New science challenges old ideas about how fat fits into a healthy diet
The famous Pogo comic strip said it best: “We have met the enemy and he is us.”
In the quest for health, popular fads — and even reasoned (but incorrect) science — have led us down blind alleys that ended up causing us more harm than good.
Take fat. A fear of fat, based on clinical recommendations to eat low-fat foods, led health seekers to remove chicken skin, avoid red meats, switch from butter to margarine, boil pork, and eat only lean protein for years. The results? Decades of low-fat diets have been tied to increasingly poor health outcomes and burgeoning obesity rates for Americans.
But the tide is changing. New research is challenging our old ideas about fat and, believe it or not, it’s beginning to look like “fat and happy” is the healthy way to go.
As long as it’s the right kind of fat.
The biology of fat
But before we get to fat and happy, we need to understand some fat basics. Let’s start under your skin, where you have fat floating freely in your blood and layers of fat cells called adipose tissue. You can think of individual adipose cells as toy balloons, which can be either empty and deflated or filled up like water balloons. But instead of water, the adipose cells store globules of fat. Why? It’s an elegant fuel-storage system, allowing your body to store fat to use as fuel when our normal fuel, food, may not be available.
The fat cells fill their balloons for storage primarily by syphoning free-floating dietary fats directly out of the bloodstream. But they also are capable of manufacturing fat directly from excess glucose in the blood.
Adipose tissue stores or makes fat because your body needs fat to function. You can’t do away with it. This is why fats, along with carbohydrates and proteins, are one of the three principal classes of foodstuffs that make up the human diet. And of the three, fat is the turbo-charged source of power for the body. Gram for gram, fats contain more than twice the energy of carbs or protein.
While providing energy reserves is a primary function of fat in our bodies, the body itself is a magnificent multitasker. Layers of fat also cushion our internal organs, providing separation and padding. Due to fat’s low rate of heat transfer, fat provides excellent insulation. This is why cold-weather animals such as whales, walruses, and arctic bears have thick layers of fat to protect themselves from the harsh elements. Fat also drives a host of smaller biological processes.
All mammals have two kinds of fat: white and brown. White is by far the most common in humans and serves the energy, padding, and insulation roles. Brown fat, on the other hand, can be burned by the body to generate heat and is found more commonly in hibernating creatures. Human infants are born with some brown fat, but the percentage of brown fat in our bodies rapidly decreases with age.
Fat is necessary, useful, and efficient. But how much do you need? The answer hinges on what kind of fat you are talking about, and whom you ask. But first, not all fats are created equal.
Types of dietary fats
Fats come from plants, animals, and test tubes. Plant fats generally come from reproductive tissues such as seeds and fruits and, interestingly, are in greater abundance in ripe nuts and fruits. Unripe seeds and fruits are composed largely of sugars and starches. Of course, animal fats come from the adipose tissue of dietary meats. Artificial fats are produced in factories and have more in common with petroleum than with biology.
All fats are broadly defined as either saturated or unsaturated, a scientific classification based on the chemical structure of the fat molecules. Saturated fats are “saturated” with hydrogen atoms, while unsaturated fats are made up of carbon chains that lack the hydrogen. If you can’t make sense of that, just realize it’s a depth of science impossible for most people to get their heads around. To be technically accurate, it is actually the fatty acids, the building blocks of fat, that make the fat either saturated or unsaturated.
But while all that might take a master’s degree in chemistry to understand, anyone easily can tell the difference between saturated and unsaturated fats in the real world by how they look. At room temperature, saturated fats are soft solids, while unsaturated fats are liquids.
Saturated fats are largely animal in origin. They include the fats in red meat, poultry, and dairy products such as butter and cheese. They also are common in commercially prepared baked goods. It used to be believed these fats would raise bad cholesterol because saturated fats trigger cholesterol production by the liver, but recent research is challenging that long-held conventional wisdom. Most experts no longer consider saturated fats the evil they were once thought to be.
Unsaturated fats come from plants and fish. They include cooking oils from olives, peanuts, and corn and fish oils. Unsaturated fats also are found in most nut butters and avocados.
The role dietary fats play in your body
Your body needs both saturated and unsaturated fats. As proof, look no further than the fuel for babies: milk, which is made up of 60% saturated fatty acids and 40% unsaturated fatty acids.
