Reference - Human health
Recently Professor Stephen Smith gave a presentation to an Australian Wagyu Association conference. He is from the Department of Animal Science at Texas A&M University and has been researching lipids in beef for the past 30 years.
The prevalence of overweight and obesity in the USA increased dramatically in the past three decades. It applies to children, adolescents and adults and is more severe in minority groups. A review of the literature back to the 1950s suggests that dietary recommendations have not been based entirely on scientific data. Despite the low-fat and low-cholesterol diet recommended by the American Heart Association since 1961, the rate of obese Americans has risen from one in seven to one in three. The incidence of diabetes has risen from less than 1 percent to more than 11 percent of adults over this period.
The latest large review of past studies on the health effects of saturated fats found no clear link with heart disease and early death, but it concluded that trans fats from hydrogenated oils significantly raised the risk for those outcomes.
The research, published in the British Medical Journal, also found no association between intake of saturated or trans fat with risk of stroke or type 2 diabetes.
For the saturated fat analysis, the researchers from Canada’s McMaster University looked at 41 studies published between 1981 and 2014.
“The association between consuming saturated fat and a higher risk for similar health issues was variable and unclear," Russell de Souza, professor at McMaster University, said in a WedMD article. "But we want to be careful. We're not saying that we're confident that saturated fat is truly benign."
The review, which was funded by the World Health Organization, noted that saturated fats, mainly from meat and dairy products, contribute about 10 percent of energy to the North American diet.
An advisory committee reviewing the U.S. government’s proposed new Dietary Guidelines for Americans recently concluded that limiting total fat does not lower the risk of heart disease.
The Canadian researchers also found that a 2-percent increase in energy from trans fats was associated with a 25 percent higher risk of heart disease and 31 percent higher risk of death from heart disease.
2005 Guidelines had been updated in May 2010 (USDA, 2010) and changes to Trans fatty acids were recently announced.
The effects of fatty acids on health is reviewed in this section. It is followed by a review of the effects of beef on cholesterol. Finally, dietary guidelines in USA, UK and Australia are presented.
Effects of fatty acids on human health
Fats in the diet are usually made up from three individual fatty acids. Fatty acids are classified by the number of double bonds they contain. They are either saturated, monounsaturated or polyunsaturated fatty acids. The properties of some individual fatty acids can overlap within a group, an investigation of data from numerous studies ranked relative risk of fatty acid groups from dietary intake (from Chowdhury et al., 2014):
The relative risk is higher from trans and saturated fatty acids. The size of the marker is proportional to the inverse of the variance of the relative risk.
There were moderate positive correlations between dietary intake and circulating composition of total omega-3 and omega-6 polyunsaturated fatty acids. There were weak positive correlations for total unsaturated and monounsaturated fatty acids.
The effects of individual fatty acids on plasma total and lipoprotein cholesterol concentrations is illustrated. Oleic acid was used as a reference between different studies (Kris-Etherton et al., 1997).
Even though this work was reviewed more than fifteen years ago, it presents the major major fatty acids in animal products in one chart and today's researchers are corroborating the same findings in their individual studies.
Saturated fat (SFA) raises total blood cholesterol levels and low-density lipoprotein (LDL) cholesterol levels which can both increase risk of cardiovascular disease. SFA may also increase risk of type 2 diabetes. Stearic acid is a long chain saturated fatty acid but, unlike other saturated fatty acids, it does not raise serum cholesterol concentrations. The average content of stearic acid in Wagyu loin from grain finishing is 8 to 10.8% of total fatty acids and up to 15% with grass finishing. In dairy products, it averages 12.2% in fresh milk, 10.7% in butter and 9.8% in cheese. The other SFA - palmitic acid, lauric acid and myristic acid - raise total, low-density lipoprotein (LDL) and high-density lipoprotein (HDL) cholesterol.
Monounsaturated fatty acids (MUFA) have only one double carbon bond. They are liquid at room temperature and turn solid when chilled. Diets with high MUFA have been found to have the following benefits: decreased risk of breast cancer, reduced LDL and total cholesterol, and lower risk for heart disease and stroke. Oleic acid is the most common fat in beef comprising at least one third of lipids and increases with grain feeding. Other MUFA in beef are palmitoleic acid and traces of myristoleic acid. Common sources of MUFA in the diet are olive oil, avocadoes, almond, cashew, pecan and macadamia nuts and corn.
Polyunsaturated fatty acids (PUFA) are either omega-3 or omega-6. They are “essential” as they cannot be made but have to be consumed by animals and man. α-linoleic acid (18:3ω3 “ALA”) is the major omega-3 fatty acid and is found in higher levels in beef which has been finished on forages.
Other PUFA in beef are eicosapentaenoic acid (20:5ω3 “EPA”) and docosahexaenoic acid (20:6ω3 “DHA”) and they attain levels around 0.5% of the total lipids. DHA is important for vision and brain function and is associated with decreased risk of breast cancer.
