A diet high in fat, especially saturated fat, has been shown to increase lipids inside muscle cells and decrease insulin sensitivity. Photo credit: Cristian Baitg Schreiweis/iStockphoto

This is an older study but it shows this was known for decades: a high-fat diet contributes to insulin resistance, a hallmark of type 2 diabetes:

Effects Of Intravenous And Dietary Lipid Challenge On Intramyocellular Lipid Content And The Relation With Insulin Sensitivity In Humans, Diabetes, November 2001

In just three days on a high-fat diet, 12 young, healthy, male, normal-weight, nondiabetic volunteers, showed substantially increased lipid levels inside their muscle cells and a decrease in insulin sensitivity, similar to what occurred after an overnight intravenous lipid infusion.

– In the diet protocol, 12 male subjects ingested both a high-fat and low-fat diet for 3 days each.
– After the high-fat diet, IMCL [IMCL is intramyocellular lipid, that is, lipid located within muscle cells] levels increased significantly. Insulin sensitivity decreased to 83.3 ± 5.6% of baseline (P = 0.033).
– There were no significant changes in insulin sensitivity or IMCL levels after the low-fat diet.

Each subject received a high-fat low-carbohydrate diet and a low-fat high-carbohydrate diet for 3 consecutive days each.

1) High-fat diet: fat: 55–60% of energy intake, carb: 30–35%, protein: 11–16%
2) Low-fat diet: fat: 18–23%, carb: 62–64%, protein: 16–18% protein

After ingestion of the high-fat diet for 3 days, both IMCL levels and insulin sensitivity were clearly affected.

This conclusion agrees with findings from several studies that have showed that a fat-rich diet can increase plasma NEFA [nonesterified fatty acid] levels, and, moreover, that this increase in NEFA levels is accompanied by a decrease in insulin sensitivity (3,10,11,24,25).