Q&A with Bill Harris, M.D.
Q. I am researching cholesterol and came across this comment in your article: "There may be some solace in my unproven suspicion that high serum cholesterol levels in a true vegan are not much of a risk since it's mostly dietary cholesterol that winds up in the arterial lining rather than the ~ 500 mg you synthesize daily yourself"
This is the first I have heard about this idea. Can you point me to any other source that deals with this idea? I've come to believe that if your cholesterol is over 150, you are at risk, and it doesn't matter where the cholesterol comes from.
A. Dear Don,
No I can't. It remains my "unproven suspicion". The definitive study to determine the metabolic fate of dietary cholesterol has not yet been done. It would involve putting a tag of some sort (most likely a radiolabel) on dietary cholesterol and then seeing where it goes, either via scan, biopsy, necropsy, or some friendlier method I haven't thought of. My suspicion is that most of the plaque cholesterol would turn out to be labeled.
I also wonder about your statement "In spite of their high fat content avocados and raw nuts lower cholesterol levels." Others, like Mcdougall and Pinckney, say that these things must be avoided if a vegan diet does not lower cholesterol enough.
I'm in substantial disagreement with the low fat school of thought. I think it's animal fat, refined plant fat, and hydrogenated fat that raises cholesterol levels but don't see a problem with the natural plant fats of raw nuts, seeds, and avocados. I append some supporting references.
Along that line, I posted this on Pincnkey's discussion group the other day but have gotten no answers so far. Do you have any thoughts on it? Don
It has been stated earlier in this forum that a vegan lifestyle is not enough for some people to reduce their cholesterol level to a safe 150. Eliminating even "good" oils like olive oil, nuts, avocado, etc. is recommended. One wonders why this should be so. I would welcome comments on this hypothesis:
I do share Neal's reservations about olive oil in spite of its 3000 year clear track record. It is nevertheless 100% fat.
"Even "good" oils are likely to cause the body to raise cholesterol levels. One reason for this is that oils, whether vegetable or animal, need bile to assist in their digestion. Bile is produced in the liver, stored in the gall bladder, and released as needed into the small intestine. Bile contains cholesterol. In fact, cholesterol is a major component in about 80% of all gallstones. They develop when bile contains an imbalance, with too much cholesterol and not enough bile salts. So, consuming oils causes the liver to increase its production of cholesterol. It becomes hyperactive in order to deal with concentrated oils, an unnatural food. Some of this bile cholesterol is then reabsorbed from the intestines and increases the amount in the blood."
This is a reasonable argument in support of the low fat position.
It is said that the cholesterol in bile is of a different form from that in the blood, and I wonder if this has any bearing on the situation.
Structurally there is no difference. Cholesterol consists of a 4 carbon-ring nucleus with a precise arrangement of carbons attached to the top of the #4 pentane ring. Since cholesterol is insoluble in water, the only variable is the form of water soluble lipoprotein that it uses for a carrier.
I can't give a final answer on the idea that low fat consumption is the key to good health. It may be, but before Nathan Pritikin came on the scene it was traditional among quite healthy vegetarians to consume raw nuts, seeds, and avocados in quantity and with no observable adverse consequences. I personally go through a cup of seeds and nuts daily and my cholesterol ranges from 120-158 mg%.
-William Harris, M.D. ***********
Effect of a high-monounsaturated fat diet enriched with avocado in NIDDM patients. Lerman-Garber I; Ichazo-Cerro S; Zamora-Gonzalez J; Cardoso-Saldana G; Posadas-Romero C Department of Endocrinology, National Institute of Cardiology Ignacio Chavez, Mexico City, Mexico. Diabetes Care (UNITED STATES) Apr 1994, 17 (4) p311-5, ISSN 0149-5992 Journal Code: EAG Languages: ENGLISH Document type: CLINICAL TRIAL; JOURNAL ARTICLE; RANDOMIZED CONTROLLED TRIAL JOURNAL ANNOUNCEMENT: 9410 Subfile: INDEX MEDICUS OBJECTIVE--To assess the effects of two controlled diets, one rich in oleic acid obtained from avocado and olive oil and the other rich in complex carbohydrates, on fasting and postprandial serum lipids and glycemic control in 12 women with NIDDM. RESEARCH DESIGN AND METHODS--A randomized crossover study was designed. During a 4-week baseline period, all patients received the isocaloric diets recommended by the American Diabetes Association. After this period the patients were randomly assigned to receive the two study diets alternatively during two 4-week periods. One diet was high in monounsaturated fatty acids (HMUFA) and the other was high in complex carbohydrates (high-CHO). There also was a 4-week washout period in between the two 4-week periods during which the patients followed the American Diabetes Association's isocaloric diet. Blood samples were obtained before and after each dietary period. RESULTS--Both diets had a minor hypocholesterolemic effect with no major changes in high-density lipoprotein cholesterol. The HMUFA diet was associated with a greater decrement in plasma triglycerides (20 vs. 7% in the high-CHO diet). Glycemic control was similar with both diets. CONCLUSIONS--Partial replacement of complex digestible carbohydrates with monounsaturated fatty acids (avocado as one of its main sources) in the diet of patients with non-insulin-dependent diabetes mellitus improves the lipid profile favorably, maintains an adequate glycemic control, and offers a good management alternative.