In general, omega-3 are used for numerous normal body functions, such as controlling blood clotting, building cell membranes in the brain, learning, hearing, taste and there are high levels in the retina of the eye. Omega-3 fatty acids are also associated with many health benefits, including protection against heart disease and possibly stroke and improvements to the function of the nervous system. New studies are identifying potential benefits for a wide range of conditions including cancer, inflammatory bowel disease, and other autoimmune diseases such as lupus and rheumatoid arthritis. Deficiencies of α-linoleic acid are altered structure and function of membranes and cerebral dysfunctions. Salmon, tuna (EPA and DHA) and walnuts (α-linoleic acid) are the most common sources of omega-3 in the diet.
The benefits from omega-3 in the diet is irrefutable and the consumption of oily types of fish, in particular, a few times a week has been associated with a reduced risk of coronary heart disease and sudden cardiac death. The advantage was less evident when long chain omega-3 supplements were taken instead of fish (Chowdhury et al., 2012). High level intake of omega-3 from fish and white chicken was associated with reduced liver cancer from its anti-inflammatory effect from an extensive review of literature. The intake of red meat, processed meat or total meat is not associated with liver cancer risk (Luo, et al., 2014).
Two serves of omega-3 rich fish per week is recommended, but daily intake of omega-3 should not exceed 3 gram unless prescribed.
Different types of salmon provide different amounts of dietary omega-3 fats. Deep red flesh from wild salmon has the highest levels that the body can readily absorb and use. Farmed salmon and pink salmon have lower omega-3 content. Omega-3 fatty acids are extremely fragile and easily lose potency.
The composition of omega-3 and other fatty acids in beef has been investigated by McAfee et al., 2011. Total PUFA from ground grass-fed beef is 98 mg per 100 g and 49 mg per 100 g from concentrate fed beef. Canned tuna contains 270 mg omega-3 in 100 g but all of these sources are trumped by herrings, sardines and 1,300 to 2,000 mg omega-3 per 100 g from red salmon.
Linoleic acid is the major omega-6 fatty acid and is common in most diets so a deficiency of omega-6 is uncommon. Omega-6 fatty acids lower LDL cholesterol and they are protective against heart disease. Some concern has been expressed about the effects of PUFA on tumour growth. The human evolved on a diet with an omega-6:omega 3 ratio of 1:1. The following foods provided omega-3: meat, wild plants, eggs, fish, nuts and berries. Omega-3 fatty acids help reduce inflammation. The typical American diet tends to contain more than 14 times more omega-6 fatty acids than omega-3 fatty acids, which many nutritionally oriented physicians consider to be way too high on the omega-6 side. Increased intake of omega-6 arachidonic acid (20:4ω6 “AA”) raised the atherogenic effect in a human trial, but intake of EPA and DHA (omega-3) blunted this effect. Mortality from cardiovascular disease has been found to decrease when the omega-6:omega-3 ratio is reduced to 4:1. Other diseases have responded to ratios of 5:1 to 2.5:1 and are specific (Simonopoulos, 2008).
The Mediterranean diet, on the other hand, has a healthier balance between omega-3 and omega-6 fatty acids. Many studies have shown that people who follow this diet are less likely to develop heart disease. The Mediterranean diet emphasizes foods rich in omega-3 fatty acids, including whole grains, fresh fruits and vegetables, fish, olive oil, garlic, as well as moderate wine consumption (University of Maryland Medical Center).
TFA is unsaturated but trans isomer/s, instead of the more abundant cis isomer, occurs naturally in some foods. Synthetic TFA are made during food processing through partial hydrogenation of unsaturated fats. This process creates fats that are easier for cooking with more convenient storage than naturally occurring oils and that are liquid at room temperature. Synthetic TFA can increase LDL, increase body weight, interfere with the incorporation of other fatty acids into cell membranes, decrease HDL, interfere with elongation and desaturation of essential fatty acids, decrease birth weight by crossing the placenta, increase platelet aggregation and increase lipoprotein.
Conjugated linoleic acid is a trans fatty acid but, unlike other trans fatty acids, it may have beneficial effects on human health and is not classified as a TFA in USA and is exempt from labelling. Although CLA is known for its anti-cancer properties, researchers have also found that the cis-9, trans-11 form of CLA can reduce the risk for cardiovascular disease and help fight inflammation.
Fatty acid composition in ground beef from cattle that were grass-fed and concentrate-fed is tabled (McAfee et al., 2011):
Fats provide nine calories of energy per gram. Fats in the food eaten should not total more than 25–35 % of the calories eaten in a given day.
Effects of fatty acids in beef on cholesterol levels
Historically the link between certain types of fat in the diet to blood levels that could lead to risk of coronary disease resulted in recommendations that little or no red meat should be consumed.
