Fatty acids

ACRONYMS AND DEFINITIONS

ALA - Alpha Linolenic acid

CHD - Coronary Heart Disease

FA - Fatty Acids

GLA - Gamma Linolenic acid (n-6 PUFA)

PUFA - n-3 and n-6 Polyunsaturated fatty acids

MUFA - Monounsaturated Fatty Acids

n-3 PUFA - n-3 Polyunsaturated fatty acids

n-6 PUFA - n-6 Polyunsaturated fatty acids

SFA - Saturated fatty acids

Trans FA- Trans fatty acids

USDA - United States Department of Agriculture

OVERVIEW OF FATTY ACIDS

Macronutrients

There are 3 types of macronutrients:

Energy

Macronutrients supply the following amounts of energy:

Fatty acids - 9 calories/gram
Carbohydrates - 4 calories/gram
Protein - 4 calories/gram

Fatty acid absorption

Fatty acids are absorbed from the intestine
Fatty acids are then linked together to form triglycerides (a triglyceride is three fatty acids joined together)
Triglycerides are later broken back down into fatty acids and absorbed by muscle cells and fat cells
Muscle cells use fatty acids to generate energy, and fat cells store fatty acids as an energy source

Illustration of fatty acid and cholesterol absorption

USDA RECOMMENDED INTAKE

USDA recommendations for fatty acids

Adults

Total calories - 20 - 35% of total calories should come from fatty acids
Saturated fatty acids - less than 10% of total daily calories should come from saturated fatty acids
MUFA and PUFA - the majority of fatty acids consumed should come from MUFA and PUFA
Trans Fatty acids - people should consume as little Trans FA as possible

Children 4 - 18 years old

Total calories - 25 - 35% of total calories should come from fatty acids

Children 2-3 years old

Total calories - 30 - 35% of total calories should come from fatty acids

SATURATED FATTY ACIDS (SFA)

Overview

Other names

Myristic acid
Lauric acid
Palmitic acid
Stearic acid

USDA Recommended Dietary Intake

< 10% of total calories

Health effects

Cholesterol

Increases in SFA intake lead to increases in total, LDL, and HDL cholesterol

For every 1% increase in calories from SFA, LDL cholesterol increases by 1.3 - 1.75 mg/dl
For every 1% increase in calories from SFA, HDL cholesterol increases by 0.429 - 0.507 mg/dl [1]

Coronary Heart Disease (CHD)

Studies evaluating the risk of CHD and consumption of SFA have been mixed [1,2,4]

In general, trends from studies tend to show the following:

SFA have an overall negative effect on cholesterol levels and may raise the risk of CHD [1,2,4]
Replacing SFA with PUFA in the diet will lower a person's risk for CHD [4]
Replacing SFA with carbohydrates does not help lower the risk for CHD [4]

Diabetes

Studies evaluating the risk of diabetes and consumption of SFA have been mixed [1,3,4]

In general, trends from studies tend to show the following:

Diets higher in SFA increase a person's risk for diabetes [1,3,4]

Obesity

Studies evaluating the intake of SFA with the development of obesity have been inconclusive [1]

Cancer

Breast cancer - there is no conclusive evidence that SFA intake affects breast cancer risk [5,6]
Prostate cancer - there is no conclusive evidence that SFA intake affects prostate cancer risk [7,8,9]
Colon cancer - there is no conclusive evidence that SFA intake affects colon cancer risk [10,11,12]

Dietary sources

Meat and dairy products

Whole milk - 5.1 grams SFA per cup
Cheddar cheese - 6 grams SFA per oz
Butter - 7.2 grams SFA per tablespoon
Ground beef (lean) - 5.5 grams SFA per 3 oz
Bacon - 3.3 grams SFA per 3 medium slices

Certain oils contain high amounts of SFA

Coconut oil - 12 grams of SFA per tablespoon
Palm oil - 6 grams of SFA per tablespoon

Stearic acid

Stearic acid is an SFA that unlike other SFA has been shown to lower or have a neutral effect on LDL cholesterol
There is interest in substituting stearic acid for Trans FA and other SFA in food processing to lower heart disease risk [4,13]

N-6 POLYUNSATURATED FATTY ACIDS (n-6 PUFA)

Overview

Other names

Linoleic acid - main dietary PUFA
Gamma Linolenic acid (GLA) - found in foods and supplements
Arachidonic acid (AA or ARA) - found in foods and supplements
Omega-6 fatty acids - collective term for all N-6 PUFA

