- How much polyunsaturated fatty acid (PUFA) should I eat?
- What are the risks with excess PUFAs?
There are 2 different hypotheses on polyunsaturated fatty acid.
Hypothesis 1: Concentrated PUFAs are harmful.
- Safe PUFA consumption is 1% – 3% of calories for linoleic acid (the most common omega-6 (n-6) polyunsaturated fatty acid). Corn oil and soybean oil are > 50% linoleic acid by volume.
- There is significant risk from excess polyunsaturated fat. Saturation is a measure of stability. Polyunsaturated fats are less stable than saturated fats. Polyunsaturated fats are more susceptible to lipid perioxidation (the breakdown of fats in the presence of oxygen). Lipid perioxidation is a cascading process, meaning lipid perioxidation will start a chain reaction of oxidation. Lipid perioxidation increases the risk of damaging arterial walls (cardiovascular disease) and the liver (liver disease).
- Supporters for hypothesis #1: Dr. Bill Lands (Nutrition/Biochemistry NIH, retired). Dr. Shou-Ching Jaminet (Molecular Biologist, Harvard)
Hypothesis #2: PUFA Vegetable Oils are good.
- Saturated fat should be kept < 6% of calories. Saturated fat should be replaced with non-tropical polyunsaturated fatty acids (vegetable oils, primarily corn oil and soybean oil).
- Optimum intake of polyunsaturated fat is 12% of calories.
- No mechanism for the benefits of polyunsaturated fatty acid are provided. The evidence consists of predictions based on statistical analysis of the results of food studies.
- No mention of the hazards of excess PUFA are mentioned by the supporters of the “Vegetable Oil is good” hypothesis.
- Supporters of hypothesis #2: Dr. Darius Mozaffarian (Cardiologist, Nutritionist, Tufts) , Professor Alice Lichtenstein (Nutritionist, Tufts), Dr. Frank Hu (Nutritionist, Harvard) , Dr. Frank Sachs (Nutritionist, Harvard).
- References: Report of the 2013 AHA / ACC Lifestyle Work Group. Report of the 2015 Dietary Guidelines Advisory Committee.
- Follow Hypothesis #1. Actively avoid vegetable oils and concentrated PUFA sources.
- Maintaining n-6 consumption at 1-3% of calories carries less risk than consuming 12% of calories of n-6.
- Cardiovascular health can be measured by measuring blood pressure, LDL particle size and stored levels of n-6 in fat tissue.
- The decision making process behind the U.S. dietary guidelines is deeply flawed. Vegetable oils are being presented as a solution to both food production challenges (feeding the population on a domestically produced plant diet) and cardiovascular disease.
- Dietary guidelines are based on the viewpoints of an insular group dominated by the Nutrition Departments of Harvard and Tufts. The group uses scientific language but focuses effort on defending a thesis (effort which is suitable for advancement within universities) versus focusing effort on identifying weaknesses in a hypothesis (scientific effort). The group discounts or dismisses conflicting evidence and makes no mention of the risks associated with their recommendations.
- There is no credible evidence supporting the dietary intervention of replacing saturated fat with polyunsaturated fat. There are risks with consumption of some sources of saturated fat but that risk is not reduced when replaced by polyunsaturated fat.
- The guidelines increase the risk of cardiovascular, liver disease and cancer. They increase the risk because polyunsaturated fatty acid deficiencies are extremely rare and polyunsaturated fats are unstable and susceptible to oxidation (which means risk increases as consumption increases).
- The language being used by the American Heart Association (AHA) and the language used by the 2015 Dietary Guidelines Advisory Committee (DGAC) exaggerates both the benefits of dietary guidelines and the strength of the evidence supporting dietary recommendations.
- The recommendations of the AHA and DGAC in a trilogy of documents from 2013, 2015 and 2017 missed the mark because the committees attention and effort were focused on grading food studies to defend a thesis, rather than measuring the risks and benefits of a medical intervention.