The cholesterol lowering effect of a low SFA diet with lean beef had not been rigorously evaluated until Roussell et al., 2012 completed a trial with elevated cholesterol participants. It was concluded that lean beef can be included in a heart healthy dietary pattern.
A trial to compare the effect of high SFA hamburger produced from pasture-fed cattle (MUFA:SFA = 0.95) with MUFA hamburger from grain-fed cattle (MUFA:SFA 1.31) was designed. Participants consumed five SFA burgers per week for five weeks, then their habitual diets for three weeks, then the high MUFA burgers for five weeks. The high SFA hamburger increased plasma palmitic acid, palmitoleic acid and TAG, and decreased HDL cholesterol and LDL particle diameter percentile distribution.
It was concluded that men with mildly raised cholesterol blood levels had increased risk for cardio vascular disease following consumption of hamburger patties high in SFA and TFA specifically by decreasing HDL-C concentration and LDL particle diameter while increasing plasma TG concentration. Rotating the men to hamburger high in MUFA increased the HDL-C concentration and reduced TG to baseline values. SCD activity in the liver may have been responsible for these effects in both SFA and MUFA groups (Adams et al. 2010).
A cross-over intervention trial compared 24% total fat patties from Angus with MUFA:SFA ratio of 0.71 from pasture fed cattle with 1.10 from grain fed cattle. Five patties were consumed per week for five weeks with a wash-out four week period.
The grain fed high MUFA ground beef provided more oleic acid, and less stearic acid, palmitic and 18:1 trans fatty acid than the pasture fed low MUFA ground beef. The habitual diets consumed in addition to the hamburgers resulted in the following final content: 30 g SFA, 26 g MUFA and 10 g PUFA at baseline, breakdown at commencement and 39 g SFA, 31 g MUFA and 11 g PUFA for low MUFA and 36 g SFA, 32 g MUFA and 12 g PUFA. 97 g total fat was consumed in both groups per day.
High MUFA ground beef increased HDL-C concentration from baseline. Both ground beef treatments decreased insulin and HDL₂ and HDL₃ particle size and increased plasma stearic acid and 20:4 (n-6) arachidonic acid above the baseline. Corn-fed beef increased LDL diameter.
Levels of ALA in beef - even the higher content in grass-fed patties - were not high enough to have any effect on the metabolism of omega-3 fatty acids in this work.
In conclusion, results with high MUFA beef confirmed human studies that have been carried out using oils. High oleic acid ground beef decreased LDL and increased HDL cholesterol (Gilmore et al. 2011).
Ground beef high in SFA and TFA increased LDL and decreased HDL cholesterol (Smith, 2012).
The American Heart Association
The FDA has taken a step towards eliminating artificial trans fats from the food supply. A 60-day comment period has commenced to collect additional data and to gain input on the time potentially needed for food manufacturers to reformulate products that currently contain artificial trans fat. In the interim, consumers are advised to choose products that have the lowest combined amount of saturated fat, cholesterol and trans fat. Products which have contained less than 0.5 grams trans fat per serving have been considered to be trans fat free (Hayes 2013).
Nutrition Committee guidelines (healthy folk over 2 years old) that are in effect:
- Limit total fat intake to less than 25–35 percent of your total calories each day;
- Limit saturated fat intake to less than 7 percent of total daily calories and substituting SFA with monounsaturated and polyunsaturated fatty acids;
- Limit trans fat intake to less than 1 percent of total daily calories;
- The remaining fat should come from sources of monounsaturated and polyunsaturated fats such as unsalted nuts and seeds, fish (especially oily fish, such as salmon, trout and herring, at least twice per week) and vegetable oils; and
- Limit cholesterol intake to less than 300 mg per day, for most people. If you have coronary heart disease or your LDL cholesterol level is 100 mg/dL or greater, limit your cholesterol intake to less than 200 milligrams a day.
British Dietetic Association
“Guideline Daily Amounts” (GDAs) for average adults of normal weight and average activity levels:
No more than 30% of the total fat intake should come from saturated fat in the diet. The daily limit should be:
The inclusion of monounsaturated fat is beneficial as it helps to promote the healthier type of cholesterol in blood. Omega 3 fats can help prevent the blood from clotting, help regulate the heart rhythm and are particularly important to improve survival after a heart attack.
National Heart Foundation of Australia
The Position statement for Dietary fats for cardiovascular health:
The key findings in relation to fatty acid classes, individual fatty acids, total fat and dietary cholesterol are as follows:
Saturated fatty acids (SFA)
• SFA intake is associated with coronary heart disease (CHD).
• Increasing SFA intake results in an increase in total cholesterol (TC) and LDL compared to carbohydrate, PUFA and MUFA.
• Individual SFA have differential effects on the lipid profile.