Beyond being used for energy, saturated fats are needed for the construction of cell membranes, organ padding, and nerve sheathes. Saturated fats play an important role in hormone production, cellular signaling within the body, and immune function. Saturated fats also are required for the proper absorption of some minerals and fat-soluble vitamins including A, D, E, and K. And some research suggests saturated fatty acids have a role to play in suppressing some types of cancers.
So much for saturated fat being evil.
Unsaturated fats boost artery-cleaning good cholesterol, lower triglycerides, regulate blood clotting, help maintain healthy blood pressure and are key players in proper brain function. Some evidence suggests unsaturated fats lower insulin resistance. Unsaturated fats include the omega-3 fatty acid family that has been linked to good cardiac health and may reduce risk of depression.
But there is still one bad fat
There is one fat that the body apparently does not need — a special subset of saturated fats called trans fat. Trans fats are the test-tube fats. Trans fat is largely a man-made substance that only very rarely occurs in nature. Modern trans fat is an invention of the industrialized food complex, and it has been strongly linked to an increase in heart disease, stroke, and possibly Type 2 diabetes. Trans fat wipes out healthy cholesterol and greatly increases low-density lipoprotein, which narrows and hardens arteries.
Trans fat is manufactured by taking a healthy unsaturated fat and forcing hydrogen atoms into its molecules using heat and heavy metals such as palladium, thereby transforming the liquid into a solid. This process also is called hydrogenation, thus the ingredient “partially hydrogenated oil” seen on some nutrition labels. Why would anyone do this? To make unsaturated oils last longer. The hydrogenation process basically pickles the oil, making it stable for long-term storage and transportation. In 2000, it was found in fully 60% of food items on grocery store shelves.
But in addition to making the fat spoil-proof, it also makes it unfit for human digestion. In fact, you can argue that it turns the fat into a near poison. A little bit can cause a lot of harm. Research by the Harvard School of Public Health found for every 2% addition of daily calorie intake that came from trans fat, the heart attack risk rose 23%. On top of that, unlike natural fats, there is no evidence trans fat has a single health benefit other than providing calories.
Trans fat has been recognized as sufficiently bad for human health that it is being phased out globally. In 2006, the U.S. Food and Drug Administration (FDA) required the food industry to begin declaring the amount of trans fats on Nutrition Facts labels, and in 2013, the FDA took the unprecedented step of making a preliminary determination that partially hydrogenated oils, the primary trans fat in the American diet, should be labeled as “not generally recognized as safe,” the agency’s way of saying a product is dangerous. The FDA said banning trans fats from the American diet could prevent thousands of heart attacks and deaths a year. A final determination released in June 2015 completely bans the oils after June 18, 2018.
How much fat do we need?
So trans fats aside, which clearly are to be avoided, how much saturated and unsaturated fat do we need? With all the chaos and new research into fats and their roles, no one really knows for sure. At the moment, the official government recommendations (which are scheduled to be updated this year) say you should limit your fat intake to 10% of your daily calories. The American Diabetes Association still supports this level, but the American Heart Association is holding the low-fat line, recommending a saturated fat limit of 5% to 6% of calories.
But a growing body of science does not support these low levels.
One recent National Institutes of Health (NIH) study, headed by Dr. Lydia A. Bazzano of Tulane University, compared the currently recommended low-fat diet to a low-carb, high-fat diet, using a randomized, parallel-group trial. The results were published in the Annals of Internal Medicine last autumn. The study group eating more fat and fewer carbs lost more weight, which was no surprise. The big surprise came when measuring cholesterol.
Even though the low-carb group took in more than double the recommended saturated fat limit of the American Heart Association — plus high levels of unsaturated fat as well — for a whopping total fat intake of fully 40% of daily calories, they still lowered their cardiovascular risk factors. They actually lowered their Framingham Risk Scores, a measure of 10-year heart attack risk.
This study, and dozens of others, have caused some experts in the field to call for saturated fat to no longer be considered a “nutrient of concern for overconsumption” in future nutrition guidelines, possibly clearing the way for no set limit on the consumption of saturated fat.
From eat-no-fat to no limits. Clearly, fat is back.
Decades of worsening health and new science challenging long-held beliefs are clearing fat’s name. While it may be decades before you can confidently ask your doctor how much fat is right for you, the answer in the short term seems to be more than less. Or, at least, don’t worry about trying to cut it out completely from your diet.
The writing is on the wall. After decades of misunderstanding and wrongfully banishing fat, modern medicine is finally realizing that we have met the enemy. And he is not fat. “He is us.”