Management of type 1 diabetes with a very-low-carbohydrate diet: a survey of patient outcomes

Abstract

Objective

The aim of this study was to evaluate glycemic control among children and adults with type 1 diabetes consuming a very-low-carbohydrate diet.

Methods

We conducted an online survey of an international social media group for people with type 1 diabetes following a very-low-carbohydrate diet. Respondents included adults, and parents of children, with type 1 diabetes. We assessed current Hemoglobin A1C (HbA1C) (primary measure), change in HbA1C after the self-reported beginning of the very-low-carbohydrate diet, total daily insulin dose, and adverse events. We obtained confirmatory data from diabetes care providers and medical records.

Results

Of 316 participants, 131 (42%) were parents of children with type 1 diabetes, 57% were female. Suggestive evidence of type 1 diabetes (based on a 3-tier scoring system taking into consideration age and weight at diagnosis, pancreatic autoimmunity, insulin requirement, and clinical presentation) was obtained for 273 (86%). Mean age at diagnosis was 16 ± 14 years, duration of diabetes was 11 ± 13 years, and time following a very-low-carbohydrate diet was 2.2 ± 3.9 years. Participants reported a mean daily carbohydrate intake of 36 ± 15 grams. Reported mean HbA1C was 5.67 ± 0.66%. Only 7 (2%) reported diabetes-related hospitalizations in the past year, including 4 (1%) for ketoacidosis and 2 (1%) for hypoglycemia.

Conclusion

Exceptional glycemic control of type 1 diabetes with low rates of adverse events was reported by a community of children and adults consuming a very-low-carbohydrate diet. The generalizability of these findings requires further studies, including high quality randomized-controlled trials.

Table of Contents Summary

Among 316 participants with type 1 diabetes following a very-low-carbohydrate diet, mean HbA1C was 5.67%, with low rates of hypoglycemia and other acute complications.

INTRODUCTION

Before the discovery of insulin, the lives of children with type 1 diabetes (T1DM) were extended, sometimes for years, by severe carbohydrate restriction.(1) After the advent of insulin treatment, recommended carbohydrate intake increased without clinical trial proof of superiority in outcomes. By the 1980s, a low-fat diet containing up to 60% of energy from carbohydrate became standard of care.(2) More recently, the American Diabetes Association (ADA) has emphasized individualization of diet rather than a focus on macronutrients.(3)

Despite major medical and technological advances, management of T1DM remains suboptimal. With an average overall HbA1C of 8.2%, only 20% of children and 30% of adults achieve the glycemic targets of HbA1C less than 7% for adults and less than 7.5% for children and adolescents, as set forth by the ADA to reduce long-term complications.(4) The greatest challenge in this regard involves difficulty controlling postprandial glycemia, a major determinant of HbA1C.(5) Even with modern insulin analogues and technical advances, a mismatch between carbohydrate absorption and insulin action typically exists after meals. Beyond a point, measures to lower postprandial hyperglycemia inevitably increase risk for hypoglycemia, with potentially life-threatening consequences.(6–9)

The source and amount of carbohydrate consumed affect postprandial hyperglycemia and glycemic variability more than any other dietary factor,(3, 10–12) providing a conceptual basis for interest in carbohydrate-modified diets for T1DM management. Regarding carbohydrate source, a low- vs. high-glycemic index diet reduces HbA1C moderately, by about 0.5%.(13) Case series and pilot studies suggest more substantial improvements in HbA1C and other benefits (less hypoglycemia, reduced glycemic variability) with a very-low-carbohydrate (VLC) diet, commonly defined as less than 50 grams carbohydrate intake per day.(14–21) However, small sample sizes and methodological issues limit the significance of these findings, and little is known about prevalence, practice, and sustainability of VLC diets for those with T1DM. In the absence of larger studies in pragmatic settings, VLC diets are generally discouraged out of concern for potential ketoacidosis, hypoglycemia, dyslipidemia, nutrient deficiency, growth failure in children, and sustainability.(22, 23) The aim of this study was to characterize glycemic control and acute adverse events among children and adults who have adopted this approach for the long-term management of T1DM.

