Today we want to analyse good fats vs bad fats to tell you exactly what you should eat and why.
Even more than cholesterol or other blood markers it appears clear that insulin resistance, elevated blood glucose and hyperinsulinemia increase your risk of heart disease, obesity, stroke, cancer andom dementia.
An understanding of the food insulin index data tends to lead people to increase the fat content of their diet in in an effort to normalise blood glucose and reduce insulin levels.
If a significant proportion of your calories are coming from fat it makes sense to look at the composition of our high fat food choices.
So let’s take a look what we could consider to be “good fats” and “bad fats” and the implications for prioritising our food choices.
Types of fats in food
You’re likely aware that there are different classifications of fat based on their chemical structure:
- monounsaturated, and
What this means is that:
- saturated fatty acids have no double bonds between individual carbon atoms (note: saturated fats are denoted by X:0 where the X is the length of the carbon chain and 0 is the number of double bonds),
- monounsaturated fats have one double bond (e.g. X:1), and
- polyunsaturated fats have more than one double bond (e.g. X:2).
If you want to learn more about this topic I suggest you check out this page on nutritiondata.self.com. It’s interesting to follow the links to see which foods are the highest in the different types of fats.
mainstream dietary advice on fat
The standard mainstream dietary advice is to to:
- avoid trans fats,
- limit saturated fats to less than 7% of energy intake,
- emphasise omega 3 fats, polyunsaturated fats and monounsaturated fats, and
- keep dietary fat to between 20 to 35% of energy intake.
The Mediterranean Diet is typically promoted as being the ideal dietary model,   although interestingly in practice people from the Mediterranean region actually consume more than the recommended amount of fat, typically from olive oils and fatty fish.   
food fat vs body fat
Jeff Volek and Steve Phinney in the Art and Science of Low Carbohydrate Performance  note that the majority of human body fat consists of monounsaturated fatty acids, with smaller amounts of saturated fats and polyunsaturated fats. They argue that if the body stores a greater proportion of monounsaturated fatty acids for energy in times of famine then it makes sense to align our dietary fat intake with these ratios.
The table below compares the composition of human adipose tissue versus the proportion of fats across the 8000 foods in the USDA database. Based on this logic it appears that we should go out of our way to emphasis monounsaturated fat given than saturated and polyunsaturated fats are plentiful in our food system.
adipose / dietary
The chart below shows the relative proportions of each of the fatty acids in human adipose tissue. Oleic acid (18:1) (a monounsaturated fat) is the most plentiful, followed by Palmitic acid (16:0) (a saturated fat) and Linoleic acid (18:2) (a polyunsaturated fat).
Taking Volek and Phinney’s logic a step further, the table below shows a comparison of the proportion of each fatty acid in our adipose tissue compared to their availability in the modern diet (based on the average across the 8000 foods in the USDA database). It appears that we have more than enough Stearic acid (18:0), Linoleic acid (18:2) and Linolenic acid (18:3) available in the food system while a number of the other fatty acids are deficient.
|adipose (mol %)||% adipose||dietary||adipose / dietary||class|
oleic acid vs linoleic acid
The two most prevalent fats in our diet and on our body are Oleic acid (18:1) and Linoleic acid (18:2).
While Linoleic acid (18:2) is considered to be an essential fatty acid  (meaning that the body cannot manufacture it from other dietary components) the data in the table above indicates that there is a relative abundance of it in the dietary system.
Many people believe that excess Linoleic acid (18:2) from vegetable oils (which causes an imbalance in our omega 3 : omega 6 ratio) is a major contributor to the obesity epidemic. 
The common wisdom is that olive oil, which is high in the monounsaturated fat Oleic acid (18:1), is a healthy ‘good fat’.  When we look at the research it appears well established that emphasising the monounsaturated Oleic acid (18:1) and reducing the polyunsaturated Linoleic acid (18:2) will improved insulin resistance.   
omega 3 fatty acids in foods
Improving the omega-3 : omega-6 ratio is widely regarded as important to reduce inflammation and optimise brain function and mental health.  Omega 3 fatty acids are typically obtained from seafood and are generally considered to be ‘good fats’ that we should be maximising for health.
