Very Low Carbohydrate Diets for Diabetes (ADA 2018)
A crowd overfilled the ballroom this Sunday afternoon at the ADA 78th Scientific Sessions to hear two presentations about very low carbohydrate diets (VLCD) for diabetes.
In the first presentation, Dr. Jeannie Tay from the University of Alabama at Birmingham summarized the current knowledge on VLCD for type 2 diabetes (T2D) patients and presented new clinical trial results. In the second presentation, Dr. Martin I. de Bock of Princess Margaret Hospital discussed the limited data on VLCD for children with type 1 diabetes (T1D), including the benefits, hypothetical concerns, and areas for additional follow-up.
Study Demonstrates Health Benefits for Patients with T2D
Dr. Tay began her presentation by summarizing the available data on very low carbohydrate diets (VLCD) for patients with T2D. She defined VLCD as that containing between 20-70 grams of carbohydrate per day.
She evaluated results from randomized controlled trials (RCTs) that followed patients for at least six months and highlighted that some data showed greater A1c improvements with the approach. The researcher noted that patients also experience an increase in HDL-C levels, a reduction in triglyceride levels, and improved insulin resistance.
Dr. Tay explained that while some studies showed an increase in LDL-C levels in patients following a VLCD, other studies did not find this. She addressed that LDL-C is becoming a controversial metric to assess cardiovascular disease risk and that context is important when discussing its relevance as a risk factor. Dr. Tay noted that it is generally believed that LDL-C increases may be a result of the higher saturated fat content of some VLCD.
Dr. Tay and colleagues set out to determine how a VLCD that is also low in saturated fat (LCLSF) compares against a high carbohydrate (HC) diet for the metabolic management of patients with T2D.
RCT of HC vs. LCLSF Diet for T2D
The researcher enrolled 115 adults with T2D and obesity with a mean A1c level of 7.3 +/- 1.1% and excluded patients with pre-existing renal conditions. The patients used a variety of methods to control their diabetes, including oral agents and/or insulin. They assigned the participants to either follow a HC diet (53% carbohydrate) or a LCLSF diet (14% carbohydrate, <10% saturated fat). Importantly, the diets were identical in calorie content.
All participants followed the same exercise program and their adherence to the diet was closely followed via food logs, regular meetings with a dietician, as well as urinalysis for ketones and urea/creatinine.
The researchers compared numerous parameters between the groups, including weight, body composition, A1c and markers for cardiovascular disease risk. Furthermore, they also used CGM technology to evaluate post-prandial blood glucose control and glycemic variability. The patients were followed for two years.
Main Study Outcomes
The drop-out rate (~50%) was not significantly different between the two groups, and the researchers confirmed that the remaining participants adhered to the prescribed diets.
While the data showed a comparable reduction in A1c (~1%), weight, and similar body composition, the participants in the LCLSF group:
- Lowered their medication use by more than two-fold compared to the HC group
- Experienced a greater than two-fold reduction in glycemic variability parameters compared to the HC group
- Experienced a greater reduction in triglycerides than the HC group
Both groups experienced comparable decreases in blood pressure, insulin use, insulin resistance, and c-reactive protein levels (a marker of inflammation).
The researchers also performed a very comprehensive evaluation of renal function and cognitive performance in the subjects following the low carbohydrate approach. The researchers found no difference between the HC and LCLSF groups in any of the measured outcomes, demonstrating its safety with regard to renal function and cognitive performance.
Also, the researchers did not observe a significant difference in the LDL-C levels between the groups. Notably, the HC group experienced a significant drop in HDL levels during the study, while the HDL levels remained unchanged in the LCLSF group.
Dr. Tay stated that a very low carbohydrate diet offers a considerable advantage over a high carbohydrate approach for patients with type 2 diabetes.
She noted that reducing medication use is not only cost-effective but can also safeguard from the considerable side effects of some second-line medications. She also explained that achieving less glycemic variability, which may be an independent risk factor for the development of diabetes-associated complications, is “of great clinical importance.”
“It is a good diet to have if you have diabetes, and the data support that,” she concluded.
Endocrinologist Discusses Considerations for Children with T1D
Dr. de Bock began his presentation by describing what he believes to be the current political climate in discussing very low carbohydrate (VLC) approaches for children with T1D. “[It is] thorny, polarizing, and controversial,” he remarked. The speaker went on to explain that while he is no way against VLC approaches for children, the main purpose of his presentation was to identify putative concerns and areas that require additional study.
“I am not a denier. One can get exceptional glycemic control on a very low carbohydrate diet,” he stated, also remarking that frequent blood glucose monitoring and dosing adjustments were key to achieving the results.
