For years, health experts have blamed the standard American diet for rising rates of diabetes and heart disease. But when it comes to finding a fix, even scientists can’t agree on what we should or should not eat.
Take fat, for example. Over the last few decades, doctors have recommended a diet low in saturated fat to avoid chronic disease.
Saturated fat is found in animal products like dairy, eggs, and meat, and in tropical plants such as coconut and palm. These fats have been a fundamental part of many traditional diets around the world for centuries, but doctors today insist saturated fat will harm our health.
The American Heart Association recommends restricting saturated fats to 5 to 6 percent of everything you eat. On its website, the organization states that decades of sound science have proven saturated fat “can raise your ‘bad’ cholesterol and put you at higher risk for heart disease.”
However, some researchers question whether saturated fat is really as bad as the medical establishment says it is. One such scientist is Dr. Deanna Gibson, an immunologist, microbiologist, and associate professor of biology at the University of British Columbia–Okanagan Campus.
In a culture obsessed with being thin, eating fat doesn’t sound very attractive. But Gibson says our biology requires that we eat some quality fats every day for good brain function and a healthy body.
“We only have three things to eat: carbohydrate, protein, and fat. For some reason, we’ve chosen in the last few decades to focus on how bad fats are in general,” Gibson said. “Your whole body depends on fat. All of our membranes are made of phospholipids. Your hormones depend on the types of fat and the amount of fat that you eat.”
The stigma against saturated fat in particular is so strong that up until the 2000s, trans fat was promoted as a healthy alternative to saturated fat. Today, dietary guidelines set by the U.S. Department of Agriculture recommend eating fat from plant sources such as soy, sunflower, and canola instead of meat and dairy fats. But Gibson suggests that conventional wisdom may be wrong again.
“We base our hypotheses on previous literature or previous assumptions, and it turns out to be wrong when you do the studies,” she said. “I’m often shocked about how little is scientifically known in nutrition. I wonder how we get to these assumptions because I can’t come up with a good answer from the scientific perspective.”
Gibson’s latest study was recently published in the Journal of Infectious Diseases. It showed that saturated fat is much easier on the intestines than most of the vegetable oils that are believed to be healthier. Although monounsaturated olive oil was the clear winner when it came to gut health, saturated fat still outperformed the vegetable oils high in polyunsaturated fatty acids (PUFAs) and omega-6.
“In the context of gut health, it was really clear from my study that if you had a high-fat diet rich in olive oil, that was fabulous,” Gibson said. “But the big thing for me was the difference between the omega-6 PUFAs and saturated fat, because both were similarly pro-inflammatory but the saturated fat actually had many protective responses that were absent in the omega-6 group.”
The study was conducted on rats, but Gibson and her colleagues are planning a similar trial that will test different fats on humans with inflammatory bowel disease. While there are conflicting studies that favor PUFA oils over saturated fat, Gibson isn’t impressed by the evidence.
“We have to be more critical about the studies that we interpret. Most of the nutrition clinical trials that are out there are very poorly done, and most of the rodent studies never led to a clinical study. It doesn’t inform the next step,” she said.
We may not have to worry about infections or nutritional deficiencies as our ancestors did, but the modern world has its own set of health problems. The diseases that plague people today stem largely from chronic inflammation, and based on the evidence she has seen, Gibson believes that our diets heavy in omega-6 are partially to blame.
“When you eat a diet really rich in things that promote those inflammatory responses, then your body really doesn’t know how to shut that down anymore,” she said.
“If we had a mixed diet, a combination of all these fats together, then it probably wouldn’t be a problem. But people today have diets that are very rich in omega-6 and are deliberately avoiding saturated fat. That’s when it becomes really problematic.”
Another nutrition researcher at UBC, Dr. Sanjoy Ghosh, points to other problems with high-PUFA vegetable oils. A study he published last year found that these vegetable fats contribute to sedentary behavior and a predisposition to insulin resistance, similar to that observed in Type 2 diabetes.
“I’ve been studying fat for 12 years,” Ghosh said. “In earlier studies, I found that sunflower oil was worse than palm oil, and people couldn’t believe it. But I’m convinced, and I think other people now understand, that saturated fat is not as bad as we thought.”
The Rise of Vegetable Oils
While many believe science alone informs dietary guidelines, Ghosh says such advice is often shaped by social, political, and economic forces. In fact, it can take decades for good scientific evidence to overcome these other influences.
“It happened with trans fats,” Ghosh said. “We’ve known they were bad since the 1980s, and 20 years later, the government finally agreed. But then all the big food companies said, ‘Hey, we can’t change our oil so fast. We need time because the new oil changes our flavor profile.'”
According to Ghosh, the demonization of saturated fat is more of a story spun to benefit industry, rather than facts based on science. He urges people to read the article “The Oiling of America” by the Weston A. Price Foundation, a food-advocacy group dedicated to promoting traditional diets. The article gives a detailed history of vegetable-oil marketing in America and unpacks many unscientific reasons for why saturated fat is shunned today.
“In the 1950s and 1960s, the North American oil crop farmers were getting hammered by the Malaysian and Indonesian imports of coconut oil. It’s the same thing that’s happening to the U.S. manufacturers with stuff from China today,” Ghosh said.
“Essentially, no saturated fat–containing plants can grow properly in North America. What we do grow is sunflower, safflower, canola, corn, etc. So from the 1950s on, saturated fat was considered to be bad.”
But what about all that “sound science” the American Heart Association says links saturated fat to heart disease? Ghosh says that when you consider how long we’ve restricted our saturated fat intake, the case against it doesn’t hold up.
“In the last 30 years, North American fat consumption has changed drastically. People used to cook with lard, but nobody does this today. Everything in the market has consciously taken saturated fat out.
“So why is heart disease still rising? If saturated fat was causing this, logically it should drop if we take it out of the diet. But it’s still going up,” Ghosh said.
According to the American Heart Association’s 2015 “Heart Disease and Strokes Statistics Update,” cardiovascular disease is the leading global cause of death, accounting for more than 17 million deaths per year. That number is expected to grow to nearly 24 million by 2030.