Diet and heart disease

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]


Overview

Diet may play an important role in causing or preventing heart disease. Doctors and nutritionists have studied numerous diets and dietary components in an effort to minimise the risk of heart diseases.

Saturated fats and cholesterol

One of the earliest suggestions that saturated fats and cholesterol could be related to heart disease was proposed by Ancel Keys in the late 1950s. While this and other similar studies were eagerly received by commercial beneficiaries such as the processed oil and food industries, other scientific studies have cast doubts on whether saturated fats should be demonized.

An analysis of American statistics covering the sixty year period from 1910 to 1970 found that the proportion of traditional animal fats in the American diet declined from 83% to 62%, and the annual consumption of butter in particular declined from 18 pounds to 4 pounds per person. The study also found that over the past eighty years, the percentage of vegetable oil consumption in the form of margarine, vegetable shortening and other refined oils has increased by around 400%, with the consumption of sugar and processed foods by 60%.[1] This suggests that hydrogenated oils (which contain trans fat, not saturated fat) and sugar should be suspected to be more at fault than saturated fats.

A famous project called the Framingham Heart Study, started in 1948, found after 40 years of testing that while those who weighed more and had abnormally high blood cholesterol levels were slightly more at risk of developing heart disease, weight gain and cholesterol levels had an inverse correlation with saturated fat and cholesterol intake in the diet.[2] It was also found that the subjects with the highest saturated fat consumption weighed the least, but also happened to be the most physically active of the population under study. A director of the Framingham Heart Study, Dr William Castelli, wrote in 1992[2]

For example, in Framingham, Massachusetts, the more saturated fat one ate, the more cholesterol one ate, the more calories one ate, the lower the person's serum cholesterol... In view of this, this study fails to describe a relationship of those traditional dietary constituents, saturated fat and cholesterol, known to have an adverse effect on blood lipids, and thereby, on the subsequent development of coronary disease end points.[3]

One large trial, the Multiple Risk Factor Intervention Trial (MRFIT) produced surprising results. It compared the death rates and eating habits of 12,000 men, and treated certain individuals by controlling high blood pressure with medicines, preventing smoking, and stipulating a low fat, low cholesterol diet. The MRFIT trial found that while those on the low fat diet had a slightly decreased mortality from Coronary heart disease, the overall mortality from all causes for those who were treated and obeyed the suggested diet was higher.[4]

Another study from the 1960s which examined the health of Yemenite Jews found that the diet of the subjects living in Yemen contained no sugar and obtained all its fat from animal sources. The subjects who had moved from Yemen to Israel altered their diets so that 25-30 percent of their carbohydrate intake was derived from sugar, and they obtained their fat from the consumption of margarine and vegetable oils. The Yemenite group was found to have few examples of heart disease and diabetes, whereas incidences of these disorders were far higher in the Israeli group.[5]

Saturated fats have gained an unjust notoriety by being confused with trans fats, both in early studies from the mid 20th century, and also as they were long grouped together in various U.S. databases used by researchers to correlate dietary trends with disease conditions.[6][7][8]

Unsaturated fats

Unsaturated fats do not reduce mortality when increased in diet, either:

However, the omega-3 fatty acid eicosapentaenoic acid may reduce cardiac events[11][12].

Trans fats

While both saturated and trans fats increase levels of LDL cholesterol (so-called "bad" cholesterol), trans fats also lower the levels of HDL cholesterol (so-called "good" cholesterol) [3]; this increases the risk of coronary heart disease (CHD). The NAS is concerned "that dietary trans fatty acids are more deleterious with respect to CHD than saturated fatty acids" [4].

The Harvard Medical School has shown that phytosterol-rich oils reduce blood cholesterol. However, more importantly they showed that hydrogenated, or trans fats, which are present in margarine and are extensively used for packaged food manufacturing, may be harmful. One of their studies published in 2005 has determined that a positive relationship exists between the consumption of trans fat and the development of endothelial dysfunction, a precursor to atherosclerosis.[13]

Trans fats are harmful because they are absorbed by the body's cell membranes as if they were cis fats, causing the cells to become partially hydrogenated, which disrupts cell metabolism.[5]

Other studies have found that hydrogenated fats made from vegetable oils block the use of essential fatty acids, which could contribute to sexual dysfunction, increased blood cholesterol and negatively affect the immune system.[14][15][16][17][18]

Salt

The UK Scientific Advisory Committee on Nutrition (SACN) review Salt and Health is probably the most authoritative single document on its stated topic. It concludes:

  • Hypertension (high blood pressure). "Since 1994, the evidence of an association between dietary salt intakes and blood pressure has increased. The data have been consistent in various study populations and across the age range in adults." (SACN, p3).
  • Left Ventricular Hypertrophy (LVH). "Evidence suggests that high salt intake causes left ventricular hypertrophy, a strong risk factor for cardiovascular disease, independently of blood pressure effects." (SACN, p3)

Homogenised milk

Main Articles: Unpasteurised milk: Homogenisation & heart disease; also Milk: Creaming & homogenisation

In recent years, there has been increased attention placed on potential health concerns relating to the homogenisation of milk and other dairy products. Studies conducted by Dr Kurt A Oster and his colleague D.J. Ross from the early 1960s to the mid 1980s suggested that homogenised milk could be a major factor in arterial plaque formation, causing heart disease.

