Can a ketogenic diet lower blood sugar?
Well, it depends. There’s a study on the “Effect of a Low-Carbohydrate Diet on Appetite, Blood Glucose Levels, and Insulin Resistance in Obese Patients with Type 2 Diabetes” (1) that looked at a a small group of obese patients with type 2 diabetes and gave them a carefully monitored low-carbohydrate diet followed for 2 weeks. It resulted in some substantial reduction in circulating blood glucose along with some weight loss and some other benefits.
This study was based on something akin to the popular “Atkins” diet – a true low-carb diet that is supposed to be low enough in carbs to start the process of ketosis and ketone generation. And, indeed, the patients in this study dramatically increased their ketone production (and ketone excretion) – as predicted by Dr Atkins. And, since ketones are produced by the liver during gluconeogenesis, it means that the dietary carbs were less than needed to maintain normal blood sugar.
So, does this study show that a ketogenic diet can lower blood sugar? Yes, but with some qualifications -
- The participants were diabetic which means they already had some deficiency in either the production or effectiveness of insulin in controlling blood sugar level;
- Their pre-study blood sugar levels were higher than normal (mean of 135 mg/dL);
- Their post-study levels were much lower (mean of 113 mg/dL), but still higher than “normal” – the dramatic reduction in dietary carbs increased gluconeogenesis, and insulin production or effectiveness could not completely regulate it to “normal”
My interest in lowering blood sugar level is to start denying nutrition to a tumor, and I’m convinced that that only starts happening when circulating glucose is reduced substantially below “normal.” This study doesn’t really illustrate that a ketogenic diet can accomplish that. I’m not saying that it can’t, just that this study hasn’t shown it.
At the other end of the human based studies is this case report on “Metabolic management of glioblastoma multiforme using standard therapy together with a restricted ketogenic diet” (2) - it’s a rather extreme case of someone with advanced brain cancer who, immediately following a surgery that removed only part of the tumor, put herself on an extreme version of a ketogenic diet in conjunction with standard radiation and chemo therapy. I characterize the diet as extreme, because it was initiated with two water fasts, each more than 24 hours and then sustained with a 600 calorie per day diet that had a very high ratio of fats to carbs & protein (more about that ratio later).
Her blood glucose was 7.5 mmol/L (130 mg/dL) at the start and urine showed no detectable ketones. The plot to the right (from the study) traces her blood glucose and ketones for the first three weeks of this regimen. She continued on this diet for several months only varying the mix of fats, carb and proteins to respond to shortages identified in ongoing testing.
The study did not provide an extended graph illustrating the longer term trends in blood glucose and ketones except to say that “the patient did not experience hypoglycemia (blood glucose levels below 45 mg/dl) at any time during the course of fasting or ketogenic diet therapy.” I take that to mean that the black line in the diagram probably leveled out between 2.5 and 3.3 mmol/L (45-60 mg/dL) which is what I’ve started thinking of as “near hypoglycemia.”
Since “normal” blood glucose is between 70 and 100 mg/dL, and this patient’s “normal” was significantly higher (130 mg/dL), this diet really had a dramatic and significant effect and successfully lowered blood sugar significantly below normal.
It’s worth noting that as some point in this case study, the mix of nutrients were adjusted to be less carb and protein restricted and more just calorie restricted (still maintaining the 600 kcal/day). The only effect was a slight reduction in urinary ketones but clearly still maintaining a ketone based metabolism. No surprise here – even if all 600 calories per day were coming from carbs she would still have to be burning some fat to satisfy daily energy needs.
It’s also worth noting that the diet really had an impact on the cancer. According to the case report, the prognosis for this patient was not good -
Long-term progression free survival remains low for most GBM patients even after complete surgical excision, combined with the best available treatment . Standard therapy for GBM includes surgery followed by concomitant radiation and/or chemotherapy. These procedures, however, extend median survival by only a few months beyond the no therapy option .
But less than three months into the diet, after an MRI, “No evidence of either the tumor or the associated edema was apparent” and “On April 21, the patient underwent positron emission tomography with fluoro-deoxy-glucose (FDG-PET), which included delayed acquisition. No evidence of recurrent disease was detected (Figure 5). An MRI, performed on July 22, was stable over the comparison time from February 24 with no clear evidence of disease recurrence.” Unfortunately, the patient went off the low calorie diet in July and a relapse followed in October.
So, does this case report show that a ketogenic diet can lower blood sugar? Even below “normal” and maybe enough to starve cancer? Yes. Maybe even a resounding YES! But again with some qualifications -
- It’s clear that the extreme nature of this diet, especially the calorie restriction to 600 kcal/day, contributed to the high rate of ketone production. The causality is less clear but a high presence of ketones is likely correlated with a reduced level of blood glucose.
- This was not a test of lowered blood glucose vs cancer. The cancer was treated with surgery, radiation, and chemo – the diet was supplemental. And this particular type of cancer is highly glucose dependent – as are many, if not most (but not all) cancer tissues.
- It’s not clear that this diet can be sustained long term. This patient clearly had remarkable self-control and determination just to maintain it for the time she did – I’m not sure many others could do the same. And the patient lost 20% of her body weight in six months and would likely have kept losing if the 600 kcal/day diet had to be maintained – that’s probably not sustainable.
- Boden MD et al., Effect of a Low-carbohydrate Diet on Appetite, Blood Glucose Levels, and Insulin Resistance in Obese Patients with Type 2 Diabetes: American College of Physicians, 2005 March, Vol 142, Num 6, 403-412
- Zuccoli et al., Metabolic management of glioblastoma multiforme using standard therapy together with a restricted ketogenic diet: Case Report Nutrition & Metabolism 2010, 7:33