Heart attacks and strokes are the crises we notice, but they result from a slow process of atherosclerosis, the hardening and clogging of the arteries with fatty substances called lipids. Immune cells stick to the walls of blood vessels, scavenge lipids, and multiply. The blood vessel walls inflame and thicken as the smooth muscle cells lining them change, swelling and dividing to create plaques, clogs, and warty growths called atheromas.

For a very long time, doctors and researchers assumed that the lipids came from eating fatty, cholesterol-rich food. But the research hasn't borne this out; some people who eat large amounts of the foods we thought were the sources of the fat, such as eggs, butter, fatty fish, and meat, don't necessarily develop heart disease.

UConn researchers believe they may have solved part of the puzzle. Using careful chemical analysis of atheromas collected from patients by a colleague at Hartford Hospital, they found lipids with a chemical signature unlike those from animals at all. Instead, these strange lipids come from a specific family of bacteria.

"I always call them greasy bugs because they make so much lipid. They are constantly shedding tiny blebs of lipids. Looks like bunches of grapes," on a bacterial scale, says Frank Nichols, a UConn Health periodontist who studies the link between gum disease and atherosclerosis. The bacteria, called Bacteroidetes, make distinctive fats. The molecules have unusual fatty acids with branched chains and odd numbers of carbons (mammals typically don't make either branched chain fatty acids or fatty acids with odd numbers of carbons).

Clogged arteries may be down to bacteria, not diet

The fat molecules in the plaques that clog up our arteries and raise risk of heart attack and stroke may come from bacteria that live in our mouths and guts, not just from what we eat.

This was the main result of a study led by the University of Connecticut in Storrs that was published recently in the Journal of Lipid Research.

The researchers suggest that the finding may explain why gum disease is often linked to atherosclerosis – a condition in which fat molecules, calcium, cholesterol, and other compounds in the blood form plaques on the inside walls of arteries.

As the plaques build up, they harden and narrow the arteries, restricting the flow of oxygen-carrying blood to vital organs and tissues. This can lead to heart attack, stroke, other serious health problems, and even death.

The immune system also plays a role: immune cells can attach to the lining of blood vessels, feed on the fatty deposits, and multiply. This results in inflammation and thickening of the smooth muscle in the artery wall, which helps the formation of plaques and other growths known as atheromas.

For the new study, the team analyzed atheromas collected from patients being treated in hospital.