A cardioprotective eating pattern is a proven mainstay of therapy for both the treatment and prevention of atherosclerotic cardiovascular disease (ASCVD). Many controversial diets, foods and supplements have made their way into the media and into our kitchen with promises to improve cardiovascular health, promote weight loss, and reduce disease risk. This article reviews current popular nutrition fads and controversies regarding healthy eating that may actually be increasing your patient’s risk for ASCVD.

Gluten-Free Diet

One current nutritional trend that some believe to be “heart healthy” and reduce the risk of coronary heart disease (CHD) is a gluten-free diet. Gluten, a storage protein found in wheat, rye, barely bulgur, farro, kamut, spelt, and oats, triggers inflammation and intestinal villi damage in people with celiac disease.1 When these villi are impaired, nutrients cannot be absorbed appropriately into the body. Celiac disease affects approximately 0.7- 1% of the population worldwide with the same proportion in the United States.2,3 To date, the gluten-free diet is the only effective treatment for patients with celiac disease. Gluten sensitivity is different from celiac disease in that it is not an immune-mediated response. An estimated 18 million Americans have gluten sensitivity and display symptoms similar to celiac disease including; abdominal cramping, bloating, diarrhea and flatulence, but do not have the intestinal damage and mal-absorption.

Due to evidence that gluten may have an inflammatory component and cause sensitivity symptoms in genetically predisposed individuals without celiac disease, concern has erupted in the medical and lay community  that gluten may increase cardiovascular risk. More specifically, gluten may increase the risk of obesity, metabolic syndrome, neuropsychiatric symptoms, and coronary heart disease among healthy individuals.4 There is no doubt that the media and supermarkets have cashed in on this “gluten health risk” concept. Approximately one-third of Americans report trying to avoid gluten because they perceive a gluten-free diet as a healthier alternative.2 In 2013, sales of gluten-free products in the United States reached 23 billion and is projected to grow another 10.2 percent by 2019.5 Data extracted from the National Health and Nutrition Examination  Surveys (NHANES) showed that the prevalence of celiac disease has remained stable in the United States from 2009-2014. In contrast, this same data revealed a statistically steady increase in adherence to a gluten free diet without celiac disease. The percent of Americans following a gluten-free diet increased from 0.52% in 2009-2010, to 0.99% from 2011- 2012 up to 1.69% in 2013-2014.5

Over the last five years, several articles have been published on potential risk related to a gluten-free diet. Risk have been associated with the lack of vitamins and minerals such as; B vitamins,  zinc, magnesium and fiber when patients eliminate whole grain foods from their diet to avoid gluten. Many gluten-free foods are marketed as healthier alternatives but may in fact have higher amounts of calories, saturated fat, cholesterol, sodium and sugar. Also, these products are often more expensive than their gluten containing alternatives.2

Despite the hoopla surrounding gluten and the rising trend in gluten-free diets, until this year, no prospective studies have evaluated the association of estimated long-term intake of gluten with the development of incident CHD. Lebwohl et al. conducted a prospective cohort study, published in BMJ May 2017, which specifically examined this association using validated data collected over 20-30 years.4 The study included 64,714 women in the Nurses’ Health Study and 45,303 men in the Health Professionals Follow-up Study without a diagnosis or history of CHD. The participants completed a 131 item semi- quantitative food frequency questionnaire in 1986 that was updated every four years through 2010. During the 26 years of follow-up, data from the two prospective cohorts found no significant association between estimated gluten intake and the risk of subsequent overall CHD, non-fatal myocardial infarction and fatal myocardial infarction.4 The lack of association was consistent among men and women. The study did find that the estimated gluten intake correlated moderately with whole grain and refined grain intake as well as glycemic index. After the adjustment for the refined grain intake, the authors noted a significant inverse relationship between estimated gluten intake and CHD. Whole grain intake has been found to be inversely associated with CHD and cardiovascular mortality.6,7 The authors concluded that these finding underscore the potential that patients on gluten-free diets, who restrict their intake of whole grains, may actually be at an increased risk for adverse cardiovascular outcomes. The promotion of gluten-free diets for the purpose of preventing CHD in asymptomatic patients without celiac disease is not recommended.4,8

Coconut Oil

The coconut oil fad has persisted and grown for several years based on claims that it aids in weight loss, prevents or cures Alzheimer’s disease and reduces risk of heart disease.9 One small study of 40 poor women in Brazil compared women on weight loss diets who were provided with coconut oil or soybean oil and instructed to use 30 ml each day in cooking.10 The coconut oil group had a small reduction (1.2 cm) in waist circumference after 12 weeks while those women using soybean oil had no decrease in waist circumference. However, there was no significant difference between the 2 groups on amount of weight lost. Only the coconut oil group had a significant increase in insulin resistance, as measured by HOMA-S.

