The Mediterranean diet has become famous far beyond its namesake sea as research increasingly backs up its long-standing reputation for boosting health and longevity.
Studies have shown that people who follow a Mediterranean diet – which emphasizes plant-based foods and fish, rather than red meat or dairy products – are healthier in their diets. several wayswith lower rates of heart disease, cancer, diabetes, dementia and overall mortality.
But why? Despite strong evidence for health benefits, it remains unclear how exactly this blend of foods, at the cellular level, can extend longevity.
However, that may change. A study led by researchers at Stanford University in the US has revealed for the first time the cellular effects of the Mediterranean diet, based on how one of the healthy fats affected the lifespan of nematodes, also known as roundworms.
Finding this link is a big deal, say the study authors, and offers new insights into the health effects of different fats and the role diet plays in longevity.
“Fats are generally considered to be harmful to health,” say Stanford University geneticist Anne Brunet. “But some studies have shown that specific types of fats or lipids may be beneficial.”
The Mediterranean diet is rich in beneficial fats, known as monounsaturated fatty acids (MUFAs), found in foods such as nuts, fish and olive oil. The new study focused on one healthy fat, oleic acidthe main MUFA in olive oil and some nuts.
Using the roundworm Caenorhabditis elegansBrunet and her colleagues discovered two benefits of oleic acid: it protects cell membranes from damage from lipid oxidation and it increases the amount of two important cellular components called organelles.
Those effects make a significant difference, the researchers report, with roundworms fed oleic acid living about 35 percent longer than worms on a more traditional diet.
One type of organelle, a fat reservoir called a lipid droplet, allowed the researchers to predict with surprising accuracy how many days a worm would survive.
“The number of fat droplets in individual worms tells me the remaining lifespan of that animal,” say Stanford University biochemist Katharina Papsdorf. “The worms with more fat droplets live longer than those with fewer droplets.”
The roundworms ate bacteria supplemented with oleic acid or elaidic acid, a monounsaturated trans fatty acid found in margarine and fried foods. The two acids have similar molecular structures, but very different health effects.
Trans fats such as elaidic acid are considered unhealthy or “bad” fats because they increase the risk of heart disease, dementia and other health problems.
“We saw that the number of lipid droplets in the intestinal cells of the worms increased when the worms were exposed to oleic acid, and that this correlated with an increase in lifespan,” Brunet say.
However, exposure to elaidic acid did not increase the number of lipid droplets or the number of days the worms lived.
Lipid droplets are important for cell metabolism, the researchers note, and help regulate the use of fat stores as energy for cells. When researchers blocked a gene for proteins that help roundworm cells make lipid droplets, the life-extending effect disappeared.
On top of the increase in lipid droplets, roundworms’ intestinal cells also had more organelles peroxisomescontaining enzymes involved in oxidation and metabolism.
Lipid droplets and peroxisomes were more abundant in cells from younger animals, the researchers report, which naturally decline as they age.
The number of these organelles also varies from person to person, and worms that naturally have more in their cells also tend to live longer, showing an effect similar to worms fed oleic acid.
In addition to its effects on organelles, oleic acid protected cells by limiting the oxidation of lipids, a chemical reaction that damages cell membranes. Elaidic acid had the opposite effect, increasing oxidation at the expense of cellular integrity.
“Membrane oxidation is very bad news for an organism,” Brunet say. “Cell membranes can begin to leak and fail, which can trigger a cascade of adverse biological effects.”
These are important insights into the links between diet and longevity, the researchers write, revealing important details about how specific components of the Mediterranean diet may increase longevity.
That could improve dietary guidelines, and it could ultimately inspire ways to counteract the effects of aging by mimicking oleic acid’s defense against oxidation.
For now, however, the researchers note that this is an intriguing discovery that warrants more research, including examining whether and how these findings apply to humans.
“For years we’ve been very interested in learning how nutrition affects longevity,” Brunet say. “It will be fascinating to see if we see a similar link between lipid droplets and longevity in mammals and humans. These findings suggest that there may be a fat-based strategy to improve human health and longevity.”
The study is published in Nature cell biology.