Oster and Ross hypothesised that the homogenisation of milk increased the dietary availability of xanthine oxidase, which could lead to the formation of arterial, or atheromatous, plaque. However a team lead by A.J. Clifford in the early 1980s asserted that Oster and Ross had not sufficiently established their arguments.[19]

While the xanthine oxidase/plasmalogen hypothesis has been disproved, the debate is hardly over. Mary Enig, co-founder and Vice President of The Weston A. Price Foundation [20], has remarked that while Oster's work has been discounted, it does not prove that the homogenisation process is benign, as it vastly increases the surface area of fat globules, and causes new globule mebranes to be formed which have a different composition to raw milk fat globules.[21] Examination of the xanthine oxidase issue has continued, with recent research by R.J. Hajjar and J.A. Leopold, "Xanthine oxidase inhibition and heart failure: novel therapeutic strategy for ventricular dysfunction", published in Circulation Research (2006) (journal of the American Heart Association).

Alcohol

The World Health Organization (WHO) states there is convincing evidence that "low to moderate alcohol intake" reduces the risk of coronary heart disease but also that "high alcohol intake" increases the risk of stroke.[22]

"A study of 50,000 people found that men who drank daily had a 41% reduced risk of coronary heart disease compared with a 7% drop in men who drank once a week. In women, the risk of heart disease fell by a third with a weekly drink but did not fall further in daily drinkers."[23]

Preventive diets

Vegetarian diet

Vegetarians have been shown to have a 24% reduced risk of dying of heart disease.[24]

One of the earliest and well-known popularizers of a diet approach to heart disease was the Pritikin diet. The Pritikin Plan was created by a non-physician, Nathan Pritikin, and consisted of diet and exercise changes in a residential program. The AHA-1 Diet is recommended by the American Heart Association.

Dr. Gabe Mirkin and Dr. John McDougall have been proponents of a diet approach to avoiding heart disease. McDougall sells "just add water" vegetarian meals in a cup on his rightfoods site.

The most powerful cholesterol-lowering agents are soluble fiber, unsaturated fats, and phytochemicals, all of which are found almost exclusively in plant foods. In the seventeen studies conducted between 1978 and 2002, the average vegan’s cholesterol level was 160 mg/dl, while the average non-vegetarian’s cholesterol was 202 mg/dl.[25]

Despite the benefits of a vegetarian diet, it is likely that with a few changes to the typical vegetarian diet such as adopting a low-fat variant, the risks of heart disease could be reduced even further. Note however that some of these vegetarian diets (for instance, vegan ones) may be low in Vitamin B12, which could lead to increased homocysteine levels--a risk factor for heart disease. It has also been argued that vegetarians may not have high intakes of Omega-3 fatty acid, considering that there is evidence that higher intakes of Omega-3 fatty acids reduce the risk of heart disease, and that fish, usually regarded as the prime source of them, is a non-vegetarian food source. Not withstanding, Omega-3 fatty acid do occur naturally in other vegetarian food sources, like soy and flax seed oils, therefore some believe this objection is easily mitigated. However, the vegetable sources of Omega-3s are primarily composed of alpha-linolenic acid (ALA). But the human body also requires eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). The human body can convert ALA to EPA, and EPA to DHA, but the efficiency, and sufficiency for optimal health, of this conversion is controversial. Studies have found EPA and DHA levels in vegans to be about two thirds lower than in omnivorous people.

It is actually likely that the primary benefit of a vegetarian diet is the elimination of the negative effects of eating commercial meat and other animal products, which are high in both saturated fats and environmental contaminants. However, to date no study has been done comparing the health of vegetarians to those who eat a whole-foods, omnivorous diet comprised solely of foods in their natural state. This would include wild-caught fish and 100% grass-fed animals. Given the well-documented benefits of the consumption of EPA and DHA, many natural health advocates feel that the most optimal health comes from such a diet.

Cretan Mediterranean-style diet

The Seven Country Study[26] found that Cretan men had exceptionally low death rates from heart disease, despite moderate to high intake of fat. The Cretan diet is similar to other traditional Mediterranean diets: consisting mostly of olive oil, bread, abundant fruit and vegetables, a moderate amount of wine, and fat-rich animal products such as lamb, sausage and goat cheese.[27][28][29] However, the Cretan diet consisted of less fish and wine consumption than some other Mediterranean-style diets, such as the diet in Corfu, another region of Greece, which had higher death rates.

