The diet of a wild gorilla is essentially a great huge salad, without dressing. Yet those foods contain enough fat for the gorillas to absorb fat-soluble vitamins from their food, and enough of the essential fatty acids for the gorillas to have a normal healthy nervous system and lots of glossy hair. So when people tell me that I need to take fat supplements, I'm not buying. A spoonful of ground flaxseed in my oatmeal in the moring, okay. But I'm not buying any sort of other fatty acid supplement until I see data that shows that they do more good than harm.
I've seen lots of evidence in the scientific literature that switching to a low-fat (<10% of calories), oil-free diet can make people heart-attack-proof, reduce their risk of cancer, and even fight arthritis. I haven't seen anyone getting results like that from swapping one fat for another in a high-fat diet, or by adding oil supplements to an unhealthy diet. If you are sick and are thinking of using some sort of fat supplement as a drug, ask your doctor and a registered dietitian about trying a low-fat, plant-based diet first.
Don't worry about suffering from a deficiency of fat on a low-fat diet. Most of the actual cases of people who had trouble because they didn't consume enough fat were getting fed nothing but sugar intravenously. In those cases, simply rubbing some vegetable oil on the skin solved the deficiency. It's also possible to get into trouble if you can't absorb fat from your food, usually because of some disease of the digestive system. But if that's your problem, you really need to be under the care of a doctor and a registered dietitian.
What's the difference between fat and a fatty acid?
An oil is merely a fat that stays liquid at room temperature. Most of the oils and other fats in our food are mainly in the form of triglycerides. Each molecule of triglylceride contains three molecules of fatty acid, bound to one molecule of glycerol.
If you’ve ever gotten soap in your eye, you’ll understand why the body prefers to store fat as triglycerides than as free fatty acids. Free fatty acids have a carboxyl group (-COOH) on one end. The carboxyl group is what gives vinegar its bite, and it causes the free fatty acids in soap to be irritating. Binding that carboxyl end to a glycerol molecule makes it much less reactive, and much less irritating!
Why aren't fats all alike?
At room temperature, olive oil is liquid but chocolate is solid. That's because the fats in them contain a different mixture of fatty acids. Olive oil contains a lot of oleic acid, while chocolate contains a lot of stearic acid. Although both of these fatty acids contain 18 carbon atoms, the stearic acid contains as many hydrogen atoms as it could possibly hold. Thus, we say that it is a "saturated fat." Oleic acid has one double bond between carbon atoms, so it is a monounsaturated fat. The two essential fatty acids also contain 18 carbon atoms but have even more double bonds in them, so they are "polyunsaturated."
According to the Food and Nutrition Board of the National Research Council, human beings can easily make all the saturated fat and monounsaturated fat that their bodies need. This means that there is no need to get any saturated or monounsaturated fat whatsoever from the diet. That means that you don't need to eat butter or olive oil. The Food and Nutrition Board also says that you don't need to get any trans fat from the diet. Trans fats are rarely found in nature, but they are common in fats that have been hydrogenated. For an explanation of hydrogenation and trans fats, click here.
According to the Food and Nutrition Board , only two fatty acids are considered to be essential in the human diet. One of them is linoleic acid, which is an omega-6 fatty acid. The other is alpha-linolenic acid, which is an omega-3 fatty acid. They are essential because we need them for various purposes but can't make our own supply. That's because we don't make the enzymes that would be necessary to put a double-bond at the omega-3 or omega-6 position.
We can burn linoleic acid and alpha-linolenic acid for energy. We can also convert them into other useful substances, but first we have to lengthen the carbon chain. Linoleic acid and alpha-linolenic acid both contain 18 carbon atoms. The human body can convert linoleic acid into arachidonic acid (AA), which has 20 carbon atoms. The body can convert alpha-linolenic acid into eicosapentaenoic acid (EPA), which also contains 20 carbon atoms. The body uses AA and EPA to make eicosanoids, which are chemical signals that play an important role in the process of inflammation and in the nervous system. The body can also convert EPA into docosahexaenoic acid (DHA), which has 22 carbons.
