose looks near normal. People with type 1 diabetes need particular caution with ketogenic eating because of their inherent ketoacidosis risk.
It also helps to understand the difference between two states that sound alike. Nutritional ketosis, the goal of a keto diet, involves modest blood ketone levels, generally in the range of about 0.5 to 3.0 mmol/L, and is a normal metabolic response to low carbohydrate intake. Diabetic ketoacidosis is a medical emergency marked by much higher ketones, high blood glucose, and dangerous acid buildup in the blood. They are not the same thing, but the distinction is one reason ketogenic diets warrant medical guidance for people with diabetes.
Beyond these, a few other considerations apply. Some people see their LDL cholesterol rise on a high-fat ketogenic diet, so lipids are worth monitoring, while others see triglycerides fall and HDL improve. Very-low-carb eating can fall short on fiber and certain nutrients, making non-starchy vegetables and adequate hydration and electrolytes important, and the transient fatigue and headache some feel in the first days, often called keto flu, usually reflects that adjustment. High protein intake needs caution in advanced kidney disease. And carbohydrate restriction is generally not appropriate during pregnancy or for people with a history of disordered eating without specialized supervision.
Which should you choose?
Because there is no single ideal eating pattern for diabetes, the decision is personal. If you want a more flexible plan you can follow indefinitely, and a steady rather than dramatic improvement, a moderate low-carb approach is often the better fit. If you are motivated to make a bigger change, want faster results, and can commit to closer monitoring and medical supervision, keto may deliver more in the short term. Your medications, other health conditions, and food preferences all weigh into the choice.
Whichever you pick, quality matters as much as quantity. A low-carb or keto diet built on non-starchy vegetables, adequate protein, and unsaturated fats from sources like olive oil, nuts, and fish is far healthier than one built on processed meats and low-carb packaged snacks. Working with a registered dietitian can help you design a plan that lowers your A1C without sacrificing nutrition, and if you need practical ideas, our roundup of smart snacks when your A1C is high leans toward lower-carb options that fit either approach.
Making either approach work
Once you have chosen, a few habits improve your odds. Monitor your glucose closely in the early weeks, especially if you take medication, so you and your clinician can catch lows and adjust doses. Focus on whole, minimally processed foods rather than simply counting carbohydrate grams. And give the change time to register in your A1C: because the test reflects roughly the prior three months, wait about that long before rechecking, as our guide on how often to test your A1C explains. In the meantime, your daily glucose readings will show progress sooner, and you can estimate where your average is heading with an A1C calculator.
When to talk to your doctor
Speak with your care team before starting either diet if you take any glucose-lowering medication, particularly insulin, a sulfonylurea, or an SGLT2 inhibitor, and if you have kidney disease, heart disease, a history of disordered eating, or are pregnant. Medication adjustments are frequently needed, and your clinician can help you make the change safely and monitor for lipid changes, low blood sugar, and other effects. Carbohydrate restriction is a powerful tool, and it is safest when it is supervised rather than improvised.
Frequently asked questions
Does keto lower A1C more than a low-carb diet?
Often in the short term, yes. Keto tends to produce larger and faster reductions in A1C and weight and greater medication cuts, but the advantage frequently narrows over a year or more because keto is harder to sustain. The best long-term results come from the approach you can maintain.
How many carbs should I eat to lower my A1C?
There is no single number. Low-carb plans often aim for under about 130 grams a day, while ketogenic plans restrict to roughly 20 to 50 grams. Greater reductions tend to lower A1C more, but the right target depends on your health, medications, and what you can sustain.
Is keto safe for people with diabetes?
It can be, with medical supervision. The main risks are low blood sugar if medication is not adjusted, a higher chance of ketoacidosis for those on SGLT2 inhibitors or with type 1 diabetes, and possible cholesterol changes. Nutritional ketosis is not the same as diabetic ketoacidosis, but the diet still warrants medical guidance.
Will I have to reduce my diabetes medication on a low-carb diet?
Very possibly. Cutting carbohydrate lowers blood glucose, so continuing full medication doses, especially insulin or a sulfonylurea, can cause dangerous lows. Dose reductions should be planned with your clinician.
Which is easier to stick with, low-carb or keto?
Most people find moderate low-carb easier to maintain because it allows more food variety, including some fruit, legumes, and whole grains. Keto is more restrictive, which is part of why its early advantage often fades over time.
The bottom line
Low-carb and keto both lower A1C by cutting the nutrient that raises blood sugar the most, and keto, as the stricter version, often works faster and further in the short term. But sustainability is what determines long-term success, and for many people a moderate low-carb pattern they can follow for years beats a rigid one they abandon. Whichever you choose, prioritize food quality, monitor your glucose, and, most importantly, involve your clinician, because carbohydrate restriction frequently requires medication changes and carries specific risks worth managing. Done thoughtfully, reducing carbohydrate is one of the most effective dietary ways to improve your A1C.