July 22, 2003 -- Researchers at the University of Toronto and St. Michael's Hospital have shown that a vegetarian diet composed of specific plant foods can lower cholesterol as effectively as a drug treatment. The study, published in the July 23 issue of the Journal of the American Medical Association, compared a diet of known cholesterol-lowering, vegetarian foods to a standard cholesterol-reducing drug called lovastatin. The special diet lowered levels of LDL cholesterol - the "bad" cholesterol known to cause clogging in coronary arteries - in subjects by almost 29 per cent, compared to a 30.9 per cent decrease in the lovastatin subjects. The special diet combined nuts (almonds), soy proteins, viscous fibre (high-fibre) foods such as oats and barley and a special margarine with plant sterols (found in leafy green vegetables and vegetable oils).
Lead author David Jenkins, a professor in U of T's Department of Nutritional Sciences and director of the Clinical Nutrition and Risk Factor Modification Centre at St. Michael's Hospital, believes the reason these foods work so well to reduce cholesterol is that humans may be evolutionarily adapted to what has been called the "ape diet," a diet very high in fibre, nuts, vegetable proteins and plant sterols.
He adds the study could have far-reaching implications for public health. "As we age, we tend to get raised cholesterol, which in turn increases our risk of heart disease. This study shows that people now have a dietary alternative to drugs to control their cholesterol, at least initially." Jenkins notes the diet can also be used to maintain normal cholesterol levels.
In this month-long study, a follow-up to one released December 2002, 46 men and women with raised cholesterol were randomly assigned to one of three vegetarian diet groups. The control group ate meals low in saturated fats (such as those found in animal products like beef and butter). The second group had the same low fat diet, plus a daily 20 mg treatment of lovastatin. The last group had a diet high in four foods known to have cholesterol-lowering properties. This special diet, designed to be easy to prepare and eat, included foods such as oat bran bread and cereal, soy drinks, fruit and soy deli slices. A typical dinner for people on the special diet was tofu bake with eggplant, onions and sweet peppers, pearled barley and vegetables.
The key components of the ape diet are plant sterols, found in plant oils and enriched margarines, viscous fibre, found in oats, barley and aubergine, and soy protein and nuts.
The margarines enriched with plant sterols (which compete with cholesterol for absorption) used in the study may have been the commercial brands Take Control, Benecol, and Benecol Light. To up your plant sterol content using natural foods one possibility is pecans with 95 milligrams of plant sterols per 100 grams. However, the level of plant sterols in the margarines is about two orders of magnitude greater (1.7 grams sterols in 14 grams of Take Control) and clinical trials in plant sterols have used about 2 grams per day. Still, the nuts have other heart-healthy benefits.
"We went right back in time to, hypothetically, five million years ago, when the diet would largely be leafy vegetables, fruits, nuts and seeds," Dr. Jenkins said.
While the researchers bill this diet as a return to the sort of diet that our ancestors ate for millions of years that is not exactly the case. First of all, it is unlikely that before the development of agriculture any humans or pre-humans ate soy as a major food source. If there are compounds in soy that have some sort of pharmaceutical effect upon cholesterol levels it is not clear (at least to me) that those compounds were present in diets thru some other food sources. Also, oats and barley would not have been major sources of calories. However, they are serving here as sources of soluble fiber and it does seem likely that whatever humans did eat provided a considerable amount of soluble fiber. So it seems likely there are elements in this diet which are not part of our evolutionary history while other elements have been added into the diet by using food sources that humans did not eat historically.
There is another important caveat to keep in mind when interpreting these results: various human subpopulations have split off from each other long enough and ate sufficiently different diets from each other to have evolved adaptations to local food sources. We see signs of this, for example, with northern Europeans who make more lactase enzyme for digesting milk. We also see it in the differing abilities of racial and ethnic groups to handle alcohol. It is unlikely that every ethnic and racial group has the same average ideal diet. Eventually declining costs of DNA sequencing and the identification of genetic variations that affect how we metabolise food will lead to the widespread practice of nutrigenomics where dietary recommendations will be personalized for one's specific genetic profile and risk factors.
The results of this study are sufficiently dramatic that JAMA recommends its use before cholesterol-lowering drugs are tried.
In an accompanying editorial, James Anderson, a professor of medicine at the University of Kentucky in Lexington, said the findings have dramatic public-health implications. He suggested that physicians prescribe the "ape diet" to patients before even considering drugs.
The daily volume of food was about a third of that of the Garden of Eden diet, Jenkins said, adding the people who followed it didn't complain about how much they had to eat but said they couldn't eat any more.
Those who lost weight were asked to, however.
Most of the reports on this study didn't pick up on one particularly interesting result the researchers observed.
Surprisingly, the diet also lowered the levels of C-reactive protein, considered a risk marker for heart disease.
Equally impressive was a 28 percent drop in C-reactive protein, a substance found in the blood that is a sign of inflammation and possible heart disease. The statin group had a 33 percent drop.
The fact that this diet lowers C Reactive Protein (CRP) levels is an added bonus. CRP is a marker for inflammation that has been found to be correlated with heart disease risk. While the importance of CRP as a marker is still debated among cardiology researchers it seems important because there is growing recognition among medical researchers of the role chronic inflammation plays as a cause of the development of degenerative diseases. Any diet that lowers inflammation markers likely will yield more benefits than just lowering the risk of heart failure.
As for how this diet lowered C Reactive Protein (CRP): there are a lot of possibilities. Vitamin E, omega 3 fatty acids, and vitamin B6 are a few of the factors that are thought to lower CRP. Losing weight helps lower CRP as well. However, statin drugs for lowering cholesterol also lower CRP. So is the cholesterol-lowering effect of the diet causing CRP to drop? Maybe.
The Scientist has a good recent survey of the many ways chronic inflammation appears to contribute to the development of many diseases. (requires free registration - and I really recommend taking the trouble as they are one of the better science news sites)
Centuries ago, this trigger was pulled on a more consistent basis as humans battled a harsher environment; Johnson attributes today's toll of inflammation on the super clean environments of Western society. Also, because humans are living longer than evolutionarily designed, and in larger numbers, says Johnson, the odds are increased for disease. "You have an immune system that's looking for something to do and is basically getting into trouble," he says. "I think the problems are caused by an ongoing, aggravated, chronic response to an immune problem that the innate system imagines is there, but isn't." Also, the various byproducts associated with immune system attack, such as reactive oxygen species that decimate joints, may be causing long-term, deleterious effects.
The argument here is that the immune system no longer has enough real enemies to attack and yet it is all hyped up ready to attack something and responds inappropriately. Of course there is a large assortment of auto-immune diseases but many scientists are looking at inflammation response (and it is hard to untangle inflammation response from immune response) as another manifestation of this general problem. However, in some cases chronic inflammation may be getting triggered by chronic infections. This can happen with helicobacter pylori in the stomach. Peridontal disease also causes arterial inflammation and increased risk of heart disease.
However, many clinicians were unclear of the cause of elevated CRP levels. A study published earlier this year in the Journal of Periodontology reported that inflammatory effects from periodontal disease, a chronic bacterial infection of the gums, cause oral bacterial byproducts to enter the bloodstream and trigger the liver to make proteins such as CRP that inflame arteries and promote blood clot formation.
Keep your teeth clean and your gums healthy.
The inflammation-lowering angle is a lot more interesting because the benefits of cholesterol lowering and the methods for lowering cholesterol are a lot more widely known in comparison. We still do not understand all the factors that contribute to chronic inflammation or the best strategies to use to reduce it.
|Share |||Randall Parker, 2003 July 24 09:27 PM Aging Diet Heart Studies|