Much is written about the comparisons between nutrients from supplements compared with whole foods. Plant foods are known to contain a number of different phytonutrients that have been shown to be beneficial to the health, and many of these chemicals have been isolated and manufactured as supplements. These supplements are useful in research because they can allow scientists to understand the absorption, metabolism and excretion of isolated nutrients. However, food is a complex mixture of many chemicals that interact in the gut, plasma and at the cellular levels and so care should be taken when interpreting this data. For example, while carotenoids have shown promise as potential anti-cancer compounds in epidemiological studies, the supplementation of smokers with isolated synthesised β-carotene is thought to increase the chances of developing lung cancer.
Research published in the American Journal of Clinical Nutrition in 19891 compared the absorption of β-carotene from whole foods with that of a supplement. Individuals consumed a single dose of either a β-carotene supplement or a high carotenoid vegetable. The research demonstrated that a supplement was able to increase plasma levels of β-carotene to a higher level that a similar amount of β-carotene from carrots. However, β-carotene levels did change after consumption of either tomatoes or broccoli. The peak levels of β-carotene occurred 24 to 48 hours after consumption of the supplement, whereas carrots produced a prolonged peak from 24 and 96 hours. Interestingly the researchers also noted that there was a wide variation in the response of individual subjects to the ingestion of β-carotene, suggesting that that different individuals can have very wide ranging nutrient needs.
Although the plasma level of β-carotene are raised to a higher level with consumption of a supplement when compared with carrots, it is important to realise that whole foods contain other nutrients that may have synergistic effects in the body. Some research has found no health benefit following the supplementation of single nutrients, which is true for both vitamin E and carotenoids. However, vitamin E is a group of eight isomers and carotenoids are a diverse group of chemicals. It is known that vitamin E isomers do interact in humans, for example high plasma levels of α-tocopherol are able to suppress plasma levels of γ-tocopherol. It is thought that similar interaction occur between the various carotenoids. It is recommended that single nutrients are not taken in isolation but that a wide variety of phytonutrients are ingested from various foods.