Low Calorie vs Low Carbohydrate Diets for Type 2 Diabetes: Evidence-Based Comparison
Type 2 diabetes has reached epidemic proportions affecting more than 400 million adults worldwide (1). It is strongly linked to weight gain in adult life and accumulation of excess fat within the liver and the pancreas. Foresight reports indicate that over half of the population in the UK could be obese by the year 2050 (2). With this anticipated rise in adult obesity, it is predicted that the incidence of type 2 diabetes could be greater than 70% by 2050 (2).
What Does the Reversal of Diabetes Actually Mean?
Whilst there is no definitive cure for diabetes, it can be reversed or placed into remission. If left untreated, type 2 diabetes can progress resulting in complete destruction to the beta cells in the pancreas. However, given the correct treatment, it can be reversed or placed into remission.
But what does remission actually mean? It’s when blood glucose levels are within the normal range again and generally no diabetes medications are required (3).
Options for Reversing Type 2 Diabetes
Bariatric surgery has dominated the discussions of type 2 diabetes remission but this option carries a high financial cost and the risk of long-term health problems.
Bariatric surgery is believed to be successful due to the amount of weight loss it can initiate. Previous research has shown that if individuals can lose more than 10% of their body weight, their diabetes can be reversed (4).
Researchers have therefore been studying other dietary options that could mimic the type of weight loss seen within bariatric surgery.
Most recently, a randomised controlled trial from researchers in the UK looked to assess whether placing individuals on a low calorie diet could produce sustained remission of type 2 diabetes (5).
Known as the Diabetes Remission Clinical Trial (DiRECT), participants were asked to follow a low energy formula diet (825-853 kcal/day; 59% carbohydrates, 13% fat, 26% protein, 2% fibre) made up of four soups and/or shakes, for three months (this could be extended to 5 months if the participants wanted this). Followed by structured food reintroduction of 2–8 weeks (around 50% carbohydrates, 35% total fat and 15% protein) with an ongoing structured programme and monthly visits for long-term weight loss maintenance.
The results showed that almost half of the participants were able to place their diabetes into remission after 1 year. Taking a deeper look, they found that those individuals who lost the most weight had a greater chance of entering remission.
These results have prompted chiefs within the NHS England to commission the roll-out of the prescription of the dietary approach to 5000 patients (6).
Is a Low Calorie Diet the Best Approach for Reversal of Type 2 Diabetes?
Whilst these results may sound encouraging, is this really the best and only form of dietary approach that should be prescribed to diabetic individuals?
The DiRECT Study
To better understand this question, we need to take a deeper dive into the DiRECT study. Firstly, the diet that was prescribed to people was that of a low calorie diet. Generally speaking, most adults of normal weight will consume anywhere between 1500-2500 kcal/day. In this study, people were asked to consume just over 800 kcal/day (830 kcal). What is interesting to note is the definition of low calorie (LCD) vs very low calorie diets (VLCD). According to NICE guidelines a LCD is classed as 800–1600 kcal/day whereas a VLCD is classed as ≤800 kcal/day (7).
Their guidelines on using a VLCD states: “Do not routinely use very-low-calorie diets (800 kcal/day or less) to manage obesity (defined as BMI over 30)”. The guidelines go on to say: “Tell them that this is not a long-term weight management strategy, and that regaining weight may happen and is not because of their own or their clinician's failure.”
The difference between the DiRECT study and a VLCD appears to be that of 30–50 kcal. Are these added calories truly enough to result in long term weight loss and not carry any of the risks associated with a VLCD? As is known and acknowledged by the researchers of this study, returning to previous food choices will cause a weight re-gain and a new ‘normal’ of food choices is a necessity.
The DiRECT Study and Long-Term Results
This brings us onto the next aspect of following this type of dietary approach — how do you maintain this in the long-term? The researchers of the DiRECT study have tried to address this by adding in a structured food reintroduction of 2–8 weeks and an ongoing programme with monthly visits for long-term weight loss maintenance.
Unfortunately, there are no details within the methodology explaining what is contained within either of these re-introduction phases. Without knowing the specifics of the phases, it is hard to say if the results observed can truly be transferred into the real-world setting.
Although the study does not report on the re-introduction, a hypothesis can be determined based on the weight loss phase. Individuals following this approach will more than likely need to maintain a state of calorie counting for life. By the researchers own admission and detailed above, if old eating habits are returned to, weight re-gain will occur (8).
The DiRECT Study and Food Quality
Next, let’s take a look at how the calories were made up. These calories were in the form of a liquid formulation, meaning it was not coming from real, whole food. Carbohydrates provided over half of the energy content at 59%, protein at 26% and fat at 13%. If we calculate this out into grams per day we can see people had – 118 g of carbohydrates, 52 g of protein and only 12 g of fat.
Although the authors termed the diet as “nutritionally complete” (meaning all essential nutrients were provided), there is no information on how these macronutrients were made up. For example, the fat sources (albeit very little) included, were they good quality fat sources or ones that are more pro-inflammatory to the body such as omega-6’s? As with the carbohydrate sources provided, were they based on high glycemic index values (GI) which could in fact have more impact on the pancreas and thus diabetes?
