Fat is back. After being banished for years, dietary fat is now recognized as not only useful, but also essential. Scientists have known for years that at least two types of fatty acids are essential, linoleic and alpha-linoleic acids. Linoleic acid is classified as an omega-6 fatty acid and is found mostly in vegetable oils. Alpha-linoleic acid is a precursor for the omega-3 fatty acids, which also exist in fattier fishes, including salmon, herring and halibut. The fat that has the worst reputation is saturated fat, which is hard at room temperature, whereas the essential fats are usually liquid under the same conditions. Fats are classified in several ways; for example, according to the number of carbons contained in the chain or the length of the carbon chain. Another classification involves whether the carbon chains have openings for hydrogen. If there's at least one such opening, the fat is said to be monounsaturated. Examples of monounsaturated fats include canola and olive oils. If there are more than two openings for hydrogen in the carbon chain, the fat is polyunsaturated. The essential fats described above are polyunsaturated.
A saturated fat has no openings for hydrogen along its carbon chain. Besides not being essential in human nutrition, saturated fat is considered a 'bad' fat by most health organizations because it's a substrate, or starting substance, for the synthesis of cholesterol in the liver. In fact, the body doesn't absorb much cholesterol from food, but it does absorb plenty of saturated fat.
Like most fats, saturated fat contains nine calories per gram. That makes it the highest-density source of food calories. Even worse, while polyunsaturated fats, especially the omega-3 fatty acids, promote increased insulin sensitivity, saturated fats do the opposite, creating insulin resistance. That, coupled with the concentrated calories it contains, makes saturated fat more readily turned into bodyfat than other fats. The body also requires less energy to metabolize fat than it needs for protein or carbs, which also tends to divert excess saturated fat to storage. When excess calories are combined with a lack of exercise, the situation is even worse.
Despite its reputation, even saturated fat isn't totally evil. Research shows that you should get at least 20 percent of your total daily calories as fat to maximize your body's testosterone synthesis. Although it's not essential, saturated fat does contribute to the overall fat-calorie requirement for testosterone synthesis. Most of the fat stored in your body is also saturated fat, which cushions vital internal organs such as the kidneys. Fat also has an insulating effect that maintains body temperature under cold conditions. If you have too much stored in your body (above 15 percent if you're male), you may get some small solace from this fact: If you and Mr. Olympia Ronnie Coleman were stranded at the North Pole, you would likely survive longer'assuming that Coleman was in contest shape.
Another advantage of saturated fat is that there's little or nothing for free radicals to hook onto. Free radicals are products of oxidation that are linked to various disorders, ranging from cancer to cardiovascular disease. In fact, saturated fat is far less subject to oxidation than the healthier but more susceptible polyunsaturated fats. The poly fats are so subject to oxidation that their unrefrigerated shelf life is nil, and they go rancid rapidly if exposed to oxygen.
From the perspective of food processing, that relatively short shelf life of fat is problematic. A remedy was introduced around 1911, when Procter & Gamble introduced a product called Crisco. It was made from an omega-6 oil that was commonly used at the time, cottonseed oil; however, what Procter & Gamble food chemists did to that cottonseed oil has been described by one noted researcher, Dr. Walter Willett of the Harvard School of Public Health, as, 'the single most harmful thing the food industry has done in the past 100 years.'
In Crisco, Procter & Gamble created a new type of processed fat that has since become ubiquitous. It's called trans fat, and it is perhaps no coincidence that with the introduction of trans fat into the food supply, a formerly rare disease generally known as cardiovascular disease began to increase. It's now the number-one killer of people around the world.
The question is, Are trans fats really that bad? That's an ongoing debate among food-processing companies and medical researchers, and it goes to the very nature of a trans fat's makeup.
What Are Trans Fats?