METHODS

Design

Using an online survey, we collected primary data from participants and confirmatory medical information from a secondary survey to their health care providers or review of their medical records. Our goals were to: 1) establish that adult respondents and children for whom an adult respondent completed the survey (both henceforth referred to as “participants”) were formally and accurately diagnosed with T1DM; 2) characterize glycemic control (HbA1C, total daily insulin dose, average blood glucose concentrations and the standard deviation as measured by a continuous glucose monitor [CGM] or glucose meter); 3) determine adverse event rates (ketoacidosis, hypoglycemia, diabetes related hospitalizations and emergency room visits); 4) assess anthropometrics (weight, height, body mass index [BMI]) and metabolic health parameters (serum lipids); 5) compare longitudinal changes in glycemic control (pre- to post- VLC diet); and 6) characterize participants’ satisfaction with their diabetes management and relationship with the healthcare system. The study was approved by the Boston Children’s Hospital Institutional Review Board and registered at clinicaltrials.gov: NCT02839174. Electronic consent was obtained from respondents.

Participants and enrollment

A volunteer sample was recruited from TYPEONEGRIT, a “closed” online Facebook community for people with T1DM following a VLC diet and diabetes management method as recommended in the book “Dr. Bernstein’s Diabetes Solution”.(20, 24) This method comprises a VLC diet with weight-based carbohydrate prescription of up to 30 grams per day, derived from fibrous vegetables and very low glycemic index nuts. High protein foods with associated fat are substituted for carbohydrate and adjusted based on outcomes, including glycemic control and weight. Participants adhere to a structured meal plan and adjust bolus insulin empirically according to postprandial glycemia. Basal insulin is adjusted according to fasting glycemia. The group was established in April 2014, with approximately 1900 members at the time of the survey.

We used an Eligibility Survey to community members between September and November 2016. Members age 18 years or older were eligible if they or a child in their care satisfied three self-reported criteria: having T1DM, receiving insulin therapy, and consuming a carbohydrate-restricted diet for at least three months. Women who were pregnant or breastfeeding were excluded. Of 493 Eligibility Survey responses, 414 (84%) individuals were eligible to participate and, 316 (76%) provided sufficient information to be included in the study (Figure 1). With respondent permission, we contacted 182 providers; 97 (53%) completed the full or short provider survey. Of 238 participants who agreed to provide medical records, 101 records were received. Primary data acquisition continued until January 2017. Confirmatory medical information was collected until March 2017.

Figure 1. Enrollment.

* The primary endpoint, current HbA1C, was available in the appropriate timeframe (at least 3 months after starting the VLC diet) for 300 participants. Data from all 316 eligible participants are included in the other analyses.

Data collection and categorization

Where possible, survey questions were modified from the T1D Exchange clinical registry (https://t1dexchange.org/pages/resources/our-data/studies-with-data)(25), and covered several domains: 1) diabetes diagnosis and treatment; 2) diet; 3) insulin regimen; 4) other diabetes-related care; 5) glycemic control, 6) diabetes complications; 7) general health and healthcare; 8) patient-diabetes care provider interactions; and 9) socio-demographics (see Supplement). Respondents were asked to provide consent so that their or their child’s primary diabetes care provider could be contacted, or to provide confirmatory medical records themselves. Data were collected and managed using Research Electronic Data Capture (REDCap, Version 7.3.5, Vanderbilt University, Nashville, TN) tools hosted at Boston Children’s Hospital.(26)