USDA Recommended Dietary Intake

USDA recommends 20 - 35% of total calories come from fatty acids with the main fatty acid sources being PUFA and MUFA
n-6 PUFA is an essential fatty acid (must be obtained from diet, body cannot make)
n-6 PUFA deficiency leads to scaly rash and growth retardation [1]

Health effects

Cholesterol

Replacing saturated fatty acids (SFA) with n-6 PUFA has been shown to have a beneficial effect on cholesterol

For every 5% of SFA replaced with n-6 PUFA, LDL cholesterol has been shown to decrease by 10 mg/dl [4,14]

Coronary Heart Disease (CHD)

Replacing SFA with n-6 PUFA has been shown to decrease the risk of coronary heart disease

In clinical trials, for every 5% of SFA replaced with n-6 PUFA, there was an average 10% risk reduction in coronary heart disease [1,14]

Diabetes

Clinical trials have shown that replacing SFA and Trans FA with PUFA lowers a person's risk of developing diabetes and improves insulin sensitivity [1,3,4]

Cancer

High linoleic acid (main dietary n-6 PUFA) consumption has been linked to the development of cancer in animals
Some population studies in humans have found a positive link between n-6 PUFA consumption and cancer [15]
Because of these findings, a number of studies have evaluated the relationship between n-6 PUFA and cancer

In general, the following has been seen:

Breast cancer - there is no conclusive evidence that n-6 PUFA intake affects breast cancer risk [1,6,15]
Prostate cancer - there is no conclusive evidence that n-6 PUFA intake affects prostate cancer risk [1,15,16]
Colon cancer - there is no conclusive evidence that n-6 PUFA intake affects colon cancer risk [10,12,15]

Inflammation and Pain

Linoleic acid (LA) and Gamma linolenic acid (GLA) are precursors in the synthesis of arachidonic acid
Arachidonic acid is a n-6 PUFA that is involved in the synthesis of inflammatory chemicals
The synthesis of arachidonic acid is complex, and even though LA and GLA are precursors to arachidonic acid, they can also inhibit its synthesis
A number of studies have looked at the use of GLA supplements to treat inflammatory disorders

Rheumatoid arthritis

There is moderate evidence that GLA helps relieve the pain associated with rheumatoid arthritis
There is no evidence that GLA helps reverse the underlying pathology of rheumatoid arthritis
Most trials used evening primrose oil (7 - 10% GLA) or borage oil (% GLA varies by product)
Doses in trials ranged from 1.4 grams/day - 2.8 grams/day of GLA [17, 18, 19, 20]

Breast Pain (Mastalgia)

There is no conclusive evidence that GLA (including evening primrose oil) helps relieve breast pain [27,28,29]

Atopic Dermatitis (eczema)

There is no conclusive evidence that GLA either improves or prevents atopic dermatitis [21, 22, 23, 24, 25]

Sjögren's syndrome

There is limited evidence that GLA may improve the dry eyes associated with Sjogren's syndrome [20, 26]

Infant Growth and Development

GLA, AA, and DHA (an omega-3 fatty acid) are involved in infant growth and neural development
There have been numerous studies comparing vision and developmental milestones in infants fed standard formulas versus formulas supplemented with GLA, AA, and DHA

In general, the following has been seen:

There is no conclusive evidence that GLA, AA, and DHA supplementation affect infant development [1, 30]

Dietary sources

Oils

Sunflower oil - 66% PUFA, 19% MUFA, 10% SFA
Corn oil - 59% PUFA, 24% MUFA, 12% SFA
Sesame oil - 42% PUFA, 38% MUFA, 14% SFA
Soybean oil - 38% PUFA, 43% MUFA, 15% SFA

Nuts and seeds

English Walnut - 13.4 grams of PUFA per oz
Sunflower seeds - 9.3 grams of PUFA per oz
Pecan - 6.1 grams PUFA per oz
Peanut - 4.4 grams PUFA per oz
Almonds - 3.5 grams of PUFA per oz

Supplements

Evening primrose oil - 70% Linoleic acid, 7-10% GLA
Borage oil - percent Linoleic acid and GLA vary by product
Black currant seed oil - varies by product

N-3 POLYUNSATURATED FATTY ACIDS (n-3 PUFA)

Overview

Other names

Alpha Linolenic acid (ALA) - mainly found in nut and seed oils
Eicosapentaenoic acid (EPA) - mainly found in fish
Docosahexaenoic acid (DHA) - mainly found in fish
Omega-3 fatty acids - collective term for all n-3 PUFA

USDA Recommended Dietary Intake

USDA recommends 20-35% of total calories come from fat with the main fat source being PUFA and MUFA

