The suggestion that "golden" rice, bioengineered to contain ß-carotene, could have "a real impact on the health of children living in Southeast Asia" deserves critical scrutiny from nutrition professionals. This rice, although not yet available commercially, has become the "poster child" of the food biotechnology industry's extensive public relations campaign to convince the public that the benefits of genetically engineered agricultural products outweigh any safety, environmental, or social risks they might pose. National magazines promote golden rice as a means to prevent the more than one million annual deaths and cases of blindness that occur among children in developing countries as a result of vitamin A deficiency. The creation of golden rice appears to confirm the belief that biotechnology is the key to solving world food and nutrition problems.

Consideration of basic principles of nutrition suggests that rice containing ß-carotene is unlikely to alleviate vitamin A deficiency. To begin with, the bioavailability of ß-carotene is quite low-10% or less by some estimates. To be active, ß-carotene--a pro-vitamin--must be split by an enzyme in the intestinal mucosa or liver into two molecules of vitamin A. Like vitamin A, the pro-vitamin is fat-soluble and requires dietary fat for absorption. Thus, digestion, absorption, and transport of ß-carotene require a functional digestive tract, adequate protein and fat stores, and adequate energy, protein, and fat in the diet. Many children exhibiting symptoms of vitamin A deficiency, however, suffer from generalized protein-energy malnutrition and intestinal infections that interfere with the absorption of ß-carotene or its conversion to vitamin A. In numerous countries where vitamin A deficiency is endemic, food sources of ß-carotene are plentiful but are believed inappropriate for young children, are not cooked sufficiently to be digestible, or are not accompanied by enough dietary fat to permit absorption.8 In addition to doubts about cost and acceptability,2 biological, cultural, and dietary factors act as barriers to the use of ß-carotene, which explains why injections or supplements of pre-formed vitamin A are preferred as interventions. The extent to which the ß-carotene in golden rice can compensate for these barriers is limited.

Vitamin A deficiency is undeniably the single most important cause of blindness among children in developing countries and a substantial contributor to illness and death from infectious diseases. Mortality rates are higher among children with even mild vitamin A deficiency, but fall by as much as 54% when vitamin A-not ß-carotene--is supplemented or injected.8 Because such intervention methods are expensive and difficult to accomplish in the field, and because so many children exhibit signs of generalized protein-energy malnutrition, food-based approaches to improving vitamin A status seem especially desirable. The addition of a one or two nutrients to an existing food does not constitute a food-based approach.

Furthermore, the use of ß-carotene as a single-nutrient supplement itself raises questions. Although fruits and vegetables containing ß-carotene are demonstrably protective against disease, the results of clinical trials of ß-carotene supplements as a means to prevent cancer or cardiovascular disease have proved disappointing. , Some laboratory studies support the idea that ß-carotene produces biological effects that might protect against cancer, but others suggest that it might be co-carcinogenic. Still others argue that ß-carotene is a prooxidant that may be harmful or beneficial, depending on circumstances. What all this means is that the short- and long-term effects of supplementation of ß-carotene as a single nutrient-distinct from the foods that contain it-are as yet uncertain.

The complexity of the physiological, nutritional, and cultural factors that affect vitamin A status suggest that no single-nutrient added to food can be effective as a remedy for dietary deficiencies. Instead, a combination of supplementation, fortification, and dietary approaches is likely to be needed, along with a substantial commitment to improve socioeconomic status. Food biotechnology may yet lead to products that improve nutrition and health, but at the moment its benefits remain theoretical.

MARION NESTLE, PhD, MPH
Professor and Chair
Department of Nutrition and Food Studies
New York University
New York, NY 10012-1172
This email address is being protected from spambots. You need JavaScript enabled to view it.

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