Very low-calorie and vegan diets improve glycemic control in type 2 diabetes

By Nidhi Saha, BDSDec 1 2022Reviewed by Benedette Cuffari, M.Sc.

A recent Nutrients study reports that both very low-calorie diets (VLCD) and vegan diets improve weight loss and anthropometric markers. Furthermore, VLCD diet intervention was associated with better glycemic control in type 2 diabetes (T2D) patients.

Study: Investigating the Effectiveness of Very Low-Calorie Diets and Low-Fat Vegan Diets on Weight and Glycemic Markers in Type 2 Diabetes Mellitus: A Systematic Review and Meta-Analysis. Image Credit: Pormezz / Shutterstock.com

Background

Obesity and its consequences are significant sources of global morbidity and mortality. Obesity is now considered a global epidemic and is often driven by T2D.

According to the International Diabetes Federation, nearly 537 million adults currently have diabetes, with 783 million expected to be diagnosed with this condition by 2045. 

Clinically an irreversible condition, with only 2% of patients having spontaneous remission, the primary management of T2D is weight loss. Optimum weight and glycemic control can be achieved by exercise, restricting caloric intake, and implementing lifestyle and behavioral changes.

Dietary modifications include restricting the consumption of fats, carbohydrates, and cholesterol in food. Such diet plans are chosen not only for management but also for reversing T2D. These are low-calorie diets (LCD) that permit an intake of 1,200-1,500 kcal daily or even less.

VLCD allows for the consumption of nearly 450-800 kcal per day. VLCD promotes rapid weight loss, lowers hemoglobin A1c (HbA1c) to pre-diabetes or normal diabetes levels, and improves insulin secretion.

Plant-based diets are not only sustainable but are also effective in managing chronic diseases, including T2D. In addition, food derived from plant sources are rich in natural antioxidants, vitamins, and minerals that can aid in weight management, glycemic control, and improve blood lipids.

The intake of a plant-based diet can lower cholesterol levels, as these food products have negligible cholesterol content, are rich in soluble fiber, and are low in saturated fats. Following such diets reduces the risk of developing cardiovascular complications of T2D.

About the study

The current review aimed to establish the efficacy of vegan diets and VLCD in managing the glycemic index and body weight of patients suffering from T2D. 

A total of 16 studies were reviewed after applying the inclusion and exclusion criteria. Overall, 834 patients with T2D between 42.1-61 years of age were included. 

The median dietary intervention period between intervention and follow-up was 17 weeks, the longest period being 74 weeks and the shortest period being 4 days.

Study findings

Vegan diet vs. control diet

Body weight, glycemic index, and anthropometric markers did not show any significant reduction with vegan diets compared to a conventional diet for diabetes (control diets). Low-density lipoprotein (LDL) cholesterol significantly decreased in people consuming a vegan diet; however, triglycerides, high-density lipoprotein (HDL) cholesterol, and total cholesterol levels were not affected by the type of diet consumed.

Fasting glucose levels did not differ between the two diets; however, patients achieved lower HbA1c when the vegan diet was followed.

Body-mass index (BMI) and triglycerides did not differ between vegan and control diets. The waist circumference also did not change, while hip circumference measurements were reduced with the vegan diet intervention. Additionally, reductions in the waist-to-hip ratio were recorded with the vegan diet, whereas no such reduction was observed with the control diet.

VLCD vs. control diet

Body weight or anthropometric markers showed no significant reduction with VLCD compared to the control diet. However, fasting glucose and HbA1c significantly reduced after following VLCD.

Furthermore, BMIs showed improvement, and body-weight reductions were documented following VLCD. When combined with exercise, more significant gains in BMI relative to VLCD alone were observed.

Meanwhile, the effects on triglyceride levels were the same with both VLCD and control diets. There was no difference in triglyceride reduction between the VLCD and control diets and non-dietary behavioral therapies and VLCDs.

Waist and hip circumference measurements decreased in both the long-intervention duration (LD) and short-intervention duration (SD) groups. The waist-to-hip ratio also decreased; however, the difference between LD and SD groups was not statistically significant.

Comparatively, the effect on total cholesterol showed varied results. While one study showed no difference between non-dietary therapies and VLCDs in reducing total cholesterol levels, another study emphasized total cholesterol level reductions following non-dietary therapies. However, mean fasting insulin and mean HDL-cholesterol did not show any alteration after non-dietary therapies or VLCDs.

Non-dietary therapies led to a more significant reduction of LDL cholesterol. In addition, participants' mean systolic and diastolic pressure after VLCDs showed greater reductions than those who followed non-dietary therapies.

Of note, none of the studies recorded urinary albumin in patients following VLCDs.

Conclusions 

VLCD and vegan diets appear to be more effective in decreasing LDL cholesterol levels and maintaining good glycemic control in patients with T2D as compared to non-dietary therapies and conventional diabetes diets. However, more detailed and thorough analyses are warranted for integrating these diets into national guidelines.