ALA, DHA and EPA

ALA is an essential fatty acid that is found primarily vegetable oils - soybean, linseed, canola, flaxseed
DHA and EPA are mainly found in fish. They are the active ingredient in "Fish Oil."
Humans can convert ALA to DHA and EPA but this occurs at a very low rate (< 5% of ALA is converted) [31, 33]

Health effects

Health effects of DHA and EPA

The majority of studies involving n-3 polyunsaturated fatty acids have involved DHA and EPA
An extensive discussion of DHA and EPA can be found here - fish oil

Heart disease

Studies evaluating the association of ALA with heart disease have been mixed

At this time, it is unclear if diets high in ALA affect heart disease risk [33, 34, 35]

Prostate cancer

When studying the association of ALA with heart disease, researchers found a surprising positive correlation between ALA intake and prostate cancer risk
This spurred further research into their association

A number of studies of various design have examined the association between ALA and prostate cancer

Overall, there is no conclusive evidence that diets high in ALA increase the risk of prostate cancer [16, 35, 36]

Diabetes and insulin sensitivity

ALA does not appear to affect diabetes risk or insulin sensitivity [35]

Inflammation

ALA does not appear to have a significant effect on inflammation or inflammatory diseases [32]

Dietary sources

Main food sources include salad and cooking oils

Linseed oil - 15 grams of ALA per oz
Canola oil - 3.2 grams of ALA per oz
Soybean oil - 2 grams of ALA per oz
Walnuts - 2 grams of ALA per oz [56]

MONOUNSATURATED FATTY ACIDS (MUFA)

Overview

Other names

Oleic acid (OA) - accounts for 92% of dietary MUFA
MUFA-rich diets are sometimes called "Mediterranean diets" because olive oil has a high percentage of oleic acid

USDA Recommended Dietary Intake

USDA recommends 20-35% of total calories come from fat with the main fat source being PUFA and MUFA

Health effects

Cholesterol

Replacing SFA with MUFA in the diet has been shown to have a beneficial effect on cholesterol levels

Increasing MUFA in the diet tends to raise HDL cholesterol and lower triglycerides
MUFA appears to have a neutral effect on total and LDL cholesterol [37, 38, 39]

Heart disease

There is no conclusive evidence that increasing dietary MUFA lowers heart disease risk [14,40]
In 2019, the FDA allowed some products that are high in oleic acid to make a "qualified claim" that the product may reduce the risk of coronary heart disease. A qualified claim means the evidence supporting the benifit is limited.
The approved claim states that “supportive but not conclusive scientific evidence suggests that daily consumption of about 1½ tbsp (20 g) of oils containing high levels of oleic acid may reduce the risk of coronary heart disease.” [59]

Blood pressure

There is no conclusive evidence that increasing dietary MUFA lowers blood pressure [38, 39, 41, 42]

Diabetes and insulin sensitivity

There is no conclusive evidence that high MUFA diets improve or prevent diabetes [1, 4, 43, 44]

Cancer

Breast cancer - there is no conclusive evidence that MUFA affect breast cancer risk [1, 45, 46, 47]
Prostate cancer - there is no conclusive evidence that MUFA affect prostate cancer risk [1]
Colon cancer - there is no conclusive evidence that MUFA affect colon cancer risk [1, 11]

Dietary sources

Vegetable oils

Olive oil - 74% MUFA, 8% PUFA, 13% SFA
Safflower oil - 74% MUFA, 14% PUFA, 6% SFA
Canola oil - 59% MUFA, 29% PUFA, 7% SFA
Peanut oil - 46% MUFA, 32% PUFA, 17% SFA
Soybean oil - 43% MUFA, 38% PUFA, 15% SFA
NOTE: PUFA includes both n-6 and n-3 PUFA

Nuts

Macadamia nuts - 16.8 grams of MUFA per oz
Hazelnuts - 13 grams of MUFA per oz
Pecans - 11.6 grams of MUFA per oz
Cashews - 7.7 grams of MUFA per oz
Peanuts - 7 grams of MUFA per oz

Meat

Beef and pork products - most beef and pork products have 2-10 grams of MUFA per 3 oz serving

TRANS FATTY ACIDS (Trans FA)

Overview

Types

Industrial

Trans FA are formed from PUFA through a process called hydrogenation
Hydrogenation raises the melting point of the PUFA making them solid at room temperature and more resistant to spoilage

Ruminant (animals that eat plants)

Trans FA occur naturally in dairy products and fats from ruminants (animals that eat plants) [4]

USDA Recommended Dietary Intake

USDA recommends daily intake of trans FA be as low as possible

Health effects

Cholesterol

Trans FA have a negative effect on cholesterol

Trans FA tend to raise LDL cholesterol
Trans FA tend to lower HDL cholesterol [1, 48, 39, 50]

