A study was recently published in BMJ Nutrition, Prevention, and Health that looked at the effect of a low carb diet on people with type 2 diabetes, and specifically, whether the low carb diet could be used to reverse type 2 diabetes and normalize blood sugar levels.
Type 2 diabetes is the type that is caused by life style choices (as opposed to type 1, which is an autoimmune disease, caused by the immune system attacking the cells that produce insulin). The prevalence of type 2 diabetes has increased enormously over the last few decades, ever since governments started telling people to eat less fat and more carbohydrates.
Of course, correlation is not causation, but it seems reasonable to hypothesize that the increasing levels of type 2 diabetes seen at a population level are due to an increased consumption of carbohydrates. If that is the case, then it should be possible to cure people with type 2 diabetes, or at least lessen the severity of the disease, by getting them to decrease their carbohydrate intake.
That is the basis for this study, which was a cohort study that followed patients with type 2 diabetes at one General Practice clinic in the UK. The authors became motivated to do the study after noticing an 800% increase in the prevalence of diabetes among their patients over the course of 30 years, and after finding that standard dietary recommendations were completely ineffective at reversing diabetes.
A cohort study means that a group of people are recruited, and then followed over time to see what happens to them. There is no control group, and no randomization to different treatments. This makes it harder to say what effect an intervention has, something we will discuss more later in the article.
The study enrolled 128 patients with type 2 diabetes (27% of the total number of type 2 diabetics in the clinic) in a low carb diet treatment program, and followed them for an average of 23 months. The average age of the participants was 63 at inclusion in the study. The average weight was 100 kg and the average HbA1c was 66.
At this point we should probably do a little detour to discuss what HbA1c is. Glucose that’s floating around in our bloodstreams has a certain tendency to attach to our red blood cells. HbA1c is a measure of how much glucose the red blood cells have bound to them, which is a good proxy for the average level of glucose in the blood stream over the course of the last few months. A normal HbA1c is less than 42 mmol/mol. The limit where someone is diagnosed with diabetes is 48 mmol/mol. Between 42 and 48 is considered pre-diabetic, i.e. the person is showing signs of insulin resistance, but has not yet developed full blown diabetes.
The low carb diet program in the study involved a couple of ten minute one-to-one sessions with a doctor or nurse per year, in which patients were coached on a low carb diet. The number of such sessions varied depending on the needs of the individual, but averaged three sessions per participant per year. The participants were also given low carb guidance during their other appointments with doctors and nurses. Optional 90 minute group sessions were also offered every six weeks.
Participants were recommended to avoid cereals, pasta, rice, bread, cakes, biscuits, and tropical fruits (bananas, oranges, grapes, mangoes, pineapples). Instead they were recommended to eat meat, fatty fish, full fat dairy, eggs, nuts, vegetables, and berries (blueberries, raspberries, strawberries). Certain fruits were also considered ok, such as apples and pears.
So, what were the results?
Over the course of follow-up (average 23 months), participants mean HbA1c decreased from 65 to 48. That is a huge reduction, and it is highly statistically significant. It means that the average participant on a low carb diet was able to go from having full-blown type 2 diabetes to a state of being pre-diabetic.
All other health markers studied also improved to a significant extent. Average weight decreased from 100 kg to 91 kg. Average systolic blood pressure decreased from 144 to 133 while diastolic blood pressure decreased from 83 to 78. Those number might not mean much to many readers, but a reduction from 144 to 133 means going from being diagnosed with hypertension to having a blood pressure within the normal range. So not only did the average patient stop fulfilling the diagnostic criteria for type 2 diabetes, they also stopped fulfilling the criteria for hypertension.
One criticism of a low carb diet from proponents of standard dietary recommendations is that it increases cardiovascular disease. This is based on the cholesterol hypothesis (which we’ve already debunked earlier on this blog), i.e. the belief that if you eat more saturated fats then your cholesterol levels will go up and you will get more cardiovascular disease. If you eat less carbohydrates, you will generally compensate by eating more fat, which is why those who believe in the standard recommendations are usually against a low carb diet.
That is why the doctors who performed this study measured the cholesterol levels of the participants. What did they find?
Total cholesterol decreased from 4,9 to 4,4 mmol/l, while HDL (so-called “good cholesterol”) increased from 1,2 to 1,3 mmol/l. At the same time triglycerides (fats in the blood stream) decreased from 2,6 to 1,7. Basically, all markers for cardiovascular disease moved in the right direction, not the wrong direction. So, it seems that the fears of proponents of standard dietary advice are unfounded.
It didn’t matter whether participants had had type 2 diabetes for a long time or a short time, or whether they had full blown diabetes or were just pre-diabetic, or whether they were older or younger. Everyone benefited from the low carb diet, and the biggest benefit was seen in those participants with the highest HbA1c at the start of the intervention.
Among the participants in the study, 29 diabetes medications were stopped, while four were started. 54 participants were on diabetes medications at the start of the study, and of these, 19 were able to become completely medication free. So overall, there was a big reduction in use of diabetes medications among participants. And apart from the reduction in diabetes medications, there was also a 20% reduction in the use of blood pressure medications.
Among the participants who had type 2 diabetes at the start of the intervention, 46% were in drug free remission at the end of the intervention (in other words, they had been cured of their type 2 diabetes, since they no longer fulfilled the criteria for it). In a normal GP practice offering standard dietary advice and regular treatment routines, only 2% are in drug free remission after two years.
What can we conclude?
First of all, there are weaknesses with this study. The biggest weakness is that there was no control group. Without that, we can’t say what would have happened to a group that was getting some kind of sham placebo treatment, and we can’t say how big the benefit of low carb is when compared with that.
On the other hand, most doctors who treat people with type 2 diabetes would probably agree that it’s relatively rare to see people go in to disease remission. As stated, only 2% are in drug free remission after two years with standard recommendations. And, in general, in a group of patients with type 2 diabetes, the number of medication prescriptions increases over time, it doesn’t decrease. That does suggest that the low carb intervention is effective.
A second problem with the study is that there was significant risk of selection bias. Participants who choose to take part in a study are usually more motivated than the average patient, so the benefit seen is often greater than would be seen in the real world. That being said, the results from this study are so impressive that, even if the real world results are much smaller, that could still mean huge health gains for a lot of people.
This study should be followed up by a large randomized controlled trial, in which participants with type 2 diabetes are randomized to either a low carb diet or standard dietary recommendations and followed for a few years, in order to confirm the results and get a clearer idea of what benefits can be expected. Although such trials have been performed earlier, they have invariably been small and/or short term. In the meantime however, I do think it makes sense for people with type 2 diabetes to try the low carb diet that was used in this study, after consultation with their primary care provider, of course, and see what happens.
You might also be interested in my article comparing a low carb vs a low fat diet for weight loss or my article about why deprescribing medications is so important for health in the elderly.