Fat is good. For real. Bring on the bacon-wrapped mayo

With the salad days of summer behind us and dark, cold days here, fat is in season. The holidays present an opportunity to think about fat, and there is much to consider. I used to assume we ate more fat in winter because our bodies wanted to pack on some insulation against the cold, but the evidence of this seemingly obvious notion – that dietary fat leads to weight gain – is being challenged. And beyond the relationship between fat and health, it’s beginning to look like other beliefs about fat might be wrong as well.

Long considered a threat to public health, some recent books, such as Big Fat Surprise by Nina Teicholz, and before that Good Calories, Bad Calories by Gary Taubes, have challenged the idea that dietary fat is the cause of obesity, heart disease and other ailments. The Economist called Surprise 2014’s “most surprising diet book.” Both Teicholz and Taubes argue that low-fat and non-fat diets, rather than fat, are behind the rise in obesity and related diseases. And Teicholz makes a strong case that fat, especially saturated fat, is actually good for you. As we speak, many government agencies, like USDA, which have long championed low-fat diets, are leaning away from their anti-fat stances.

Other shifts are underway. One is the science of how fat is perceived by the body.

A friend of mine who went to cooking school was fond of saying, “fat is flavor.” This idea has so infiltrated the restaurant industry that recipes for many dishes might as well be written as, “Heat edible materials, add butter, and serve.” Not nuanced, but it works.

According to traditional scientific understanding of flavor perception, however, fat doesn’t have any flavor. This isn’t to say that anyone ever claimed fatty foods aren’t delicious – that is beyond debate. But it was thought that other qualities of fat made this so. It’s long been understood that the texture of fat, and the creamy, viscous, lubricating qualities that it imparts to food, are what makes the food to which it is added taste better, and easier to chew and swallow.

But flavor is a specific metric, a combination of taste – what is perceived by the tongue – and smell. And fat, until recently, was thought to contain neither taste nor smell. New research suggests cooks might have been right all along.

Earlier this year, researchers at the Monell Center, a nonprofit institute dedicated to research on taste and smell, reported humans can smell fat. And in the last few years, fat receptors on the human tongue have been discovered and confirmed by other research teams. If we can taste it and smell it, then it has flavor.

Whether by taste, smell, or texture, our attraction to fats has been assumed to stem from the fact fat is the most calorie-dense type of food. Our hunting, gathering, and often hungry ancestors were programmed to eat as much as they could, goes the logic, and this genetic disposition remains. Fat is also crucially important to brain development in children, and according to Teicholz’s research, a lot of other bodily functions too. But in a surprising twist, the fats to which these receptors are tuned taste bad, not good. They detect free fatty acids, which are found in large quantities in rancid fats, which can be poisonous.

The form of fat that is so pleasing in our mouths is a type in which fatty acids are bound into molecules called triglycerides, which often comprise fats we eat.

It appears we’re programmed to be attracted to the triglyceride form of fat, while being repulsed by free fatty acids. But there’s yet another rub: When we chew those yummy, non-toxic triglycerides, enzymes in our saliva break them down and release the free fatty acids.

Richard Mattes, a professor of nutrition science at Purdue University, has researched and published extensively on fat perception. He told me he believes there is a delicate balance at work. A small quantity of free fatty acids, coupled with the glorious mouthfeel (and subtle smell) of triglycerides, tells the body that this is good stuff. Too many free fatty acids triggers a rejection.

To a certain extent, Mattes said, we can be trained to tolerate higher levels of fatty acids. Stinky cheeses, he pointed out, have a characteristic foul element to their flavors due to high levels of free fatty acids. But we’re able to learn to accept those free fatty acids in this context because we know that stinky cheese won’t kill us, and actually tastes pretty good. But the same amount of fatty acids in, say, a glass of milk would be a red flag.

These fatty acid taste receptors are also present in muscle, skin, blood, spleen, intestine and brain cells. Free fatty acids are the breakdown products of triglycerides, and it is thought that these receptors are dispersed in the body so various tissues can appropriately deal with the free acids from fat consumption.

So one doesn’t just taste fat in one’s mouth, but in one’s whole body. While we don’t consciously experience pleasure when our spleen detects a free fatty acid, this revelation suggests a broader level of meaning to taste perception. One thing that all of these new developments haven’t changed is that eating fat makes us happy, which is important during this dreary time of year. Pass the mayo.