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| Vegan Food Reducing Cholesterol |
Vegan Food Reducing Cholesterol
Why do these regimens produce such rapid and substantial improvement in coronary disease? Substantial reductions in LDL cholesterol no doubt play an important part. The modest reductions in saturated fat and total fat intake recommended by the American Heart Association tend to reduce LDL cholesterol by just a few percentage points – not more than about 5%. In contrast, the Pritikin/Ornish regimens typically decrease this risk factor by about 20% or more.
Very-low-fat vegan diets are extremely low in saturated fat – the type of fat which tends to raise serum cholesterol by inhibiting the liver’s capacity to manufacture receptors that remove LDL cholesterol from the bloodstream. Such diets also tend to be low in saturates relative to total fat intake – in other words, they have a high unsaturate-to-saturate ratio; this is important because the level of saturated fattyacids in the liver will reflect not only the absolute dietary intake of these compounds, but also the proportion of total dietary fat which they represent.
In addition, the fact that vegan diets are essentially cholesterol-free (plants don’t manufacture cholesterol) contributes significantly to their cholesterol-lowering efficacy. In the population as a whole – most of whom are omnivores - each 100 mg increase in daily cholesterol intake translates into an increase of only about 2.2 (mg/dl) in serum cholesterol – barely more than a 1% increase in most people.
However, this increase tends to be notably higher in people whose baseline dietary cholesterol intake is quite low – most notably vegans; as Dr. Paul Hopkins notes, “modest amounts of cholesterol added to a cholesterol-free diet would be expected to most efficiently elevate serum cholesterol". Dietary cholesterol also raises serum cholesterol more efficiently in people who are lean12 – which most long-term vegans are. Furthermore, since vegans tend to have quite low serum cholesterols, a given absolute increase in serum cholesterol has a larger impact percentage-wise. So it is clear that the virtual absence of cholesterol in strict vegan diets contributes quite meaningfully to their favorably low LDL cholesterol values.
You should be aware that flesh foods somewhat lower in fat or in saturated fat than red meats – for example, poultry and fish – are just as high in cholesterol as red meat is. With respect to eggs – a rich source of cholesterol (about 250 mg per egg) that is rather low in saturated fat – some recent studies conclude that egg consumption in moderation does not increase the cardiovascular risk of non-diabetics. Vegans should be aware that these studies examined populations that contained few if any vegans, and that this result therefore cannot be presumed to apply to them – and almost certainly doesn’t.
The protein content of vegan diets also contributes to a reduction in serum cholesterol. For decades, it has been known that if you feed rabbits diets featuring any of a number of plant-derived proteins – in comparison to diets that are identical in every respect save that they feature animal protein – their serum cholesterol levels will be decisively lower on the plant protein diet. Though a number of these studies made use of soy protein – inasmuch as soy protein isolates are readily available – other types of plant protein were comparably efficacious in this regard. The mechanism responsible for this effect has never been clearly pinpointed, though the fact that plant proteins tend to be somewhat lower in certain essential amino acids – and thus are considered of “poorer quality” – is thought to be of key importance.
These rabbit studies were the inspiration for the original efforts by Dr. Cesare Sirtori and colleagues to lower elevated cholesterol in humans by feeding diets high in soy protein. These studies compared low-fat omnivore diets (featuring lean meats and reduced-fat dairy products) with virtually vegan diets high in texturized vegetable protein (a soy product). To insure that the studies tested the impact of protein per se, the diets were designed so that the quantity and type of dietary fat were nearly identical on the soy and omnivore diets; total protein intakes also remained nearly constant.
The researcher found that, when the patients switched from the omnivore diet to the soy-based diet, total and LDL cholesterol dropped by about 20%! Although the low-fat omnivore diet contained a small amount of cholesterol, theoretical considerations, as well as a study in which the soy diets were supplemented with cholesterol, indicated that absence of cholesterol was not primarily responsible for the dramatic fall in blood cholesterol during the soy diets. Subsequent similar studies, often enrolling subjects whose initial cholesterol was less elevated, often did not see such dramatic results, and it became clear that soy-based diets had their greatest impact on patients with high cholesterol.
A “meta-analysis” (a statistical analysis which lumps together the results of many comparable studies) of 38 controlled studies of soy protein diets concluded that, on average, both total and LDL cholesterol fell by about 20 points on the soy diet (corresponding to a reduction of about 13% in dangerous LDL cholesterol). It is important to note that these studies compared omnivore diets with vegan diets that happened to be high in soy products. They did not show that you could simply add some soy protein to your omnivore diet and achieve marvelous improvements in your blood fats – contrary to the expectations of many consumers who are now being hustled to buy soy products.
