The research by University of Glasgow, presented at this week’s European Congress on Obesity found the rule applied to adults of any age and weight, and was unaffected by smoking and alcohol consumption.
Biomarkers can have bad and good health effects, promoting or preventing cancer, cardiovascular and age-related diseases, and other chronic conditions, and have been widely used to assess the effect of diets on health.
University of Glasgow researchers performed a cross-sectional study analysing data from 177,723 healthy participants aged between 37 and 73 years reporting no major dietary changes over five years. They were trying to understand whether dietary choice can make a difference to the levels of disease markers in blood and urine.
Participants were categorised as either vegetarian (not eating red meat, poultry or fish) or meat-eaters according to their self-reported diet, with the groups numbering 4,111 and 166,516 respectively.
The researchers examined the association with 19 blood and urine biomarkers related to diabetes, cardiovascular diseases, cancer, liver, bone and joint health, and kidney function.
The study accounted for potentially influential factors, including age, sex, education, ethnicity, obesity, smoking, and alcohol intake. The analysis found that compared to meat eaters, vegetarians had significantly lower levels of 13 biomarkers, including:
- Total cholesterol
- Low-density lipoprotein (LDL) cholesterol – the so-called 'bad cholesterol’
- Apolipoprotein A and B – linked to cardiovascular disease
- Gamma-glutamyl transferase (GGT) and alanine aminotransferase (AST) – liver function markers indicating inflammation or damage to cells
- IGF-1 – a hormone that encourages the growth and proliferation of cancer cells
- Creatinine – a marker of worsening kidney function
However, vegetarians also had lower levels of beneficial biomarkers including high-density lipoprotein ‘good’ (HDL) cholesterol, Vitamin D and calcium (linked to bone and joint health).
In addition, they had significantly higher levels of triglyceride fats and cystatin-C (suggesting a poorer kidney condition) in their blood.
No link was found for blood sugar levels (HbA1c), systolic blood pressure, aspartate aminotransferase (AST; a marker of damage to liver cells) or C-reactive protein (CRP; inflammatory marker).
“Our findings offer real food for thought,” said the University of Glasgow’s Dr Carlos Celis-Morales, who led the research.
“As well as not eating red and processed meat, which have been linked to heart diseases and some cancers, people who follow a vegetarian diet tend to consume more vegetables, fruits, and nuts which contain more nutrients, fibre, and other potentially beneficial compounds.
“These nutritional differences may help explain why vegetarians appear to have lower levels of disease biomarkers that can lead to cell damage and chronic disease."
The authors emphasised that, despite its size, the study, was observational, so no conclusions could be drawn about direct cause and effect.
They noted several limitations, including that they only tested biomarker samples once for each participant. And they recognised that it was possible that biomarkers might fluctuate depending on factors unrelated to diet, such as existing diseases and unmeasured lifestyle factors.