While there appears to be plenty of DHA (22:6 n-3) available in the diet when we simply consider the composition of adipose tissue, it’s worth noting that DHA makes up 30% of the brain and 50% of our retina, so it is probably going to fall into the category of ‘good fats’ that we should be going out of our way to pursue in our diet.
A recent mouse study showed that fish oil (high in omega 3 fatty acids) is better than lard (high in saturated fatty acids, particularly palmitic acid (16:0) and stearic acid (18:0)) when it comes to weight gain, gut bacteria, obesity and insulin resistance. While people are clearly different from mice, it’s not unreasonable to think that fish oil might be better than eating lard.
Omega 3 fats are relatively rare in our food system which means we need to go out of our way to incorporate them into our diet. The table below shows the omega 3 fatty acids that I think we should count as good fat along with the foods they are commonly found in.
|isomer||common name||common foods|
|22:6 n-3 (DHA)||Docosahexaenoic acid (DHA)||fish oil, caviar, seal oil, cod liver oil, sardine oil|
|20:5 n-3 (EPA)||Eicosapentaenoic acid (EPA)||fish oil, caviar, fish|
|18:3 n-3 c,c,c (ALA)||Alpha-linolenic acid||peanut butter, flax seed, butter|
|22:5 n-3 (DPA)||Docosapentaenoic acid (DPA)||seal oil, fish oil – menhaden, fish oil – salmon.|
MCT oil types
You might have heard a lot of talk about MCT (medium chain triglycerides) oils recently. These shorter chain fats appear to bypass the lymphatic system and are transported directly to the liver via the portal vein.
Many people find benefit from using MCT oil as an aid to extend periods between meals or and cognitive enhancement. MCT oils are more readily turned into ketones which provide an alternative fuel source to the brain. In turn, ketones can increase satiety and decrease appetite, both of which may facilitate weight loss.
MCTs make up about 1.1% of the fats in our food supply in coconut oil, butter, cheese and cream, however to get higher levels you will to supplement.
|isomer||common name||common foods|
|12:0||Lauric acid||palm kernel oil, coconut oil|
|10:0||Capric acid||cheese, coconut oil, palm kernel oil|
|8:0||Caprylic acid||coconut oil, coconut cream, palm kernel oil|
|6:0||Caproic acid||butter, cheese, cream|
trans fats in foods
Artificial trans fats (a.k.a. partially hydrogenated oils) are one of the few components of the diet that are widely accepted as unhealthy. If you look at the foods in which artificial trans fats are the most prevalent, it’s hard to disagree.
|18:1 t (g)||soy shortening, margarine, canola oil|
|18:2 t (g)||KFC, margarine|
|18:2 t,t (g)||McDonald’s, fast foods|
|16:1 t (g)||thickshake, cheeseburger, hamburger, fast foods|
Given that the USDA database does not differentiate between partially hydrogenated oils and naturally occurring trans fats, I have not assigned trans fats a negative mark. Emphasising other ‘good fats’ will demote foods that contain artificial trans fats.
the effect of replacing carbohydrates with fat
The common view is that dietary fat, particularly saturated and trans fats, should be avoided in order to optimise blood cholesterol markers. But what happens when we substitute fat for carbohydrates?
The chart below from a paper by cardiologist Dariush Mozaffarian indicates that trans fats (TFA) have a negative impact on all blood markers (i.e. TC/HDL, LDL and HDL). So there’s no disagreement there.
However increasing dietary saturated fat:
- increases LDL (note: this is generally considered to be bad although it’s not clear if this is large buoyant of small dense LDL),
- has minimal effect on the total cholesterol to HDL ratio, and
- increases HDL (good).
Replacing carbohydrates (CHO) with either monounsaturated (MUFA) or polyunsaturated (PUFA) have what are generally regarded to be positive outcomes.
Whether or not saturated fat is beneficial starts to become a little clearer when we look at the effect of individual fatty acids. The data below shows that while Lauric acid (12:0) increases LDL it also has very a positive effect on increasing HDL and decreasing the TC : HDL ratio.
saturated fats and insulin resistance
“SFA has been considered a risk factor for insulin resistance and diabetes mellitus, but review of the current evidence indicates surprisingly equivocal findings. SFA consumption inconsistently affects insulin resistance in controlled trials and has not been associated with incident diabetes in prospective cohort studies.”
