There are four types of fats: saturated fats found in animal products and coconut, palm fruits, and palm kernel oil; trans fats, now banned in U.S. products, which are made from partially hydrogenated vegetable oils; and mono- and polyunsaturated fats found in vegetable oils.

Mono- and polyunsaturated fats are generally more heart-healthy than saturated fats. Extra-virgin olive oil and monounsaturated fats in tree nuts are highlighted as especially heart-healthy, and may help with blood sugar regulation, according to the Mayo Clinic.  

But now a lab study has revealed that a high-fat diet — even from soy oils — might cause serious health problems.

For 24 weeks, researchers fed mice diets in which 40% of the calories came from fat. One group got saturated fat from coconut oil; another group got an unmodified soybean oil high in polyunsaturated fat; a third from monounsaturated, modified soybean oil.

The control group's diet provided 14% of calories from fat. 

All three of the high-fat diets caused changes in gene expression (called epigenetic changes) that were linked to increased inflammation, decreased immune responses, altered gut-brain communication, and growth of unfriendly gut bacteria. That can lead to obesity, colon cancer, irritable bowel syndrome, increased risk of infection, and cognition/mood issues.

Coconut saturated fat caused the most gene changes, but even monounsaturated soy oil caused problems when overconsumed. (Tofu and edamame aren't bad for you, but soy oils — the most commonly consumed fat in America — are good to avoid, say the researchers.)

We want this study replicated in humans before we're certain of its implications, but for now you should stick with non-soy monounsaturated oils such as extra-virgin olive oil.