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Okay, so I wanted to call this “the Skinny on Fats” – but it’s SOooooo cheesy! (Okay, and it’s been done. A lot.)
Undaunted, I tossed around some other possibilities:
‘Grease – The Untold Story,” Rejected. Too “Olivia Newton-John.”
Continuing, I tried “Hey Fatty” – but it somehow just didn’t convey my usual academic style.
So I’ll settle on “Mmmmm fat!”
Really, it’s my favourite macronutrient. There’s just something so … sensuous about this unctuous wonder. And we’re hard-wired to love it. Unlike proteins and carbohydrates, which contain roughly 4 kcal/g of energy, fat has more than double this – 9 kcal/g. No wonder part of our survival mechanism tells us to love this stuff – it’s a very rich fuel!
(As always, skip to the very end for the “I don’t care, just tell me what to take” section.)
What is it?
Of the three macro nutrients – protein, carbohydrate, and fat – only two (1) are considered “essential”: protein and fat. Mr. Gentilcore did an excellent job on the first two - Protein Power and The Carbohydrate Conundrum. I’ll see if I can avoid butchering the third. What we commonly refer to as “dietary fat” is a category of lipid known as triglyceride. This is glycerol (glycerin) that has been esterified with three fatty acids.
Doesn’t mean that much to me either, but I had to say it – it was in Wikipedia. I’ll give a stab at describing what I’m talking about: think “Charlie Brown’s Christmas tree” – a skinny pathetic thing with room for three ornaments.
Below would be glycerol – a three-carbon molecule, each with 1 OH group. (2)
Glycerol – a three-carbon molecule
The three “ornaments” we’re going to hang on it to make a triglyceride are the fatty acids - basically carbon atoms chained together and populated to varying degrees with hydrogen atoms. (3) There’s something called an “acid group” at one end of this chain, and at the other end, an extra hydrogen, forming a methyl group. Variations in this simple structure (see below) will be discussed below.
Fatty Acids - Variations
Moving right along, these fatty acids attach to the OH groups via something called “dehydration synthesis” (the hydrogen on the fatty acid “acid group”-end joins up with the OH group on the glycerol to form H2O) to yield an “ester” bond. (4) Voilà – a triglyceride is born!
When you eat them, fats (triglycerides) are split back into glycerol (the Christmas tree) and fatty acids (the ornaments) through the process of digestion, and are re-assembled in our blood stream into lipoproteins - structures which (among other functions) shuttle fatty acids to and from fat cells. (5)
When the body needs fatty acids for energy, glucagon (a hormone) signals the breakdown of triglycerides to release them. The brain can’t use fatty acids directly as a fuel source, but glycerol can be converted to glucose for brain fuel. Fat cells can also be broken down for this purpose. (6)
So, although the body can use dietary fat or body fat for this purpose, for simplicity, this article will focus on dietary fat.
Fats serve many purposes in the body. Aside from being yummy and satisfying, we need them for good health. The various dietary fats are an important source of calories in our diets.
Fat is used in the production of hormone-like compounds called eicosanoids that help regulate blood pressure, heart rate, blood vessel constriction, blood clotting and the nervous system. Fat keeps your skin and coat nice and shiny (good dog!), pads your organs, and insulates your body. (7)
Fats are important for testosterone production (8) (which helps you gain muscle mass), partitioning (which helps you lose fat) (9) , the control of inflammation (10), and for the metabolism of fat-soluble micro nutrients such as vitamins A, D, E and K. (11) Fats can help or interfere with the metabolism of other fats (12) (13), , and eating fats with your veggies helps you get more nutrition out of them than if they were eaten without fat. (14) Clearly, you cannot do without this stuff, although its unfortunate caloric price tag makes cutting dietary fat seem like an easy fix when looking to lose weight.
