Large data sample from the UK Biobank study
“Specifically, we wanted to know if vegetarians were healthier because they are generally leaner and lead healthier lives, or whether their diet specifically was responsible for their improved metabolic and cardiovascular health,” Dr. Celis-Morales explained.
Data were included from 177,723 healthy participants from the UK Biobank study who were aged 37-73 years and had reported no major dietary changes over the last 5 years. In total, 4,111 participants were self-reported vegetarians who followed a diet without red meat, poultry, or fish, and 166,516 participants were meat eaters.
Nineteen biomarkers related to diabetes, hypertension, cardiovascular diseases, cancer, and liver and renal function were included, and the associations between vegetarian diet and biomarkers, compared with meat eaters, were examined.
To minimize confounding, the findings were adjusted for age, sex, deprivation, education, ethnicity, smoking, total sedentary time, type of physical activity, alcohol intake, body mass index, and waist circumference.
Compared with meat eaters, vegetarians had significantly lower concentrations of 14 biomarkers, including total cholesterol (21% lower); LDL (16% lower); lipoprotein A (1% lower), lipoprotein B (4% lower), and liver function markers (GGT: 354% lower, and ALT: 153% lower), IGF-1 (134% lower), urate (122% lower), total protein (29% lower), creatinine (607% lower), and C-reactive protein (10% lower).
However, the researchers found that, compared with meat eaters, vegetarians had significantly higher concentrations of some unhealthy biomarkers, including triglycerides (15% higher) and cystatin-C (4% higher), and lower levels of some beneficial biomarkers including high-density lipoprotein (HDL) cholesterol (5% lower), vitamin D (635% lower), and calcium (0.7% lower).
No associations were found for hemoglobin A1c, systolic blood pressure, and aminotransferase.
“Some biomarkers, for example urate, were very low in vegetarians, and this served to verify our results because we expected meat eaters to have higher levels of urate,” remarked Dr. Celis-Morales.
Diet commitment and cardiovascular outcomes
Many people, whether vegetarians or meat-eaters, follow short-term diets, for example, the Atkins or the 5:2 diet, and often lack continuity switching from one diet to the next, or back to regular eating.
“They are healthy, but they do not commit for long enough to make a difference to metabolic markers or potentially long-term health. In contrast, vegetarians are usually fully committed but the reasons behind this commitment might be a concern for the environment or animal welfare, for example,” Dr. Celis-Morales pointed out.
However, he added that many vegetarians replace the meat in their diet with unhealthy alternatives. “They often eat too much pasta or potatoes, or other high-energy food with low nutritional value.”
Having identified metabolic markers specific to long-term vegetarian diets, Dr. Celis-Morales wanted to know what happens to vegetarians’ long-term cardiovascular health. He analyzed and published these outcomes in a separate study published in December 2020.
“Over 9 years of follow-up, we have found that vegetarians have a lower risk in terms of myocardial infarction in the long-term, as well as other cardiovascular disease,” he reported.
Asked whether there was an optimum age or time in life to become a vegetarian to improve health, Dr. Celis-Morales explained that the healthier you are, the less likely you will reap the health benefits of dietary changes – for example to being a vegetarian.
“It is more likely that those people who have unhealthy lifestyle risk factors, such as smoking, and high consumption of high-energy foods or processed meat are more likely to see positive health effects,” he said.
Lifestyle changes to improve cardiovascular outcomes are usually more likely to be required at 40 or 50 years old than at younger ages. He also noted that metabolic markers tend to show clear improvement at around 3 months after adopting a particular diet but improvements in disease outcomes take a lot longer to become evident.
Dr. Celis-Morales and his team are currently conducting a further analysis to understand if the vegetarian diet is also associated with a lower risk of cancer, depression, and dementia, compared with meat-eaters.
Dr. Celis-Morales, Dr. Mathers, and Dr. Gallegos have reported no relevant financial relationships.
A version of this article first appeared on Medscape.com.