Of all the reasons people try a ketogenic diet, blood sugar is one of the best studied. Type 2 diabetes is, at its heart, a problem with how the body handles carbohydrate, so it makes intuitive sense that eating far less of it would help. The good news is that this is not just intuition. There is a sizeable body of trial evidence, and in 2025 researchers pulled much of it together in one place.
The study, in brief
A team led by Yan and colleagues published what is called an umbrella review in the journal Diabetology and Metabolic Syndrome. Rather than running a new trial, they gathered 21 existing meta-analyses, each of which had itself combined the results of many randomised controlled trials, and looked at what the weight of evidence says about low-carbohydrate, very-low-carbohydrate and ketogenic diets for blood sugar control in people with type 2 diabetes. Stacking the reviews up like this gives a broad view across thousands of participants.
What they found on blood sugar
The headline measure for long-term blood sugar is HbA1c, which reflects your average glucose over the previous few months. Sixteen of the 21 reviews found that cutting carbohydrate produced significant reductions in HbA1c, with the other four finding no significant change. That is a clear majority pointing the same way. People also tended to see improvements in body weight alongside the better glucose readings, which is part of how the effect works.
The honest part: time matters
Here is the finding that an enthusiastic blog would skip and that you deserve to know. The improvements were strongest in the short term, over roughly three to six months, and they tended to fade with time. In some studies the advantage over a normal diet had largely disappeared by the two-year mark. This is not a reason to dismiss the approach, but it reframes it. A low-carb or ketogenic diet looks like a genuinely effective tool for getting blood sugar down, especially early on, rather than a permanent fix you do once and forget.
The likeliest reason is not that the biology stops working but that the diet gets harder to stick to over years. The benefit depends on keeping carbohydrate low, and life has a way of eroding strict eating plans. That points to the real challenge being sustainability rather than effectiveness.
Why it works
The logic is straightforward. Carbohydrate raises blood glucose more than fat or protein, so eating very little of it means smaller glucose rises to manage, less demand on whatever insulin response a person still has, and over time often some weight loss, which itself improves insulin sensitivity. Our beginners guide explains how the diet shifts the body towards burning fat for fuel, and it is that same shift that eases the carbohydrate load the body has to cope with.
What this means in practice
The most important point is one of safety rather than diet design. If you take medication for type 2 diabetes, particularly insulin or sulfonylureas, cutting carbohydrate sharply can lower your blood sugar enough to cause a hypo if the medication is not adjusted to match. This is genuinely something to manage with the doctor or team who prescribe for you, before and during any big change in how you eat, not afterwards. People do reduce or come off medication under supervision, but the supervision is the point.
Beyond that, the research supports keto as a reasonable, evidence-backed option worth discussing for blood sugar, with realistic expectations: a strong likelihood of better readings in the first months, a real question mark over how well that holds across years, and an outcome that rests heavily on whether the way of eating fits your life. Keeping your electrolytes in order in the early weeks makes the diet far easier to stay on, which, given that adherence is the weak link, matters more than it might seem.
The bottom line
A 2025 synthesis of 21 reviews found that low-carbohydrate and ketogenic diets significantly improve blood sugar in type 2 diabetes for most people, with the clearest gains in the first few months and weaker evidence that the advantage lasts for years. Used with medical support and an eye on medication, it is a credible tool, not a miracle, and its long-term value lives or dies on whether you can keep it up.
This is general information about the ketogenic diet, not medical advice. If you have type 2 diabetes, especially if you take any glucose-lowering medication, do not change your diet without talking to your doctor or diabetes team first, because your medication may need adjusting to avoid dangerously low blood sugar.
Source: Yan Y, Asemani S, Jamilian P, Yang C. The efficacy of low-carbohydrate diets on glycemic control in type 2 diabetes: a comprehensive overview of meta-analyses of controlled clinical trials. Diabetology and Metabolic Syndrome. 2025;17:341. Read it here.