Ascertainment of T1DM diagnosis

We created a 3-tiered scoring system to ascertain T1DM diagnosis with varying levels of confidence, using participant-reported and confirmatory medical information. Participants were classified as having Diagnostic Evidence of T1DM if they had a diabetes diagnosis at age < 20 years, a non-obese body weight (BMI < 30 kg/m² in adults or BMI standard deviation score (SDS) < 1.645 [~ 95th percentile] in children), and positive diabetes antibodies. A classification of Strong Evidence was assigned for participants with a diabetes diagnosis at age < 10 years; or diagnosis between age ≥10 and <20 years, immediate insulin requirement and a non-obese body weight; or diagnosis between age ≥20 and <40 years, immediate insulin requirement, positive diabetes antibodies and a non-obese body weight. A classification of Suggestive Evidence was assigned for participants with a diagnosis at age ≥20 and <40 years, immediate insulin requirement, a non-obese body weight, and one additional factor (including low c-peptide at diagnosis, physician-specified diagnosis of T1DM, or other evidence [abrupt onset with consistent symptoms, history of ketoacidosis, or negative genetic tests for Maturity Onset Diabetes of Youth (MODY)]); or diagnosis at age >40 years, immediate insulin requirement, a non-obese body weight, and positive diabetes antibodies or one of the mentioned additional factors.

Statistical analysis

Analyses were performed using SAS v9.3 (SAS Institute Inc., Cary, NC, USA). A nominal p < 0.01 was used to define the threshold of significance.

To assess agreement between data sources, we performed Lin’s concordance correlation between patient-provider pairs of each clinical measurement. The following statistical comparisons were made according to an a priori analysis plan. Comparisons between participants were made by independent sample t-test or chi-squared test for participants with vs. without confirmatory medical information and adults vs. children. Within-subject, paired, two-tailed T-test was used for pre-and post-diet data and height SDS comparison. Multiple comparisons for diagnostic evidence groups were made by ANOVA. We performed a linear regression of current self-reported HbA1C on age, years with diabetes, years on VLC diet, carbohydrate intake goal, educational status, and income class.

Post-hoc analyses were performed with Pearson’s correlation between pediatric height SDS and carbohydrate intake, and by Wilcoxon signed-rank test and McNemar’s test to compare participant- and provider satisfaction data.

RESULTS

Participants

Descriptive characteristics are listed in Table 1. Most participants were from the US, Canada, Europe or Australia, 57% were female, 42% were children, 88% were white non-Hispanic; 84% of respondents completed college or the equivalent. Mean age at diabetes diagnosis was 16 ± 14 years, duration of diabetes was 11 ± 13 years, and time following a VLC diet was 2.2 ± 3.9 years.

Table 1.

Participant-reported Descriptive Characteristics

Characteristics	No. Responses	Finding
Anthropometrics
Female, No. (%)	281	161 (57)
Age, mean ± SD, y	316	27 ± 19
Pediatric, No. (%)	316	131 (42)
Height SDS, mean ± SD	272	0.37 ± 1.1
BMI (adult), mean ± SD, kg/m2	168	24 ± 3
BMI SDS (pediatric), mean ± SD	106	0.44 (0.96)
Diabetes related Data
Age diagnosed, mean ± SD, y	316	16 ± 14
Years with T1DM, mean ± SD, y	316	11 ± 13
Diagnostic Category
Diagnostic evidence of T1DM, No. (%)	316	85 (27)
Strong evidence of T1DM, No. (%)	316	153 (48)
Suggestive evidence of T1DM, No. (%)	316	35 (11)
T1DM unascertained, No. (%)	316	43 (14)
HbA1C at diagnosis, mean ± SD, %	173	11.20 ± 2.72
Diet
Years on VLC diet, mean ± SD, y a)	313	2.2 ± 2.9
Use of a specific carbohydrate intake goal, No. (%)	313	223 (71)
Carbohydrate intake goal, mean ± SD, g	223	36 ± 15
Goal achieved, mean ± SD, days/wk	216	6.4 ± 1.0
Sociodemographic, No. (%)
Country	284
USA/Canada		193 (68)
Europe/UK		40 (14)
Australia		36 (13)
Other b)		15 (5)
Race/Ethnicity	284
White, non-Hispanic		250 (88)
Hispanic or Latino		8 (3)
Black		0 (0)
Asian		2 (1)
Other		24 (8.5)
Education	283
Primary or less		1 (0.4)
Secondary		13 (5)
Upper-/post secondary		31 (11)
Tertiary		238 (84)
Income	284
Lower		22 (8)
Middle		200 (70)
Upper		62 (22)
Diabetes Care Provider Subspecialty	288
Endocrinology		234 (81)
Pediatrics/Family Medicine		38 (13)
Other		16 (6)

^a)Median 1.7 years, range: 0.2–31.7 years

^b)New Zealand, South Africa, UAE, Saudi Arabia, Singapore, Israel, India, Aruba

Validation of participant-reported data

Confirmatory medical information (from providers and/or medical record) was available for 148 (47%) participants (Figure 1; eTable 1). Participant and provider-reported data showed good agreement for relevant clinical variables. Participants with and without confirmatory medical information did not differ (eTable 2). Therefore, only participant-reported information is reported below.

