Plant contain many chemicals that appear to show beneficial health properties in humans. Lignanas are polyphenolic plant compounds that are produced as a result of the oxidative coupling of β-hydroxyphenyl propane. Lignans are often present in plant material along with dietary fibre, and are sometimes grouped into this macronutrient division. Plants such as flax and sesame are important dietary sources of lignans in humans nutrition, but other sources include wheat, red wine, rye, brassica vegetables and barley. Lignans may have some important biological properties in human which include alterations to gut function through interaction with colonic microflora. However, lignans or their metabolites may be bioavailable in humans and evidence suggests that they can interact with human tissues and cause cellular effects. For example, rat experiments have shown that the lignan sesamin, found in high concentrations in sesame seeds, may be able to increase tissue levels of both vitamin E and vitamin K.
In the study1 rats were fed a diet containing 0.2 % sesamin or a control diet without sesamin for 7 days. After this time the liver concentrations of phylloquinone (vitamin K1), menaquinone (vitamin K2) and γ-tocopherol (an isoform of vitamin E) were greater in the sesamin fed rats compared to the control rats. In a subsequent experiment the authors fed rats sesamin at 20 % of their dietary intake over 40 days. The rats fed sesamin had elevations in their heart, lung, lung and testis tissue compared to rats fed a control diet devoid of sesamin. However, the levesl of sesamin required to cause elevations in vitamin E and vitamin K may be quite low. When the authors tested varying amounts of sesamin for the ability to raise liver levels of vitamin K, there was no difference between the 1, 5 or 10 % of dietary intake doses. Therefore dietary sesamin increase tissue levels of vitamin K and vitamin E in healthy male rats. These effects are interesting because they provide a mechanisms by which the known health benefits of sesamin might be explained in humans.
In human studies consumption of 50 grams of sesame seeds per day for 5 weeks increased tissue levels of γ-tocopherol and decreased the metabolism of γ-tocopherol to the excretion metabolite carboxyethyl-hydroxychroman (CEHC). The rats study suggests that these effects in humans are due to the presence of sesamin in the sesame seeds. Interestingly the phytyl and prenyl chains in phylloquinone and menaquinone, respectively are also present in tocopherols and tocotrienols (isoforms of vitamin E). Vitamin E and vitamin K therefore share some common steps in their metabolism and excretion. This suggests that sesamin, or one of its metabolites, is able to inhibit these common steps and it is in this way that sesame seeds are able to increase plasma levesl of these vitamins in humans. In particular sesamin may inhibit the α-hydroxylation of the vitamins by cytochromes. Because lignans of similar structures are also present in other foods, it may be that these foods also have vitamin E and vitamin K elevating effects.
Dr Robert Barrington’s Nutritional Advice: Sesame seeds have some important health effects in humans. Some of these effects may be explained by the ability of sesasim to increase tissue levels of both vitamin E and vitamin K. Because a number of plant sources contain lignans of different structures, and because the effects of these lignans may differ slightly, consuming a range of lignan containing foods may provide additional benefits over consuming a single dietary source.
RdB
