The Complex World Of Dietary Fat; What's The Latest?


As I am desperately trying to clarify the muddy water we call nutrition advice, I am cautious that this may all change ‘tomorrow’.  All I can do is provide the facts as best as I can based on the science that is available.  However, studies are published every day that change the way we feel about certain foods/diets.  The next question is a perfect example of this.  I am not sure if I will be answering this question the same way in 2 years once more data is available.  I certainly would have answered it differently 10 years ago when I was doing my Doctorate.


Question:  What is the deal with saturated fat?  Is it really that bad for you and if so, why is there a shift towards eating it again?

Brace yourself- we are going to have to have a quick lesson in biochemistry to attack this question correctly!  I am going to briefly discuss the types of fat in our diets because it’s becoming increasingly clear that different fats have different effects on the body.

Fats can be found in the form of triglycerides (the most abundant form found in our food and bodies) as well as phospholipids and sterols.  The terms you hear; saturated, trans, monounsaturated, polyunsaturated, omega-3, omega-6; refer to the structure of fatty acids, which are a component of the fats.

The terms ‘saturated’ and ‘unsaturated’ refers to the structure of the bonds in the fatty acid.  If the molecule is saturated, there are no double bonds between carbons so the molecules can pack together quite closely.  A lot of saturated fatty acids in a food generally make a solid fat at room temperature (ex. butter is highly saturated).  If the molecule is unsaturated, there are double bonds in the molecule making its structure ‘kinked’.  This does not allow the molecules to fit so closely together therefore the fat is liquid at room temperature (ex. olive oil).

The fatty acids can also be classified into short, medium, and long chain fatty acids (from 4-24 carbons).  Unsaturated fat can also be further classified into monounsaturated (one double bond) or polyunsaturated (multiple double bonds).  Then comes the placement of the double bonds; omega-3 has the first double bond 3 carbons from the end, omega-6 being 6 carbons from the end.


I know this seems like an overabundance of information but all these small structural differences have an effect on how the fatty acids function in the body.

In addition to all these natural fats (from food or synthesized in our body), we also have trans fats.  Trans fat come from a process called hydrogenation where hydrogen is added to polyunsaturated fats to make the bonds saturated.  This has two benefits to manufacturers; 1its reduces the amount of oxidation thereby increases shelf life of products and 2 it also makes vegetable oils solid at room temperature (i.e margarine and shortening).  However, this process rarely results in total hydrogenation and some of the remaining unsaturated fatty acids get altered in the process resulting in trans fatty acids (called partial hydrogenation). It’s very important when buying spreads (margarine) you ensure they do not contain partially hydrogenated fatty acids (and thus trans fatty acids).

Now we are going to try to sort out which of these tiny molecular differences are good/bad for us?  You can tell why this is not a simple question (for anyone) to answer.

Recommendations over the years to reduce fat intake have been to primarily to prevent weight gain (fat is very energy dense) and prevent cardiovascular disease (CVD).  In particular, saturated and trans fat have been implicated in the development of CVD through their role in increasing LDL cholesterol (bad cholesterol) levels.

  • The American Heart Association (AHA) recommends reducing saturated fat to no more than 7% of total calories and reducing trans fats under 1% of total calories.

Seems cut and dry right?  The biggest agencies in the US say to reduce saturated fat.  Well, now it’s getting a bit more controversial.  Even within the world of saturated fat, there seem to be differences.  The chain length of saturated fat differs according to the source.  Coconut oil in particular, has been gaining momentum in the ‘trendy’ foods market because, while it is over 90% saturated fat, over 50% of this fat is lauric acid (a 12 C fatty acid) which is particularly good at increasing HDL (good) cholesterol, but also increases bad LDL cholesterol.

The media has been very quick to pick up on any studies suggesting that saturated fat may not be as bad as previously thought and often the messages are misconstrued.   Diet is never about one thing; if you take something out you replace it with something else and this often causes mixed messages.  Strong evidence suggests replacing saturated fats with mono or polyunsaturated fat can lead to beneficial changes in your cardiovascular disease risk. However, this benefit is lost when saturated fat is swapped with starchy foods or protein (hence the confusion- the media reports this later data as evidence that saturated fat is good!). These confusing media messages have also led to increasing chatter about butter and ghee (clarified butter with milk solids removed), both of which are also high in saturated fat.  While society seems to welcome the idea that butter is good for you, it seems more likely that it’s just not as bad as we thought.

While we cannot unequivocally say that all saturated fat is bad for you, we can say that replacing saturated fat with mono and polyunsaturated IS good for you.


What does this translate to in real life?  For me and my family, it means eating fat in moderation and choosing fats high in mono and polyunsaturated fatty acids. 

To help you, here’s a list of the major sources of the various fatty acids in the diet.  Remember, nothing has exclusively one type of fatty acid so this is a bit of a generalization:

Saturated Trans Monounsaturated              Polyunsaturated
Coconut oil Commercial baked goods Olive oil Safflower oil
Butter Fast Food Canola oil (Rapeseed) Sunflower oil
Beef fat Fried food Peanut oil Corn oil
Palm oil Shortening Avocados Soybean oil
Pork fat Snack foods (crackers, chips) Nuts Flaxseed oil
Chicken fat Margarine (partially hydrogenated) Seeds Fish oil

 Healthy eating is not about eating or not eating one type of food but it’s about healthy dietary patterns (which has been strongly emphasized in the 2015 Dietary Guidelines).  Fats are a healthy (and necessary) part of the diet as long as they are the correct fats.  Aim to make the best choices for you; if you LOVE toast and butter, go easy on the butter and be aware of your total saturated fat intake for the day.  However, you might also consider other options; a non-hydrogenated spread or olive oil?

Here’s a few other practical considerations for you.

  1. Stay away from processed foods (see a recurring theme to my blogs!?).
  2. Read food labels; look for hidden saturated and trans fats- For hints on reading labels see http://www.fda.gov/Food/IngredientsPackagingLabeling/LabelingNutrition/ucm274593.htm
  3. Choose lean meats; for hints on selecting healthy options see http://www.choosemyplate.gov/protein-foods-tips
  4. Bake, grill, or broil; don’t fry foods
  5. Choose low fat dairy products
  6. Incorporate nuts and seeds into the diet (in moderation)
  7. Think ‘Mediterranean diet’ (high in monounsaturated fats, low in processed foods)
  8. Try to have fish twice a week (high in omega-3 polyunsaturated fats)

So, the big question I keep hearing; do I jump on the coconut oil/butter bandwagon!?  Well, for me, I would prefer to stick with oils I KNOW have benefit (eg. olive) as opposed to switching to one which ‘might’ not be as bad as we originally thought…..but, I am also open to changing my opinion should some hard evidence come out.

Best

Tara

References

Hooper L et al. (2015). Reduction in saturated fat intake for cardiovascular disease. Cochrane Database of Systematic Reviews. Issue 6. Art. No.: CD011737.

Willet et al. (2014). Association of dietary, circulating, and supplement fatty acids with coronary risk. Annals of Internal Medicine. 16th September, vol 161. No 6.


 

Topics: Nutrition, Food, Education

Dr. Tara Coletta, PhD

Written by Dr. Tara Coletta, PhD

Tara's research focused on obesity and metabolism. She studied exercise science (MS, UMass Amherst) before earning a PhD in nutritional biochemistry (Tufts University). Wellness remains an integral part of Tara’s life as she works to balance being a mother of three.