The Lyon Heart Study[30] set out to mimic the Cretan diet, but adopted a pragmatic approach. Realizing that some of the people in the study would be reluctant to move from butter to olive oil, they used a margarine based on rapeseed (canola) oil. The dietary change also included 20% increases in vitamin C rich fruit and bread and decreases in processed and red meat. On this diet, mortality from all causes was reduced by 70%. This study was so successful that the ethics committee decided to stop the study prematurely so that the results of the study could be made available to the public immediately.[31]

Summary

Current indications suggest that the best way forward at present may be to be wary of manufactured foods (especially those containing hydrogenated oils), to increase intakes of fresh fruits and vegetables, and to consider eating unrefined foods including dairy products, meats, nuts and grains.

Avoiding smoking and homogenized milk, reducing salt and sugar consumption, and adopting regular physical activity are also likely to be beneficial.

See also

External links

Government advice

Science sites

Other sites

References

  1. Enig, Mary G, PhD, "Trans Fatty Acids in the Food Supply: A Comprehensive Report Covering 60 Years of Research", 2nd Ed., Silver Spring MD, (1995), pp. 4-8.
  2. Hubert H., et.al., Circulation (the journal of the American Heart Association), (1983), 67:968; Smith, R. and E.R. Pinckney, "Diet, Blood Cholesterol and Coronary Heart Disease: A Critical Review of the Literature", Vol.2, 1991, Sherman Oaks, CA.
  3. Castelli, William, "Concerning the possibility of a nut...", Archives of Internal Medicine, Jul 1992, 152:7:1371-1372.
  4. Multiple Risk Factor Intervention Trial Research Group 1982, "Multiple risk factor intervention trial. Risk factor changes and mortality results", Journal of the American Medical Association, 1982; 248:1465-77.
  5. Cohen, A, American Heart Journal, (1963), 65:291
  6. Enig, Mary G., Nutr Quarterly, (1993), 17:(4):79-95
  7. Enig, Mary G., "Trans Fatty Acids in the Food Supply: A Comprehensive Report Covering 60 Years of Research", 2nd Ed., Silver Spring MD, (1995), pp. 148-154.
  8. Enig, Mary G., et.al., Journal of the American College of Nutrition, (1990), 9:471-86.
  9. Abdelhamid AS, Brown TJ, Brainard JS, Biswas P, Thorpe GC, Moore HJ; et al. (2018). "Omega-3 fatty acids for the primary and secondary prevention of cardiovascular disease". Cochrane Database Syst Rev. 7: CD003177. doi:10.1002/14651858.CD003177.pub3. PMID 30019766.
  10. Hooper L, Al-Khudairy L, Abdelhamid AS, Rees K, Brainard JS, Brown TJ; et al. (2018). "Omega-6 fats for the primary and secondary prevention of cardiovascular disease". Cochrane Database Syst Rev. 7: CD011094. doi:10.1002/14651858.CD011094.pub3. PMID 30019765.
  11. Bhatt DL, Steg PG, Miller M, Brinton EA, Jacobson TA, Ketchum SB; et al. (2019). "Cardiovascular Risk Reduction with Icosapent Ethyl for Hypertriglyceridemia". N Engl J Med. 380 (1): 11–22. doi:10.1056/NEJMoa1812792. PMID 30415628.
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  15. Science News Letter, Feb 1956
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  18. Watkins, B.A., et.al., British Poultry Science, (Dec 1991), 32(5):1109-1119.
  19. Clifford A.J., Ho C.Y., Swenerton H., "Homogenized bovine milk xanthine oxidase: a critique of the hypothesis relating to plasmalogen depletion and cardiovascular disease", American Journal of Clinical Nutrition, (1983) 38;327-332.
  20. Weston A Price Foundation Board of Directors
  21. Know Your Fats Mary Enig
  22. World Health Organization Population nutrient intake goals for preventing diet-related chronic diseases
  23. BBC A daily drink 'only good for men' 25 May 2006
  24. Key TJ, Fraser GE, et al., "Mortality in vegetarians and nonvegetarians: detailed findings from a collaborative analysis of five prospective studies", American Journal of Clinical Nutrition, Sep 1999, 70:516S-524S)
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  30. Lyon Heart Study
  31. de Lorgeril M, Salen P, Martin JL, Monjaud I, Delaye J, Mamelle N. (1999). "Mediterranean diet, traditional risk factors, and the rate of cardiovascular complications after myocardial infarction: final report of the Lyon Diet Heart Study". Circulation. 99 (6): 779–85. PMID 9989963.



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