Type 1 diabetes is a chronic autoimmune condition where the pancreas produces little to no insulin. Insulin is a hormone that facilitates the movement of glucose from the bloodstream into cells for energy. People with type 1 diabetes require insulin injections to manage their blood sugar levels. Recent research has explored the potential benefits of a vegan diet in managing type 1 diabetes, particularly in reducing insulin needs and improving cardiometabolic health.
The Rising Costs of Insulin and the Need for Alternative Treatments
According to the American Diabetes Association, spending on insulin in the US tripled in the past ten years, reaching $22.3 billion in 2022, due to the increased usage and higher price of insulin. The inflation-adjusted cost of insulin increased by 24% from 2017 to 2022 [1]. Furthermore, the costs associated with type 1 diabetes have been shown to be about 32% higher, compared to those for type 2 diabetes [2]. Despite recent efforts to restrain insulin pricing, novel treatments for type 1 diabetes are urgently needed for both health and financial reasons. With the rising costs of insulin and the increasing prevalence of type 1 diabetes, there is a growing need for alternative and cost-effective management strategies. Dietary interventions, particularly plant-based diets, have emerged as a promising avenue for improving glycemic control and reducing insulin requirements.
Investigating the Impact of a Vegan Diet on Type 1 Diabetes
A study published in Clinical Diabetes in March 2024, led by researchers at the Physicians Committee for Responsible Medicine, investigated the impact of a vegan diet on individuals with type 1 diabetes. This randomized clinical trial split 58 participants into two groups: one followed a low-fat vegan diet, eating as much as they liked, while the other followed a non-vegan, portion-controlled diet, with overweight participants reducing their calorie intake by 500 to 1,000 calories a day. Participants followed their prescribed diets for 12 weeks, recording their nutrient intake and insulin dosages at each meal.
Study Design and Key Findings
The study, conducted between August 2021 and November 2022 in Washington, DC, enrolled men and women with diagnosed type 1 diabetes who were ≥18 years of age and had a stable insulin regimen for the previous 3 months. Participants were randomly assigned in a 1:1 ratio to the vegan group (n = 29), which was asked to follow a low-fat vegan diet, or the portion-controlled group (n = 29), which was asked to follow a portion-controlled diet. The low-fat vegan diet (∼75% of energy from carbohydrates, 15% from protein, and 10% from fat) consisted of vegetables, grains, legumes, and fruits, with no limits on calories or carbohydrates. Participants were instructed to avoid animal products and added fats and to favor foods with a low glycemic index. No meals were provided. The portion-controlled diet included individualized diet plans that reduced daily energy intake by 500-1,000 kcal/day for overweight participants (BMI >25 kg/m2) and kept carbohydrate intake stable over time. This diet derived 60-70% of energy from carbohydrate and monounsaturated fats, 15-20% from protein, and <7% from saturated fat and contained ≤200 mg/day of cholesterol. Both groups received weekly online nutrition education classes and support from registered dietitians. Participants in both groups took a vitamin B12 supplement (100 µg/day). For both groups, alcoholic beverages were limited to one per day for women or two per day for men. All study participants were asked not to alter their exercise habits and to continue their preexisting medication regimens for the duration of the study except as modified by their personal physicians. Insulin doses were reduced in cases of repeated hypoglycemia. Participants recorded their carbohydrate intake and insulin dose for each meal and calculated the carbohydrate-to-insulin ratio for each meal. The primary clinical outcomes were insulin requirements (total daily dose [TDD] of insulin), insulin sensitivity, and glycemic control (A1C). TDD was calculated as a sum of basal and bolus insulin units injected per day. Insulin sensitivity was assessed by the carbohydrate-to-insulin ratio, which was calculated as the number of total grams of dietary carbohydrate to total units of insulin administered. For these variables, an average from three consecutive days (two weekdays and one weekend day) was used. Dietary intake data were collected and analyzed by a staff member certified in Nutrition Data System for Research, v. 2021-22, developed by the Nutrition Coordinating Center of the University of Minnesota in Minneapolis (12).