Things start to get more interesting when you look at the relationship between individual fatty acids, insulin resistance and type 2 diabetes.
The investigators found that saturated fatty acids with an odd number of carbon atoms in their chain (15:0 and 17:0) were associated with a lower risk of type 2 diabetes, whereas even-chain saturated fatty acids””14:0, 16:0, and 18:0″”were associated with a higher risk. Longer-chain saturated fatty acids (20:0, 22:0 and 24:0) also were found to be inversely associated with incident type 2 diabetes.   
This also aligns with the mouse study that mentioned above where fish oil was found to have a better outcome on obesity and gut health compared to lard (which is high in 16:0 and 18:0).
The table below shows the foods that these ‘good fats’ are contained in. Meat and nuts are embraced in the paleo and low carb scenes. The benefits of dairy are debated, but this is typically related to the casein and lactose content which some people don’t tolerate well.
|isomer||common name||common foods|
|17:0||Heptadecanoic acid||tofu, lamb, beef|
|20:0||Arachidic acid||macadamia nuts, peanut butter|
|22:0||Behenic acid||peanut oil, peanut butter, sunflower oil, macadamia nuts|
|15:0||Pentadecanoic acid||cream cheese, sour cream, lamb, beef|
|24:0||Lignoceric acid||peanut butter, rosemary, macadamia nuts, cashew nuts, sunflower seeds|
Listed below (in order of prevalence in the dietary system) are the ten fatty acids that I think should be included in the list of ‘good fats’ along with the common foods that they are contained in and the basis for their inclusion.
|fatty acid||common foods||comment|
|Oleic acid (18:1)||olive oil, sunflower oil, hazelnut oil, safflower oil, soybean oil, almond oil, avocado oil||commonly associated with positive health outcomes and key component of Mediterranean diet
improves insulin resistance.
most abundant fatty acid in human adipose tissue
underrepresented in food system.
reduces TC:HDL ratio
|Lauric acid (12:0)||palm kernel oil, coconut oil||increases HDL
decreases TC:HDL ratio.
|Alpha-linolenic acid (18:3 n-3)||peanut butter, flaxseed, nuts, cloves, cheese||omega-3.
improves insulin resistance
|Capric acid (10:0)||cheese, coconut oil||MCT oil.
Improves HDL:LDL ratio.
|Docosahexaenoic acid (DHA) (22:6 n-3)||fish oil – salmon, caviar, seal oil, cod liver oil, sardine oil||essential fatty acid
abundant in human brain.
|Arachidonic acid (20:4)||salmon, chicken heart, liver, brain||conditionally essential.
rare in food system.
|Eicosapentaenoic acid (EPA) (20:5 n-3)||fish oil, caviar, fish||omega-3.
improves brain function.
|Margaric acid (17:0)||tofu, lamb, frankfurter, beef sausage||reduced risk of type 2 diabetes.|
|Docosapentaenoic acid (DPA) (22:5 n-3)||seal oil, fish oil – menhaden, fish oil – salmon||omega-3 though small quantities.|
|Pentadecanoic acid (15:0)||cream cheese, sour cream, lamb.||lower risk of type 2 diabetes|
And for completeness listed below (in order of their prevalence in the dietary system) are the fatty acids in the USDA food database that didn’t make the ‘good fats’ list.
|fatty acid||common foods||comment|
|Linoleic acid (18:2)||safflower oil, grapeseed oil, sunflower oil, walnut oil||n-6 component is essential however overly abundant in food system
substituting linoleic acid for oleic acid has been shown to improve insulin resistance
|Palmitic acid (16:0)||palm oil, fish oil – menhaden, butter, lard||higher risk of type 2 diabetes
poor gut bacteria outcomes in mice study
|Stearic acid (18:0)||cocoa butter, shortening, margarine, lard||increased risk of type 2 diabetes.
poor gut bacteria outcomes in mice study.
