Low-fat vegan diet a game-changer for T1D?

New research has shown that a low-fat vegan diet rich in vegetables, fruits, whole grains, and legumes can improve insulin sensitivity in adult patients with type 1 diabetes (T1D), thus reducing their daily insulin requirements. The finding may fuel the momentum for dietary shifts in this population.

Over 12 weeks, patients on the low-fat vegan diet improved insulin sensitivity by 127 percent and required 28 percent less insulin.  “This is a ground-breaking finding,” said principal study author Dr Hana Kahleova, director of clinical research at the Physicians Committee for Responsible Medicine in Washington, DC, US.  “Reducing insulin dose is unheard of in terms of what nutrition can do.”

The vegan diet also improved other important outcomes such as weight loss, blood lipids, and kidney function.

The reduction in insulin use with the vegan diet corresponds to a 9-percent decrease in cardiovascular risk, according to Kahleova. The reduction in serum HbA_1c, a marker of glycaemic control, corresponds to a 12-percent reduced risk of heart attack and a 9–12-percent reduced risk of cardiovascular disease (CVD). Meanwhile, the reduction in LDL cholesterol (LDL-C) corresponds to a 20-percent reduced risk of a major cardiac event, including stroke.

“Our findings underscore the potential benefits of a plant-based diet in managing T1D and promoting cardiovascular health,” said Kahleova. “When you choose the best diet for T1D, the low-fat vegan diet is the way to go. This diet could be a game-changer for patients.”

Risk of dying higher in T1D

In T1D, the pancreas produces little to no insulin, which controls blood sugar. This causes glucose to remain in the bloodstream longer than it should, damaging the blood vessels.

“We know that the risk of dying from any cause is higher in people with T1D than the nondiabetic population. That’s mainly because of the deaths secondary to heart disease and myocardial infarction,” explained Kahleova.

She shared that in the DCCT/EDIC* study of 1,441 patients with T1D followed up for 30 years, an increase in insulin dose was associated with a higher BMI, heart rate, and impaired blood lipids. “Each 0.1 unit/kg/day increase in insulin dose was associated with a 6-percent increase in CVD in that study.”

Patients with T1D require life-long insulin replacement with multiple daily insulin injections, insulin pump therapy, or an automated insulin delivery system. Without insulin, diabetic ketoacidosis can develop and can be fatal.

“The conventional wisdom is for patients to count their carbs and adjust their insulin dose for each meal, stay away from complete junk, and eat healthily,” said Kahleova.  Insulin is critical for patient survival, but access has not always been ideal.

“With the cost of insulin remaining a concern for many patients, our finding that low-fat vegan diet decreased insulin doses comes with health and financial benefits,” she pointed out. “Plant-based diets may be the prescription for reducing insulin demand, managing blood sugar levels, and improving heart health in T1D patients.”

First-of-a-kind trial

This randomized clinical trial was the first to compare the effects of a low-fat vegan diet with a conventional portion-controlled diet in adults with T1D.

Participants (n=58) were randomly assigned into two groups: those on a low-fat vegan diet were told to limit their fat intake to 20–30 g daily and favour fruits with a low glycaemic index; those on a portion-controlled diet were asked to watch their carbohydrate intake and portions and limit their cholesterol and saturated fat intake. Both groups followed their prescribed diets for 12 weeks, recording their nutrient intake and insulin doses at each meal.

While insulin sensitivity increased significantly in the vegan group, it did not change in the group receiving the portion-controlled diet. Both diets improved glycaemic control, though slightly better with the vegan diet (-0.8 percent vs -0.6 percent).

As diabetes and heart disease are closely intertwined, the researchers also ran lipid panels at the beginning and end of the trial. Total cholesterol in the low-fat vegan group dropped by 32.3 mg/dL relative to a 10.9 mg/dL decrease in the portion-controlled group. LDL-C – the bad cholesterol – also fell by 18.6 mg/dL in the vegan group but did not change significantly in the portion-controlled group.

Similarly, the ratio of blood urea nitrogen (BUN) to creatinine, an indicator of kidney function, decreased in the vegan group but not in the portion-controlled group.

“Overall, HbA_1c and total cholesterol improved with the portion-controlled diet. By contrast, the vegan diet improved all the outcomes – it reduced insulin demand, insulin sensitivity, glycaemic control, total cholesterol and LDL-C, and body weight,” recapped Kahleova. “The vegan diet was superior to the portion-controlled diet, having improved all the cardiometabolic outcomes.”

A global health issue

T1D is less common than type 2 diabetes (T2D), but the prevalence has been increasing in recent years. In 2021, there were 8.4 million people with T1D worldwide. Of these, 1.5 million were <20 years of age, 5.4 million were between ages 20 and 59, and 1.6 million were ≥60 years. About 500,000 were new cases (median age of onset 29 years); 35,000 died undiagnosed within a year of symptom onset. [Lancet Diabetes Endocrinol 2022;10:741-760]

A plethora of studies have consistently highlighted the potential health benefits associated with plant-based diets, which typically have lower saturated fats and cholesterol levels.

“Plant-based or plant-forward eating patterns focus on foods primarily from plants. These include fruits, vegetables, nuts, seeds, oils, whole grains, legumes, and beans. It doesn’t mean you are a vegetarian or a vegan and never eat meat or dairy. Rather, you are proportionately choosing more of your foods from plant sources,” explained Kahleova.

Can diet reduce meds?

“T1D cannot be cured with diet,” commented Physicians Committee for Responsible Medicine President Dr Neal Barnard, an adjunct associate professor of medicine at the George Washington University School of Medicine in Washington, DC, US. “However, dietary changes can help reduce medications and the risk of complications.”

Barnard led the first major randomized clinical trial comparing a plant-based diet and a more conventional, portion-control diet in 2003, but this was in patients with T2D. The plant-based diet led to a 300-percent greater reduction in HbA_1c. He hoped the latest study could spur similar improvements in managing patients with T1D.

A recent umbrella review also showed that plant-based diets may be beneficial in reducing cardiometabolic risk factors, CVDs, cancer risk, and mortality. [PLoS One 2024;19:e0300711]

 The bottom line

Dr Christopher Gardner, professor of medicine at Stanford University School of Medicine in Palo Alto, California, US, said that while most people would probably not go vegan, nudging may help to promote a shift to plant-based diets and improve overall health. “A vegan diet can also confer additional benefits such as increased gut bacteria and reduction of telomere loss, which slows ageing.”

“Enjoying vegan multicultural foods like Indian masala, Asian stir-fry, and African lentil-based dishes can be a great first step,” added Gardner, who himself was the author of a previous study showing that a healthy vegan diet improved cardiometabolic outcomes in as little as 8 weeks among identical twins. [JAMA Netw Open 2023;6:e2344457]