The results showed that participants in the vegan group experienced significant weight loss, averaging 11 pounds, while the non-vegan group saw no significant changes in weight. Compared with the other group, participants on the low-fat vegan diet saw a 28% reduction in insulin needs and 127% improvement in insulin sensitivity. The researchers also noted improvements in A1C (a measure of average blood sugar) for both groups, with the vegan group seeing a slightly larger improvement. Furthermore, both groups saw reductions in their total cholesterol, the vegan group saw a larger drop-off-about 32 points, compared with an 11-point drop among the non-vegan group.
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Detailed Analysis of Insulin Use and Costs
A secondary analysis specifically assessed insulin use and insulin costs associated with both dietary interventions. The total dose of insulin decreased by 12.1 units/day in the vegan group (p = 0.007), compared to no significant change in the portion-controlled group (treatment effect − 10.7 units/day [95% CI, -21.3 to -0.2]; p = 0.046). Total insulin costs decreased by 27% ($1.08/day; p = 0.003) in the vegan group, compared to no significant change in the portion-controlled group (-$0.38/day [95% CI, -$2.13 to +$1.38]; p = 0.66).
The dose of basal insulin decreased in both groups: by 7.7 units/day; p = 0.009 on the vegan diet and by 4.5 units/day; p = 0.03 on the portion-controlled diet (treatment effect − 3.2 [95% CI, -9.9 to + 3.5]; p = 0.34). Basal insulin cost decreased on the vegan diet by 34% ($0.73/day) (p = 0.003), compared to no significant change on the portion-controlled diet (between-group difference p = 0.69). The dose of bolus insulin and its cost did not change significantly in either group. As reported earlier [3], despite these major reductions in insulin use, HbA1c values were reduced by 0.8% point on the vegan diet and by 0.6% point on the portion-controlled diet (between-group difference p = 0.34), and there was no increase in hypo- or hyperglycemic events in either group.
Plant-Based Dietary Indices and Weight Loss
The PDI score increased on the vegan diet (p < 0.001) from 51.8 to 60.4, and did not change on the portion-controlled diet [effect size +6.0 (95% CI + 1.0 to +10.9); p = 0.02]; the hPDI increased on both diets, more on the vegan diet [effect size +9.1 (95% CI + 3.7 to +14.5); p = 0.002]; and uPDI increased on the vegan diet, and did not change on the portion-controlled diet [effect size +7.3 (95% CI + 1.9 to +12.7); p = 0.01]. As expected, compared to the portion-controlled diet, the intake of all animal foods was significantly reduced on the vegan diet. Furthermore, the scores for the “healthful” plant foods changed as follows: legumes, whole grains, and fruits significantly increased, while the scores for vegetable oils and nuts significantly decreased (as the consumption of these foods decreased) on the vegan diet. On the portion-controlled diet, only the score for whole grains increased. The participants lost 5.2 kg on the vegan diet (p < 0.001), while there was no change on the portion-controlled diet [effect size −4.3 kg (−6.1 to −2.4); p < 0.001]. The changes in PDI and hPDI scores were associated with changes in body weight (r = −0.35; p = 0.04 for PDI; and r = −0.52; p = 0.001 for hPDI) and remained largely unchanged after adjustment for changes in energy intake (r = −0.37; p = 0.04 for PDI; and r = −0.53; p = 0.001 for hPDI]. There was no correlation between the changes in uPDI and changes in body weight [r = −0.07; p = 0.68; see Table 2). A 1-kg weight loss was associated with an increase in hPDI by 6.1 points (p = 0.01).
Potential Mechanisms Behind the Benefits
The reductions in insulin use in the vegan group likely reflect improved insulin sensitivity, resulting from the reduction in liver and muscle fat [5]. This lower insulin use on the low-fat vegan diet reflects a marker of improved cardiometabolic health [6] and of reduced treatment costs, in addition to the likelihood of lower food costs on a vegan diet, as previously reported [7]. A crucial point in the physiology of glycemic control is that dietary fat increases hepatocellular and intramyocellular lipids, which in turn increase insulin resistance, with both acute and chronic effects on glycemic control. The improvements in glycemic control were strongly associated with weight loss, even after adjusting for baseline BMI. However, insulin dose units per kilogram of body weight decreased by 24% on the low-fat vegan diet, so weight loss is apparently not an adequate explanation for these effects. In addition, the low fat content of the vegan diet is likely to play a significant role at each mealtime because dietary fat has been shown to have a major impact on insulin sensitivity and insulin requirements in people with type 1 diabetes.