Dr. de Bock believes that it is also possible to get “good control” on a high carbohydrate diet. To support this, he presented very limited blood glucose records for one teenage patient who consumes more than 300 g of carbohydrate per day, and also showed some data on pediatric A1c levels. Notably, while the A1c levels were below the average for that age group with T1D, they were still above normal.
Dr. de Bock identified five areas that he believes to be of relevance regarding the potential concerns regarding children eating a VLCD: 1) growth; 2) long-term metabolic profile; 3) bones; 4) exercise and 5) psychosocial impact and conflict. As published data specific to VLCD in children with T1D is limited, the speaker presented some data from animal studies, case studies, and children with epilepsy who followed a ketogenic diet.
Dr. de Bock did not define the specific nutrient distribution of VLCD and the data that he presented on varied greatly in the carbohydrate content, from “ketogenic” to “30% carbohydrate” for one particular case.
Since data on the exact diet composition or on glycemic control for the case study subjects that experienced adverse outcomes was not presented, it was impossible to gauge whether these could be attributed to suboptimal glycemic control or the specific macronutrient distribution.
Dr. de Bock stated that the available data on pediatric growth on a low-carb diet is contradicting and requires further investigation. His main theoretical concern is that those on a VLCD may use less insulin, and insulin is very important for numerous physiological processes, including growth. However, he did not discuss the administration of insulin to account for protein consumption, which is an important consideration. Dr. de Bock also addressed the importance of identifying any nutritional deficiencies, in particular, iron.
Long-Term Metabolic Profile
Dr. de Bock presented some data about elevated LDL-C levels in individuals on a VLCD, although the study results were variable. He stated that for those individuals who experience an uptick in LDL-C, it is unclear whether the improved glycemic control mitigates the LDL-C increase. Notably, the LDL-C metric is a controversial one and needs to be considered in the context of triglycerides, HDL, and other metabolic parameters.
Dr. de Bock pointed to some studies on children with epilepsy who followed the ketogenic diet and exhibited low bone density. He noted that individuals with T1D are prone to low bone density, so it is an important parameter to follow. Dr. de Bock did not mention the relevance of optimizing glycemic control, as chronic hyperglycemia is a relevant factor in low bone density in patients with T1D.
The speaker stated that the exercise capacity of children following a VLCD appears to be variable. He noted that some individuals do not have any problems, while others may experience fatigue. He believes the data on the subject is “inconclusive.” Careful assessment of the specific nutrient distribution of the diet to ensure appropriate nutrient intake may be at the heart of the matter.
Psychosocial Impact and Conflict
The speaker focused heavily on the potential mental and emotional implications of following a “restrictive” diet. He suggested that children (unlike adults) do not yet have the “executive thought” to make a rational decision to eat a VLCD. As such, he believes that children on a VLCD may feel deprived or resentful.
“We are a society that celebrates with food,” de Bock pointed out, as a photograph of excited children gathered around a birthday cake appeared on his presentation slide. He stated that eating cake “may or may not result in a postprandial blood glucose excursion,” depending on the management, and did not discuss that low-carbohydrate dessert recipes are widely available.
He also attempted to draw parallels between the perfectionism and idealism associated with the pursuit of very tight glycemic control on a VLCD and how these qualities are common to individuals who are at an increased risk for developing eating disorders. However, while there is no evidence to support that children on a VLCD are specifically at an increased risk for anxiety and eating disorders, there is evidence to suggest that these issues are more common in people with type 1 diabetes, in general, suggesting that they are likely related to glycemic control.
Dr. de Bock did not address the tangible concerns of suboptimal blood glucose management in pediatric patients, or the potential psychological impacts of increased anxiety, depression, and resentment that may arise from frequently abnormal blood glucose levels and the associated physiological consequences.
Dr. de Bock does not deny that a VLCD for children with type 1 diabetes can help to achieve exceptional glycemic control, as recently demonstrated in a study showing normal average A1c levels in a large cohort of patients. The speaker remarked that the patients in that study had very low glycemic variability.
He believes that more research needs to be conducted to evaluate the relevance of the potential concerns that he outlined. Until then, he advises parents of children who follow a VLCD to work closely with their medical care providers to monitor growth, cardiac, nutritional, and mental/emotional parameters.
Undoubtedly, very low carbohydrate diets for the management of diabetes have been gaining popularity and acceptance in recent years. It is difficult to deny that they constitute an effective and important tool for optimizing glycemic control for both type 1 and type 2 diabetes patients.
This symposium received considerable attention at the meeting and in social media channels. As always, we welcome your comments on the topic and hope that this review has been useful in summarizing the key points and relevant considerations in the broader context of the discussion.