Evidence review favors whole foods over supplements; Fish oil proves a major exception, but fish remains the favored omega-3 source
by Craig Weatherby
Research into the health effects of foods has tended to focus on isolated constituents: primarily vitamins, minerals, and food factors such as fiber, omega-3s, and antioxidants.
But studies have produced disappointing results with regard to the supposed health effects of supplements like beta carotene, calcium, vitamin E, and lycopene.
In clinical trials, individual nutrients and food factors such as antioxidants and fiber sometimes fail to produce the big disease-prevention benefits observed in people whose diets are high in foods containing the compounds being tested.
Trials testing the effect of vitamin supplements and low fat diets have failed to show reduced rates of chronic diseases, and in some cases have even shown increased risk.
For example, numerous epidemiological studies that prompted the trial show that people who eat foods high in beta-carotene have a reduced risk of lung cancer.
But when beta-carotene was put to a controlled clinical test among thousand of male smokers in Finland, those who took beta-carotene supplements actually developed higher rates of lung cancer, compared with smokers who did not take the vitamin A precursor.
Prompted by puzzling failures like this, scientists who study the effects of foods on health are beginning to challenge the reductionist, “magic bullet” approach toward nutrition research, which mimics methods used to test and make drugs.
Instead, it's looking more and more as though many whole foods offer much more than the sum of their parts.
Researchers' “foods first” essay challenges conventional research
The authors of a recent evidence review fired a shot across the bow of conventional biomedical wisdom, and argue that the synergies among food constituents can no longer be ignored.
The review was penned by University of Minnesota Professor David R. Jacobs, PhD and Linda C. Tapsell, PhD of Australia's University of Wollongong, and appeared in the October, 2007 issue of the journal Nutrition Reviews (Jacobs DR Jr, Tapsell LC 2007).
Jacobs and Tapsell noted that the habits of researchers who approach food factors like drugs will be hard to break, because, as he wrote, “…the temptation to study larger doses of apparently valuable food components in clinical trials seems to be irresistible.”
They cite the example of cereal fiber, intake of which has been associated with reduced risk of colon cancer.
As the duo wrote, “…the phytochemicals [antioxidants] that distinguish whole grain from refined grain food are apparently more healthful than the cereal fiber.”
They relate the example of two groups of participants in the Iowa Women's Health Study.
Both groups were eating about 6 grams of cereal fiber per day, but one group consumed about 75 percent of that fiber from whole grain sources, while the other consumed it from refined grain sources.
And, as they point out, “The women who ate cereal fiber from whole grain sources had significantly reduced total and non-cancer, non-cardiovascular mortality, compared to the women with equal intakes of cereal fiber, but mostly derived from refined grain sources” (Jacobs DR Jr, Tapsell LC 2007).
They also point to three other recent examples in which whole foods proved more effective than specific anti-tumor, antioxidant constituents within them.
These included lab studies that compared the health benefits of broccoli versus its glucosinolates, pomegranate juice versus its various polyphenols, and tomato sauce versus its red lycopene pigment.
In every case, the whole food outperformed the isolated constituents.
The team also presented evidence that healthful synergies can increase further when people enjoy combinations of whole foods, instead of eating each one in isolation:
- When combined, a given amount of oranges, apples, grapes, and blueberries equals the antioxidant activity of the same amount of any one of the fruits alone.
- When a pinch of marjoram was added to salad, it doubled the antioxidant capacity of the dish.
The authors did not dismiss the value of studying individual nutrients: “A nutrition perspective that focuses on food components has been successful in improving public health in a number of cases, from identifying the cause of deficiency diseases such as scurvy or pellagra to finding that folate… [prevents] congenital birth defects.”
However, as they said, “…these conditions represent only one domain where nutrition intervention is required… it is the combination of foods [that explains] diet and health relationships, including relations with many chronic diseases...”
We agree whole-heartedly with the duo's conclusion: “…this new understanding… reminds us emphatically of the central position of food in the nutrition-health interface, which begs for much more whole food-based research, and which encourages us… to 'think food first'” (Jacobs DR Jr, Tapsell LC 2007).
- Jacobs DR Jr, Tapsell LC. Food, not nutrients, is the fundamental unit in nutrition. Nutr Rev. 2007 Oct;65(10):439-50. Review.