After about age 20, we may have all the insulin-producing beta cells we’re ever going to get. So, if we lose them, we may lose them for good. Autopsy studies show that by the time type 2 diabetes is diagnosed, we may have already killed off half of our beta cells.

You can kill pancreatic cells right in a petri dish. If you expose the insulin-producing beta cells in our pancreas to fat, they suck it up and then start dying off. Fat breakdown products can interfere with the function of these cells and ultimately lead to their death. A chronic increase in blood fat levels can be harmful to our pancreas.

It’s not just any fat; it’s saturated fat. As you can see in my video, What Causes Diabetes?, predominant fat in olives, nuts, and avocados gives a tiny bump in death protein 5, but saturated fat really elevates this contributor to beta cell death. Therefore, saturated fats are harmful to beta cells. Cholesterol is, too. The uptake of bad cholesterol (LDL) can cause beta cell death as a result of free radical formation.

Diets rich in saturated fats not only cause obesity and insulin resistance, but the increased levels of circulating free fats in the blood (non-esterified fatty acids, or NEFAs) may also cause beta cell death and may thus contribute to the progressive beta cell loss we see in type 2 diabetes. These findings aren’t just based on test tube studies. When researchers have infused fat directly into people’s bloodstreams, they can show it directly impairing pancreatic beta cell function. The same occurs when we ingest it.

Type 2 diabetes is characterized by “defects in both insulin secretion and insulin action,” and saturated fat appears to impair both. Researchers showed saturated fat ingestion reduces insulin sensitivity within hours. The subjects were non-diabetics; so, their pancreases should have been able to boost insulin secretion to match the drop in sensitivity. But no, “insulin secretion failed to compensate for insulin resistance in subjects who ingested [the saturated fat].” This implies saturated fat impaired beta cell function as well, again just within hours after going into our mouth. “[I]ncreased consumption of [saturated fats] has a powerful short- and long-term effect on insulin action,” contributing to the dysfunction and death of pancreatic beta cells in diabetes.

Saturated fat isn’t just toxic to the pancreas. The fats found predominantly in meat and dairy—chicken and cheese are the two main sources in the American diet—are considered nearly “universally toxic.” In contrast, the fats found in olives, nuts, and avocados are not. Saturated fat has been found to be particularly toxic to liver cells, contributing to the formation of fatty liver disease. If you expose human liver cells to plant fat, though, nothing happens. If you expose our liver cells to animal fat, a third of them die. This may explain why higher intake of saturated fat and cholesterol are associated with non-alcoholic fatty liver disease.

By cutting down on saturated fat consumption, we may be able to help interrupt these processes. Decreasing saturated fat intake can help bring down the need for all that excess insulin. So, either being fat or eating saturated fat can both cause excess insulin in the blood. The effect of reducing dietary saturated fat intake on insulin levels is substantial, regardless of how much belly fat we have. It’s not just that by eating fat we may be more likely to store it as fat. Saturated fats, independently of any role they have in making us fat, “may contribute to the development of insulin resistance and its clinical consequences.” After controlling for weight, alcohol, smoking, exercise, and family history, diabetes incidence was significantly associated with the proportion of saturated fat in our blood.

So, what causes diabetes? The consumption of too many calories rich in saturated fats. Just like everyone who smokes doesn’t develop lung cancer, everyone who eats a lot of saturated fat doesn’t develop diabetes—there is a genetic component. But just like smoking can be said to cause lung cancer, high-calorie diets rich in saturated fats are currently considered the cause of type 2 diabetes.

I have a lot of videos on diabetes, including:

Preventing the disease:

And treating it:

In health,

Michael Greger, M.D.