- 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:
- Fatty acids
- Carbohydrates
- Protein
- 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
- 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
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