A commercially  prepared medium chain triglyceride (MCT) oil product has been associated with improved cognitive scores in patients with mild to moderate Alzheimer’s disease.11 Because coconut oil contains MCT, proponents claim coconut oil is healthier than other oils. However, a recent review points out that only about 4% of the triglycerides in coconut oil are medium chain. So, results from studies of MCT products to not translate to coconut oil, either regular or virgin coconut oil.8,12 No quality studies have been done showing that using coconut oil reduces symptoms of Alzheimer’s disease.

While coconut oil raises HDL cholesterol, it also raises LDL cholesterol.13 The clinical importance of raising HDL-C is uncertain, whereas raising  LDL-C would be expected to increase CVD risk. The rise in LDL is similar between butter and coconut oil. In studies, coconut oil has been compared to unsaturated oils including safflower and olive oils. The coconut oil significantly raised LDL cholesterol in most of the studies.  Experts from the American College of Cardiology and the American Heart Association have carefully reviewed the evidence and advise against the use of coconut oil because it raises LDL cholesterol.8,13  In addition, the National Lipid Association (NLA) Expert Panel consensus view is that, if coconut oil is used it should be within the context of a healthy dietary pattern that meets recommendations for saturated fat.16 The NLA recommendation for saturated fat is less than 7% of calories. For a person eating 1500 calories/day, 7% would be 11.6 g saturated fat/day. One tablespoon of virgin coconut oil has approximately 12 g saturated fat. 

Dairy Fat Controversy

Dairy fat is comprised of 51% saturated fats that raise LDL cholesterol when compared with unsaturated fats.13 The 2015 Dietary Guidelines for Americans, the 2013 ACC/ AHA Guidelines, and 2015 NLA Lifestyle recommendations all encourage the use of low and non-fat dairy products to help achieve the low levels of saturated fat intake that have been shown to lower LDL cholesterol and decrease the risk of CVD.14-16  Some recent studies have suggested that full fat dairy products are not associated with an increased risk of cardiovascular disease.17,18  However, a recent AHA scientific statement pointed out that “although dairy fat may be slightly less harmful than other food sources of saturated fats, it is far less beneficial than plant based fats, especially polyunsaturated fatty acids.”19 In 3 large cohorts of US adults from the Health Professionals Follow-Up study and the Nurses’ Health Study (original and II), it was shown that replacement of animal fat, including dairy fat with vegetable sources of fat and PUFA, may reduce the risk of CVD.20 The replacement of dairy fat with meat fat was associated with a higher risk of CVD. Replacing diary fat with refined starch and added sugar was not beneficial, but replacement of dairy fat with whole grains was associated with lower risk of CHD.

The popular press has communicated the idea that dairy fat may not be as bad as once thought and have even suggested that full fat dairy is actually heart healthy. Some patients have even switched from olive oil to butter after hearing reports that full fat dairy is healthy. A very recent AHA Presidential  Advisory on Dietary Fats and Cardiovascular Disease reviewed many studies on dairy fat and lipids and CVD risk and determined that randomized clinical trials have demonstrated that replacing saturated fat from meat and dairy with polyunsaturated fats from vegetable oils reduces the risk of CVD. 13

Fish Oil Supplements

Of the myriad of dietary supplements consumed by Americans regularly, fish oil supplements tops the list.21 These supplements are generally utilized to obtain the potential anti-inflammatory or lipid benefits of Omega 3-Fatty Acids, but there are common misconceptions about these supplements.23 

The principal Omega 3 Fatty Acids in extracted fish oils include eicosopentanoic acid (EPA) and docosohexanoic acid (DHA), but many other fats including saturated fats may be present in commonly available supplements.23 Unlike prescription Omega-3 Fatty Acid agents which contain just under a gram of EPA &/or DHA per 1 gram capsule, many dietary fish oil supplements contain less than 1/3 of the contents as EPA &/or DHA. Additionally, studies of many supplements reveal that it is not uncommon for the amount on EPA/DHA listed on the supplement label, in some cases, to be in fact substantially greater (and occasionally less) than the actual content.27  Thus it would be necessary in most cases to take multiple (even 2-9 in some instances) capsules to achieve the 1 gram of Omega-3 Fatty Acids found in prescription capsule sources. Since 3-4 grams of EPA &/or DHA are required to effectively lower triglycerides, the number of dietary supplement capsules necessary to effectively treat hypertriglyceridemia in many instances would be just simply prohibitive. Furthermore, it should be remembered that other undesired contaminants and saturated fatty acids found in some supplements would also be multiplied by the number of capsules that are consumed.