The technical crap (skip unless you’re white and nerdy like me)
The designation “fat” or “oil” depends upon its melting point: at room temperature, fat is solid, where oil is liquid. I will use these terms interchangeably because everybody else does, and I’ve learned to pick my battles (remind me to talk about wide-grip chins sometime…)
Fatty-acid carbon chains (the ornaments mentioned above) are populated to varying degrees with hydrogen - the more hydrogen, the higher the level of saturation. Each carbon in the chain has room for two hydrogen’s.
Sometimes, every carbon in the chain has two hydrogen’s, because all the carbons in the chain are attached with single bonds. (16) (see below)
Saturation - every carbon in the chain has two hydrogen’s
..but when the bond between two carbons is double, the affected carbons only have enough room left for a single hydrogen. In the jargon of the fatty world, this is referred to as unsaturation. (see below)
Unsaturation - affected carbons only have enough room left for a single hydrogen
Hang in there - almost done with the icky stuff.
In the example here (and above), the hydrogen’s attached to each of the double-bonded carbons are on the same side of the chain. We call this the “cis” formation. (see below)
“cis” formation - each of the double-bonded carbons are on the same side of the chain
When the hydrogen’s are on opposite sides of the double-bonded carbons, we have what is called the “trans” formation. Note that both of these are types of unsaturation. (see below)
“trans” formation - the hydrogen’s are on opposite sides of the double-bonded carbons
What it means
Saturation raises the melting point of a fat – lard is solid; olive oil (monounsaturated) is cloudy in the fridge but liquid at room temperature. Sunflower oil (polyunsaturated) is liquid even when refrigerated.
The more double-bonds, the more unsaturated the fat, making it not only more liquid at room temperature, but also increasingly prone to rancidity because of the readily-oxidized double-bonds. Oxidation of unsaturated fatty acids is behind rancidity. This wrecks the taste and decreases the nutrition of the oil, and may even render it toxic. Even at room temperature, oxygen molecules can react with the double bonds (auto-oxidation due to free radicals). Heat increases this effect, so unsaturated fats are a poor choice for high-temperature frying. (17)
Saturation improves the shelf life of fats. It also improves food qualities such as mouth feel and “shortness” – saturated fats in baking prevent long gluten strands from forming, so baked foods remain tender. That’s why commercial baked goods use shortening – it makes the food taste good and last forever.
As the name implies, polyunsaturated fats (PUFAs) have many unoccupied spaces for hydrogen. Examples would be corn oil or sunflower oil.
It is very hard to find optimizing guidelines for a healthy ratio of Omega-3:Omega-6 we need, but it is certainly higher than the 1:20 ratio often seen in typical North American diets. Some guidelines suggest anything from 1:1 to 1:10 as being optimal, and this may vary from person to person according to the health problems they are trying to correct. (18)
“The North American diet is typically high in linoleic acid (n-6) (LA), which has been promoted for its cholesterol-lowering effect. It is now recognized however, that dietary LA favours oxidative modification of LDL cholesterol, increases platelet response to aggregation, and suppresses the immune system. In contrast, alpha linolenic acid (n-3) (ALA) has been found in several studies to exert positive effects in reducing CHD mortality risk. The major effect of n-3 PUFA appears to be anti-arrhythmic rather than anti-atherothrombotic. The emphasis is on the dietary ratio of LA to ALA, rather than the absolute amounts of ALA, that is critical for disease prevention, due to the competition between these two essential PUFAs for their entry into the elongation and desaturation pathways leading to the synthesis of their respective eicosanoids.” – Khor, Asia Pac J Clin Nutr. August 2004 (19)
For reference, eicosanoids are a type of signal-transmitter: “…eicosanoids influence a multitude of processes in the body. Some examples: They participate in the regulation of blood pressure, blood clotting and the action of the heart, they influence the contraction of the bronchial tubes, they protect the mucous membranes of stomach and intestine against the acids in the digestive juices, they regulate inflammatory and immune reactions, and they also play a role in reproduction.”– Schering Stiftung, September 2000 (20)
So, um, EFAs are kind of important. And stuff.