Ascertainment of T1DM

At least Suggestive Evidence for T1DM was reported by participants or providers in 273 (86%), at least Strong Evidence was reported in 238 (75%), and Diagnostic Evidence was reported in 85 (27%). Evidence was unavailable for 36 (10%), and 7 (2%) did not satisfy criteria only because of obesity (Table 1). Apart from expected differences related to the scoring system (e.g., age, age at diagnosis, obesity), participants with and without supportive evidence of T1DM did not differ (eTable 3). Therefore, data of all participants regardless of evidence category are presented together.

Clinical outcomes

Participants reported a mean daily carbohydrate intake of 36 ± 15 grams, n=223. Mean participant-reported current HbA1C was 5.67 ± 0.66% among the 300 who provided this information in the acceptable timeframe (Table 2, Figure 2) and 97% of participants achieved the ADA glycemic targets. Participant-reported change in HbA1C from pre- to post- VLC diet was −1.45 ± 1.04% (n = 127, p<0.001). Average participant-reported blood glucose by CGM was 104 ± 16 mg/dL, (n = 137) with a low SD of 28 ± 12 mg/dL (n =115). In the regression analysis, a priori covariates explained little of the variation in HbA1C (r²=0.06). Carbohydrate intake goal was the only significant predictor (F=10.4, p=0.001), with an increase in HbA1C of 0.1% per 10 grams of carbohydrate consumed (eTable 6). Mean daily insulin dose was 0.40 ± 0.19 units/kg/day.

Table 2.

Participant-reported Clinical Variables

Clinical Variables	No. Responses	Finding
Glycemic control
HbA1C, mean ± SD, %	300	5.67 ± 0.66
CGM avg., mean ± SD, mg/dl a)	137	104 ± 16
CGM SD, mean ± SD, mg/dl a)	115	28 ± 12
Blood Glucose Meter avg., mean ± SD, mg/dl b)	77	106 ± 21
Blood Glucose Meter SD, mean ± SD, mg/dl b)	36	36 ± 35
Insulin daily dose, mean ± SD, units/kg/d	282	0.40 ± 0.19
Insulin percent basal, mean ± SD, %	198	64 ± 21
Adverse Events
Diabetes related hospitalizations, No. (%), persons/year d)	300	7 (2)
DKA		4 (1)
Hypoglycemia		2 (1)
Other		4 (1)
Diabetes related emergency encounters, No. (%), persons/year d)	301	10 (3)
DKA		3 (1)
Hypoglycemia		2 (1)
Other		7 (2)
Hypoglycemia with seizure/coma, No. (%), persons/year	298	7 (2)
Hypoglycemia requiring help from others, No. (%), adults/year e)	174	20 (12)
Hypoglycemia requiring glucagon, persons/year	299	11 (4)
Symptomatic hypoglycemic episodes, No. (%), persons/month	297
0		92 (31)
1 to 5		112 (38)
5 to 10		40 (13)
10 to 20		30 (10)
21 or more		23 (8)
Monthly symptomatic hypoglycemic episodes, mean (SD), n	101	6.1 (8.5)
Lipids e)
Total cholesterol, mean ± SD, mg/dl	79	234 ± 89
Total cholesterol ≥ 200 mg/dl, No. (%)		47 (60)
LDLc, mean ± SD, mg/dl	81	147 ± 83
LDLc > 130 mg/dl, No. (%)		39 (48)
HDLc, mean ± SD, mg/dl	80	74 ± 21
HDLc < 35 mg/dl, No. (%)		0 (0)
Triglycerides, mean ± SD, mg/dl	81	74 ± 37
Triglycerides > 150 mg/dl, No. (%)		5 (6%)
Dyslipidemia (TC > or LDLc > 130 or HDLc <35 mg/dl)	82	51 (62)