In terms of their carbon-chain structure, polyunsaturated fats are typically missing four or six hydrogens or more. In place of the missing hydrogens, the carbons adjacent to the hydrogen 'gaps' double-bond with each other, giving the carbon chain a curved appearance. The more hydrogens that are missing, the greater the susceptibility to oxidation. Thus, polys are more easily oxidized than mono fats.
In chemistry, the curvature of the double bonds along the carbon chain of a mono or poly fat is known as a cis configuration. That doesn't apply to saturated fats, which are filled with hydrogen along the length of the carbon chain and appear as straight chains. The way fat carbon chains are laid out'either straight (saturated) or curved (poly and mono) also imparts physical attributes, such as the hardness of saturated fat at room temperature and the liquid appearance of poly and mono fats (there are some exceptions to that rule, such as coconut oil, a saturated fat that's liquid at room temperature).
In making trans fats, food processors start with either a mono or a poly fat'both comparatively unstable compared to saturated fat'and add hydrogen to the missing areas on the carbon chain. Depending on how many hydrogens are added, the fat then becomes either a partially hydrogenated fat or a fully hydrogenated one. Most trans fats are partially hydrogenated fats. They have the same number of carbons in their structural chain as they had originally'and even the same length. What's changed is their shape. They've gone from the natural cis configuration to a straight chain that looks and acts like a saturated fat.
It isn't an entirely unnatural process. It turns out that trans fatty acids are produced in the rumen, or stomach, of many farm animals and exist naturally in dairy foods. Even so, the amount in food is minuscule compared to what you get from artificially produced trans fatty acids. A food like butter may contain 2 to 3 percent naturally occurring trans fat, while a processed food may contain 30 to 40 percent artificial trans fat. A point of interest here is that the body can synthesize conjugated linoleic acid from natural trans fat sources'not the synthetic type.
Why Are Trans Fats Bad for You?
The primary problem with artificial trans fats is that the body doesn't know what to do with them. They displace natural fats, including saturated and unsaturated types, in structures such as cell membranes, which radically changes the structures' characteristics. They also inhibit enzymes that work with essential fats in the synthesis of vital chemicals and hormones, including testosterone. Important hormonelike chemicals made from fats called eicosanoids control myriad vital processes in the body, from blood pressure to hormonal secretion. Trans fats displace the normal fats used in such conversions and also inhibit the enzymes needed to catalyze the reactions.
One example of such enzymatic interference has to do with an enzyme called delta-6-desaturase, which is involved in promoting the conversions of omega-6 and omega-3 fatty acids into the elongated forms needed for the synthesis of prostaglandins and other eicosanoids. Thus, trans fats interfere with the activity of essential fatty acids, possibly leading to a deficiency or worsening an existing deficiency.
Trans fats are used in most processed foods, including frozen so-called diet meals (a brand called Healthy Choice has trans fats in every one of its products!), baked foods, such as crackers and cookies (30 to 50 percent trans fat), french fries (40 percent), potato chips and fast-food fried foods (KFC chicken is brimming with trans fats)'even ice cream. Police officers reading this should know doughnuts derive an average of 35 to 40 percent of their calories from trans fats. Any food label that lists 'partially hydrogenated fat' as an ingredient contains trans fats. Trans fatty acids are estimated to represent 11 to 20 percent of total fat intake in the American diet. The main source is probably stick margarine. That delicious popcorn you ate at the movies contains an ocean of trans fat'even if you leave off the 'butter-flavored topping.'