Although these alternative dietary fish oil supplements are often referred to as “over the counter,” they are not in fact subject to the same manufacturing standards and FDA regulations as prescription capsules, being exempt in safe harbor under the Dietary Health Supplement and Education Act of 1994. Thus, these alternative sources of Omega-3 Fatty Acids are considered as “dietary supplements,” rather than “over the counter” medications; they do not claim to prevent, treat, diagnose, or cure disease. As such these agents are “off the shelf” but not technically “over the counter” since they are typically not FDA approved.25

FDA approved prescription Omega-3 capsules provide highly purified and regulated marine-derived Omega-3 Fatty Acids without significant other contaminants and are considered medications.28 They are available in either pure EPA or blended EPA/DHA formulations. These capsules are highly regulated to strict standards of production and purity, and have both been FDA- reviewed and granted FDA-approved indications to treat high triglycerides over 500 mg/dl.28 They have additionally been shown useful in clinical trials to lower triglycerides between 200-499 mg/dl, with 5-10% reduction typically observed per 1 gram capsule.29 Additionally, 1.8 grams of daily EPA (in the setting of high background dietary fish consumption and statin therapy) was shown in the JELIS trial in a mixture of primary prevention and secondary prevention CHD Japanese patients with total cholesterol >250 mg/ dl to reduce cardiac events.26 Potentially more definitive outcome trials, including STRENGTH and REDUCE-IT are underway at this time.

Patients often relate that they take their fish oil supplements to “treat their cholesterol.” While overall modest lowering of total Cholesterol might accompany significant triglyceride reduction with some reduction of VLDL lipoproteins, LDL-cholesterol is not generally reduced with Omega-3 supplementation. While EPA is generally neutral on LDL-C, in fact DHA has been reported to variably raise LDL-C levels.23 Only minimal effects on HDL-C are seen with either Omega-3 Fatty Acid.

There are also reports of practical recommendations made in some cases to freeze some non-prescription fish oil supplement capsules before consumption to reduce the nasty “fish burp” that may accompany their use. This reportedly delays capsule dissolution until further down the intestinal tract to reduce reflux possibilities. If partial rancid lipid content of a supplement capsule leads to this “freezing” necessity for tolerability, then it is likely better avoided, as oxidized Omega-3 Fatty Acids are probably proatherogenic rather than cardioprotective.24

Knowing about the manufacturing standards of the companies producing dietary fish oil supplements can be helpful in deciding if a particular supplier is providing a source you want to consider recommending. There are some that are clearly better than others. When National Formulary Standards or Dietary Supplement Current Good Manufacturing Practices are used, then impurities and accuracy of contents are somewhat less of an issue.25 Simply letting the patient seek the cheapest source of fish oil “off the shelf”” to substitute for an indicated prescription Omega-3 product should be of concern to the practitioner, as the patient is often subject to “buyer beware” standards. Furthermore these patients may lack enough knowledge about the fish oil products to make informed and better choices, and avoid sometimes undesirable sales staff influences. Teaching the patient to become “label literate” in trying to decide about whether to even use a particular dietary fish oil supplement rather than a prescription product is a worthy service lipid practitioners should provide.

Because nutrition research is so dynamic and confusing to lay people and there is so much conflicting information online and in the lay press, it is essential that healthcare providers keep up with current evidence to provide our patients with beneficial nutrition guidance and referral to Registered Dietitian Nutritionists familiar with the current evidence-based recommendations to reduce the risk of ASCVD. We can help our patients understand the importance of an overall cardioprotective pattern of healthy eating that they can live with given their cultural, economic and taste preferences.19  We can also help to clarifying confusing information regarding dietary supplements like fish oil. The most recent NLA nutrition recommendations for reducing LDL- cholesterol and non-HDL-cholesterol are useful for providers that want to provide evidence based nutrition advice to their patients.16

Current evidence-based recommendations support the use of nuts, olive oil, plant- based diets and plant based proteins, green leafy vegetables; and other high antioxidant foods. However, evidence does not support the use of coconut oil, whole milk dairy products or a gluten free diet for the reduction of ASCVD risk.8,13

The authors wish to thank Kevin Maki, Geeta Sikand and Penny Kris-Etherton for helpful suggestions in the preparation of the coconut oil and dairy fat sections of this article. 

Disclosure statement: Nancy Smith and Dr. Friedrich have no disclosures to report. Dr. Bramlet has received honoraria from Sanofi, Regeneron, Amarin, Kowa, Aralez, Kastle and Genzyme.

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