^a)obtained over 20 ± SD 18 days

^b)obtained over 20 ± 18 days, 8 ± 3 measurements per day

^c)Data overlap as some participants report events in different categories

^d)Only assessed in adults as help from others is always required in children

^e)Low-density lipoprotein Cholesterol (LDL-c), High-density lipoprotein Cholesterol (HDL-c); fasting

Figure 2.

HbA1C distribution, adult (light grey) and pediatric (dark grey) age group.

Participant-reported rates of adverse events were low, and many declined after initiation of the VLC diet (eTable 4). Of 300 participants, 7 (2%) reported hospitalizations in the past 12 months (14 separate occurrences, 0.05 hospitalizations per person per year); 4 (1%) had 4 (0.01 per person per year) hospitalizations for ketoacidosis, and 6 (2%) had 9 hospitalizations (0.03 per person per year) for other reasons. Symptomatic hypoglycemia within the past month was reported by 205 (69%) participants, with the majority (112 [55%]) having few (1–5) episodes per month. Likewise, rates of severe hypoglycemia were low with 7 (2%) reporting hypoglycemia with seizure or coma and 11 (4%) requiring glucagon in the past year. Other conventional chronic disease risk factors showed a mixed profile, with low triglycerides, and elevated high density lipoprotein cholesterol (HDLc), but high total and low density lipoprotein cholesterol (LDLc) (Table 2).

Pediatric age group and growth

Children compared with adults had similar participant-reported HbA1C and other clinical parameters (eTable 5). Participant- and provider-reported height SDS were 0.26 ± 1.21 (n=107 [82% of children]) and 0.25 ± 1.00 (n=49 [37%]), respectively. There was no correlation of height SDS with carbohydrate intake goal (r=0.15, p=0.20) or diet duration (r=0.14, p=0.16). Provider reported current height SDS compared to that at diagnosis was 0.20 ± 1.02 vs. 0.41 ± 1.27 p=0.05 among the small subset of children for whom data were available (n=34 [26%]). Of the 2.3 ± 2.0 year interval since diagnosis, these children had followed the VLC diet for 1.2 ± 0.8 years.

Health and healthcare satisfaction

Participants reported high levels of overall health and satisfaction with diabetes management but not with their professional diabetes care (Table 3), and 27% did not discuss their adherence to a VLC diet with their diabetes care provider. Of those who did discuss their diet, only 49% agreed or strongly agreed that their diabetes care provider was supportive. Narrative explanations by participants for not discussing their diet included disagreement on treatment goals and approach, perceived provider disinterest or unfamiliarity with a VLC diet, desire to avoid conflicts with the provider and, for parents, fear of being accused of child abuse. Participating providers corroborated the overall health ratings and reported even greater satisfaction with diabetes control compared to participants (Z −4.09, p<0.001). The therapeutic relationship was perceived as very good or excellent by 82% of providers. Interestingly, providers perceived themselves as more supportive of the VLC diet compared to participant perception (Z −2.69, p 0.007).

Table 3.

Participant- and Provider-reported Health, Satisfaction with Diabetes Control and Care