Whilst we know that the quantity of the food contained within your diet is important, so too is the quality of the food sources to the health of your body.
The researchers from DiRECT have developed a programme to mimic the diet in the study with a food-based approach (8). The diet has been termed the “no doubts diet” and shows how it can be followed without the pre-packaged sachets.
Although this low calorie diet approach is using real food, the options are still very restrictive and predominantly feature liquid based options e.g. soup for lunch and dinner. The calorie content of the no doubts diet is also based on 850 kcal and advises following the approach for three months in order to lose 15 kg. Similar to that of the study though, there is no consistent information on what happens after these three months and how long-term maintenance is ensured.
Is There Another Dietary Option to Put Type 2 Diabetes into Remission?
Although the results of the DiRECT trial appear to offer a solution for diabetes remission, is this really the best dietary approach to follow?
As a part of the study, an online search of clinical evidence was carried out using the search terms “diabetes and remission” and “clinical trial” between the years of 1980 to 2017. No trials were identified leading the authors to conclude that there exists no evidence of a dietary approach for the remission of type 2 diabetes.
Low-Carbohydrate Diets for Reversal of Type 2 Diabetes
However, contrary to this conclusion, in 2005 one of the first pilot studies testing a low carbohydrate, ketogenic diet was initiated (9). A total of 21 participants were asked to follow a low carbohydrate diet (<20 g) for a period of 16 weeks. The results showed not only a significant decrease in body weight (6.6%; p<0.001), but a significant reduction in HbA1C (decreasing from 7.5% to 6.3%; p<0.001), with 17 out of the 21 participants reducing or completely eliminating their need for diabetes medications.
By definition, this pilot study would indicate that a low carbohydrate diet can indeed induce diabetes remission. What is more interesting to note is regression analysis showed that the reduction in HbA1c was independent of weight loss.
Since this study, there have been a total of 11 randomised clinical trials carried out on the use of the low carbohydrate diet within diabetic individuals (10). Although all had variations in the methodology, the results were consistent in showing the positive impact that the diet has on weight loss, insulin levels and glycemic control; ultimately resulting in diabetes remission in a vast amount of individuals.
In 2008 the American Diabetes Association (ADA) acknowledged that a low carbohydrate diet may be effective for weight loss and glycemic control in diabetic individuals (11). However, there is still some controversy around this type of dietary approach with many debating the short and long term safety of the approach.
Are Low-Carb Diets Easier to Follow Long-Term?
One of the biggest criticisms about following a low carbohydrate diet is its impact in the long term, particularly being able to follow it for a long period of time. However, a long-term study showed almost 90% of participants were able to adhere to a low-carbohydrate diet for up to two years (12). The follow-up period within the DiRECT study was only 12 months but the authors concluded that this is able to demonstrate long-term maintenance.
Most recently, an open-label study looked at the impact of a digitally delivered low-carbohydrate type 2 diabetes self-management program in over 700 people (13). Included in the program was education around carbohydrate restriction using behavioural techniques, including goal setting, peer support and behavioural self-monitoring. The results showed that over 40% of people were able to reduce or eliminate the amount of diabetes medications they were taking.
Can We Really Say a Low Calorie Diet is Best for Diabetes Remission?
Although the spotlight is currently being placed on the use of a low calorie approach for diabetes remission, the question comes back to is this really the best option?
Current guidelines focus primarily on the use of pharmacotherapy, with diet and lifestyle mentioned as an adjunct to this. However, we know that certain diabetes medications can actually cause further issues with weight gain and many side-effects (14).
The DiRECT study does appear to show promising results of being able to place diabetes into remission for at least half of the people that followed the diet. But in order for this to occur people have to:
- Follow a very restrictive diet of only 800 kcal per day
- Have a diet that is predominantly based on liquid foods or powered sachets if being prescribed these (which contains an unknown amount of added food stuff)
- Continuously count calories to ensure that weight re-gain does not happen
- Not be able to eat-out or socialise whilst in the weight loss phase
Whilst some may be able to follow the above, for many this would not be an approach that is sustainable in the long term. Regardless of the dietary approach you follow, we know that in order for something to work long term it needs to fit in with your lifestyle.
Take Home Message
Although there is no dietary approach that is a true silver bullet, the evidence that is mounting for a low carbohydrate approach for use in type 2 diabetes is vast.
The common concerns of using a low carbohydrate approach in the long-term is comparable to a low calorie approach. If the results of the DiRECT study are enough for NHS chiefs to implement this as a pilot, then the argument for using a low carbohydrate dietary approach is warranted now more than ever.
We know that for a diet to become a full lifestyle change, it has to meet the unique parameters of each individual — there is no one size fits all. For some, using the low calorie diet may be sufficient, but for many this may not be sustainable or what is best for them. Therefore, offering them a dietary approach that can still provide powerful results for diabetes remission should be made available.
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