overly abundant in food system
|18:1 c||canola oil, margarine||subset of 18:1 – no need to double count|
|18:2 n-6 c,c||soy oil, sunflower oil, soybean oil, mayonnaise||subset of 18:2.|
|Myristic acid (14:0)||nutmeg, coconut oil||Increased risk of type 2 diabetes|
|Palmitoleic acid (16:1)||macadamia nuts, fish oil, seal, whale||Increased risk of type 2 diabetes|
|Linolenic acid (18:3)||flax seed, chia seed, walnuts, basil||adequate in food system.
only count n-3 ALA component.
|18:1 t||Soy shortening, margarine, canola oil.||trans fat|
|Gadoleic acid (20:0)||seal, eel, fish oil – herring, fish –halibut, fish oil – cod liver, salmon||small quantities and limited research.|
|Caprylic acid (8:0)||coconut oil, coconut cream.||MCT but rare in food system other than manufactured foods|
|Erucic acid (22:1)||herring, halibut, sardine, cod liver||no clear health benefits / research|
|Butyric acid (4:0)||butter, cheese||MCT but rare in food system other than manufactured foods|
|16:1 c||KFC, Popeye’s, fast food||predominantly in fast foods.|
|Caproic acid (6:0)||butter, cheese, cream.||MCT but rare in food system other than manufactured foods|
|Arachidic acid (20:0)||macadamia nuts, peanut butter.||reduced risk of type 2 diabetes but rare in food system.|
|Behenic acid (22:0)||peanut oil, peanut butter, sunflower oil, macadamia nuts,||reduced risk of type 2 diabetes but rare in food system.|
|Myristoleic acid (14:0)||frankfurter, beef sausage, bologna, cream cheese||minimal research.
small quantities in food system
|18:2 i||soy oil, canola oil, margarine, French fries||minimal research.
small quantities in food system
|Heptadecenoic acid (17:0)||tofu, broccoli, beef||minimal research.
small quantities in food system
|18:2 t||KFC, margarine||trans fat|
|18:4||fish oil – sardine, fish oil – salmon, fish oil – menhaden, oysters||very small quantities in food system|
|Eicosadienoic acid (20:2 n-6 c,c)||English muffin, margarine, fast foods, pine nuts, ham|
|Lignoceric acid (24:0)||peanut butter, rosemary, macadamia nuts, cashew nuts, sunflower seeds||reduced risk of type 2 diabetes|
|18:2 t,t||MacDonald’s, fast foods||trans fat|
|Eicosatrienoic acid (20:3)||pine nuts, mustard, whitefish, seal, salmon||appears beneficial but minimal quantities in food system|
|Pentadecenoic acid (15:0)||tofu, miso, beef sausage||appears beneficial but minimal quantities in food system|
|Gamma-linolenic acid (18:3 n-6)||margarine||omega 6
|16:1 t||thick shake, cheeseburger, hamburger, fast foods.||trans fat|
|20:3 n-6||KFC, Popeye’s, fast food.||Omega 6 and primarily in fast food|
|Nervonic acid (24:1 c)||mustard, salmon, seal, flax seed||likely beneficial, but minimal quantities|
|22:1 c||margarine.||minimal quantities in food system|
good fat foods
Shown below is the list of fatty foods sorted by their relative quantity of the good fats with their percentage of insulinogenic calories also shown. The order itself is not that important (otherwise the seals and whales would be even more endangered due to this article), however the big winners are:
- fish oil (seal, whale, menhaden, sardine, herring, salmon, cod liver),
- fish (smelt, salmon, herring, caviar, mackerel, caviar, trout, swordfish),
- lamb, pork and beef, and
- cheese, butter and cream.
|food||% insulinogenic||nutrient density|
|oil – bearded seal||0%||20.6|
|oil – beluga whale||0%||17.9|
|oil – spotted seal||0%||17.4|
|smelt – dried||33%||14.4|
|fish oil – cod liver||0%||14.0|
|fish oil – salmon||0%||13.4|
|fish oil – sardine||0%||13.1|
|fish oil – menhaden||0%||13.0|
|fish oil – herring||0%||12.7|
It’s important to keep in mind that consuming enough “good fats” is only part of the nutrition story. In the next article we’ll look at how we can use this understanding of good fats along with our understanding of vitamins, mineral and amino acids to identify the most nutrient dense foods for different goals.