Clinical Variables	Participant, all	Participant with provider response	Provider	Z, p a)
Health, overall rating
No. Responses	288	79	65	−1.87, 0.06
Excellent, N. (%)	119 (41)	40 (51)	50 (77)
very good, N. (%)	130 (45)	34 (43)	10 (15)
Good, N. (%)	32 (11)	5 (6)	4 (6)
Fair, N. (%)	5 (2)	0 (0)	0 (0)
Poor, N. (%)	2 (1)	0 (0)	1 (1.5)
Diabetes control, satisfaction
No. Responses	288	79	66	−4.09, <0.001
Very satisfied, N. (%)	104 (36)	25 (32)	51 (77)
Satisfied, N. (%)	147 (51)	39 (49)	11 (17)
Neutral, N. (%)	22 (8)	12 (15)	3 (4.5)
Dissatisfied, N. (%)	14 (5)	3(4)	1 (1.5)
Very dissatisfied, N. (%)	1 (0)	0 (0)	0 (0)
Satisfaction with professional diabetes care
No. Responses	287	78	64
very satisfied, N. (%)	53 (19)	16 (21)	-
Satisfied, N. (%)	89 (31)	36 (46)	-
Neutral, N. (%)	67 (23)	12 (15)	-
Dissatisfied, N. (%)	50 (17)	8 (10)	-
Very dissatisfied, N. (%)	28 (10)	6 (8)	-
Therapeutic relationship
Excellent, N. (%)	n/a	-	35 (55)
Very good, N. (%)	n/a	-	17 (27)
Good, N. (%)	n/a	-	10 (16)
Fair, N. (%)	n/a	-	2 (3)
Poor, N. (%)	n/a	-	0 (0)
Diet/lifestyle not discussed with diabetes care provider
No. Responses	287	79	65	0.12
N. (%)	77 (27)	15 (19)	4 (6)
Diabetes Care Provider supportive of diet
No. Responses	210	64	61	−2.69, 0.007
Strongly agree, N. (%)	34 (16)	12 (19)	22 (36)
Agree, N. (%)	70 (33)	22 (34)	21 (34)
Neutral, N. (%)	64 (30)	19 (30)	12 (20)
Disagree, N. (%)	27 (13)	8 (13)	5 (8)
Strongly disagree, N. (%)	14 (7)	3 (5)	1 (2)

^a)Wilcoxon signed-rank test for ordinal variables and McNemars test for binomial variables

DISCUSSION

In this survey of children and adults following a VLC diet for the long-term treatment of T1DM, we observed measures of glycemic control in the near-normal range, low rates of hypoglycemia and other adverse events, and generally high levels of satisfaction with health and diabetes control. These findings are without precedent among people with T1DM, suggesting a novel approach to the prevention of long-term diabetes complications.

The Diabetes Control and Complications Trial achieved an average HbA1C of 7.2% in the intensively treated group, but with increased rates of hypoglycemia.(6, 7, 27) In a recent survey of 3 international pediatric registries, an HbA1C below 7% was not associated with higher rates of hypoglycemia.(28) Nevertheless, targeting a near-normal HbA1C is generally not recommended out of concern for hypoglycemia. The participants in our survey had an average HbA1c in the normal range and low rates of hypoglycemia compared to other surveys.(29, 30) Likewise, hospitalizations for ketoacidosis or all diabetes related causes compared favorably to prevailing rates.(29–31)

The effect of a VLC diet on cardiovascular disease risk has been subject to debate. Consistent with the known effects of low carbohydrate and (presumed) associated higher saturated fat intakes, participants had low triglycerides and high HDLc and LDLc. The remarkably low ratio of triglycerides to HDLc of 1.1, together with the low total daily insulin requirement, suggests high insulin sensitivity and good cardio-metabolic health.(32) In contrast, total LDLc is considered a conventional cardiovascular risk factor. However, total LDLc elevation on a VLC diet may reflect large, buoyant lipoprotein particles, a relatively low risk subtype.(33) Furthermore, in the DCCT cohort of 1441 adolescents and young adults, HbA1C had the largest effects on cardiovascular risk, followed by triglycerides and LDLc.(34) Postprandial hyperglycemia has been proposed as an independent cardiovascular disease risk factor,(35) for which a VLC diet would plausibly provide benefit. Another major cardiovascular risk factor, BMI, was significantly below population averages for study participants, possibly reflecting another benefit of a VLC diet.(36)

Children generally did as well as adults, a promising finding in view of the adverse effects of diabetes-related hyper- and hypoglycemia on brain development (37, 38) and growth.(39–43). The commonly reported growth deceleration in T1DM is generally ascribed to poor glycemic control.(39–43) Concerns have also been raised that a VLC diet or chronic ketosis may adversely affect growth and pubertal development.(22) While pubertal development was not assessed in this survey, we obtained children’s height data from parents and medical providers. Participant-reported current mean height was modestly above average for age and sex (SDS +0.33). Provider-reported data corroborated this finding and also suggested a marginal (but not statistically significant) decrease in height SDS since diabetes diagnosis. This possible growth deceleration may have preceded or occurred during the diet, and is comparable in magnitude to the previously described decreases in height SDS in T1DM. Taken together these data do not suggest an adverse effect of the VLC diet on growth, but additional research into this possibility is warranted.