- Nutrients are chemicals. Chemicals in the body follow the rules of Goldilocks, not gold. With gold, more gold has more value. With nutrients there are zones of too little, beneficial and too much. With nutrients there is danger in both too little and too much. Every nutrient, even water and oxygen, has a safe upper limit.
- Saturation is a measure of stability. Saturated is fat is stable, polyunsaturated fat is not.
- Polyunsaturated fatty acid deficiencies are extremely rare.
- The damage mechanism of excess polyunsaturated fatty acid (lipid perioxidation) is well understood from a molecular biology point of view.
- The hypothesis of the AHA and 2015 DGAC is based on an assumption that saturated fat increases LDL-C and the increase in LDL-C causes heart disease. During the 2013 AHA Systematic Evidence Review, the 2015 DGAC Evidence Review and an independent 2015 review by the Credit Suisse Research Institute there were zero studies identified which showed a link between saturated fat and cardiovascular disease.
- Nutrition recommendations are dominated by professors from Harvard and Tufts. The Nutrition Departments of Harvard and Tufts are dominated by Epidemiologists (where epidemiology is the study of the spread of disease)
- The primary tool of Epidemiology is statistical analysis.
The 2015 Dietary Guidelines recommend restricting saturated fat consumption to no more than 10% of calories. The American Heart Association (AHA) is more restrictive, recommending no more than 6% of calories.
To meet these restrictions, the 2015 Dietary Guidelines Advisory Committee (DGAC) and the AHA recommend replacing saturated fat with polyunsaturated fat.
A trilogy of documents captures the thought process of the individuals from the 2015 DGAC and the 2013 and 2017 AHA committees who developed the recommendations.
There are two significant issues with the DGAC and AHA recommendations:
1) The recommendation is a dietary intervention. Every intervention has both benefits and risks. There is no mention of risk or a discussion of risk vs benefit in the 2013, 2015 or 2017 documents.
2) There is an assumption that the reduction of LDL-C by consuming n-6 reduces the risk of cardiovascular disease. The assumption is based on predictions made by statistical regression analysis.
2013 American Heart Association / American College of Cardiology (AHA / ACC) Report from the Lifestyle Work Group
2015 Report from the Dietary Guidelines Advisory Committee
2017 American Heart Association Advisory Statement
Professor Alice Lichtenstein
New York Times Editorial
The 2013 ACC/AHA Review cited by Professor Lichtenstein did not investigate links between saturated fat and heart disease (cardiovascular disease or CVD)
The Lifestyle Work Group provided recommendations on dietary changes to lower LDL-C (low density lipoprotein – cholesterol).
The 2013 AHA/ACC Review was a systematic review of Nutrition Studies. What the 2013 AHA / ACC Report focused on (a database review of nutrition studies):
What the 2013 AHA / ACC recommended: (consume a diet with 6% or less of saturated fat. Replace saturated fat with polyunsaturated fat) and the basis for the recommendations (Evidence Statements (ES) 11, 12 and 13).
The grading criteria for a 1A (highest) recommendation (multiple randomized controlled trials or meta-analysis, diverse population base, benefits >>> (much greater than) risks).
The evidence base used:
ES 11: Three Studies (DASH, DASH-S, DELTA). In two of the studies (DASH and DASH-S) the relationship between saturated fat and LDL-C could not be determined.
ES 12 & 13: Two meta-analysis, conducted 11 years apart by the same authors. The meta-analysis generated a prediction of ‘what would have happened, if…’ dietary changes were made. They were not a measure of actual results.
To summarize the evidence base, 6048 studies were reviewed and for the recommendations on saturated and polyunsaturated fat, 5 studies were chosen.
Three evidence statements were made to justify the recommendations on saturated and polyunsaturated fat. For a 1A rating (the highest rating level) multiple (two or more) studies were required showing the benefits outweighed the risk.
For ES 11, three studies were cited but only 1 of the 3 showed a link between saturated fat consumption and LDL-C.
For ES 12 &13, two meta-analyses we’re cured, both by the same authors using the same criteria, 11 years apart.