[Effects of avocado on the level of blood lipids in patients with phenotype II and IV dyslipidemias] Efectos del aguacate sobre los niveles de lipidos sericos en pacientes con dislipidemias fenotipo II y IV. Carranza J; Alvizouri M; Alvarado MR; Chavez F; Gomez M; Herrera JE Departemento de Investigacion Clinica y Biomedica, Hospital General Dr. Miguel Silva, Morelia, Michoacan. Arch Inst Cardiol Mex (MEXICO) Jul-Aug 1995, 65 (4) p342-8, ISSN 0020-3785 Journal Code: 7AA Languages: SPANISH Summary Languages: ENGLISH Document type: CLINICAL TRIAL; JOURNAL ARTICLE English Abstract JOURNAL ANNOUNCEMENT: 9605 Subfile: INDEX MEDICUS To examine the effects of avocado on plasma lipid concentrations a two-diet trial involving 8 phenotype IV and 8 phenotype II dyslipidemia patients was carried out. A diet rich in monounsaturated fatty acids (DRCA) using the avocado as their major source (30% of the total calories were consumed as fat, 75% of the total fat from the avocado), with restriction of saturated fat and less of 300 mg of cholesterol per day was evaluated. Patients also were in a low-saturated fat diet without avocado (DRSA). The three daily meals were eaten at our clinical unit. Diets were four weeks in duration and they were assigned in a crossover design. In phenotype II both DRCA and DRSA significantly reduced total cholesterol and LDL-cholesterol levels. On phenotype IV DRCA produced a mild reduction on triglyceride levels while DRSA increased them. On HDL-cholesterol concentrations DRCA produced a significant increase in both phenotypes while DRSA did it only in phenotype IV. Avocado is an excellent source of monounsaturated fatty acids in diets designed to treat hypercholesterolemia with some advantages over low-fat diets with a greater amount of carbohydrates.
Nuts ******** American Journal of Clinical Nutrition, Vol. 70, No. 3, 500S-503S, September 1999 ©© 1999 American Society for Clinical Nutrition
Nut consumption, vegetarian diets, ischemic heart disease risk, and all-cause mortality: evidence from epidemiologic studies1,2 Joan Sabatéé 1 From the Departments of Nutrition and Epidemiology and Biostatistics, School of Public Health, Loma Linda University, CA. Perhaps one of the most unexpected and novel findings in nutritional epidemiology in the past 5 y has been that nut consumption seems to protect against ischemic heart disease (IHD). Frequency and quantity of nut consumption have been documented to be higher in vegetarian than in nonvegetarian populations. Nuts also constitute an important part of other plant-based diets, such as Mediterranean and Asian diets. In a large, prospective epidemiologic study of Seventh-day Adventists in California, we found that frequency of nut consumption had a substantial and highly significant inverse association with risk of myocardial infarction and death from IHD. The Iowa Women's Health Study also documented an association between nut consumption and decreased risk of IHD. The protective effect of nuts on IHD has been found in men and women and in the elderly. Importantly, nuts have similar associations in both vegetarians and nonvegetarians. The protective effect of nut consumption on IHD is not offset by increased mortality from other causes. Moreover, frequency of nut consumption has been found to be inversely related to all-cause mortality in several population groups such as whites, blacks, and the elderly. Thus, nut consumption may not only offer protection against IHD, but also increase longevity.
American Journal of Clinical Nutrition, Vol. 70, No. 3, 504S-511S, September 1999 ©© 1999 American Society for Clinical Nutrition
Supplement Nuts and their bioactive constituents: effects on serum lipids and other factors that affect disease risk1,2 Penny M Kris-Etherton, Shaomei Yu-Poth, Joan Sabatéé, Hope E Ratcliffe, Guixiang Zhao and Terry D Etherton 1 From the Graduate Program in Nutrition and the Department of Dairy and Animal Science, The Pennsylvania State University, University Park, and the Department of Nutrition, School of Public Health, Loma Linda University, CA. 2 Address reprint requests to PM Kris-Etherton, Nutrition Department, S-126 Henderson Building, Pennsylvania State University, University Park, PA 16802. E-mail: firstname.lastname@example.org.
TOP ABSTRACT INTRODUCTIONPREDICTIVE EQUATIONS FOR BLOOD... FAT, FATTY ACID, AND... FEEDING STUDIES THAT USED... EVIDENCE OF NONFAT... BEYOND LIPIDS: OTHER NUTRIENTS... PLANNING HEART-HEALTHY DIETS... SUMMARY AND CONCLUSIONS REFERENCES
Because nuts have favorable fatty acid and nutrient profiles, there is growing interest in evaluating their role in a heart-healthy diet. Nuts are low in saturated fatty acids and high in monounsaturated and polyunsaturated fatty acids. In addition, emerging evidence indicates that there are other bioactive molecules in nuts that elicit cardioprotective effects. These include plant protein, dietary fiber, micronutrients such as copper and magnesium, plant sterols, and phytochemicals. Few feeding studies have been conducted that have incorporated different nuts into the test diets to determine the effects on plasma lipids and lipoproteins. The total- and lipoprotein-cholesterol responses to these diets are summarized in this article. In addition, the actual cholesterol response was compared with the predicted response derived from the most current predictive equations for blood cholesterol. Results from this comparison showed that when subjects consumed test diets including nuts, there was an 25% greater cholesterol-lowering response than that predicted by the equations. These results suggest that there are nonfatty acid constituents in nuts that have additional cholesterol-lowering effects. Further studies are needed to identify these constituents and establish their relative cholesterol-lowering potency. 1999(suppl);70:504S11S.