Although participants reported high levels of satisfaction with health and diabetes control, relationships with diabetes care providers were often fraught. A minority of participants did not disclose their adherence to a VLC diet to their providers, citing concerns for being criticized, pressured to change behavior, or accused of child abuse. This distrust may increase risk for a catastrophic adverse event, if patients feel unable to seek medical support at times of need (e.g. impending ketoacidosis) and instead make diabetes management decisions beyond their competencies. Notably, most providers described the therapeutic relationship as very good or excellent, and perceived themselves as more supportive of the VLC diet than described by the participants. This discrepancy warrants follow-up in qualitative research.

Strengths of this study include verification of self-reported information by independent sources (diabetes care providers and medical records), a rigorous approach to establish T1DM diagnosis, and the pragmatic setting. Our study has 3 main limitations. First, we cannot prove that all participants had T1DM. However, we found no important discrepancies between those who did or did not have diagnostic evidence (e.g. childhood onset, diabetes antibodies, non-obese body weight). Second, the generalizability of the findings is unknown. We cannot determine how many of the members of the online group are active, have T1DM (vs. being health care providers, family members or others with general interest) and would be eligible to participate in the study. In addition, children and adults adhering to a VLC diet and remaining in this online community may represent a special subpopulation, with high levels of motivation and other health-related behaviors (e.g., physical activity), presenting another source of selection bias. Therefore, the study sample may not be representative of all people with T1DM in the social media group and may differ from the general T1DM population in ways that could influence the safety, effectiveness and practicality of a VLC diet. Third, we did not obtain detailed information on participants’ diet and other components of this diabetes management approach, nor did we assess factors contributing to glycemic control before the self-reported start of the VLC diet.

CONCLUSION

This study suggests that a VLC diet may allow for exceptional control of T1DM without increased risk of adverse events. This possibility is mechanistically plausible, because of the dominant effects of dietary carbohydrate on postprandial glycemia and the lower insulin doses required with a VLC diet. The results, if confirmed in clinical trials, imply that the chronic complications of T1DM might be prevented by diet. In light of study limitations, these findings by themselves should not be interpreted as sufficient to justify a change in diabetes management. Additional research is needed to determine the degree of carbohydrate restriction (and other dietary aspects) necessary to achieve these benefits; optimal insulin regimen to accompany a VLC diet specifically with regard to avoiding severe hypoglycemia; safety and efficacy, in randomized controlled trials; and if this work succeeds, trials to evaluate effectiveness for preventing long-term diabetes complications.

What’s Known on This Subject

Despite pharmacological and technological advances, optimal glycemic control of type 1 diabetes remains elusive, putting millions of people worldwide at increased risk of micro- and macrovascular complications. One conceptually promising but poorly-studied approach is dietary carbohydrate restriction.

What This Study Adds

Exceptional glycemic control of type 1 diabetes without high rates of acute complications may be achievable among children and adults with a very-low-carbohydrate diet. However, the generalizability of these findings and long-term safety of carbohydrate restriction remain unknown.

Abbreviations

ADA

American Diabetes Association

BMI

body mass index

CGM

continuous glucose monitor

HbA1C

Hemoglobin A1C

HDLc

high density lipoprotein cholesterol

LDLc

low density lipoprotein cholesterol

MODY

Maturity Onset Diabetes of Youth

NIDDK

National Institute for Diabetes and Digestive and Kidney Diseases

SD

standard deviation

SDS

standard deviation score

T1DM

type one diabetes mellitus

VLC

very-low-carbohydrate