• Lowering dietary SFA to < 7% of energy intake with restricted dietary cholesterol results in further LDL lowering than diets containing < 10% of energy intake from SFA.
• Replacing SFA with omega-6 PUFA (n-6) to achieve a ratio of PUFA to SFA of greater than 1 will reduce the risk of CHD.
Trans fatty acids (TFA)
• TFA intake is associated with an increased risk of myocardial infarction.
• TFA intake is associated with increased CHD incidence and risk of CHD.
• The consumption of TFA increases LDL and decreases high-density lipoprotein cholesterol (HDL).
• Replacing TFA and SFA with MUFA or PUFA is an effective measure for improving blood lipid profiles.
Polyunsaturated fatty acids (n-6 PUFA)
• n-6 PUFA intake lowers LDL-C.
• There is no direct relationship between total fat intake and the incidence of CHD.
• Dietary cholesterol increases TC and LDL, but substantially less so than SFA and TFA (1999 evidence statement retained).
• Within a low SFA diet, individuals can consume up to six eggs per week without adversely affecting CVD outcomes.
The key findings in relation to fish, fish oils and polyunsaturated fatty acids are as follows:
• Fish and fish oil consumption is associated with a reduced risk of CHD, CHD mortality and stroke.
• In secondary prevention, 2 g per day alpha-linolenic acid (ALA) and ≥ 850 mg per day of omega-3 polyunsaturated fatty acids (n-3 PUFA) as fish oil reduces the risk of CHD.
• 1,000–4,000 mg per day of n-3 PUFA as fish oil decreases triglycerides (TG) by 25–30% and increases HDL by 1–3%.
• Australian fish, seafood and fish oil are generally very low in methylmercury, dioxins and other environmental contaminants.
• Consuming fish high in methylmercury may result in neurological damage, especially in unborn children.
• While caution should be taken in consuming fish high in methylmercury, the benefits of consuming fish and fish oil are numerous and should be encouraged in the general population.
• n-3 PUFA fortification of food and farmed fish are likely to play an increasing role in the Australian diet.
Source of healthy fats:
A healthy balanced diet should include the healthier monounsaturated and polyunsaturated fats.
Monounsaturated fat is found in foods such as avocados, almonds, cashews, peanuts and cooking oils made from plants or seeds such as sunflower, canola, soybean, olive, sesame and peanut oils.
Polyunsaturated fat (omega-6) is found in foods such as fish, tahini (sesame seed spread), margarine, linseed (flaxseed), sunflower and safflower oil, pine nuts and Brazil nuts. Polyunsaturated fat (omega-3) is found in oily fish such as tuna, salmon, sardines and blue mackerel as well as walnuts and linseeds.
World Health Organization
The WHO goal is to limit the intake of trans fats to 1 per cent of total energy intake. Food Standards Australia New Zealand found the average Australian's intake of trans fats was 0.5-0.6 % (Browne, 2013).
Adams, T.H., Walzem, R.I., Smith, D.R., Tseng, S. and S.B. Smith. 2010. Hamburger high in total, saturated and trans-fatty acids decreases HDL cholesterol and LDL particle diameter, and increases TAG, in mildly hypercholesterolaemic men. B. J. Nutr. 103:91-98.
Body Ecology. 2008. The 6 benefits of monounsaturated fats. 20th August 2008.
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Chowdhury, R., Warnakula, S., Kunutsor, S., Crowe, F., Ward, H., Johnson, L., Franco, O.H., Butterworth, A.S., Forouhi, N.G., Thompson, S.G., Khaw, K.-T., Mozaffarian, D., Danesh, J. and E.D. Angelantonio. 2014. Association of dietary, circulating, and supplement fatty acids with coronary risk. Ann Intern Med 160:398-406.
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Gilmore, L.A., Walzem, R.L., Crouse, S.F., Smith, D.R., Adams, T.H., Vaidyanathan, V., Cao, X. and S.B. Smith. 2011. Consumption of high-oleic acid ground beef increases HDL-cholesterol concentration but both high- and low-oleic acid ground beef decrease HDL particle diameter in normocholesterolemic men. J. Nutr. 141:1188-1194.
Grundy, S.M. 1994. Influence of stearic acid on cholesterol metabolism relative to other long-chain faty acids. Am.J. Clin.Nutr. 60:986S-9890S.
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McAfee, A.J., McSorley, E.M., Cuskelly, G.J., Fearon, A.M., Moss, B.W., Beattie, J.A.M., Wallace, J.M.W., Bonham, M.P., and Strrain, J.J. 2011. Red meat from animals offered a grass diet increases plasma and platelet n-3 PUFA in healthy consumers. Brit. J. Nutr. 105:80-89.
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USDA: Report of the Dietary Guidelines Advisory Committee on the Dietary Guidelines for Americans. May 2010.