These oils are delicate and are easily damaged by heat – although rumours of them converting to trans fats when cooking at high heats are unfounded. Foods like walnuts and pumpkin seeds (21) are rich sources of these EFAs, particularly Omega-3.
Eat ‘em cold; eat ‘em raw.
When there is only one double-bond, we say a fat is monounsaturated. Examples of foods containing monounsaturated fat include natural peanut butter, avocados and olive oil. Monounsaturated fat is one of the “healthy fats” we are encouraged to eat – it is associated with heart health. (22) Monos are more stable when heated than PUFAs – while not suitable for high-heat cooking - they are fine at lower temperatures. Even better on your salad - the addition of avocado enhances the absorption lycopene and beta-carotene in foods containing these micronutrients, such as salsa. (23)
When all the available slots on the carbon chain are populated with hydrogen, we say the fat is saturated. Saturated fats are stable at higher heats – fry your steak in butter or even coconut oil. While implicated in increasing both good and bad cholesterol, saturated fat is important in the production of steroid hormones, such as testosterone. (24)Unfortunately, saturated fat also increases insulin resistance. So you do need SOME saturated fat in your diet. Just not an all-bacon diet, okay?
A note about dietary cholesterol: While not technically a fat (although it is a lipid) (25), dietary cholesterol is worth mentioning here. Recent studies suggest that there is at best only a weak relationship between the consumption of dietary cholesterol and blood lipids. (26) “Harvard researchers actually found that increasing cholesterol intake by 200 mg for every 1000 calories in the diet (about an egg a day) did not appreciably increase the risk for heart disease.” . (27) (One large egg contains about 190mg of cholesterol.) (28) Bottom line – there are other far more important factors to consider than dietary cholesterol when looking to improve your lipid profiles.
Although usually lumped in with saturated fats, I prefer not to. Natural saturated fats have a place in a healthy diet. Hydrogenated fats do not.
Hydrogenation was developed by Procter & Gamble in 1907 to create a solid fat (from cheap liquid cottonseed oil) that could be used as an inexpensive substitute for tallow in candle and soap making. When electricity became commercially available, candle sales dropped, so P&G started looking for new ways to market this crystallized cottonseed oil. It was dubbed “Crisco” and sold as a substitute for lard. (29)
Natural vs. artificial saturated fat
Saturated fat gets a bit of a bad rap. There is a difference between natural and artificial (partially) saturated fats. The part that makes the artificially saturated fats bad is due to the shape of the molecule – namely the “cis” and “trans” stuff I spoke of earlier – the orientation of the hydrogens attached to the double-bonded, unsaturated carbons (partially saturated fats have some unsaturated slots). In natural fats, hydrogens attached to the double-bonded unsaturated carbons tend to occur on the same side of the chain (cis), making the molecule all kinked-up and bendy. With (partial) hydrogenation, some of the unsaturated fatty acids become trans-fatty acids – the hydrogens are repositioned to opposite sides of the chain (trans) and the molecule is straight. Apparently, the body doesn’t like these ones, and doesn’t quite know what to do with them. Well-known cardiovascular and other problems ensue. In fact, trans fats actually interfere with the body’s ability to metabolize essential fatty acids. (30) I’ll leave further discussion as an exercise for the reader and move on to the stuff you SHOULD be eating.
Note: there are SOME naturally occurring trans-fats that are healthy. For example, conjugated linoleic acid (found in milk and beef) may have anti-cancer properties. (31) This is NOT the same stuff, okay? When you hear that “even natural fat has some trans fat”, it’s not an excuse to eat Krispy Kremes™ and call them health food!
Different types of Dietary Fats
How much fat do I need?
