A major focus for the biofortification of food now being warmly embraced by governments in developing countries is beta-carotene, or 'pro-vitamin A' .
Beta-carotene is a precursor of vitamin A, an essential micronutrient whose deficiency can seriously damage vision, the immune-system, and the embryo. The assumption that putting beta-carotene into rice, a staple food which doesn't naturally produce any vitamin A precursors, will benefit the health of the poor sounds good, until you look at the devil in the detail.
Vitamin A is a specific substance (retinol) derived from dietary 'carotenoids' after processing by the liver. Carotenoids are the orange, yellow and red colours naturally found in vegetables and fruit. There are around 600 different carotenoids, of which 50 or so can be used to form vitamin A, and of these about 40 are regularly consumed by humans: beta-carotene is just one of these, albeit a major one.
Both vitamin A and carotenoids break down into highly reactive, and therefore potentially toxic, substances. For example, research indicates these can impair the function of the vital energy-producing bodies (mitochondria) in cells, and can directly or indirectly damage DNA, a hallmark of cancer. Carotenoid break-down products are recognised as being part of a micro-nutrient network whose overall damaging/protective effects depends on all such pro- and anti-oxidant substances present.
Traditional small-holders in areas now suffering vitamin A deficiency at one time grew abundant, diverse leafy-green vegetables in their yards and between the rice in the paddy fields. The Green Revolution with its chemicals and weed-free monocultures changed all this: their diet is now green-free white rice and more white rice .
Will adding a single GM carotenoid back into this nutritional desert benefit the health of the poor?
'Paddy' rice harvested from the field is inedible. Paddy rice is hulled to produce brown rice which retains the oil- and nutrient-rich germ (the bit of the seed which grows into a new plant). Brown rice doesn't store well because the nutrient part turns rancid. It's therefore polished to remove the germ that doesn't keep, producing white rice which can be stored for three years or more.
Adding GM beta-carotene into this scenario has its own problems.
First, rice doesn't naturally produce carotenoids. The levels so far achieved in GM versions are dependent on the strain of rice, and are comparatively low. For example, even the highest concentration of beta-carotene in golden rice is only about a quarter of that found in amaranth and carrots, and one-sixth of that found in mangoes.
Second, the conversion of beta-carotene to vitamin A isn't very efficient and can be as low as a single unit of vitamin A to every 28 units of beta-carotene.
Third, carotenoids are fat-soluble and can only be absorbed if there's sufficient fat in the diet. Fat is something the poor in the developing world can hardly afford.
Fourth, during storage of golden rice under normal Asian conditions, beta-carotene degradation amounts to a loss of around 80%.
Beta-carotene integrity is compromised by exposure to heat, oxygen, light, humidity, microbial contamination, and even by physical disturbance. In Bangladesh, for example, the warehouses where the government stores its rice have no system in place to control temperature and rice is stored there in sacks. To prevent dampness, the warehouse doors and windows are often kept open, letting air and light in. Rice in the Bangladeshi market-place is sold from open containers. These all present highly favourable conditions for promoting the degradation of beta-carotene in golden rice.
Fifth, cooking degrades the beta-carotene by a further 17-24%.
In short, as GM Watch points out, "you'd have to eat a truckload of GM golden rice each day to get sufficient daily beta-carotene to meet your daily requirement of vitamin A, and that's when the golden rice is freshly harvested." Even this 'truckload' of rice will be insufficient for a person whose digestive system is compromised, or who has no oil to add to their diet. More to the point, that person will still be deficient in all the other, interacting, micro-nutrients needed for health.
What golden rice eaters will likely be consuming, however, is a multitude of toxic carotenoid break-down products.
Aware of the storage problems of golden rice, a team of Indian scientists investigated beta-carotene loss from the GM rice under various storage conditions to devise "an effective delivery system for golden rice to the consumer".
Contrary to expectations, beta-carotene in polished golden rice with the fatty content of the husk removed, deteriorated most rapidly. The best they could come up with was vacuum-packed paddy or brown rice.
Vacuum packaging is literally absent in, for example, the whole of Bangladesh.
What does this all add up to?
Well, golden rice might be effective in reducing vitamin A deficiency if the poor have access to:
- an elite strain of the GM rice
- vacuum packing equipment
- enough fuel and water to cook brown rice (brown rice takes longer to cook than polished rice)
- oil to add to the rice on their plate
- enough money to get all of the above
This suggests that to get any benefit from golden rice, the poor will have to have money so they're not poor any more.
A more realistic scenario is that golden rice won't address their vitamin A deficiency, they'll still suffer other nutritional deficiencies from eating such a restricted diet, plus the toxic effects from all the carotenoid breakdown products.
As GM Watch says "Developing and promoting golden rice has swallowed up millions of dollars and over two decades' worth of research time and brain power. The saddest aspect of this waste of money and resources is that simpler, safer, and cheaper measures have proven effective in reducing vitamin A deficiency (in the Philippines, for instance ). If these measures had benefited from the level of support given to the GM golden rice project, they would likely have solved the problem by now."
 BIOFORTIFICATION - BLINDLY REINFORCING MALNUTRITION - August 2019
 THE REAL GOLDEN RICE STORY - August 2016
- Werner Siems, et al., 2009, β-Carotene Degradation Products - Formation, Toxicity and Prevention of Toxicity, NCBI Forum of Nutrition (?) 61
- Haritha Bollinedi, et al. 2019, Kinetics of β-carotene degradation under different storage conditions in transgenic Golden Rice lines, Food Chemistry 278
- GM golden rice must be vacuum packed to retain beta-carotene, GM Watch, 6.06.19
- Emran Hossain, Golden rice beta carotene disappears fast:
study, New Age (Bangladesh), 27.06.19
Picture International Rice Research Institute (IRRI) [CC BY 2.0 (https://creativecommons.org/licenses/by/2.0)]