Nor am I aware of any evidence that adding soy protein to a relatively low protein vegan diet has any important effect on serum cholesterol. Furthermore, the common assumption that the isoflavone content of soy protein concentrates was largely responsible for the cholesterol-lowering benefit appears to be dead wrong – Sirtori recently assayed the texturized vegetable protein used in his initial studies and found that it was essentially devoid of these phytoestrogens! The obsessive focus on soy and soy isoflavones ignores that fact that virtually all plant proteins are associated with low serum cholesterol in rabbit studies.
Thus, while texturized soy protein products can come in handy if you want to eat a vegan diet while pretending to be an omnivore, there is no strong reason to expect that vegan diets in which other types of plant protein predominate will not have a comparably beneficial impact on LDL cholesterol. (As we shall see, regular consumption of soy isoflavones may indeed provide some valuable health benefits – albeit reduction of serum cholesterol is not one of them!) One theory regarding the favorable effect of plant proteins on cholesterol levels is that plant proteins tend to provoke less insulin secretion (and greater secretion of a competing hormone known as glucagon) than animal proteins do.
While this is unlikely to be the whole explanation – the quality of dietary protein can influence liver metabolism in more direct ways - it is clear that high insulin levels have effects on the liver that would tend to increase blood cholesterol and triglyceride levels, including an increase in the level and activity of the rate-limiting enzyme for cholesterol synthesis. Insulin secretion can also be moderated by choosing whole foods with a relatively low glycemic index. The Pritikin and Ornish clinics have always emphasized the importance of whole foods and have discouraged use of added sugars. When Dr. David Jenkins and colleagues – progenitors of the glycemic index concept – put healthy young men on two strictly controlled diets that differed only in glycemic index, serum cholesterol was about 15% lower during the low-glycemic-index diet.
Thus, a number of interacting factors contribute to marked cholesterol reduction on an optimal vegan diet: a very low intake of saturated fat, the absence of dietary cholesterol, the characteristic impact of plant protein, and a low glycemic index. In the long run, a substantial reduction in body fat (we’ll discuss this later) often amplifies this benefit.
A classic study provides insight into the magnitude of the benefit achievable when such a diet is consumed in the long term. Back in the 1970s, Dr. Frank Sacks and colleagues from Harvard did a survey of macrobiotic vegan communes in the Boston area. The people in these communes work in a range of ordinary jobs in the outside community, but get together to share their meals communally. The macrobiotic diet which they practice is low-fat, whole-food vegan, but they don’t put any strictures on salt, and they try to keep fruit intake low, their calories coming chiefly from whole grains (especially brown rice), beans, and fresh vegetables. Some members eat fish once or more a week. Of particular note is the fact that they ban all wheat flour products, and don’t use added sugars – thus eliminating the chief sources of high-glycemic-index carbohydrate in the American diet.
Thus, aside from the facts that they don’t discourage salt and they minimize fruit intake, their dietary practices are highly consistent with my recommendations. You may be aware that a total cholesterol level over 200 is considered in the “danger zone”, whereas a cholesterol below 150 is thought to be extremely safe. Sacks found that the average total cholesterol in these Boston communes was 126! In contrast, a group of control subjects drawn from the Boston area, matched by age and sex to the commune subjects, had an average cholesterol of 184. The fact that most of the people in the commune were under 30 certainly contributed to their exceptionally low cholesterol readings – but the handful of commune residents over 40 had an average cholesterol of only 146.
Also of note is the fact that the triglyceride levels of the commune members were also low, averaging 59 (mg/dl) as compared to 86 in the controls. (As we will see, this is an intriguing finding given the fact that the macrobiotic diet is extremely high in carbohydrates – and high-carbohydrate diets are said to raise triglycerides!) Some members of these communes use occasional eggs or dairy, and Sacks found that recent consumption of these foods did indeed correlate with higher cholesterol levels. Sacks reported the case history of one commune member who evidently was genetically prone to high cholesterol..
After 18 months at the commune, his cholesterol was 123. He then left the commune for 6 weeks, at the end of which time his cholesterol had shot up to 219. He returned to the commune, and after 3 weeks his cholesterol was back down to 116. Evidently, having “bad genes” does not mean that you have an inexorable date with the coronary care unit! The effortless leanness of these vegans no doubt was an important factor in their low blood fat levels – their average skinfold thickness (a measure of subcutaneous fat) was only about one-third that of the control subjects. We’ll return to this important point soon.
Sacks is not the only investigator to have noted the highly favorable blood fat levels of free-living American or European vegans. One of these described a vegan diet as “a model for risk reduction”. Evidently, the exceptionally low cholesterol levels enjoyed by rural Asians – and their virtual freedom from coronary heart disease - are not just a function of semi-starvation, chronic infection, or good genes, as some might assume.
article source: Low-Fat, Low-Salt, Whole-Food Vegan
Mark F. McCarty NutriGuard Research, Inc. Second Edition: December 2008
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