Broader Implications and Cost-Effectiveness
In a retrospective study of United Healthcare patients (2015-2017) that included 12,700 people with type 1 diabetes, the average yearly medical costs to the payer totaled $18,800 per person with type 1 diabetes, $4,600 higher than the cost of treating a person with type 2 diabetes, and far higher than for those without diabetes. Of the costs associated with type 1 diabetes, the average prescription costs were $10,200 (±$11,000) per person per year [2]. In another retrospective study using 2011-2016 IBM MarketScan and electronic medical record data, the average cost per person with type 1 diabetes per year was approximately $9,600. The majority of these costs (55%-61%) were due to pharmacy costs [8].
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Insulin prices have been increasing steadily and are projected to increase even further, despite efforts to rein in such costs. Between 2014 and 2019, the average price of insulin in the US increased by 55%, from $3,819 to $5,917 per year [9]. The out-of-pocket costs of insulin differ greatly depending on the population and the type of insurance. In a 2018 IBM Marketscan Database study of 65,000 people with type 1 diabetes covered by private insurance, the average annual out-of-pocket cost per person using insulin varied between $472 (±$625) and $1,037 (±$1,039) [10]. The yearly out-of-pocket insulin costs for Medicare Part D recipients increased from approximately $588 in 2014 to $696 in 2019 [9]. These studies highlight the need for interventions that will help people with type 1 diabetes save on the cost of insulin. A low-fat vegan diet appears to be a promising option, partly due to its ability to reduce body weight and ectopic fat, and to increase insulin sensitivity.
Strengths and Limitations of the Research
The strengths of this study include the randomized parallel design, in which all participants started simultaneously, allowing the investigators to rule out possible effects of seasonal fluctuations in the diet. The study duration was reasonably long, providing sufficient time for adaptation to the diet. A vegan diet is healthy and nutritionally adequate, and provides all the needed nutrients and macronutrients, except for vitamin B12, which needs to be supplemented [11]. Given that the participants were living at home and preparing their own meals or eating at restaurants, our results are applicable outside the research setting, in free-living conditions.
The study also has important limitations. Dietary intake was calculated based on self-reported diet records, which have well-known limitations [12], but this was partly offset by the repeated collection of the dietary data by each participant. That means that participants served as their own controls for the dietary data collected at different time points, which minimized the impact of inter-individual differences. The same applies to the self-reported insulin data. While the 3-day average only represents a snapshot of the overall insulin use, it has been found to be a fairly accurate representation, which has allowed people with diabetes to achieve comparable glycemic control as with physician-directed titration [13]. Furthermore, the study requirements included careful meal and blood glucose monitoring for research purposes, beyond that required for self-care, which contributed to a substantial attrition rate. The small sample size was modest, and the study duration was limited. Prices for short-acting and long-acting insulins vary over a wide range, which may explain why the between-group difference in insulin price did not reach the statistical significance, although the groups differed in total insulin dose. The expenses associated with dietetic instruction and may or may not be covered by insurance. However, all individuals with type 1 diabetes receive dietetic instruction, and these costs would be expected to be similar, regardless of diet type. Some may supplement instruction with free resources, such as books and pre-recorded videos. Finally, our participants were health-conscious volunteers and may not be representative of the general population, but they are likely representative of individuals seeking clinical care.
Considerations for Implementing a Vegan Diet for Type 1 Diabetes
While the study results are promising, it's important to note that type 1 diabetes cannot be cured with diet alone. However, dietary changes can help people reduce medications and reduce the risk of complications. Individuals considering a vegan diet for type 1 diabetes management should work closely with their healthcare team, including a registered dietitian, to ensure that their nutritional needs are met and their insulin dosages are appropriately adjusted. It is also important to monitor blood glucose levels closely and be prepared to adjust insulin dosages as needed.
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