Unlike human beings, cats can't make arachidonic acid from linoleic acid. As a result, they have to get arachidonic acid from their food. Since arachidonic acid is rarely found in plants, those animals have to eat meat. In other words, they are "obligate carnivores." If you want to design a plant-based diet for cats, you'll have to supplement it with arachidonic acid, among other things.
How much of the essential fatty acids do we need?
Human requirements for the essential fatty acids are surprisingly low, only about 2% of our calorie requirements. To find people who have a deficiency of linoleic acid, you have to look at people who have been fed a lot of sugar intravenously. They end up with signs of fatty acid deficiency partly because they aren't getting any linoleic acid from food and partly because their high insulin levels keep them from releasing the omega-6 fatty acids from their fat stores. To find people with an out-and-out deficiency of omega-3 fatty acids, you have to look at hospital or nursing-home patients who had been tube-fed something that was practically devoid of alpha-linolenic acid for an extended period.
Absolute deficiency of the omega-6 or omega-3 fatty acids is extremely rare; however, there has been considerable concern about the balance between omega-6 and omega-3 fatty acids in the diet. If people eat too much omega-6 fatty acid, compared to their intake of omega-3 fatty acid, they could end up making more of the eicosanoids that come from arachidonic acid and less of the ones that come from eicosapentaenoic acid. This could end up shifting the body toward a pro-inflammatory as opposed to anti-inflammatory state. The obvious solution to this problem is to eat a low-fat diet with lots and lots of vegetables. Although vegetables don't contain much fat, a lot of the fat they do contain is alpha-linolenic acid. To make sure that you get enough alpha-linolenic acid to balance your linoleic acid intake, you can eat a spoonful of ground flaxseed every day, or perhaps a few walnuts.
Can you get too much omega-6 or omega-3?
Americans tend to think that you can't get too much of a good thing. We tend to think that if more is better, then too much is just right. Yet it is possible to get too much fat in the diet, even too much of the essential fatty acids. People should keep this in mind, especially if they are considering using fatty acid supplements as a drug.
Eating too much fat makes you fat. If you eat more calories than you burn up, your body will tend to burn the dietary carbohydrates first and store the excess fat you just ate. The fat goes straight to your fat cells, and where very little energy is consumed in turning it into body fat. In contrast, you waste about 30% of the calories from sugar when you turn sugar into body fat. That's one of the reasons why high-fat diets are more fattening than high-carbohydrate diets.
Eating too much fat, even too much of the omega-3 fatty acids, can promote atherosclerosis, which is the buildup of plaque on the insides of the arteries. A high-fat diet causes the body to produce more cholesterol, which helps to digest fat. People who eat animal products also get some cholesterol ready-made in their diet.
Atherosclerosis can lead to heart attack and stroke. The best way to prevent these problems is to eat a low-fat (<10% of calories), high-fiber, plant-based diet. Plant foods contain no cholesterol, and a low-fat diet reduces the amount of cholesterol that your body makes. Some kinds of dietary fiber bind to cholesterol in the intestine, to keep your body from recycling it. Together these effects help reduce cholesterol levels to the "heart-attack-proof" zone of <150 mg/dL.
Is omega-3 fatty acid a medicine?
Although the best way to prevent atherosclerosis is to switch to a low-fat, plant-based diet, some people argue that eating fish will prevent heart disease. The truth is a bit confusing. You might be able to reduce your risk of a fatal heart attack a little by eating fish instead of other fatty animal products. However, you can make yourself heart-attack-proof by shifting to a diet that contains no animal products whatsoever and gets less than 10% of its calories from fat of any kind.
Besides promoting atherosclerosis, eating too much omega-3 fatty acid can cause other problems. Because it thins the blood, it can increase the risk of bleeding. Research also suggests that eating too much polyunsaturated fat, including omega-3 fatty acids, can promote the growth of cancer.
Many of the diseases that people hope to manage by using omega-3 fatty acid supplements are actually a result of the standard American diet. Heart disease results from eating too much fat and cholesterol. Arthritis is often the result of eating animal protein instead of plant protein. Even depression could be related to the standard American diet. It would make more sense to correct the diet by shifting to a low-fat, plant-based diet, instead of trading one fat for another or adding fat supplements. If you have a disease that you want to manage by using omega-3 fatty acid supplements, talk to a registered dietitian as well as a medical doctor.