Peter Wehrwein
For years, it was an article of dietary faith: eat a low-salt diet and be rewarded with healthful blood pressure readings. However, as is so often the case in nutrition, a small but vocal group of scientists were critical of the popular stance. Falling into the skeptical middle was Professor Frank M. Sacks, a blood pressure and cholesterol expert and one of the leading researchers in the powerhouse nutrition department at the Harvard School of Public Health. He had seen the study results. The impact of salt on blood pressure just didn't seem that large.
Now Sacks is a low-salt convert. He was the first author on a paper published earlier this year in the New England Journal of Medicine showing that people who ate a low-salt diet (no more than 2.5 grams per day) for a month had a sizable drop in blood pressure. The effect of reducing salt intake was particularly strong for people on a conventional diet. But it also was seen in study subjects on the DASH diet. DASH stands for Dietary Approaches to Stop Hypertension, a diet heavy on fruits, vegetables, and low-fat dairy foods that Sacks and his colleagues developed several years ago to test if diet alone could markedly decrease blood pressure (the answer: yes). Says Sacks, "From a strategic point of view, I wasn't sure it made sense to put a whole lot of effort into decreasing salt. But now I don't feel that way at all. The data are so clear from the DASH study."
Data and their ability to clarify come up often in a conversation with Sacks. He says data's authority over subjective arguments is what drew him into science. He is also mindful that data from almost any nutrition study should come with a large handle-with-care sign on it. Results are too easily distorted into fad diets or misleading take-home advice. "Nutrition scientists haven't always gotten the message right, scientifically. The low-fat, high-carbohydrate message was not necessarily the right message, scientifically. And even if it were, its application has been disaster."
Like many other prominent researchers, Sacks showed a proclivity for science at a young age; the chemistry set was a constant source of amusement during his childhood in the Greenville section of Jersey City, N.J. But Sacks also had musical talent and, after graduating from Brown University with a degree in biology in 1970, he attended Boston's New England Conservatory of Music. A fan of avant-garde jazz, Sacks played the sax (a feeble play on words he has endured many times). Being a musician seems more glamorous, but Sacks, now 52, believes scientists fare better over the long haul: "Very few musicians continue to be innovative their whole careers. There are many instances in science when creativity continues over time--and even gets greater. There is a certain maturity that I think unlocks creativity. Things are more exciting to me than ever."
His career switch had other motivations. Sacks had become fascinated with what good nutrition might do to improve people's health, which was "completely underappreciated" in the early 1970s, at least in academic circles. The interest came from his exposure to the macrobiotic movement, which was going strong in Boston in those days. Invented by Japanese businessman George Ohsawa, macrobiotics featured a lot of Eastern philosophy, but the dietary recommendations were what grabbed people's attention--eat no animal products of any kind, consume whole grains and vegetables, avoid sugar and white bread, which are as bad for you as meat. Not everything made sense. Some of the ideas were flat-out wrong and dangerous. But anyone who kept up with nutrition research could see that Ohsawa was on to something.
Sacks's first paper, entitled "Blood Pressure in Vegetarians" and published in the American Journal of Epidemiology in 1974, won an award for predoctoral research. Just a year later, he was the first author on a paper called "Plasma Lipids and Lipoproteins in Vegetarians and Controls" in the prestigious New England Journal of Medicine. "The cholesterol levels were so low in those vegetarians," he says. "Hardly anyone had appreciated what diet really could do." His 1990 study showing that oat bran didn't have much effect on cholesterol (also published in NEJM) made news. It trumped a slew of lesser studies that had found oat bran was a good cholesterol reducer. "To me that oat bran paper was an example of just going with what the data said," he remarks.
Sacks was making a name for himself as a biochemist and cholesterol expert,
but cholesterol wasn't yet a household world. In nutrition circles, few had
expertise on how to properly measure and analyze blood lipids. Sacks says he
found he was better off doing the work himself. Therein lies a tension in his
career: although originally drawn into detailed lab work, when it came to what
people ate, Sacks notes that he's always been more interested in the big picture
of dietary patterns, not the individual vitamin or nutrient. "The reductionist
approach, at least with blood pressure, has really not paid off because we have
not been able to identify that one nutrient or one pill that can reproduce the
effects of the vegetarian diet. That is partly where DASH came in…because
of the failure of the reductionist approach."
In 1997 Sacks and his colleagues reported that the DASH diet could reduce blood
pressure as much as blood-pressure medications. The results of an eight-week
trial were "better than we ever dreamed of," notes Sacks. Blood-pressure
pills are more popular than ever, but if people followed the DASH recommendations,
he asserts, "it could be a substitute for the gazillions of dollars"
spent on them every year.
But the initial DASH findings had an unintended effect. They encouraged the low-salt critics. Here was proof, they said, that something else other than lower salt intake could lead to lower blood pressure. Although Sacks believes the most recent results of the DASH study should settle the argument, predictably, the hard-core critics are not giving up without a fight. They say some people being especially "salt sensitive" could explain the results. Sacks agrees that some groups are, on average, more salt sensitive than others but says the effect salt had on blood pressure was widespread and couldn't be explained by an isolated spike. Besides, Sacks says, until a genetic or some other kind of reliable lab test is developed, salt sensitivity is "clinically meaningless" and can't be applied on an individual basis. The study has also been criticized for being too narrowly focused on blood pressure when salt may have other effects that ameliorate heart attack risk. His riposte: blood pressure is such a prominent risk factor that the focus on blood pressure makes perfect sense.
Sacks says he is currently hatching ideas for his future research pursuits and public health applications. He is developing themes to better understand the biology and clinical meaning of triglycerides in blood, a little understood counterpart of the much better known blood cholesterol story. Because the United States and many other parts of the world are struggling with an obesity epidemic, he and many others are taking up the study of weight loss. In a small pilot study, Sacks has already found that a moderate-fat diet, rich in naturally occurring unsaturated fats, may be a better way of losing weight than the low-fat approach. That goes against everything we've been told, but such is the power of data.
Harvard Public Health Review Winter 2002/text version
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