Netherlands Study: Can a Vegan Diet Affect Muscle Mass After 65?

A study from the Netherlands is tackling one of the most pressing questions for aging adults who are considering a plant-based diet: does going fully vegan put your muscle mass at risk after age 65? Researchers at Wageningen University & Research — one of the world's top nutrition science institutions — have launched a 12-week randomized controlled trial to find out.

What the Dutch Researchers Are Testing

The study, known as the Vold Study, enrolled 72 community-dwelling adults aged 65 and older with a BMI between 23 and 32 kg/m² (roughly 140–210 lbs for a 5'7" adult). Participants were divided into three groups:

• Continue their usual omnivorous diet (control group)
• Switch to a self-designed vegan diet for 12 weeks
• Follow a vegan diet plus twice-weekly resistance exercise

The primary measurement is thigh muscle volume, tracked using MRI scans at the start and end of the trial. Secondary measures include body composition, muscle strength, bone density, insulin levels, vitamin B12 (cobalamin), iron, vitamin D, and inflammatory markers like hs-CRP — all highly relevant to people managing diabetes.

Why Vegan Diets May Be Tricky for Older Muscles

Plant-based proteins — from beans, lentils, tofu, and grains — generally contain lower amounts of essential amino acids and are absorbed less efficiently than animal proteins. For older adults, who already experience natural muscle loss (called sarcopenia), this protein gap may accelerate decline. The Dutch team wants to know whether resistance exercise can compensate for any muscle loss caused by switching to a fully vegan diet.

The study also measures muscle protein synthesis rates during the first 10 days using a specialized deuterium oxide (heavy water) protocol — a cutting-edge technique rarely used in nutrition studies of this scale.

Converting the Numbers for US Readers

The study monitors participants' insulin levels as a secondary outcome. While specific glucose thresholds aren't listed in this protocol, the American Diabetes Association (ADA) defines normal fasting blood sugar as under 100 mg/dL (5.6 mmol/L), prediabetes as 100–125 mg/dL (5.6–6.9 mmol/L), and diabetes at 126 mg/dL or higher (7.0 mmol/L). Results from this trial will be interpreted against those benchmarks.

Why This Matters for US Patients

Plant-based diets are increasingly recommended for people with type 2 diabetes in the US, and the ADA's 2024 Standards of Care acknowledge plant-forward eating patterns as beneficial for blood sugar control, weight management, and cardiovascular health. However, US guidelines do not yet fully address the muscle-preservation risks of fully vegan diets in older diabetic patients — a population already vulnerable to muscle loss due to insulin resistance.

If the Vold Study finds that vegan diets reduce thigh muscle volume, it could reshape dietary counseling for older Americans with diabetes. If resistance exercise proves protective, it may become a standard recommendation paired with plant-based diet advice. Either way, the results will offer evidence that US guidelines currently lack.

Results are expected to inform future plant-based dietary guidelines in both Europe and the United States. US patients and their care teams should watch for the findings — this study could directly influence what your dietitian recommends at your next visit.

Source: Domić, Grootswagers, Pinckaers et al. "The effect of a vegan diet with or without resistance exercise on thigh muscle volume in older adults." BMC Geriatrics, 2025. PMID: 41454225. DOI: 10.1186/s12877-025-06708-9