The figure 30% gets tossed around quite a bit in many dietetic circles. In the bodybuilding world, most of us are learning to abandon the ratio approach to dieting, preferring to think in terms of lean body mass (LBM)-dependent “dosing.” The figure I generally rely upon is 0.5g/lb LBM. (32) But let’s see where this 30% figure fits in.
For a “normal” person (ever met one?) with a functioning endocrine system (i.e. no thyroid or other unpleasant metabolic problems), the Harrison-Benedict formula for basal metabolic rate probably works relatively well for estimating caloric requirements.
Once again, it’s all about me. Let’s pretend I’m normal (work with me, people), and only moderately active.
I plugged my numbers into an online BMR calculator. (33)
5’7” tall, 131 lbs, 43 years old, female
BMR = 1337.65
If I were “lightly active,” the multiplier would be 1.375, giving me maintenance calories of about 1840. 30% of this number works out to about 550 calories, which translates to just over 60g of fat.
For my roughly 114 lbs of LBM, half a gram of fat per pound LBM works out to just under 60g of fat. So 30% is sufficient, right?
But what happens when I diet? At 30% of total calories, if I drop my calories to 1400, my fats drop to 47g – under half a gram per pound LBM, and this at a time when my body is under the most stress AND when I’m at my hungriest. It hardly seems prudent to reduce the amount of an essential macronutrient just because I want to fit into smaller jeans. (By analogy, the same argument fits protein requirements – on a cut, keep protein up by targeting it to LBM). In practice, on a cut, I take most (but not all) of the calories I cut from carbohydrate, the macronutrient I need the least. What little carbohydrate remains, I target around my activities.
How much of each type?
As difficult as it is to nail down an amount of fat to eat, it’s harder still to determine how much of each type.
Polyunsaturated fats are often called the “good” fats and saturates the “bad” fats, but this isn’t entirely true. All the natural fats have a place in a healthy diet – it’s just a question of balance. Some PUFA is required because the essential fatty acids Omega-3 and Omega-6 are PUFAs. But too much Omega-6 can put the balance out of whack and lead to inflammation, among other problems. Saturated animal and vegetable fats increase good AND bad cholesterol, but are important for testosterone production. Monounsaturated fats are heart-healthy, but still have calories. And unlike PUFAs, there are no essential saturated or monounsaturated fats – although swapping saturates for monounsaturates may mean you should watch the amount of PUFA you get or good cholesterol levels may suffer. (34)
Many guidelines suggest no more than 10% of your calories coming from saturated fat . (35) These same guidelines usually suggest 30% of your calories should come from dietary fat, so it might seem prudent to suggest getting in about a third of your total dietary fat from saturates. Berardi would agree – he suggests splitting your fats equally amongst polyunsaturates, saturates, and monounsaturates. He further suggests half your PUFAs are Omega-3, and half are Omega-6. (36)
Turning all this into guidelines, for someone with 150 lbs of lean mass, 75g of fat divided amongst saturated, monounsaturated and polyunsaturated fat would probably be a reasonable rough target, although I would argue limiting PUFAs and taking up the slack with monounsaturates to be on the safe side.
Summarizing, for our mythical 150-lb lean mass individual, based on the above guidelines:
75g total dietary fat daily
- 25g saturated fat
- 25g polyunsaturated fat MAX, half from Omega-6, half from Omega-3
- 2-3g of this from the combined EPA/DHA contained in 6-10g of fish oil (37)
- The rest coming from monounsaturated fat
If 10g of your fat comes from fish oil, you’ll ensure that at least 3g of your PUFAs come from Omega-3, which will do much to improve your ratio of Omega-3 to Omega-6, particularly if you keep the rest of your PUFA consumption down to a dull roar.
Now stop reading and go eat your peanut butter.
Written by MariAnne Anderson, BSc, MSc (B) - Copyright 2006
Discuss, comment or ask a question
If you have a comment, question or would like to discuss anything raised in this article, please do so in the following discussion thread on the Wannabebig Forums - Mmmmm Fat discussion thread.