Heart disease

Ruminant trans FA has not been proven to increase the risk of heart disease [50, 51]
Consumption of Industrial trans FA increases the risk of heart disease
For every 2% increase in calories from Industrial trans FA, heart disease risk increases by 20 - 32%

Dietary sources

Industrial

Over the last ten years, health and government agencies have promoted and sometimes enforced by law (New York) the removal of trans FA from foods
Because of this, industrial food sources of trans FA have changed significantly

The following food types have traditionally contained trans FA:

Donuts
Pastries
Cookies
Fried chicken
French fries
Margarines
Imitation cheese

Ruminant

Red meat, chicken, and sausage typically contain 0 - 2.5 grams of trans FA per 3 oz serving
Whole milk contains less than 1 gram of trans FA per serving

Conjugated linoleic acid (CLA)

CLA is a ruminant trans FA that is sold as a dietary supplement and often promoted as a weight loss aid

Studies evaluating the effectiveness of CLA in weight loss and body fat composition have been mixed

CLA appears to have a modest effect in reducing body fat mass
CLA does not appear to promote weight loss [52, 53, 54, 55]
CLA has a negative effect on cholesterol [48]

FOOD LABELING AND FATTY ACIDS

The FDA has set forth the following requirements for fat content on food labels:

Required listing

Total fat
Trans fat
Saturated fat

Voluntary listing

MUFA (required if claim about cholesterol or fatty acids is made on label)
PUFA (required if claim about cholesterol or fatty acids is made on label) [57]

Estimating MUFA and PUFA

If MUFA and PUFA are not listed, they can be estimated by taking Total Fat and subtracting Trans and Saturated Fat

Example:

Total Fat 15g
Saturated Fat 2g
Trans Fat 1g

To calculate the sum of MUFA and PUFA from the example above:

Total Fat 15g - Saturated Fat 2g - Trans Fat 1g = approximately 12g of MUFA and PUFA

RESOURCES FOR FOOD CONTENT

USDA food composition database - extensive nutritional information about numerous foods including restaurant foods
myfitnesspal - commercial website that has extensive database of food calorie content
Lose it! - commercial website that has extensive database of food calorie content

FATS AND SATIETY

Satiety is defined as the sense of fullness or satisfaction a person feels after eating food
Because of the obesity epidemic, there has been interest in the satiety of macronutrients (protein, carbohydrates, and fat) as a means to control weight gain
A number of studies of varying designs have been performed to measure the effect of different macronutrients on satiety
In short, there is no conclusive evidence that one macronutrient is superior to another in providing satiety that leads to reduced calorie intake [1,58]

BIBLIOGRAPHY

1 - Dietary Reference Intake, Institute of Medicine, 2005
2 - PMID 20711693
3 - PMID 19032965
4 - USDA Dietary Guidelines for Americans, 2010
5 - PMID 19130632
6 - PMID 17503428
7 - PMID 18765116
8 - PMID 17893870
9 - PMID 17414514
10 - PMID 9394716
11 - PMID 9398044
12 - PMID 8162586
13 - PMID 19939984
14 - PMID 20351774
15 - PMID 9665108
16 - PMID 17585059
17 - PMID 12709541
18 - PMID 21328257
19 - PMID 8214997
20 - PMID 10617996
21 - PMID 10233322
22 - PMID 12663296
23 - PMID 15099370
24 - PMID 16618360
25 - PMID 20579590
26 - PMID 16303936
27 - PMID 12439536
28 - PMID 17509880
29 - PMID 15647077
30 - PMID 18253974
31 - PMID 16188209
32 - PMID 16841861
33 - PMID 16825676
34 - PMID 15890766
35 - PMID 19664246
36 - PMID 19321563
37 - PMID 9129503
38 - PMID 21041432
39 - PMID 16287956
40 - PMID 19211817
41 - PMID 17490960
42 - PMID 16249527
43 - PMID 20739418
44 - PMID 18957534
45 - PMID 12433711
46 - PMID 16022739
47 - PMID 17940510
48 - PMID 20209147
49 - PMID 8615347
50 - PMID 19424218
51 - PMID 18077475
52 - PMID 12923219
53 - PMID 17490954
54 - PMID 20847896
55 - PMID 16522907
56 - PMID 1970702
57 - Code of Federal Regulations, Title 21, Sec 101.9
58 - PMID 12499328
59 - PMID 30620358 Oleic Acid Can Make Heart Claim Without Hard Evidence, JAMA (2019)

FATTY ACIDS