So what's the bottom line on damage caused by trans fats? The health effects include the following:
1) They lower a protective form of cholesterol called high-density lipoprotein (HDL) in a dose-response manner, meaning the more trans fat you eat, the lower the HDL. Interestingly, poly fats also lower HDL, while saturated fats raise it. Mono fats have a neutral effect on HDL. One study of 80,082 women between the ages of 34 and 59 found that the replacement of 2 percent of energy from trans fat with energy from unhydrogenated, unsaturated fat would reduce cardiovascular risk by 53 percent. An ongoing heart study in Framingham, Massachusetts, found that seven teaspoons a day of hard margarine doubled the subjects' risk of having a heart attack or stroke.1
2) At the same time they raise the level of low-density lipoprotein (LDL), a form of cholesterol associated with increased cardiovascular disease. In that effect they act similarly to saturated fat; however, the increase with trans fat is double that of saturated fat. In a total of nine out of 10 trials trans fat also increased the level of lipoprotein(a) in the blood, a substance that acts similarly to LDL in promoting cardiovascular disease. Trans fats also increase the plasma level of total cholesterol and triglycerides, both of which are risk factors for cardiovascular disease. Another study found that trans fats increase total cholesterol levels by inhibiting the breakdown of cholesterol in the body.2
3) Trans fats may increase blood insulin levels in response to a glucose load. That effect likely relates to a change in cellular membranes induced by trans fats that interferes with the functioning of cellular insulin receptors, leading to a relative insulin resistance. Such a scenario can set the stage for diabetes in a person who's genetically predisposed to it.
4) Trans fats adversely affect immune function by lowering the B cell response while increasing the proliferation of T cells. The B cell effect probably results from interference with either cytokine synthesis (cytokines are immune system messengers that modulate immune response) or eicosanoid synthesis, which also regulates immune response.
5) Studies done with rats show that trans fats may decrease serum testosterone levels while increasing the amount of abnormal sperm production.3
6) Trans fats interfere with a system in the liver (P450 and mixed oxidase) that helps to metabolize carcinogens and various drugs, including steroids.
7) Trans fats may promote breast cancer in women. One study that analyzed tiny fat samples taken from the buttocks of 698 European women found a 40 percent increased risk of breast cancer in the women who had higher levels of trans fat stored in their bodies. The researchers also found that the high-risk women ate lower levels of polyunsaturated fat, which led them to suggest that trans fats may have interfered with a protective function of poly fat that would have helped prevent breast cancer. They also noted that even if the women stopped eating all food containing trans fat, it would still take up to a year for a decline in trans fat to show up in the women's fat stores.
Can You Counter the Effects of Trans Fats?
When you diet, trans fat stored in your bodyfat is released, which can interfere with the function of essential fatty acids, as described above. The increased trans fat may predispose some people to increased risk of serious cardiovascular events due to blood clotting. One antidote to that potentially dangerous scenario is to make sure you increase your intake of essential fats, especially omega-3 fatty acids, when you diet.4 A recent rat-based study found a nutritional antidote to trans fat: soluble fiber. The resarchers found that psyllium, a soluble food fiber, binds with trans fats and prevents the deleterious changes in blood lipids they cause.5
Even the Food and Drug Administration has stated that 2,100 to 5,600 lives could be saved each year in the United States if food labels listed trans fat content. In the meantime, the best course is to avoid all foods that list 'partially hydrogenated oil' as an ingredient. Avoid hard margarines and fried fast foods. If you have to use margarine, stick with the soft version that comes in tubs, or better yet, use only the newer spreads that don't contain any trans fats. When using oils, make sure they're always unprocessed.
1 Hu, F.B., et al. (1997). Dietary fat intake and the risk of coronary heart disease in women. New Eng J Med. 337:1491-1499.
2 Cuchel, M., et al. (1996). Impact of hydrogenated fat consumption on endogenous cholesterol synthesis and susceptibility of low-density lipoprotein to oxidation in moderately hypercholesterolemic individuals. Metabolism. 45:241-247.
3 Zidek, H.T., et al. (1989). Effects of dietary trans fatty acids on reproductive performance of Wistar rats. British J Nutrition. 61:519-29.
4 Jones, D. (1993). Trans fatty acids and dieting. Lancet. 341:1093.
5 Fang, C., et al. (2000). Dietary psyllium reverses hypercholesterolemic effect of trans fat in rats. Nutrition Research. 20:695-705. IM
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